An Analysis of Slocum 37 Yawl

8/18/2019 An Analysis of Slocum 37 Yawl

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An Analysis of Slocum's 37' Yawl

'SPRAY'

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Spray Original Sail Plan | Spray Original Sail Plan Inverse | Spray Original Hull Lines |

Spray Original Body Lines

Article & Screen Sots Copyrigt !"## $ !"#% icael 'asten

QUALITIES OF SLOCUM'S SPRAY

(irst) it sould *e kno+n tat I am actually a fan of te original Spray $ i,e, te one tat

-osua Slocum sailed around te +orld, Ho+ever I am only a fan in a limited sense,

Allo+ me to ela*orate,,,

http://www.kastenmarine.com/_drawings/spray_sail_plan.gifhttp://www.kastenmarine.com/_drawings/spray_sailplan.gifhttp://www.kastenmarine.com/_drawings/spray_sailplan.gifhttp://www.kastenmarine.com/_drawings/spray_lines.gifhttp://www.kastenmarine.com/_drawings/spray_body_lines.gifhttp://www.kastenmarine.com/copyright.htmhttp://www.kastenmarine.com/_drawings/spray_body_lines.gifhttp://www.kastenmarine.com/_drawings/spray_sail_plan.gifhttp://www.kastenmarine.com/_drawings/spray_sailplan.gifhttp://www.kastenmarine.com/_drawings/spray_lines.gifhttp://www.kastenmarine.com/_drawings/spray_body_lines.gifhttp://www.kastenmarine.com/copyright.htm


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.at te O/I0I1AL Spray +as a*le to contri*ute most nota*ly for Slocum2s voyage +as

e3cellent directional sta*ility) i,e, outstanding and apparently infalli*le course keeping

a*ility, 4is inerent self$steering a*ility +as te result of several factors5

• A long straigt keel) deepening aft

•

A full and rounded *o+• A long straigt run aft

• A for+ard$of$amidsips center of *uoyancy,

4is com*ination allo+ed te vessel to *eave some+at like a dart) +it te +eigtfor+ard and te featers aft, Alternately you can imagine a tear$drop saped *om* +it

fins aft $ te ideal sape for sta*ility in a free$fall environment,

4is made te Spray rater poor to +ind+ard) *ut super* off te +ind, 4e Spray +as not

slo+) as many migt tink, On te contrary) te Spray +as capa*le of 6uite fast sailing+en off te +ind or on a reac, 4is +as due to er soal draft) far for+ard CB) long

straigt run of te *uttock lines aft) e3treme stiffness due to er e3cessive *eam andsallo+ draft) and aving a lo+ aspect *ut very ample gaff ya+l rig, In oter +ords) aslippery sape and plenty of sail area,,,7

RA!"AC#S OF SLOCUM'S SPRAY

As a long distance voyaging *oat te Spray did ave several dra+*acks) te most

important of +ic +ere e3cessive *eam and e3tremely soal draft, 4is com*ination

resulted in te vessel *eing 8ust as sta*le upside do+n as it +as uprigt, In plain +ords)te Spray ad 9ero self$rigting a*ility,

It sould *e noted tat te +ooden oyster smack tat Slocum named te :Spray: +as

presented to im as a gift) i,e, for free, At tat point it +as a rotten old ulk +ic Slocum

ten proceeded to restore on a very limited *udget, ;ue to Slocum +it ample sail area for tat purpose,

4is is a prime e3ample of a commonly sared caracteristic amongst many of te +ellkno+n long distance sailing accomplisments,,, tey +ere not te result of long arduous

planning to create te :ideal: voyaging *oat, Instead) te most spectacular individual

sailing acievements occurred +en a determined sailor encountered a more or lesssuita*le craft tat tey could ac6uire ine3pensively and put to sea in +itout too muc

fooling around, In oter +ords) tey +ere opportunists +o made e3pedient use of +at

+as ready to and,,, It is a good lesson7

Slocum2s spectacular voyage +it te Spray +as no e3ception,


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FAIT$FUL REPLICAS%%%

4e a*ove comments apply to te O/I0I1AL Spray) as re*uilt *y -osua Slocum) +icas su*se6uently *een reproduced *y oters suc as Pete Culler and 0il*ert 'lingel)

often +it good success, ost of tem +ere igly faitful to te original,

I +as fortunate enoug to go a*oard a very good replica of te Spray in Ha+aii in #?@?)

