Conference unifix::sailing

See Notes 946 and 558. As I recall, you sail in Maine, home to uncounted 
and far, far too many lobster traps. Since Maine waters are deep, since
the performance improvements (if any) of a wing keel are small, and
since lobster trap warps tangle themselves instantly around anything
remotely resembling a sailboat hull, I'd suggest that you get a 
conventional fin keel. A trap warp around your propeller or keel can be 
very dangerous (last summer we set a new record -- three warps and two 
divers). 

Alan

PS May we assume you're no longer a nervous sailor?

Oh, yes, if you have any interest in trucking your boat home for the
winter ...... all the trailers I've seen would probably be unable to
handle a wing keel. 

    Right!!!  I have gotten over "most" of the nervousness.  And really
    enjoy sailing.
    
    thanks, Sandy

    SAIL magazine Jan. '89 has a article about a test conducted by
    Jeanneau of France. They tested one of their 28' cruisers in five
    configurations.
    
             1. Fin Keel
             2. Centerboard
             3. Hydrokeel   (wing keel design used by O'Day & Carroll)
             4. Castro wing keel
             5. Collins wing keel
    
    They tested pointing ability, speed upwind, beam reach, broad reach,
    running, righting and directional stability. The crews were rotated
    from boat to boat and weren't told what design they were evaluating.
    In nearly all categories, the fin and centerboard designs scored
    better than the wing keels.
    
    "Altogether, the trials seem to confirm what hydrodynamicists have
    insisted all along: You can't beat draft for performance and stability.
    At the same time, where draft is restricted the centerboard is still
    a good alternative to winged keels."
    
    -Paul
    

    
    Where draft is restricted the centerboard may have to be retracted
    which will diminish its effectiveness.  However, there are other
    advantages.  Launching is not restricted to times of high tide since
    the boat won't draw much with the the board up.  There will be less
    fouling on the board if it's kept retracted while the boat is on
    the mooring.
    
    - gene

    Sandy,
    
    We purchased a Pearson 31, wing keel, in the spring of
    1987.  We love it.  We sail out of Osterville on the
    Cape -- on day sails or to the islands.  We have it
    hauled for the winter and the truck had no problems
    with the keel.
    
    Katy
    

    RE .7
    
    The SAIL article didn't contain a lot of detail about sizing the
    wing keels for each boat. My impression is that the wings were
    not "bolt on". The three wing keel designs are a good representation 
    latest design trends. I was impressed by the statement saying that
    Jeanneau was trying to cut through the hype and do a scientific
    comparison.
    
    Given that the same computer modeling is used and the same number
    of design variations tried: full size tests of real boats in real
    conditions are more accurate than reduced scale tank tests. For
    a boat builder, full size tests may even be cheaper.
    
    I do feel that the sales of wing keel designs have been helped by
    the glamour of 12 meters. And it may turn out that wing keels are
    best for shoal draft. But for speed and stability, my choice is
    the deep fin.  

 re .8:

>>> .... full size tests of real boats in real conditions are more 
>>> accurate than reduced scale tank tests. 
    
Extremely doubtful. You're trying to determine whether a new design in a
small improvement over an older design. Assume for the moment that the
two boats are absolutely identical in every way, including crew (such an
assumption is of course totally unrealistic). Then in match racing, each
boat should win half the time (otherwise, they wouldn't be identical).
Now assume that the two boats are identical except for the keels, one
fin and one wing and assume that the wing keel provides a 0.1%
improvement. Now the wing keel boat should win every match race. 

But real life isn't that simple. Crews, sails, hull shapes, etc, aren't 
identical. And even more importantly, the wind and sea conditions aren't 
identical. Wind speed and direction can vary significantly (and here 
significantly might be 1 knot and 1 degree) over a small area. Waves 
will vary over a small area. To eliminate the effect of differences in 
crew, sails, wind, waves, etc, sufficiently to say that the wing keel is 
definitely better (whatever better means) than the fin keel is simply 
impossible. One of the Stars and Stripes 12 meter design team commented 
that the effect on performance of many design changes is small, so small
that verifying the increase (or decrease) in performance requires
extensive, and careful, testing. In many cases the Stars and Stripes
designers simply told Conner and crew that the new rudder or whatever
was better. And the crew always came back and said 'right, it is
better'. 

In tank testing the test conditions are carefully controlled and
repeatable (within some reasonably narrow limits). There is then some
hope of being able to determine in a small design change really is or is
not better (in whatever sense). 

