Conference unifix::sailing

>>>    It seems that modern underbodies, if balanced, could give much better
>>>    performance and  maneuverability, particularly with a high-aspect rig
>>>    (see Dec Cruising world's #1 offshore design article), but full keels
>>>    could give much more stability, righting moment, hull rigidity, and
>>>    perhaps safety. 
    
You've made a pretty good short summary of the major points right there.

If you want some background on yacht design which will help you evaluate 
many of the tradeoffs, a pretty good (and readable) start can be had with 
Skene's Elements of Yacht Design, ed. by Francis Kinney.  It's an old 
standby, and doesn't discuss ULDB's and the latest trends, but it'll give
you an appreciation of the designer's art. 

Also Tony Marchaj's treatise on Seaworthiness; not quite as accessible to 
the non-technical reader, but probably *the* current authority on design 
factors affecting monohull seaworthiness.  (Ask Alan for a pithy summary.)

Analysis and theory of multihull seaworthiness, most involved would agree,
is currently being led by John Shuttleworth. 

J.

   Re: .0
   
   To net out all of the comments that could be made on this subject, it 
   really depends on what is important to you and where you plan to 
   cruise. If you have been out there, or read some of the surveys about 
   cruisers you know that people do make crossings in just about anything 
   that floats. You have asked a divergent question of which there is no 
   one right answer. I do not expect to read of the discovery of the 
   "perfect" cruising hull form that all subsequent cruising boat designs 
   conform to. However, to me the issues are seaworthiness, comfort and 
   risk.
   
   On seaworthiness Marchaj makes an interesting point: that the natural 
   evolution of hull designs (over several thousand years) continued to 
   evolve into more seaworthy designs as man found by observation what 
   worked out there and what didn't. It wasn't until the competitors and 
   designers started tinkering with artificial constraints (eg. racing 
   rules where raw speed became the overriding objective) that the 
   evolution of seaworthiness reversed direction and hopefully hit bottom 
   with Fastnet. Note that the older traditional designs were often based 
   on deep, full keels.
   
   Comfort at sea is generally associated with heavier displacement which 
   again often involves a large or full keel. Again Marchaj has some 
   interesting information regarding boat motion and the onset of 
   sea-sickness. The relationship is quite simple: the lighter the boat 
   and flatter the bottom, the more rapid the motion, and the less 
   comfortable relative to a heavier round bilge design.
   
   Friends of ours that have been cruising for 10 years now once pointed 
   out that since they were at anchor over 90% of the time, having the 
   space that deep bilges provided for tankage and stowage was far more 
   important than the minor performance improvement that a lighter 
   displacement, higher performance boat would provide less than 10% of 
   the time.
   
   Comfort also involves the boat being easy to sail (tracking, balance, 
   etc.) which is more important when shorthanded. Full keel boats 
   typically track very well and are quite easy to balance.
   
   Skeg/Spade rudder designs carry a higher inherent risk of damage than 
   other designs. For example a Valiant 40 was nearly lost off the west 
   coast of Vancouver Island in moderate conditions at night after a 
   floating log rolled under the keel, seriously bent the prop shaft, and 
   broke most of the skeg and rudder off. Thanks to the Canadian Coast 
   Guard they were rescued and the boat was eventually repaired in 
   near-by Victoria. If your plans include cruising Papua New Guinea for 
   example (where there are also floating logs in the water due to heavy 
   logging in the area) where there is no Coast Guard or repair 
   facilities then that risk might be an important factor.
   
   There is no question that a full keel, heavy displacement boat will 
   not point as high, or easily go fast in light wind. From my 
   observations of cruising in Mexico, the South Pacific, and Hawaii this 
   seems to be a minor penalty since most cruisers there are going down 
   wind 80-90% of the time, and when once in the trade winds, light air 
   is less of an issue and sea-kindliness is of greater importance. 
   
   Gee, I hope that my biases haven't shown through too much ;-)
   
   	Howard

re .0:
    
>>>    Question: Are modern underbodies (fin keel with spade rudder or skeg
>>>    rudder) or full keel with attached rudder better underbodies for long
>>>    term offshore work?  Why?
    