*uilt *y Bo* Carr in ermont) and +ic e single anded from tere to Honolulu, Head *een some #" days from Panama to Ha+aii) possi*ly a record for te slo+est

passage on tat route,,7 Ho+ever Bo* ad encountered long periods of calm) and a

num*er of storms, His mains2l +as *lo+n out) and e +as nearly do+n to te *ottom ofis :*ean *arrel: even toug e did catc a lot of fis,,7 It +as impressive to see tree

large gar*age pails in te store room5 one for *eans) one for rice) one for +eat,

A friend icael Colfer and I elped Bo* Carr paint te *oat2s *ottom +ile e +as

auled out at 'eei Lagoon) near Honolulu, .e eard several good stories during tat

time and +e +ere +ell fed) al*eit on cicken ste+ of 6uestiona*le vintage, 4ere *eingno refrigeration a*oard) tis +as cause for concern, Like many *efore im) Bo* Carr

sailed +itout an engine so e used kerosene for ligts and kerosene for cooking, 4eonly electricity a*oard +as inside is flasligt and enit transoceanic radio,,,7

Anoter friend) 0eorge aynard) *uilt a faitful replica of Slocum2s Spray in 1oank)

Connecticut) Slocum2s original starting place, aynard named is vessel :Scud: and

su*se6uently sailed it around te +orld +it is +ife and young cildren $ a daugter andt+o sons, aynard2s voyage) like tat of Slocum and Bo* Carr) +as accomplised

+itout te aid of an engine or any fancy electronics,,,

/ecently I ave read tat a sailor purcased aynard2s :Scud: and as once again circumnavigated in te vessel) also +itout an engine, Duite a num*er of Spray replicasave acieved similar success, Oters ave met +it sip+reck or loss +itout a trace

suc as te Pandora, 4is in fact is +at appened to te original) +ic took along r,

Slocum imself,

%%% A& T$E U&FAIT$FUL

In recent years te name =SP/AE> as *een used *y a fe+ *oat designers in order to takeadvantage of name recognition for marketing purposes, ost nota*ly) several steel

:Spray: models ave *ecome popular among amateur steel *oat *uilders, 4is is largely *ecause te plans are very ceap to *uy, ;espite te o*vious fact tat tose designs avenoting in common +it te original Spray) te reno+n of te name itself is apparently

convincing to tose amateur *uilders, 4e lack of any sem*lance to te original is also

te case in terms of te rig) te ull sape and many oter parameters) *ut most nota*ly itis so in terms of teir appearance,


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I regard tese so$called =Spray> designs as *eing e3tremely crude attempts) especially in

terms of capturing te *eauty of te original Spray, In my opinion tese =Spray> poseurs

ave little if any relationsip to te original e3cept to say tat tey ave *orro+ed te:Spray: name) and tat tey are fat) over+eigt) and total dogs to +ind+ard $ noting

else in any +ay resem*les te original,

(urter) tose vessels ave failed to improve upon te inade6uate ultimate sta*ility of te

original Spray, As insult to in8ury) te structure of tese vessels is inordinately comple3)in oter +ords poorly adapted to amateur construction) as is teir claim, I am 6uite sure

you kno+ te vessels of +ic I speak,,, I do not need to name names,

MOELI& T$E ORII&AL SPRAY

Having said te a*ove) I ave al+ays *een curious a*out te SP/AE) in particular to

understand and possi*ly replicate its e3cellent course keeping a*ility for use on oter

designs, In order to kno+ more a*out te SP/AE) I +ent to te trou*le to model tedesign so tat I could investigate its ydrostatics) sta*ility) *alance and sailing

performance in greater detail, Images tat so+ te results of tat modeling effort can *eseen in te follo+ing links and te image *elo+5