But what is better? The results of any testing (tank or other) apply
only to the conditions in which the testing was done. To say that a wing
keel is better because it is faster upwind in light winds says nothing
about whether the wing keel is faster downwind in heavy winds or more or
less capsize resistant in a force 10 storm or whatever.

Keel design is only a very small part of the overall design of a boat. 
One might ask why are boat builders hyping wing keels. A cynical answer 
is that sailboats aren't selling well, and some major, new design 
innovation is needed to increase (or even maintain) sales. And hey, 
nobody is going to buy a design innovation if that innovation isn't 
somehow better, and better invariably means more speed. (If you want 
speed, buy a powerboat.) I have yet to see an advertisement for a wing 
keel that discusses how much more likely a wing keel is to catch lobster 
pot warps or how much more (or less) a wing keel is damaged by bashing 
a granite ledge (compared to a fin keel or Scheel keel or whatever).

What Alan says about the affect of crew, sails, tuning, conditions etc is
quite true, but their are reasons to argue that tank testing may not provide
an absolute measure either. There are two reason for this, as follows:

Tank testing measures the resistance of the hull, and for sophisticated tanks,
the hydrodynamic forces generated by the hull (including the keel). To do this,
the hull is put at a series of heel and yaw angles, assumed to represent the
attitude of the boat under sail, and the resulting forces are measured. These
conditions are presumably exactly duplicated for each test, which is good. The
catch is they may not precisely match what the boat achieves under sail.

The other gotcha is the effect of scaling. Hydrodynamic effects do not scale
properly down to model size. This is the reason that the most expensive testing,
as in 12 meter, is done with large models, as much as 1/3 the size of the
actual boat. It reduces scaling errors. Scaling errors are particularly likely
in the flow conditions around wing keels, where the tip vortices and end effects
may be significantly different than in the real thing, yet are in fact the
important factor in the efficiency of the keel (if you are using wing keels at
least in part to reduce the end effects of a fin, where flow off the end
represents lost lift). If these test are conducted with relatively small
models, say 1/8 to 1/10 life size, the results will be poor. If tested with
boats at 1/3 life size, results are better but expensive. I wouldn't be
surprised to hear that it's much cheaper for Jeanneau to bolt different keels
on a full size boat than to do conclusive tank testing.

Ross Faneuf

    RE: .-1 
    
    I worked for over 1 year performing tank testing for the Ship
    Hydrodynamics Laboratory at the University of Michigan.  It was a great
    job and I really enjoyed it, but the process is not as refined as you
    might expect. 
    
    
    As .10 states the larger the models the better up to a point.  At some
    point the physical dimensions of the tank start to interfere with the
    flow around the model. The accuracy of the strain gauges used, the
    precision of the testing crew, water temperature, and much more come
    into play.  We used to consider a 5 to 10 percent error in tank results
    vs actaul measured results good.  But I still remember the day we
    tested in a propeller that defied all laws of fluid dynamic. Seems that
    the technican wired all the strin gauges backwards. These mistakes get
    expensive with tank time running up to 10k for an 8 hour shift.
    
    I talked with one of the Start and Stripes hydrodynamics staff and they
    also got hurt by these sorts of things.  One of the models they were
    testing was awful, the computer models, and logic said it should be a
    little better, or equal to other models.  They spent most of a night
    chasing it down.  The testing facility they were using had installed
    the wrong filters in the measuring equipment.  They also raced with a
    keel that was very poor due to misreading the testing data.
    
    
    Forrest
    
    Ps.  My degree is in Naval Architecture and Marine Engineering so it
         was more than a College part time job.

    Re .9
    
    I was going to mention a few things about tank tests, about
    dimensionless scaling factors like Reynolds etc., and how they
    are violated when you scale up. But I think the previous two
    replies cover it.
    
    As far as real life, full scale tests are concerned; trial horses
    are always used as a constant to measure against. The tests are
    not performed by competitive racing. But rather the two boats are
    set on parellel courses a few boat lengths apart with similar sails.
    Since the trial horse has been around for awhile, the optimum sail
    trim for the wind vel and sea is known. You then proceed to experiment
    with the new boat. For each change, it's easy to see if you doing
    better or worse against the trial horse. This is done for various
    points of sail and conditions.
    
