http://www.kastenmarine.com/aluminum.htmCelebrating Thirteen
Years Online - Also See Our Alternate Web Site
Home | Intro | Custom Yacht Design | Stock Designs | Motor Yacht
Gallery | Sailing Yacht Gallery | Prototypes Gallery | Plans List
Articles | Our CAD Design Stream | MAXSURF For Marine Design |
News..! | Design Team | Site Map | Site Search | Contact Us
First appeared in slightly different form in Cruising World
magazine, September 1997, entitled "To Thine Own Chines Be
True"Aluminum For BoatsCopyright 1997 - 2009 Michael Kasten
Aluminum is a sheet material with virtues aplenty. To honor them
best, I advocate simplicity, ample framing... and yes, even single
chine hull shapes!
Why Build An Aluminum Boat?For things that go bump in the night.
For ease of construction. For longevity. For good resale value. For
the benefit of being able to create a custom design and build it
economically, without the huge penalty of having to build a mold
first, as with fiberglass. For freedom from the stench of
fiberglass, and from the dread fiberglass boat pox. For
repair-ability. For lightness and strength. For the competitive
edge in performance. And most importantly, for the security of safe
cruising. It takes over 60,000 pounds per square inch (psi) to tear
apart a chunk of mild steel, and 30,000 psi to deform the same
piece; to make it yield. With aluminum, around 45,000 psi will tear
it apart, and around 35,000 psi will deform it. Yes, you read that
correctly: size for size, aluminum has a higher yield strength. In
these facts lie the extreme benefits of metal for hull
construction: The "plastic range" of either metal is quite high, so
the material can take a terrific beating without failure. Aluminum
is light, strong, corrosion-resistant, non-sparking and weldable.
Because aluminum is not abrasion-resistant, it can be cut with
carbide tools. Aluminum is subject to electrolysis, pitting and
crevice corrosion, but these liabilities can be managed as long as
the installation of dissimilar metals and electrical items are
correctly done. After that, it is a matter of attending to these
matters during the life of the boat. In terms of seakindliness,
some boat shapes may be better if built in steel. Aluminum's
extreme lightness can introduce a faster pitching and rolling
motion in some hulls. For example, very beamy boats will exhibit a
gentler roll if built in steel. Fairly narrow or light-displacement
boats, which tend to have a narrower waterplane and less inherent
form stability, will benefit most from aluminum construction. These
are of course generalizations. Given a blank sheet to begin a
design, the roll behavior will be considered along with the choice
of materials. In terms of size, one can successfully build a steel
boat for coastwise cruising and serious blue-water sailing down to
around 30 feet LOD. Below that, the steel vessel will either have
to be built with excessive displacement or with quite thin plate
that will be more difficult to build due to distortion while
welding. An aluminum bare hull, built to the same strength
standard, will weigh roughly 45% less than the same hull in steel.
As a result, if high strength is of the highest priority, the
aluminum boat can be built to the same structural weight as the
steel vessel, and then be considerably stronger. We can therefore
create aluminum cruising boats down to, say, 22 feet. One could
still build a safe aluminum boat in a size smaller than that, but
who'd want to go to sea in it? On CostThe aluminum to build a bare
hull costs just under twice as much as the mild steel to build the
same design. But aluminum is faster to work with, so the savings in
labor helps even the score. The labor saved can be substantial
since aluminum can be cut with common carpentry tools and is welded
much faster than steel. Another significant advantage with aluminum
is that there is no need to sandblast or paint the interior. You do
have to insulate an aluminum hull, but that won't ordinarily
require sandblasting. Painting the exterior of an aluminum boat is
unnecessary, representing another big savings. After you've
factored in the added costs of painting steel, the margin for
building an aluminum hull drops to being a very minor amount when
compared to building in steel. As a percentage of the entire
construction project, the additional cost of the aluminum becomes
very slight indeed. Once built, maintenance on an aluminum boat is
less expensive, and resale value higher. These factors more or less
even the score between the two materials. New construction methods
have trimmed metal hull building costs substantially. The most
dramatic savings can be effected by computer lofting, and then
computer cutting the actual parts for the hull. Essentially, the
builder receives a "boat kit" ready for assembly. A parallel
method, also ideally done by computer, involves cutting and fitting
the plate only, by itself, without a prior support structure. One
last note about cost: When comparing like for like, boat costs
tends to vary more or less directly with displacement (not length),
assuming a given level of complexity in the design. Displacement,
and therefore cost, varies as the cube of the overall dimensions.
On Hull ShapeAesthetics are a personal thing. For my own part, I am
attracted to the single-chine shape for metal boats because metal
is a flat-sheet material. When building a boat using sheet
material, it makes the most sense to think in terms of that
material's characteristics and how one may optimize a hull design
without incurring extra labor. In metal, a single-chine hull is
easier and less costly to build than one with radius or multiple
chines or one that is fully rounded. Further, with a good design
there is no performance penalty with a single-chine hull. The
slight gain in wetted surface, if any, can be offset by slightly
greater sail area, made possible by slightly greater ability to
carry sail due to the form stability provided by the chine. This
line drawing and the ones that follow demonstrate degrees of design
complexity for sheet materials, from single chine to a fully
rounded hull. I prefer the simplicity and economy of a single-chine
metal hull, as shown here. In my view, it is a more honest shape
for a metal boat.
Further, the reputed seakindliness of a radius-chine or
round-bottom hull can be approached in a single-chine hull by
giving it a slightly more "slack" shape. A big advantage of the
single-chine shape is economy; the cost to build a rounded or
radius-chine hull is considerably higher due to the work involved
with the added shaping and welding. A single chine can look quite
appealing, especially when used with a more traditional style. In
my view, it makes the most sense to take any extra money available
and use this to make a graceful single-chine boat longer rather
than radius chine or multiple chine, thereby netting some real
speed and comfort benefits in other words, a bigger boat for the
same money, with inherently greater speed potential due to the
increased length. Multi-chine designs allow building with flat
plate, without requiring that any plates be rolled. Although
considerably more time consuming than a simple single chine, these
shapes remain within the construction realm of the amateur or
one-off builder.