Original Spray A*ove Aft | Original Spray A*ove (or+ard

http://www.kastenmarine.com/_screenshots/spray_original_above_aft.jpghttp://www.kastenmarine.com/_screenshots/spray_original_above_fwd.jpghttp://www.kastenmarine.com/_screenshots/spray_original_above_aft.jpghttp://www.kastenmarine.com/_screenshots/spray_original_above_fwd.jpg


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Click Image for Larger ie+

PARTICULARS ( COMME&TARY

Pa)*icula)s of Slocum2s Original Spray are5

• Lengt on ;eck5 F%2 $ ?:

• Lengt on .L5 F!2 $ !: Gincluding stem

• Lengt on .L5 F#2 $ F: Ge3cluding stem

• Beam on ;eck5 #2 $ #:

http://www.kastenmarine.com/_screenshots/spray_original_above_fwd.jpg


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• Beam on .L5 #F2 $ ?,J:

• ;raft at ;.L5 2 $ !,J:

• ;isplacement5 #%,# Long 4ons Gincluding keel

• ;isplacement to Lengt5 F

• Long2l Position of CB5 J"K Gincluding keel) measured from stem ra**et

•

Prismatic Coefficient5 ,%@F Gincluding keel• Prismatic Coefficient5 ,%% G*ody only

• Beam to Lengt on ;eck5 F,JK

• .L Beam to .L Lengt5 K Ge3cluding stem

• Ea+l /ig Sail Area5 #)#F@ s6, ft,

• Sail C Lead vs CL/5 ,?K Ga*out rigt considering e3treme *eam) soal draft)

and lo+ aspect rig

• SA M ;isplacement /atio5 #%,% Gtypical range5 #% to !#) terefore fairly lo+

• SA M .etted Surface /atio5 !,J Gtypical range5 !," to !,%) terefore a*out rigt

Comm+n*a)y5 Looking at te a*ove) a fe+ comments are in order,

• A ;isplacement to Lengt of F is 6uite ig, Please see my Calculations P;(

for te ranges one sould e3pect) +ic indicate a ;ML more on te order of

around F"" to F!J for fairly eavy cruisers,

• 4e Prismatic Coefficient at ,%@F is very ig, Spray) aving *een originally *uilt

as an oyster smack) +as designed for ma3imum carrying capacity on a sallo+

draft) terefore a ig Cp is not entirely out of place, Suc a ig Cp means very

full ends) in tis case +eigted sligtly more in favor of te *o+ tan +ould *e a

modern sail*oat, A ig Cp favors ig speed) *ut is a disadvantage in terms of+avemaking resistance +en sailing at slo+er speeds as is more often te case,

• ore typically a sailing yact2s Cp sould *e in te range of *et+een ,JJ and ,Jfor all$around cruising) possi*ly a *it iger for a racing sail*oat,

• In my vie+) for tis type of vessel used as a yact) Cp +ould ideally *e reduced to

some+ere in te range of ,J to ,%# at te most) +ic +ould still favor iger

sailing speeds) *ut +ic +ould confer improved pitc dampening and added

*uoyancy in te ends for eavy +eater,

• Sail area to +etted surface is 6uite good in te original Spray) indicating good

ligt +eater performance) o+ever SA to ;isplacement is less tan optimum,

Sail area could terefore *e increased) especially so given te enormous initial

sta*ility Gstiffness under sail, See my Sail Area /atios P;( for more information,

• A ratio of .L Beam to .L Lengt of K is really rater e3treme, Someting on

te order of around FFK is muc more in keeping +it sea$going sail *oats,• Assuming a C0 of % inces a*ove te ;.L Gan assumption only) te