Depends on the particular boat. Many (most is my biased opinion) of the 
current cruiser/racer or racer/cruiser fin keel designs are not suitable for 
offshore sailing, but not necessarily because they have fin keels.

>>>    It seems that modern underbodies, if balanced, could give much better
>>>    performance and maneuverability, particularly with a high-aspect rig ...

True.

>>>    ... but full keels could give much more stability, righting moment, 
>>>    hull rigidity, and perhaps safety. 
    
More stability? Not necessarily. Stability depends on ballast weight, how low 
the ballast is carried, and hull shape. Some modern fin keel designs may well 
have more stability. 

Righting momemt? Depends on ballast weight, how low the ballast is carried, 
rig weight, and more. A modern design may have a greater righting moment, at 
least at low angles of heel.

Hull rigidity? Depends on the construction, not the keel design. Modern hulls 
are much more rigid than traditional plank-on-frame hulls.

Safety? Depends on the strength of construction, not keel design per se.

In choosing a boat, I'd look at more than keel design. For example, wide beam 
gives more interior volume, but also increases the probability of capsize 
(discussed in an old note). And once capsized, wide boats are more likely to 
stay upside down for a longer time. [I'd not buy a boat with a capsize 
screening factor over 2.00.] Also consider ultimate stability: how far can the 
boat roll before capsizing? A lot of modern designs have rather low ulitmate 
stability (which is not necessarily due to keel design). 

Length-displacement ratio: Light boats sail faster, but their motion can be 
excessive (see Marchaj). This increases fatigue and seasickness and reduces 
safety. [I'd want a ratio over 250 -- our Valiant 32 is about 300 and has a 
slow and very comfortable motion.]

And on and on and on. Any design is the result many compromises. 

re .2:

Contrary to myth, full-keeled boats are not the only ones that track well. 
Valiants (long fin keel, skeg-hung rudder) track very well and are quite 
easily steered by an autopilot or windvane.

Also, a fin keel does not preclude deep bilges and ample stowage. Again, 
later Valiant 40s and the Valiant 32 are examples. The Valiant hull is 
quite V-shaped and is more akin to older full-keel designs than the 
contemporary ilk. 

True, a separated rudder (and especially a spade rudder) is more vulnerable to 
damage than a rudder on the keel. But, since full-keel designs don't sail as 
well to weather, they are more vulnerable to fetching up disastrously on a lee 
shore. Your choice may depend on what you fear most. 

Me? I'm an admirer of Bob Perry designs. I think the Valiant 32 and 40 are 
among the very best cruising and offshore boats sailing. 

RE:.3 by MSCSSE::BERENS "Alan Berens"

>>    ... but full keels could give much more stability, righting moment, 
>>    hull rigidity, and perhaps safety. 
    
> More stability?  Not necessarily.  Some modern fin keel designs may well 
> have more stability. 

What do you mean by stability?  Stability is not a single idea or number,  it 
is a whole list of things,  some of which have nothing to do with keel types.
Directional stability of a fin keeled boat is less,  for the same reasons that
maneuverability is better.  Roll dampening is worse on a fin keeled boat for 
the same reason that light air speed is better.  Of course,  you better compare
very similar boats.  A fin keeled boat with a narrower beam than a full keeled
boat could well have a better roll dampening factor!  And a fin keel can have 
many different "aspect ratios",  and a low aspect ratio fin keel is going to 
react a lot more like a full keeled boat than a high aspect ratio fin keeled 
boat.


Phil

    Based on no experience whatsoever, it seems that the popularity
    of full keeled designs for serious cruising has less to do with
    their sailing characteristics than with their out-of-the-water
    performance; as when running aground.  With a nice long gently sloping
    keel, you land softly when that submerged reef.  As the tide recedes,
    you only have to worry about which side you want to lean on.  And
    it won't lean that much since the keel doesn't potrude that much
    from the hull.  Lashing a boom or spinnaker pole over the side will
    be enough to keep the boat upright while still allowing the occupants
    freedom to roam the full length of the hull without sending the
    bow or stern crashing down.  In areas of the world without boatyards
    and travel lifts, this ability can be put to good use when the need
    to work on the bottom arises.  All you need is a sandy beach with
    enough tidal range.
    