Radius-chine hulls employ flat panels everywhere except for a
narrow 'rounded' plate that joins topside to bottom, rendering a
quasi-rounded hull without requiring that every metal sheet be
rolled; only those at the radius. However... it will always be
recognized as a radius chine vessel, and not a true rounded hull
shape. Therefore if a radius chine is being considered, there is
very little reason not to simply take the next step and go to a
true rounded shape, as follows...
A fully-rounded metal hull is beautiful to behold. They need not
be expensive to build if correctly designed, where only the minimum
amount of plating needs to be rolled. These are not "radius chine"
boats. They are instead just easily plated, rounded hulls with no
reverse curvature, so these hulls can be built economically.
Radius-chine and multi-chine boats cost about the same amount to
build, and a true rounded hull - provided it's designed correctly -
need not be any more time consuming nor any more expensive to build
than a multi-chine or radius-chine shape. And as a very big
bonus... it will look vastly better!It is generally our first
choice to make use of a single chine hull shape for metal boats. If
for some reason a chine shape is not desired, we nearly always find
that a well-designed rounded hull is the next best choice. It will
share the same ease of construction as a multi-chine or radius
chine vessel, but with a little bit of transverse curvature in the
topsides and bottom. Designing true rounded metal hulls for ease of
plating is not at all difficult. Our goal with a rounded metal hull
is that the topsides and bottom will not require any pre-forming at
all, there being just enough curvature to sweeten the appearance,
but not so much as to require rolling. In other words, 90% or more
of the vessel is still able to be plated using flat sheets, and
without any fuss at all. One excellent technique when building a
completely rounded metal hull involves using "joggled" plate seams,
akin to "lap strake" planking in wood. According to this method, an
offset is pressed in along one edge of the plate. The offset is
just enough to take the thickness of the plate below it. Each plate
is a strip about 12 to 18 inches wide. Bernard Moitessier's steel
boat Joshua was built that way, and it certainly withstood the
ultimate test...! Alternately, the plating can be lapped by instead
jogging the frames to match the plate contour. Just above the lap,
the frame jogs out to meet the plate above, etc. These lapped plate
methods provide a much easier fit-up, and a much more easily
achieved weld seam. If "lined off" nicely, as one would do with
wooden planking, they can also look very good. The plate overlap
creates its own longitudinal stringer and reinforcement. With any
of these types including the fully rounded metal hull, as can be
seen in each of the examples above, it is most economical in terms
of labor if the keel is attached as an appendage. In other words
given the strength of metal, there is no particular need to create
a large reverse-curved garboard area merely for the sake of
strength, as would indeed be the case with a glass or wooden hull.
This saves an enormous amount of construction time, and is
therefore the most practical approach. On "Frameless"
ConstructionWith the notion of metal's extreme strength, we have
come to a point of faith which has at times created a
misconception: There is potentially misleading and incorrect
information pandered by some in the implied promise of "frameless"
metal boats. The concept of frameless metal boats is attractive,
but flawed. The definition of "frameless" must be clarified
Achieving the required strength in a metal vessel without using
framing imposes an enormous weight penalty due to the required
increase in plate thickness. If one applies well-proven engineering
principles to the problem, one quickly discovers that frames are
simply a requirement. Designers may employ devious strategies, such
as using bulkheads, interior furniture or other features to achieve
the required reinforcement, but responsibly designed and built
metal boats, whether of steel or aluminum, definitely do use
framing. Despite recent talk about "frameless" construction,
responsibly designed and built metal boats do use framing. The
added plate thickness required to forego framing completely would
render a heavy hull indeed. Here, just three out of a total of 17
transverse frames for this design are illustrated.
Without the aid of metal internal framing, many metal boats are
successfully plated, and the plating then is welded together prior
to the addition of the frames. This construction technique renders
a high degree of fairness. Other methods use a "folded plate"
strategy, with perhaps one large plate per side, to make the
plating much faster to erect. To give the vessel adequate strength
in the final product, though, frames must be added before the hull
can be considered finished. Many so-called "frameless" boats make
extensive use of longitudinals, which, in "folded-plate"
construction, are often pre-welded to the plate. Bulkheads or other
internal transverse structures are used to reduce the span of these
longitudinals. Strictly speaking, then, these boats do have
framing, and with good design, the framing will be adequate to the
task. Classification societies, such as the American Bureau of
Shipping, Lloyds, and Det Norske Veritas are somewhat conservative
in their approach, but working through their formulae demonstrates
the benefit of framing, primarily to bring the weight of the vessel
within a reasonable range while maintaining the required hull
rigidity. Studies of failures in aluminum crew boats and offshore
supply vessels show the need for being very conservative in terms
of the allowable areas of unsupported plating, in terms of
scantlings for framing, and in terms of the welding between frames
and plating. Most often, the best framing style makes use of a
series of strong transverse frames combined with longitudinals
which provide the primary support for the plating. The longs, then,
are held by the frames. In my view, the frames in a metal boat
should always be located where required by the interior bulkheads.
Bulkheads can then be bolted directly to these web frames, and all
is as it should be, simple and strong. With a few tricks of the
trade up your sleeve, an absolutely fair hull is the result. Some
boats are built "Frames First" while others are built by applying
the "Plating First" as described above. For further reading about
the various advantages of each, please see our online article:
Metal Boat Building Methods. On Protection And CoatingsAluminum
alloys for use on boats are generally limited to the 5000 and 6000
series. These two alloy groups are both corrosion resistant in the
marine environment due to the formation of a tough aluminum oxide.