;ellen*aug Angle is calculated to *e J, degrees +it #J knots of +ind a*eam,/aising te C0 to ?: a*ove te ;.L only results in a small increase in eel) to

% degrees,,, in oter +ords N4/LE stiff) as +ould *e e3pected, A typical

range of eel angles for tis si9e sail *oat is on te order of #F to #? degrees,Duite a difference,,7

http://www.kastenmarine.com/_pdf/coefficients_of_form_equations.pdfhttp://www.kastenmarine.com/_pdf/sail_area_ratios.pdfhttp://www.kastenmarine.com/_pdf/coefficients_of_form_equations.pdfhttp://www.kastenmarine.com/_pdf/sail_area_ratios.pdf


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Mo,+l &o*+s- It sould *e pointed out tat Slocum


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+ould te C0, 4is com*ination +ould preserve a considera*le measure of te vessel2s

e3cellent stiffness +itout degrading its inerently e3cellent voyaging capa*ilities,

After I created a 1/BS surface model of te original SP/AE) I ten made te a*ovementioned modifications to te model to see +at tey migt offer, 4oug my

modifications may not *e all tat easy to detect in te images linked *elo+) tey aveindeed produced te desired result,,,

odified Spray Perspective (or+ard | odified Spray Perspective Aft

T$E MOIFIE SPRAY MOEL

Lengt on deck is increased to feet) and te .L lengt to around # feetQ *eam is

uncangedQ dept of ull is increased and draft is ,@! feetQ displacement is increased to

!!,? long tonsQ and sail area is increased, As a result of aving *een made longer *ut not

http://www.kastenmarine.com/_screenshots/spray_fwd_above.jpghttp://www.kastenmarine.com/_screenshots/spray_aft_above.jpghttp://www.kastenmarine.com/_screenshots/spray_fwd_above.jpghttp://www.kastenmarine.com/_screenshots/spray_fwd_above.jpghttp://www.kastenmarine.com/_screenshots/spray_aft_above.jpg


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+ider) te ;isplacement to Lengt as *een reduced to around F!?) +ic is still a ro*ust

ull sape *ut not overly eavy,

4e Prismatic Coefficient is do+n to ,% including te keel and stem) and ,%% for te ull *ody only, 4is is still a *it too ig for optimum performance at typical sailing speeds)

*ut is indicative of a ig speed potential and ample *uoyancy in te ends for *ettersupport in eavy +eater, 4e Center of Buoyancy remains appro3imately amidsips)

terefore is uncanged, 4e fore and aft distri*ution of displacement is uncanged) i,e,still a full *o+ and fine run aft,

4e rudder +as made +olly e3ternal) +ic re6uired tat te transom rake *e canged

sligtly) and tat te dead+ood *e e3tended sligtly farter aft, 4e aft deck as *eengiven an overang 8ust sufficient to ouse and protect te rudder) and to create a

convenient landing for te mi99en mast,

In te image a*ove) you +ill notice tat I ave also raised te aft deck to te eigt of te

*ul+ark top) ten introduced a toe rail around te aft deck, /aising te aft deck is not atall necessary) *ut it does provide advantages in terms of reserve *uoyancy and self

rigting) as +ell as providing considera*ly greater interior space aft,

Along +it tose ull refinements) a fe+ improvements +ill ideally also *e made to te

rig R not to cange it from Slocum2s Ea+l rig) *ut to increase te relative si9e of te rigfor te sake of improved performance, Ideally te SA M ;isplacement ratio +ould *e

a*ove #) prefera*ly closer to !", 4is implies a Sail Area of around #)J"" s6, ft, or more,

I ave proposed a sail area of #)@"" s6, ft,

4e amount of lead from te C to CL/ sould stay te same) i,e, appro3imately ?K) or

possi*ly it could *e reduced sligtly due to te reduced *eam ratio, By increasing sailarea) a iger C +ill result) *ut tis +ill *e offset *y te lo+er C0 inerent in te

deeper ull, 4e result of aving less *eam +ill *e an increased amount of eel vs teoriginal SP/AE, Having a lo+er ;ML ratio) increased sail area) a deeper ull and e3ternal