    One rule of thumb I've encountered that makes sense when evaluating
    an offsure boat is "buy the least amount of boat for the money".
    That is to buy the smallest boat for your budget.  This is based
    on the assumption that boats are priced by the pound and that the
    difference in length will be translated into more robust hull and
    equipment.  Again, the emphasis here is on hull integrity rather
    than room or performance.  Remember, the slowest and most cramped
    sailboat is more comfortable than the fastest and most spacious
    liferaft.
    
    Full keels, deep displacement hulls and low apect rigs don't imply
    poor performance.  The old twelve meters have all of these but they
    lack neither speed nor weatherliness.  A deep displacement hull
    will generate some lift by itself which will offset the lack of
    lift in the shallow keel.  What they and other boats of this
    configuration will lack is room.  For their length, they're tight
    inside.
    
    A "modern" high freeboard canoe body with a shallow fin keel and
    a high aspect rig is a hopless performer upwind.  Charter companies
    love these because they accomodate small armies inside.  Because
    the hull is mostly above water, the layup can be thinner and the
    cost lower.  Acceptable if you don't go upwind, know where the rocks
    are, and have a large family.
    
    These are two extremes and anything in between is possible.  I think
    you'll find that many of the more highly regarded blue water cruisers
    aim for some happy medium.
    
    - gene

    I appreciate the comments thus far.... I understand the issue of
    initial stability, roll moments and angle of stability issues. I also
    want a boat that has sufficient stowage in her hold and is sea-kindly
    like the previous note mentions.
    
    Actually I want it all!!!
    
    However, Let me elaborate a bit on the question: Understanding that
    everything is a compromise, does it truely come down to a matter of
    personal taste? I've seatrialed an Ericson 36 with a wing keel that you
    could release the helm without an autopilot and it would continue to
    track within 2 degrees of her initial setting. She's quick, responsive,
    and touted by the manufacturer to be built for just such
    circumnavigation efforts. I've also sailed Full keel boats that were
    extremely sea-kindly (like this particular Ericson -perhaps due to the
    damping effect of the Wing keel) maneuvered like slugs but gave the
    feeling of such safety you felt like you could go through anything and
    survive. The had the stowage, seakindliness, etc that you would want.
    
    Don't get me wrong, I own a full keel boat now. I've been one of the
    people who've touted advantages of full keels (within my limited
    knowledge) in the past. What I don't what to do is limit myself
    unnecessarily. I'd like a boat that can snake through coral heads in
    island chains safely, survive the rough seas, be seakindly, be able to 
    be worked on in primitive yards should she need to, have ample stowage, 
    be safe, fun, and all the other words you care to tack on the end of the
    sentence. In short, I want a boat that you could safely circumnavigate
    in for several years and have the best of all worlds. I want it all; 
    but realizing I may not get it all, I would like to understand enough of 
    the pro's and con's of each bottom design that I can make an informed 
    decision on what my next boat is to be.

re .5:

In the context of the base note, I assumed stability meant stiffness and 
resistance to capsizing. But yes, stability means many things. 

As I said in an earlier reply to this note, I disagree that a fin keeled 
boat is less directionally stable than a full keel boat. Many fin keel 
boats are woefully lacking in directional stability, but a fin keel boat 
may be quite directionally stable (Valiants are). It really depends on the 
design. Much of the directional instability of fin keel designs is the 
result of the effect of racing rules on design. By the way, in a 
simplistic analogy, airplanes are fin keel designs with skeg-mounted
rudders, and airplanes are, so far as I (a non-pilot) know, directionally 
stable. 

The usual meaning of stability is stiffness (resistance to heeling) and, 
ultimately, resistance to capsizing. A beamy boat will often be quite 
stiff at small angles of heel (a few degrees) but might also capsize at 
a relatively small roll angle (say 110 degrees). A narrower boat may be 
tenderer at small heel angles but might not capsize until a really large 
roll angle (say 150 degrees). There is an interaction of hull shape and 
ballast position here. Keel design (fin or full) may not be particularly 
important. 