Aluminum alloys are subject to crevice corrosion, since they depend
on the presence of oxygen to repair themselves. What this means is
that wherever aluminum is in contact with anything, even another
piece of aluminum or zinc, it must be painted with an adhesive
waterproof paint such as epoxy, or it must be protected with a
waterproof adhesive bedding, or both. A plastic wafer alone as an
isolator is not enough. Salt water must be prevented from entering
the crevice; otherwise corrosion will result. Anodizing, a process
of electrically causing the formation of a tough oxide film on the
surface of aluminum, slows pitting, but anodizing will not prevent
pitting or crevice corrosion. Aluminum is very active galvanically
and will sacrifice itself to any other metal it contacts either
directly or indirectly. Aluminum is anodic to everything except
zinc and magnesium, and must be electrically isolated from other
metals. In this case, paint, bedding, and a non-conductive plastic
or rubber isolator should all be used together. Unlike tankers,
small metal boats are not designed with an appreciable corrosion
allowance. In terms of the paint system, aluminum boats are dealt
with more easily than steel boats. Aluminum must be painted
wherever things are mounted to the aluminum surface, and below the
waterline if left in the water year-round. Otherwise, marine
aluminum alloys do not require painting at all. Present technology
for protecting metal boats is plain and simple: epoxy paint. Once
the metal is protected with a 12- to 16-mil dry-film thickness of
epoxy, it can then be top coated with whatever is appropriate to
the situation. The top coats can be, for example, foam, enamel,
linear polyurethane, or bottom paint. More durable top-coats better
protect the investment in epoxy. To assure that this "secondary
system" sticks to the epoxy barrier, use a standard
extended-recoat-time epoxy primer, which makes an excellent
tie-coat. For anti-fouling paint, the excellent offerings from the
E-Paint Company should be of interest to metal-boat owners. Called
"No-Foul," these paints release hydrogen peroxide to prevent marine
growth, eliminating the inherent problems that accompany
copper-based paints on aluminum hulls. Whether on steel or on
aluminum surfaces, paint preparation is critical. Thorough cleaning
and sandblasting provide the best surface for adhesion of paint or
bedding. Alternately for aluminum, cleaning and then grinding with
a coarse 16-grit disk will provide enough tooth for the paint to
stay put. If the surface finish must be extra fine, as on an
aluminum spar, then a thorough sanding, cleaning and etching with a
product like Alodine before painting will give good results. The
interior of an aluminum boat does not require painting. It would be
the ultimate, though, to epoxy prime the interior if a blown-in
urethane foam will be used. A chromated vinyl-acid "wash primer"
would be a very acceptable second choice inside, in order to
provide the best surface for adhesion for the foam. Regardless of
the bottom paint used, zincs must be used to control stray-current
corrosion, to which we can become victim with a metal boat, even
without an electrical system! With a scratch at the bow, and
another at the stern, the boat itself becomes the preferred path
for any ambient currents in the water. In the best of all possible
worlds, there would be no stray currents in our harbors, but that
is not reality. Zinc anodes should always be used on an aluminum
boat, and generally in the same quantities as with a steel boat, in
order to prevent stray-current corrosion. The quantity and
placement of zincs are discovered by experiment over time, and will
differ from one marina to the next. As an example, on a 40-foot
metal hull, the best scheme is to start with two zincs forward, two
aft, and one on each side of the rudder. With a larger boat, say
over 45 feet, an additional pair of zincs amidships would be
appropriate. Surface area, not zinc volume, is the important
factor. After the first few months, inspect the zincs. If they
appear active but plenty of material remains, the zincs are doing
their job. If they are seriously wasted, the area as well as the
weight of zinc should be increased. Of course, welding zincs on is
best, but for an aluminum boat, the zincs will instead usually be
bolted to studs welded onto the hull plate, or bolted using
stainless bolts into a heavy bolting plate welded to the hull. Good
electrical connection between the zinc and the hull is imperative.
The Bottom LineCan aluminum compete with fiberglass as a production
hull material? Jimmy Cornell's Ocean Cruising Survey, a valuable
indicator of trends among world-voyaging cruisers, shows that metal
boats are on the increase. A metal hull was the number-one wish of
those with other hull materials. "My next boat will be metal..."
was heard over and over, particularly by those who were already
cruising aboard a metal boat. It is said among dedicated blue water
cruisers in the South Pacific, "50% of the boats are metal; the
rest of them are from the United States...." Although it may seem
so at times, this statement is fortunately not 100% true!! In terms
of cost, we usually observe that displacement is more important
than length. Aluminum is the ideal material for building a
lightweight boat. The second cost determinant is complexity. This
reaches into all aspects of the design, including hull shape. The
simpler the design, the lower the cost. For example, a
well-designed single-chine hull will perform extremely well, and
the savings will allow a slightly longer boat. Dollar for dollar,
this translates into a *real* performance advantage.With correctly
applied protective coatings where needed, adequate zincs, a proper
electrical system, and good care over time, an aluminum boat will
last indefinitely. Further Considerations...?We believe in metal as
the ultimate boat structure, and as a result we have created quite
a number of metal boat designs. To review them, please see our Sail
Boats Gallery and our Power Boats Gallery. We have also created
quite a number of Prototype Designs, most of which are also
intended for metal structure. Sail or power - mono or multi-hull -
if the structure is well-designed and well built, the resulting
boat will be excellent. We are often asked about one metal vs.
another - most commonly steel vs. aluminum. Despite the excellent
case we have made for aluminum above, we do not have a distinct
preference. There are so many varying factors that will contribute
to making that decision for each boat, and for each owner. Some
boats are designed for one material only, other boats can make use
of either. In general, any of our designs that have been developed
for steel can very quickly be re-specified for construction in
aluminum. The design conversion from steel to aluminum is done for
a minimal extra cost. Where NC cutting files exist for a steel
boat, they will need to be re-done in order to work for aluminum
structure, and there will be a cost incurred for that conversion.