*allast) te result +ill *e *etter performance on all points of sail) especially to +ind+ard,

All of tese canges are possi*le +itout aving to degrade te inerent e3cellent

tracking of te original Spray design on a passage) nor to adversely affect te traditionalaestetics of te original,

T$E ORII&AL SPRAY /s T$E MOIFIE SPRAY%%%

In 4e /udder maga9ine) ol, !#) #?"?) tere is an article *y C, Andrade tat attempts to

analy9e te Spray, It is interesting to note tat te article +as +ritten rougly a mont

after Slocum +as lost at sea,,, It is also interesting to read a fairly ela*orate *ut raterarcane analysis using te e3tant naval arcitecture principles of te day,,,7 Anyone

curious can read te article on 0oogle Books,


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In any analysis of te 6ualities of te Spray) it must first *e pointed out tat5

#, 4o my kno+ledge te vertical center of gravity of te original Spray as never *een

documented,!, 4e lines of te Spray as pu*lised *y Slocum in Sailing Alone Around te .orld are

not accurate, In oter +ords) as noted a*ove te tree vie+s do not matc7

Oters ave pu*lised teir o+n version of te lines of te Spray) including .eston

(armer) Pete Culler) and C, Andrade, I ave not cecked tose versions of te linesagainst te original) nor against my o+n model of te Spray) *ut I +ill say for certain tat

te lines tat Slocum pu*lised are not accurate, As mentioned a*ove) per my o+n

modeling efforts te lines and calculations done *y C, Andrade are likely to *e te closestto te original,

SLOCUM'S ORII&AL SPRAY

As noted a*ove) te model I created of te original Spray is as close as I can make it

according to Slocum2s pu*lised lines, In my analysis of te original Spray model I aveassumed te C0 to *e appro3imately inces a*ove te .L, 4is is only an

assumption) since I ave not taken te trou*le to actually calculate te C0) o+ever it

is an assumption tat2s *ased on aving calculated te C0 of several oter eavily *uilt+ooden craft) so it is pro*a*ly not far off,

sing tat C0) te sta*ility curve so+n *elo+ +as derived, 4is curve takes credit for

te volume of te deck ouses) as +ell as te floatation of te masts, ;espite tose

credits) it is evident tat sta*ility is lost at #"" degrees of eel) after +ic te vessel is

6uite sta*le +en inverted,


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Click for Larger Image

If I lo+er te C0 to te .L eigt) ten te righting moments tat I calculate closely

matc tose calculated *y C, Andrade, It is terefore evident tat C, Andrade made teassumption tat te C0 is located at te .L) +ic I *elieve to *e muc too optimistic)

especially considering te inside *allast of stones and cement,,7

Ho+ever if te C0 +ere to actually *e located at te .L Gigly unlikely) ten te point of vanising sta*ility +ould *e appro3imately ##% degrees R 6uite a difference,,7 In

oter +ords) te rigting curve derived *y C, Andrade is likely to *e in error *y tat

amount) or possi*ly even more Gsay in te event tat I ave also *een too optimistic +itregard to te C0,

A range of positive sta*ility of #"" degrees or less is considered to *e inade6uate for a

sailing vessel, In te ) a Sta*ility Inde3 is calculated) called te S4IN value, .it teC0 located inces a*ove te .L per my assumption) Spray earns a S4IN score of !J)+ereas te re6uirement for all ocean operations is a minimum S4IN score of F!,

Thus the Spray fails the STIX criterion by over 20%. Ideally tere +ill *e a su*stantial

margin of safety above te minimum score) i,e, a S4IN score in te mid to upper "2s orgreater,

http://www.kastenmarine.com/_screenshots/slocum%27s_spray_righting_curve_VCG_8_inches_above_WL.png