Regarding roll damping: I'd have to reread Marchaj. My recollection is 
that keel lateral area is more important than keel shape. Also, the rig 
is a major contributor to roll damping, and a heavier rig provides more 
roll damping than a light rig. 

re .7:

I don't understand why a wing keel would make a boat more seakindly or 
would provide any more or less roll damping. Warning: personal 
prejudice. I wouldn't own a boat with a wing keel, most especially if I 
were planning a circumnavigation. 

Query re your seatrial of the Ericson: how rough was it and how much was the
boat heeling? I would think that any boat ought to be reasonably stable
directionally in calm seas and with little to moderate heeling. More
important, how directionally stable is it in big seas and high winds? Can a
windvane or autopilot steer it easily then? 

"..... touted by the manufacturer ....." Believing what you are told by the 
manufacturer can be hazardous to your health. Nurture an extremely skeptical 
attitude. Valiant claims, or used to, that the Valiant 32 has the performance 
of a modern 3/4 tonner. Yeah, right. Probably not true in 1977 and certainly
not true today. 

And finally, re having it all: as someone said recently, "God has answered 
your prayers. The answer is 'no'."

RE:.8 by MSCSSE::BERENS "Alan Berens"

> As I said in an earlier reply to this note, I disagree that a fin keeled 
> boat is less directionally stable than a full keel boat.  It really depends 
> on the design.  Much of the directional instability of fin keel designs is 
> the result of the effect of racing rules on design. 

Granted and agreed as to the effect of rules.  While you are rereading 
Marchaj,  read the section on the interaction between the keel and the rudder 
in "unsteady flow" conditions...Low aspect ratio keels (with the lowest 
possible being a full keel) will do better (all other things equal),  and 
isn't the Valiant a long,  low aspect keel?  The effect of saying fin vs full 
is to ignore that the choice is really a range,  not two points.  A low aspect 
ratio fin will be better upwind than a full keel,  and will be more 
directionally stable than a high aspect ratio fin.  We can't "have it all",  
but we can have a good compromise that suits the conditions we sail in.  


> By the way, in a simplistic analogy, airplanes are fin keel designs with 
> skeg-mounted rudders, and airplanes are, so far as I (a non-pilot) know, 
> directionally stable. 

Interesting.  Fighter planes are designed to be _not_ directionally stable so 
they can turn faster.  Also they use a spade rudder (at least F-14's). If the 
computer system goes down,  you bail out.  For an all out racing machine on 
sheltered water,  directional stabilty is a non-goal,  as long as an expert 
helmsman can keep it in control for an hour or two it's ok.  A little more 
speed or a little faster rate of turn is much more important!

Small planes are designed to avoid the unsteady flow interaction by offsetting 
the "keel"  and the "rudder".  This might suggest twin keels or twin rudders
have an advantage in rough conditions.  Just offsetting the keel and the 
rudder might work if you usually sailed on one tack,  much as a plane usually
flies right side up!


> Regarding roll damping: I'd have to reread Marchaj.  My recollection is 
> that keel lateral area is more important than keel shape. 

The "end plate effect" as much as doubles the effective area of a low 
aspect ratio foil on damping.


Phil

Splash!  Splash!  (Jumping in with both feet....)

re: .4,

>> Contrary to myth, full-keeled boats are not the only ones that track well. 

Alan's right.  Perhaps the current supreme example among monohulls are the 
semi-custom ($$$) Deerfoot series, which can be steered with one hand 
while surfing at nearly 20kts -- so shows the video, anyway.  Their 
"technique" is to shorten the fin keel enough to allow 6'-8' draft for a 
60'-75' waterline, and build a rudder large enough to intentionally 
provide an uncommonly large proportion of the lateral plane.  (Mind you, 
they boast such exotica as a 4"-5" titanium rudder post to provide what
they feel is a prudent margin of stength, but the idea seems to work.) 
Valiants can be viewed as far less extreme examples of this configuration.