Designs originally developed for aluminum structure are not as
readily converted, since they will have been designed specifically
to save weight. To convert an aluminum design to steel will
ordinarily require a re-work of the hull shape in order to support
the extra weight of steel. If a conversion of one of our designs
from steel to aluminum or vice versa is of interest, please
inquire.For more information on the question of hull materials,
please see our web articles on the following:Metal Boats for Blue
Water | Aluminum for Boats | Aluminum vs. Steel | Steel Boats |
Composites for Boats | The Evolution of a Wooden Sailing
TypeCopyright 1997 - 2009 Michael Kasten
Direct Quote from an aluminum boat owner... As an owner since 5
years of an aluminum boat I could not agree more with your
preference for this material. She is a great sailboat and requires
very little in the way of maintenance. I do a lot more reef
snorkeling than the paint, polish, varnish and wax guys! --Peter
KminekPlease see the Plans List page to review our available Boat
Plans.
Home | Intro | Custom Yacht Design | Stock Designs | Motor Yacht
Gallery | Sailing Yacht Gallery | Prototypes Gallery | Plans List
Articles | Our CAD Design Stream | MAXSURF For Marine Design |
News..! | Design Team | Site Map | Site Search | Contact Us
All Web Site Graphics, Layout, and Written Content at this
Domain Created by Michael Kasten. All Graphic and Written Materials
at this Domain Copyright 1989 - 2010 Michael Kasten. All Content
Registered with US Library of Congress and US Copyright Office.
Copyright Violations will be Prosecuted. All Rights Reserved.
http://www.kastenmarine.com/frames_first.htm
Home | Intro | Custom Yacht Design | Stock Designs | Motor Yacht
Gallery | Sailing Yacht Gallery | Prototypes Gallery | Plans List
Articles | Our CAD Design Stream | MAXSURF For Marine Design |
News..! | Design Team | Site Map | Site Search | Contact Us
Frames First... or Plates First...?A Discussion of Metal Boat
Building MethodsThere are a number of approaches one can take when
fabricating a new metal boat. Among them are methods that erect the
framing first and apply the plating to that structure afterward,
and others that favor pre-planning the plate shapes in order to
create the hull shape before the frames are introduced inside. The
following is a discussion of the various approaches taken, their
rationale and the pros and cons of each.With extreme luck, the
following will be taken as intended - purely for information's
sake. I hope also it will shed light on what has in the amateur
metal boat building world become at times a heated debate. You can
review our approach to the various metal boat building methods in
our article on Aluminum for Boats where they are discussed in
detail, including the various pros and cons of each approach toward
fabricating. In that article and among the links provided there
you'll also find our thoughts on boat shape itself: single vs.
multi-chine vs. radius chine vs. rounded hull, etc. Rather than to
discuss the merits of different hull shapes here, we will limit
ourselves to the question of Build Methods. In this article I will
divide the various metal boat building approaches into two broad
categories of BUILD METHODS, and then I will address a few basic
notions regarding STRUCTURE.The main thing I hope to accomplish
here is to attempt to define and to therefore help the reader to
understand the various different terms being used when discussing
different boatbuilding methods.Here are several thoughts that I
hope may help clarify the picture...Structure First, in terms of
STRUCTURE, we have in recent years encountered several proponents
of so-called "frameless" construction. Unfortunately, when the word
"frameless" is used it is commonly mis-construed to imply that a
vessel can do entirely without internal structure. Regardless of
the various approaches taken toward fabricating and plate
development for boats, there will always be a requirement for hull
plate reinforcements, whether they occur in the form of floors,
longitudinal stringers, bulkheads, web frames, mast steps, engine
girders, tank faces, deck beams, or whatever. These are all various
types of internal reinforcements, any of which will legitimately
qualify for the term "framing." The very notion of "frameless"
metal boat construction is by definition therefore a flawed and
incorrect concept insofar as it refers to the possibility of a
completed vessel being able to exist entirely without frames or
other internal metal structure.While it is certainly possible to
increase plate thickness in order to increase frame spacing and to
therefore reduce the number of frames, it is not at all desirable
to eliminate frames altogether. Even with aluminum, the thickness
of plate required to completely eliminate frames would end up
weighing far too much (and would cost too much) to be practical.
Our approach to the so-called "frameless" metal boat construction
methods are addressed thoroughly within our article on Aluminum for
Boats, in our article on Metal Boats for Blue Water and below under
the heading, The Question of Pedigree...Build MethodsIn terms of
BUILD METHODS, we observe the following broad categories:1.
"Framing First" with the plating being patterned and applied to the
already erected frame, and 2. "Plating First" with the frames
patterned to the already erected and welded plating - often making
use of temporary moulds to help guide the plate and maintain the
intended hull shape.This latter method is often incorrectly
referred to as being "frameless" because the plating occurs prior
to the frames being introduced. This is most unfortunate
terminology, is inaccurate and therefore misleading, and is all too
often cause for misunderstanding and unnecessary argument.The
"Frame First" MethodWith the Frame-First method, the hull shape is
controlled by first having a rigid "armature" over which the
plating is applied, in other words: the frames. The primary
advantage of this method is that it allows exact control over the
shape. As a result it is by far the most common approach to metal
boat building, whether being used for ships (nearly 100% used) or
for yachts (possibly 90% used if Europe is included). We'll limit
our discussion to small yachts here (boats under around 60 feet),
so we need not involve methods used for larger vessels such as
modular construction. In order to achieve a fair exterior hull
surface, the "frame-first" method requires that the builder be
skilled in the lofting, the set-up of the frames, the patterning of
the plate, and the final weld-up of the hull. It is of course
exacting work to achieve this level of precision and fairness in
the completed hull, but the attention to detail is well worth it in
the end..The question then becomes, "How shall we save the builder
time...?"With the "frame-first" method, quite a lot of the
builder's fabricating time can be saved by having all the frames
and plating pre-planned by CAD and pre-cut by NC Cutting via plasma
or water jet. What is NC...? It literally means "Numerically
Controlled." The high level of precision offered by NC Cutting
takes the traditional "frame-first" method to the next level...