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/egardless of all te many discussions of te Spray and er admira*le 6ualities) and

not+itstanding te o*vious acievements of te vessel) te sta*ility caracteristics of te

original Spray are plainly inade6uate,

T$E IMPRO0E SPRAY MOEL

I ave gone to te trou*le of modeling te original Spray so tat I could see +at

improvements could *e made starting +it te original Spray lines, I +anted to modifyte model in suc a +ay as to preserve te good 6ualities of te Spray) *ut to improve te

sta*ility range and sailing performance,

sing te modified Spray model tat I eventually settled on at 2 lengt on deck and #2

.L lengt +it a deeper ull *ody) and assuming te C0 to *e F: a*ove te .L)Gpossi*ly too conservative) i,e, a iger C0 tan +ould actually *e te case) te

sta*ility range increases to #!# degrees) and te S4IN score comes to F,%,

Assuming it is possi*le to lo+er te C0 all te +ay to te .L Gpossi*ly acieva*le

+it te deeper ull) deepening te keel farter) and *y using e3ternal *allast) ten testa*ility range comes to #!% degrees and te S4IN score is ?,#,

Click for Larger Image

http://www.kastenmarine.com/_screenshots/KMD_improved_spray_righting_curve_VCG_at_WL.png


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4is is a dramatic improvement) even toug I +ould like to do even *etter +it te

range of positive sta*ility

y primary goals in making suc t+eaks to te SP/AE ave *een to see +at could *edone to make te design safer and more sea+orty, I also +anted to so+ tat suc

improvements could *e made +itout affecting Gi,e, scre+ing up te e3cellent traditionalaestetics of te original) nor to adversely affect its e3cellent tracking a*ility and its

conse6uent value as an ocean voyager,

4e updated model preserves te *alance and course keeping of te original) and makes a

variety of improvements for te sake of performance on all points of sail) and +ould *e a

muc safer platform for voyaging on te *riny deep7

OT$ER C$A&ES%%%..

4e 6uestion arises) :.ould I make additional canges,,,:

Ees, I +ould prefer to reduce te *eam some) *ut +itout canging te distri*ution of

displacement, ;isplacement +ould decrease) and te resulting model +ould ave a moremodest ;ML ratio, .it tat cange made) I2d prefer to reduce te prismatic coefficient to

*et+een ,J@ and ,%" for te sake of improved all around sailing performance, 4is

com*ination +ould result in a more comforta*le ride) and +ould actually increase te

range of positive sta*ility,,,7

CO&CLUSIO&S%%%

any are attracted to te SP/AE simply on te *asis of it aving *een te first vessel tocarry a uman around te +orld) sailing single anded, It is 6uite an acievement to say

te least, .at must *e reali9ed o+ever is tat te voyage +as accomplised *y a

determined and very e3perienced professional sea captain) not *y your ordinary *eac *um,

-ust like many oter +orld$voyaging sailors +o ave also acieved e3traordinary sailing

feats) Slocum +as an opportunist +o made e3cellent use of +at +as availa*le to im)

in is case a freely provided old +reck +ic e re*uilt on a soe$string) and +ic eten 6uite stunningly sailed into permanent fame and an onored place in our istory of

te sea,

Before Slocum left on is istoric voyage) dockside +ags said of te SP/AE) "It'll

crawl...!"

.en e returned) is dockside advisors +ould only deign to say) "ou were lucy...!"


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Luck or no) one cannot deny Slocum2s e3traordinary acievement) +ic +as

accomplised more or less in spite of te tool tat e +as given) i,e, te SP/AE, In oter

+ords) it +as Slocum2s .ILL and long e3perience at sea tat allo+ed im to acieve tisfeat) rater tan it aving *een some sort of caprice conferred upon im *y some

imagined magical attri*utes inerent in te vessel on +ic e sailed,

Copyrigt !"## $ !"#% icael 'asten
http://www.kastenmarine.com/copyright.htmhttp://www.kastenmarine.com/copyright.htm

An Analysis of Slocum 37 Yawl

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