re: .6,

Most of the stories I've heard about grounding on reefs involve serious 
waves, and far more worry than which bilge she'll lay over on.  ;-).  
Strength, whatever underbody configuration one chooses, is the key to 
survival; obviously a full keel has potentially more area over which to 
distribute the stress of such a grounding.

re: .7,

I've sailed a few boats that easily track within 2 degrees of initial 
setting when the helm is released.  Some are skittish, some are solid in 
the groove.  For a couple of the big gaffers among them, it was easy
thanks to worm-gear steering.  *No* rudder feedback, other than increased
friction with increased weather helm.  ;-).  Moral: There can be more to
tracking stability than just underbody configuration. 

J.

Any other factor in the fin keel/full keel debate is a nomenclature problem.
To a significant extent, the  nomenclature depends on structure. If the keel
is structurally homogeneous with the rest of the hull, then it usually is
called a full keel design. If the keel is structurally an add-on (typically
a bolt-on), then it is called a fin keel. The distincition is often somewhat
blurred in production fiberglass boats; it is typically much clearer in
wooden boats (particually traditional ones), custom racers, and metal boats.

Virtually any boat with the rudder mounted on a skeg, or at not mounted
directly to the after edge of the keel, will be called a fin keel boat.

Actually, we've seen a nomenclature shift anyway. A 'real' full keel boat is
the type Marchaj seems to particularly like, such as the Bristol Channel cutter,
whose hull has nearly full depth from stem to stern. Racing boats from the
end of the nineteenth century began to cut away this fullness, and the
so-called cut-away forefoot (in which the hull is shallow near the bow) has
become the norm, and is often now called a 'full keel'.

Marchaj again has good info on directional stability. In essence, boats with
a low yaw moment of inertia and rudder to near the yaw center won't be
stable; some racing machines from the turn of the century were the worst
offenders, with most of the lateral area concentrated near the center of the
boat, and with the rudder mounted on the keel rather than a skeg.

The other factor which affect tracking and directional stability are the
relationship between the lateral center of resistance and the center of effort
of the sails. This determines the amount of weather/lee helm. This is not
the same as directional stability, but in practice both factors strongly
influence how much pleasure or effort go into steering a boat. The ideal is
a near-neutral helm with good stability, and few boats possess it.

Ross Faneuf

> For an all out racing machine on 
> sheltered water,  directional stabilty is a non-goal,  as long as an expert 
> helmsman can keep it in control for an hour or two it's ok.  A little more 
> speed or a little faster rate of turn is much more important!

If directional stability is a goal, it's still possible to get a pretty good all 
out racing machine.  The skeg on my Etchells allows remarkable tracking 
ability.  The design objective was to produce an "old man's" performance 
boat.  No hiking, no heavy steering.  The skeg gets back a lot of the 
stability lost in the deep fin keel.  But I hate to run aground on a 
falling tide.  Balance is precarious on the knife edge bottom of the keel.

- gene
                                            

re .9:

rolling:

Yes, Valiants have long, low aspect ratio fin keels. Their hull shape is 
also very Y-shaped, similar to a full-keel design. This also contributes 
significantly to roll damping.

Regarding the added effectiveness of a wing keel in damping rolling: 
Could you provide a reference? So far as I can find, Marchaj doesn't 
even mention wing keels in "Seaworthiness". 

aircraft analogy:

Fighters certainly need to be manueverable, and yes, some recent designs 
require computer control. Some older designs without computer control 
have, I gather, rather high crash rates in the hands of less than 
exceedingly good pilots (eg, National Guard). Too manueverable for the 
weekend pilot? I certainly hope commercial passenger aircraft are more 
like full-keel boats.


To complicate matters further .....

"..... the heavier the boat, other things being similar, the safer she 
is in rough seas." A boat with a length/displacement ratio of 310 could 
have six times the resistance to capsize as an ULDB with a 
length/displacement ratio of 80. (Marchaj) Plus, heavier boats tend to have 
gentler motion while requiring more sail area for reasonable performance. 