When using pre-cut metal parts, there is no lofting needed, and
there is no cutting required for the frames or plates or other key
structures. NC Cutting therefore provides substantial efficiencies
to the builder, thus considerable time savings, in addition to
offering a degree of accuracy that is simply unachievable by manual
lofting and cutting.While NC Cutting can effect substantial labor
savings in the hands of a professional builder, it has the
potential to save even more time in the hands of an amateur
builder. Why? Mainly this is due to the elimination of quite number
of "What do I do now?" questions, and the relatively huge amount of
time expended on them - inevitable for a first time builder when
having to loft, plan, spile, and cut every part of the
structure.Needless to say, the NC approach requires a high degree
of skill and actual building experience on the part of the vessel's
designer in order to be able to pattern all the frames, plates, and
other parts correctly. It also requires a high degree of accuracy
on the part of the builder who must then place everything as
intended, i.e. exactly where it belongs. Ordinarily when using NC
Cutting, aside from just the frame shapes being pre-defined, the
frames will also have mouse holes for weld-throughs, and will have
notches pre-cut to receive the longitudinal stringers.
Additionally, there will be all the other parts such as the engine
girders, tank faces and lids, stem and horn piece shapes, mast
steps, deck beams, bulkheads, and of course all the exterior
plating - all of it pre-cut to an accurate fit-up.The result of
these efforts is that since all parts are machine-cut to an
exacting shape, and the hull can be erected with precision, the
builder - amateur or otherwise - can avoid the distortion problems
associated with poor fit-up of plates.For further information about
the NC Cutting process and how NC Cut Files are developed, we have
posted a number of NC cutting articles online. The "Plate First"
MethodWith the "Plating-First" method, the plate outlines are
precisely defined. They are either developed manually, or from a 3D
physical scale model, or they are defined using a 3D CAD model.
Then the plates are cut to their perimeter outline, and arranged so
they can be pulled into place one by one and tacked together, and
finally the plates are welded up. This much can sometimes be done
without using internal or external moulds as a guide, but more
commonly moulds of some sort will be used. The moulds can be frame
segments or they can be other types of temporary guides to the
shape. After the hull plate seams are welded up, the frames are
patterned to the interior of the hull plating, then the frames are
installed and welded in place.The primary advantage of placing the
frames afterward is to allow the plating to be welded up first
without there being any potential distortion introduced by the
presence of a relatively un-yielding frame inside. This can produce
an extremely fair hull, and can do so even without there being much
skill involved on the part of the builder, thus although it has
enormous appeal to amateur or back-yard builders, it also has
substantial appeal to many professional boat builders. It is for
example the most common method in use throughout the Netherlands,
where there is a very highly developed metal boat building
industry.The main disadvantages of the "plate first" approach are:
That unless the plating is patterned very accurately there can be
unpredicted variations in the shape of the hull, there being no
internal frame to control the overall shape, nor to provide an
indication that the hull shape may be turning out differently than
intended; and That the actual shape of the hull must conform to
what is a readily developable plate shape, limiting the design
somewhat. This "hull shape" restriction is the only significant
drawback to the "plate-first" method. It just means that the
designer must use fully "developable" hull forms. Though this
limits what is possible aesthetically and in terms of being able to
optimize the underwater hull form, it is fortunately not a
crippling limitation...!When we are discussing any of the various
"plate-first" methods, it should be recognized that this approach
is really only applicable to the hull bottom and side plating,
possibly including the transom. This method however is generally
not applicable to appendages such as the keel or rudder, nor
ordinarily to the deck and house structures. Therefore, really only
about 35% to 50% of the vessel's total plating surface is even
under consideration when referring to any of the plate first
methods.Just as with the "frame first" method, in order to address
the issue of accuracy, the "plating first" method can take
excellent advantage of CAD for patterning and NC cutting. This
approach will yield an extremely precise plate definition and
consequent cutout, and therefore will provide a much more accurate
as-welded hull shape. By using NC cutting, the frames too can be
pre-planned and pre-cut, making allowances at their joins for the
inevitable small variations introduced by the weld shrinkage during
the weld-up of the plating prior to the frames being put in
place.It should be mentioned that even when using the "plate-first"
approach, it may be advantageous to attach a number of internal
frame members to the plating prior to it being offered up to the
boat, in particular this will often apply to the longitudinal
stringers. This kind of "plate-first" approach is rather common
among professional builders in the Netherlands. Often, frames are
placed as there are opportunities to do so in order to retain the
overall shape. For example, once the bottom plating and
longitudinal stringers are in place and welded to the keel sides,
internal bottom frames can be introduced while the structure is
easily accessed, then the topside plating attached and welded up
prior to introduction of the side frames. This results in an
extremely fair hull, as well as a highly accurate shape.In my view,
this hybrid strategy has the most to offer, especially when used
with NC cutting. In order for the designer to plan the shape and
the NC cutting so that construction can proceed smoothly, it must
be determined in advance just what sequence the builder will use to
assemble the plates and frames. Variations on a Theme...Within the
"plate-first" approach, there are two main divisions: 1. The
"Pre-Cut-Plate" method as described above, and2. The "Folded-Plate"
or so-called Origami method.With the "Pre-Cut-Plate" approach, the
plating is all planned for developability (curvature in one
direction only, i.e. not saddle shaped or dome shaped). Here, the
plating is all pre-cut, pulled into place - ordinarily over a mould
or temporary supports - then stitched together along the seams.
This is essentially the "plate-first" method described above.Taking
this pre-cut-plate approach one step farther, we have the "Folded
Plate" or Origami method, whereby as many of the hull plate weld
seams as possible are eliminated via an ingenious layout of the
seams and a shape that allows there to be a number of "pre-joined"
areas. The advantage of the "Folded Plate" method is that with an
accurately pre-planned outline that's cut out of plate, the entire
hull plating can first be laid out flat - port and starboard -
welded where necessary to create the sizes and shapes required,
then it's all pulled together and stitched into place. Using this
method, once the plate shapes have been determined, the hull
plating can be erected in a very short time - often in a matter of
days. Of course this looks impressive...! It actually is
impressive! Naturally this concept has captured the imagination of
the amateur metal boat building community, thus a possibly
significant contingent among potential owner-builders.With the
Folded Plate / Origami method however, one must realize that the
designer is unfortunately extremely limited in terms of the
possible hull shapes that will actually do this trick. Try it with
paper cutouts and you will be immediately convinced. You can
achieve a few minor variations and still get shapes that will fold
together, but regional subtleties of hull form are just not
possible. If a different type of hull form is desired, then quite a
lot of trial and error time must be spent - usually by making
actual trial cutouts and seeing if they will fit together in an
attempt to discover a totally flat plate layout that will provide
the intended shape when folded together. This is not only a severe
limitation on the designer - it also restricts the builder who may
as a result have only one basic model to offer. In other words,
variations to the hull shape are difficult and time consuming to
create, so the vessels are limited to being either larger or
smaller, fatter or more slender, taller or shorter, having more or
less sheer, yet essentially the same in their general shape and
appearance.Further, it must be kept in mind that just as with the
"pre-cut-plate" method, the "Folded-Plate" or Origami method is
generally only applicable to the hull plating itself, and not to
the keel, rudder, deck, or superstructure.We observe then the
following disadvantages of the "Origami" method:1. Only a limited
portion of the total plate surface will be addressed by the Origami
method;2. The variety of hull shapes that are possible both
aesthetically and functionally are quite limited;3. There will be
quite a lot of fussing around with trial shapes prior to achieving
the desired result. As a result of these factors, I have not so-far
been tempted to pursue the Origami approach in my design
work.Except for the initial "wow" factor, which holds a certain
well deserved appeal among amateur boat builders, I don't see much
advantage to it, especially in a professional boat building
context. In particular, this is so due to the extreme restriction
on the variety of possible hull shapes that can be offered. The
hull shapes become extremely alike, therefore ordinary and
uninteresting. Ask any of the proponents of the Origami method how
many truly "different" hull shapes they have been able to design or
build using that approach (hulls which are not simply stretched or
squished versions of the same thing), and I believe you'll
immediately see what I mean.One can just as easily make use of the
"pre-cut-plate" approach, and have considerably more freedom with
subtleties of hull form.Strategy...?If one is able to begin with a
blank sheet, in other words if one is able to create a new custom
yacht design, it becomes possible to choose between a frame-first
vs. a plate-first building method. In this case, the first task in
the design cycle belongs to the owner, and that is to find a
designer who can bring about the owner's vision and purpose for the
vessel they have in mind.The designer's role is to act as the
owner's advocate throughout the whole process, attempting to meld
their requirements / requests with what is practical / achievable /
safe / etc., at the same time as attempting to achieve the
aesthetic, the layout, and the performance being sought. Then once
the vessel has been designed, to follow through during the
construction of the vessel, first to connect the owner with a
builder who is suited to the task, and then to follow through
during construction to assure that what has been designed gets
built as planned.Occasionally this order of events gets turned
around, and the owner first finds a suitable builder, then together
they forage for a design that the owner likes and that the builder
wants to build. While this can often result in great success, it
can also result in great compromise. However if the compromise is
not too great, and the cost is attractive, then a deal may be
struck that is satisfying to all involved. More often than not
though the builder or the owner will want to introduce changes to
the design. Subtle variations to the interior, usually introduced
by the owner, are to be expected and are usually not of any
consequence. Major changes to the layout that involve changes to
the structure, or that involve relocating tanks, bulkheads,
engines, major machinery, masts, etc. are very often sought.
However, any of these kinds of changes must necessarily involve the
designer.What is not often realized is that collectively, these
changes can quickly eliminate any possible advantage to having
selected a stock design. At this point, it can become advantageous
to begin from a blank sheet - even if it is largely based on a
prior design. Thus, our nearly 100% focus on new custom yacht
design.If a stock design is entirely suitable as is, or if minor
changes are all that's needed, then certainly the designer will be
able to "customize" that design to suit - it is all part of a
designer's usual routine.The Question of Pedigree... All the
building methods mentioned above can be made to satisfy the
structural requirements of the ABS or other rules - with the
exception of the so-called "frameless" building method, which
cannot. In considering any existing design, one should inquire as
to whether the structure has been designed according to the
standards of one or more of the yacht classification societies.For
motor vessels, we calculate structure per the requirements of the
ABS Rule for Motor Pleasure Yachts, or for sail boats, the ABS Rule
for Ocean Racing Yachts, or both, taking the most conservative
result from each, then adding our own factor of safety. We also
consult applicable portions of the German Lloyd's rule and other
classification society rules such as Lloyd's Register wherever they
may be appropriate, such as for spars and rigging or for wooden
structures, etc.Aside from the structure, when inquiring about any
stock design or new custom design it will be prudent to inquire
about the stability compliance of the vessel being considered. For
example, we impose the EU Recreational Craft Directive stability
requirements on our designs - both sail and power. Even though
there are legally no stability standards imposed on pleasure craft
built and registered in the US, we feel this is quite important,
therefore the EU-RCD is our base-line standard.You can read about
our rationale for use of these standards, what they mean, and how
they apply by reviewing our various articles related to "Boat
Design" on the Articles web page. In terms of safety equipment,
while we very much advocate the use of the ABYC guidelines for
safety and systems, there are a few specific areas where we
disagree with the ABYC recommendations. Mainly this is limited to
those chapters where the ABYC guidelines are at present
inadequately developed and are rapidly changing - in particular
with regard to bonding and electrical isolation on metal vessels.