RE:.7 by DPDMAI::CLEVELAND "Grounded on The Rock"

> .. an Ericson 36 with a wing keel 

Personal feeling:  Ericson's are nice coastal crusiers:  However,  they are
very beamy,  and the beam of a boat is the lever that waves use to cause a
boat to roll.  Also,  a wing keel is usually used to reduce draft and to
reduce wetted area.  Both of these reduce damping.  My feeling is that the
right (wrong) conditions would make it roll like a drunken pig,  and you might
find it hard to steer in the right (wrong) conditions.

Now it is true that if you took a given design and glued wings to the keel,
it _would_ be (at least somewhat) more damped,  but that is not the way that 
most wing keel designs are done.  The reason for the slightly better damping 
is the "end plate effect".  Water at point a has a longer path to get to 
point b,  so some of the wing area gets "mirrored" into effective lateral 
area.  

     \   /     \   /
      \ /       \ /
       "         "  
      b"a       b"a 
                ---



Phil

    Alan,
    
    I should know this by now, but how is length/displacement ratio
    calculated. Hope is 34' LOA and 24'WL and net 8 ton.
    Don

100 !	PROGRAM TO CALCULATE TWO BASIC PERFORMANCE RATIOS AND THE
110 !   CAPSIZE SCREENING VALUE

120 !                                   AREA
130 !   SAIL AREA/DISPLACEMENT = ---------------------
140 !                            (DISP/DENSITY)**(2/3)

150 !                              DISP/2240
160 !   DISPLACEMENT/LENGTH    = ------------
170 !                            (.01*LWL)**3

180 !	and the CAPSIZE SCREENING FACTOR

190 !              Bmax
200 !	CSF = ----------------
210 !         (DISP/64)**(1/3)
220 !
230 !    where CSF is the capsize screening factor
240 !          Bmax the maximum beam of the boat (in feet)
250 !          DISP is the displacement (in pounds) including all equipment
260 !          LWL is the waterline length (in feet)
270 !          AREA is the sail area -- conventionally mainsail area
275 !          plus 100% foretriangle area (in square feet)
280 !          DENSITY is the density of sea water (pounds per cubic foot)

290 SET NO PROMPT

300 DENSITY = 63.99                               ! sea water
310 TON = 2240                                    ! long ton

320 PRINT
330 INPUT 'SAIL AREA     '; AREA                  ! 100% foretriangle sq ft
340 INPUT 'DISPLACEMENT  '; DISP                  ! pounds
350                                          ! enter lengths as feet.inches
360 INPUT 'LWL (ft.in)   '; LWL                   ! feet.inches
370 LWL1 = INT(LWL) + 10*(LWL - INT(LWL))/12
380 INPUT 'BEAM (ft.in)  '; BEAM
390 BEAM1 = INT(BEAM) + 10*(BEAM - INT(BEAM))/12  ! feet.inches
400 PRINT
410 DLR = (DISP/TON)/(.01*LWL1)**3
420 DLR = INT(DLR+0.5)
430 ADR = AREA/((DISP/DENSITY)**(2/3))
440 ADR = INT(10*ADR+0.5)/10
450 CSF = BEAM1/((DISP/DENSITY)**(1/3))
460 CSF = INT(100*CSF+0.5)/100
470 PRINT 'length/displacement    ';
480 PRINT USING '###', DLR
490 PRINT 'sail area/displacement  ';
500 PRINT USING '##.#', ADR
510 PRINT 'capsize factor           ';
520 PRINT USING '#.##', CSF;
530 IF CSF > 2 THEN PRINT "     (do not sail offshore)" ELSE PRINT " "
540 PRINT

550 GOTO 320
560 END

    Thanks Alan,
    Hope comes out to be 581 L/D ratio, 11.4 S/D ratio, 1.37 CSF.
    Am watching you folks discussion to try to understand what these
    things mean to a duffer like me.
    
    Don

re .17:

Interesting numbers. What is your displacement? The net 8 tons you mention 
sounds like Coast Guard documentation tonnage, which has apparently nothing to 
do with actual displacement, and, at least for the two boats I've owned, the 
documentation tonnage has been considerably greater than the actual 
displacement. I suspect from your numbers that your actual displacement may be 
less than 16000 pounds.