We address these matters thoroughly in our Vessel Specification
which accompanies each design, often amounting to well over 50
pages.ConclusionsA number of our designs are fully developable, and
are thus directly adaptable to the "pre-cut plate-first" approach,
in particular if NC cutting were to be employed. Examples that come
to mind are the 36' ketch Grace and her larger sisters: the 42'
schooner Highland Lass and the 42' ketch Zephyr, which have fully
developable hulls. Many of our other designs, while largely
developable, have intentionally violated developability locally in
order to achieve the right aesthetic shape or the right
distribution of displacement or the right waterlines or buttock
lines, etc. Examples include the 44' schooner Redpath or those
designs for which a rounded hull form was preferred such as the 36'
cutter Fantom, the 40' schooner Benrogin, or the 50' schooner
Lucille.Although we have no particular interest in pursuing the
"origami" approach as such, we do believe there to be considerable
merit to the "pre-cut-plate-first" approach. More particularly we
have observed big advantages to the hybrid
"plates-first-then-frame-as-you-go" approach mentioned above. Even
though hull shapes are thus limited to only what is developable,
there are innumerable good shapes that one can achieve which are
aesthetically pleasing and that have a water-friendly shape.To be a
success, the pre-cut plate shapes must be precisely planned and
cut, but this is not at all difficult when combined with CAD driven
NC cutting. We have developed NC cutting files for a number of our
designs, and we're continually involved in the development of new
designs - and of NC files to ease their construction.Further
Considerations...?We believe in metal as the ultimate boat
structure, and as a result we have created quite a number of metal
boat designs. To review them, please see our Sail Boats Gallery and
our Power Boats Gallery. We have also created quite a number of
Prototype Designs, most of which are also intended for metal
structure. Sail or power - mono or multi-hull - if the structure is
well-designed and well built, the resulting boat will be excellent.
We are often asked about one metal vs. another - most commonly
steel vs. aluminum. We do not have a distinct preference. There are
so many varying factors that will contribute to making that
decision for each boat, and for each owner. Some boats are designed
for one material only, other boats can make use of either. In
general, any of our designs that have been developed for steel can
very quickly be re-specified for construction in aluminum. The
design conversion from steel to aluminum is done at no extra cost.
Where NC cutting files exist for a steel boat, they will need to be
re-done in order to work for aluminum structure, and there will be
a cost incurred for that conversion. If that's of interest, please
inquire.Designs that were originally developed for aluminum
structure are not as readily converted, since they will have been
designed specifically to save weight. To convert one of them to
steel structure will ordinarily require a re-work of the hull shape
in order to support the extra weight of steel. For some boats, that
is not much trouble. For other boats, in particular small ones,
steel may not even be an option. If a conversion to steel is of
interest for one of our aluminum designs, please inquire. for more
information.You will find more information about costs and other
considerations between these metals among the essays linked from
our Articles web page, and especially in the two articles listed
below. For more information about any of the above, please feel
free to contact me.Related ArticlesMetal Boats for Blue Water |
Strength of Aluminum vs SteelPlease see the Plans List page to
review our available Boat Plans.
Home | Intro | Custom Yacht Design | Stock Designs | Motor Yacht
Gallery | Sailing Yacht Gallery | Prototypes Gallery | Plans List
Articles | Our CAD Design Stream | MAXSURF For Marine Design |
News..! | Design Team | Site Map | Site Search | Contact Us
All Web Site Graphics, Layout, and Written Content at this
Domain Created by Michael Kasten. All Graphic and Written Materials
at this Domain Copyright 1989 - 2010 Michael Kasten. All Content
Registered with US Library of Congress and US Copyright Office.
Copyright Violations will be Prosecuted. All Rights Reserved.
Boat Materials
Aluminum. We use only the finest materials available. The 5000
series marine grade aluminum alloy is specifically made for
full-time saltwater applications. ALCOA, Aluminum Company of
America, put a plate of this aluminum in Narragansett Bay, RI for
thirty years and took it out because nothing was happening. We have
chosen the 5086 alloy for the whole hull. This aluminum alloy is
the absolute best available and thick to boot. With either 3/16 or
1/4 construction, these boats are 2-3 times as thick as most
aluminum boats you may be familiar with. If youve ever seen a U.S.
Coast Guard 47 footer than youve seen 5000 series aluminum alloy at
work afloat.
Gunwale. This 2 3/4 oval in cross-section extrusion gives the
edge of your boat incredible durability. Weve had demo rides where
a prospective customer inadvertently slammed the boat into cement
pilings with just a slight rub to show for it. The only reason to
own fenders is to protect the other guys boat.
Chine. Along the length of the chine is an extrusion that both
the side and the bottom plates fit into. This high impact area is
then double welded the length of the boat. This level of quality is
unheard of even in custom aluminum boats.
Non-Skid. This material is applied to the self bailing deck and
consists of a polyurethane base and topcoat surrounding an
aggressive non-skid abrasive. Not for the faint of heart, nor the
bare of foot, this material is similar to the new bedliner material
you may be familiar with as an aftermarket application in pick-up
trucks. It gives you tough, durable, surefooted-ness in all weather
conditions.
Foam. We inject closed cell foam beneath the self-bailing deck
into all voids below decks (except around the fuel tank). This
high-end system assures you of both unsinkability and upright
flotation should you ever swamp the boat.
In short, no expense is spared in making for you the finest boat
available anywhere. These materials, used for the first time in a
production model boat, truly represent the first in a whole new
category of boats.
Black Lab Marine Partners, LLC
207-400-7404
Aluminium Alloys Used in the Marine IndustryAluminium alloys
commonly used in the marine industry include: Aluminium-magnesium
alloys - 5000 series, used primarily for rolled materials
(sheet/plate). Most common are 5083 & 5383.
Aluminium-magnesium-silicon alloys - 6000 series, used primarily
for extruded sections. Most common are 6082, 6061, 6005A &
6060.
Source: Capral AluminiumFor more information on this source
please visit Capral Aluminium.
Aluminum Distributing Inc 5086-H111, 5086-H116, 5083-H116
aluminum for marine use/ sheetwww.adimetal.com/ Marine GradeAlloy
Aluminum 5083 5086Structural Marine GradeAlloy Aluminum 6061
Sheet and Plate (5086-H116 or 5083-H116 or Dual)
Check up to five results to perform an action.
Aluminum 6061Chemistry Data : Aluminum : Balance Chromium : 0.04
- 0.35 Copper : 0.15 - 0.4 Iron : 0 - 0.7 Magnesium : 0.8 - 1.2
Manganese : 0.15 max Other : 0.15 max Remainder Each : 0.05 max
Silicon : 0.4 - 0.8 Titanium : 0.15 max Zinc : 0.25 maxAluminum
5086Chemistry Data:Aluminum: BalanceChromium: 0.050.25Copper: 0.1
max.Iron: 0.4 max.Magnesium: 44.9Manganese: 0.41Remainder Each:
0.05 max.Remainder Total: 0.15 max.Silicon: 0.4 max.Titanium: 0.15
max.Zinc: 0.25 max.
largerimage Several sizes dual certified
The following specifications cover Aluminum 5083
QQ A250/6Aluminum 5083Chemistry Data:Aluminum: BalanceChromium:
0.050.25Copper: 0.1 max.Iron: 0.4 max.Magnesium: 44.9Manganese:
0.41Remainder Each: 0.05 max.Remainder Total: 0.15 max.Silicon: 0.4
max.Titanium: 0.15 max.Zinc: 0.25 max.
Mechanical Data :
Aluminum 6061-T6Ultimate Tensile Strength, psi : 45,000Yield
Strength, psi : 40,000Brinell Hardness : 95Rockwell Hardness :
B60Aluminum 5086Form : Sheet Condition : H116 Temperature :
68Tensile Strength : 42Yield Strength : 30Elongation : 12Aluminum
5083Form : Sheet Condition : H116 Temperature : 68Tensile Strength
: 42Yield Strength : 30Elongation : 12
Principal Design FeaturesThis is a non-heat treatable alloy for
strengthening. It has very good corrosion resistance, is easily
welded and does have good strength.
ApplicationsCommonly used in the manufacture of unfired, welded
pressure vessels, marine, auto aircraft cryogenics, drilling rigs,
TV towers, transportation equipment, and in missile components.
Aluminum Mill Product Specifications
Available Forms:Sheet and Plate ASTM-B928 ,
FEDERAL-QQ-A-250/7
5086 Marine Grade Aluminum Alloy
Click on a Product to view details.
Angles - 25 Ft (5086-H111)(19)
Pipe (5086-H32) Drawn Seamless(29)
Sheet and Plate (5086-H116 or 5083-H116 or Dual)(35)
Flat Bar (5086-H111)(28)
Round Tube (5086-H32) Drawn Seamless(18)
Round Rod (5086-H111)(16)
The Butt Weld Fittings and Flanges (5086)(7)
Sheet and Plate (5086-H116 or 5083-H116 or Dual)
Check up to five results to perform an action.
largerimage Several sizes dual certified
The following specifications cover Aluminum 5083
QQ A250/6
Chemistry Data:Aluminum: BalanceChromium: 0.050.25Copper: 0.1
max.Iron: 0.4 max.Magnesium: 44.9Manganese: 0.41Remainder Each:
0.05 max.Remainder Total: 0.15 max.Silicon: 0.4 max.Titanium: 0.15
max.Zinc: 0.25 max.
Mechanical Data : Form : Sheet Condition : H116 Temperature :
68Tensile Strength : 42Yield Strength : 30Elongation : 12
Principal Design FeaturesThis is a non-heat treatable alloy for
strengthening. It has very good corrosion resistance, is easily
welded and does have good strength.
ApplicationsCommonly used in the manufacture of unfired, welded
pressure vessels, marine, auto aircraft cryogenics, drilling rigs,
TV towers, transportation equipment, and in missile components.
Aluminum Mill Product Specifications
Available Forms:Sheet and Plate ASTM-B928 ,
FEDERAL-QQ-A-250/7
6061 Structural Marine Grade Alloy Aluminum
Click on a Product to view details.
Structural Equal Angle (6061-T6)(17)
Structural Unequal Angle (6061-T6)(4)
Structural Flat Bar (6061-T6511)(46)
Structural "U" Channel (6061-T6)(8)
Structural Beams (6061-T6)(3)
Structural Tee (6061-T6)(2)
Round Tube (6061-T6)(4)
Square Tube (6061-T6)(4)
Pipe (6061-T6)(14)
Round Rod (6061-T6511)(14)
Square Bar (6061-T6511)(6)
Flat Sheet (6061-T6)(5)
Flat Sheet (6061-T6)
Check up to five results to perform an action.
largerimage The following specifications cover Aluminum 6061
6061 Aluminum is, by most any measure, the most commonly used
aluminum alloy. It is specified in most any application due to its
strength, heat treatability, comparatively easy machining, and
weldability. If that were not enough, it is also capable of being
anodized, adding a layer of protection for finished parts. The main
alloy ingredients of 6061 aluminum are magnesium and silicon.
Physical and Mechanical PropertiesUltimate Tensile Strength, psi
: 45,000Yield Strength, psi : 40,000Brinell Hardness : 95Rockwell
Hardness : B60
ASTM B209, QQ A-250/11
Chemistry Data : Aluminum : Balance Chromium : 0.04 - 0.35
Copper : 0.15 - 0.4 Iron : 0 - 0.7 Magnesium : 0.8 - 1.2 Manganese
: 0.15 max Other : 0.15 max Remainder Each : 0.05 max Silicon : 0.4
- 0.8 Titanium : 0.15 max Zinc : 0.25 max
Principal Design Features Probably the most commonly available,
heat treatable aluminum alloy.
Applications Commonly used in the manufacture of heavy-duty
structures requiring good corrosion resistance, truck and marine
components, railroad cars, furniture, tank fittings, general
structural and high pressure applications, wire products, and in
pipelines.