Your length-displacement ratio is very high -- contemporary coastal 
cruiser/racer designs tend to be in the 200 to 250 range. My Valiant 32 
(length/displacement ratio of 300) is heavy compared to contemporary designs 
and light compared to older designs. 

Sail area/displacement ratios seem to be in the 15 to 17 range for 
contemporary, not-all-out-racing designs. Your low ratio indicates the need 
for big, big sails in light winds for good performance. 

The capsize screening number is a rough indication of how likely a boat is to 
be capsized. The recommendation of the committee that developed the formula is
that any boat with a number greater than 2 not be allowed to race offshore. 

>>>  The net 8 tons you mention sounds like Coast Guard documentation
>>>  tonnage, which has apparently nothing to do with actual displacement...

Registered tonnage is in fact more a measure of volume than weight.  Based 
on an archaic formula, essentially it is supposed to reflect the interior 
volume of a vessel, with subtractions for engine room and certain other 
spaces.  The result is intended to reflect the hold capacity or cargo 
space, expressed in the tonnage of Egyptian cotton that would occupy that 
volume.

Useful background knowledge, eh?  

J.

    I am doing something very wrong.  Doing the calculations manually I
    come up with wierd numbers for Wildside.  Roughly speaking, our sail
    area is 850 ft, displacement is 14000 lbs., beam is 13'1", LWL is
    33'5".  What should these numbers give me in S/D etc.?
    
    Dave

length/displacement       167
sail area/displacement     23.4
capsize screening factor    2.17

    re: .20
    
    Dave, 
    
    Using Alan's basic program, and the numbers you provided for Wildside,
    I come up with the following ratios:
    
    
    Length/Displacement -- 167
    
    Sail Area/Displacement -- 23.4
    
    Capsize Factor -- 2.17   (do not sail offshore)
    
    
    
    Note: Remember, these figures are for comparison purposes only.
          Your actual mileage may vary  :>)
    
    
    
    JC
    
    

    Thanks for the info.  I have a table of these kinds of metrics for
    different types of racing boats at home (courtesy of Seahorse magazine)
    and will compare ours to the others.  Sounds like the numbers bear out
    what intuition says by just looking at Wildside.  Similar boats do
    Bermuda all the time, but I sure as heck wouldn't.
    
    Dave

           
    
    Well Gang,
    
    I wanted to thank all of you who helped educate me and give me lots of
    things to think about in this note and in note 1057 (What's too tiny
    for the Atlantic?). I wanted to let you know the outcome of all the
    discussions and terrific input....
    
    My new wife and I just purchased a 1981 Bob Perry designed Alden 36.
    She's 36 feet on deck, 45 feet overall with the stern pulpit and bowsprit.
    For those of you who aren't familiar with the hull shape, it looks like
    it was popped out of the same mold as a Hans Christian 36. It has a 
    "full keel" with a cut-away forefoot; a displacement of 28,000 lbs
    according to the documentation I can find on her, has wheel steering
    and is Cutter rigged. Whatever was lacking on the original boat when
    new is not lacking now. The previous owner dumped serious $$$ beefing
    up this boat. He had replaced the mast and all the rigging with a 
    strong offshore rig and beefed up everything else in her he could
    reach. The surveyor was familiar with this style of boat and remarked
    that this was the best one he had ever seen. 
    
    If my figures are right, she has a lenght/disp ratio of 332, a
    sail/disp ratio of 14.7 (I'm not sure if I remember the exact sq ft.),
    and a capsize screening number of 1.51.
    
    My wife and I have now had it out in light winds (5-12kts) and gusty
    winds (20-30 w/gusts to 35) and she handles like a dream! Granted, I
    won't win any races with the heavy beast, but then I didn't have the
    troubles other boats were having in the heavier air either.
    
    Her new name is "Time and Tide", she's a Turquoise green color (hard to
    miss) and is located in Kemah, Tx. If any of you Texas gulf coast
    sailors see us on the water, come by and say Hi!
    
    
    Thanks again for all your help,
    
    Robert