    This is also an excellent way for anyone to tune for racing. Find 
    a friend who has the same boat or one with similar speed. If you
    can't find someone with the same speed, get someone faster and have
    them drag a bucket. Find a wide open body of water where you can sail 
    for half an hour without tacking and the wind is steady. Then take 
    turns tuning up.
    
    -Paul
    

    
    The cost to the manufacturer for full size testing is probably very
    low.  The hulls will all be sold as new boats.  Those with the
    benchmark standard keels will be sold unmodified.  If the wing keels
    are absolutely terrible, they may be melted down and recast before
    being refitted to their hulls.  I cynically suspect they may be
    sold in their original state regardless of performance on the theory
    that the buyer will either beleive the marketing hype or not be
    able to tell the difference.  This wouldn't be the first case of
    a marketing solution to an engineering problem.
    
    - gene

Well, J Boats admits that the J37 with their UFO (whatever that is) 
shoal draft keel is 9 seconds per mile slower upwind (otherwise equal) 
than their deep draft fin keel. "Not much to give up for shoal draft 
cruising capability."

   Here are some good quotes I found in last Sunday's Providence Journal.
The article was about the proposed America's Cup 75's. These boats are
a cross between ultra lights and maxi's.

Britton Chance: "This boat is deep enough and the hull itself will be
                 shallow enough so that hydrodynamically there probably
                 will be no advantage in putting wings on the keels.
                 Wings are only efficient if you're dealing with a shallow
                 draft configuration, this isn't."

Dave Pedrick: "We don't really know exactly what the right kind of keel for
               these new boats is going to be. Certainly the ballast wants to
               be as low as it can be configured and, that lends itself to a
               bulb or wings or some kind of clever combination of them."

The twelve meter rule was biased towards heavy displacement,  high aspect keels
were prevented by the draft/girth input to the formula. This new "75" formula
is biased towards light dispacement (canoe hull), so now there is room for a 
high aspect ratio keel. Since high aspect ratio's produce high lift and
reduced tip vortices, the benefits of a wing/endplate are reduced. Keel
designers try to get the center of mass as low as possible and the center of
lateral resistance as high as possible. Looks like the fin keel with bulb tip
is good at this and has an end plate too.

-Paul

The advertising copywriters had better get right to work. Having 
convinced the gullible masses that wing keels are the latest and 
greatest, they now face the formidible task of convincing everyone that, 
sorry, we were wrong, deep fins with bulbs are absolutely the best and 
only way to go. All the America's Cup boats have these exciting new 
keels, so they must be the best, right? 

I do love reading ads ..... they're the best humor around. The lastest 
Harken ad tours the roller furling system that conquered Cape Horn. Oh, 
really?

    It seems to me that keel design is lagging  car styling by about
    30 years. In the 50's, lots of cars had chrome bulbs on the fenders
    and wings on the tail!
    
    Alan, if you buy an old cadillac, strip it out, caulk it tight,
    float it upside down with your Valiant rig, you'll be at the cutting
    edge of racing technology! You can even compete with Dennis Conner
    when it comes to giving the press and challengers verbal abuse! ;)
    
    -Paul
    

re -.1:

Me, at the cutting edge of racing technology? Not a chance (unless we're 
talking oh, say, maybe 1960 technology or whenever dacron sails became 
available). 

And compete with Dennis Connor in giving anyone verbal abuse? No hope, 
the man has retired the world championship trophy. Besides, I have too 
much couth.
    
:-)

For those of us foolish enough to sail offshore, capsizing is always a 
bit of a worry in bad weather. A "boat lying broadside to the waves 
skids sideways down the seas with the attendant danger it will trip on 
its own keel. This is probably truer with long, deep keels than with 
shallow keels. Fin keels, even though deep draft, pose less of a 
tripping problem because of their narrow chords. End-plated keels 
(fitted with proturberances like winglets, could very well trip the boat 
into a roll over, however." Earl Hinz, "Ocean Voyager", 1989 edition

RE:.19 by MSCSSE::BERENS "Alan Berens"

> "End-plated keels,  could very well trip the boat into a roll over"

Interesting comment.  Once a boat has been knocked down to 90 degrees and
beyond,  the keel (and whatever end-plate attached to it) is behind the hull
(or up in the air).  Before this,  there would be a range of angles where the
keel end-plate did add a little area to the "effective beam".  As long as the
end-plate area is much smaller than the deck,  and is much closer to the
centerline of the boat (the usual case),  I think it will be a very small
effect.  Beam is what causes capsizes in waves.  Mass (or more correctly the
moment of inertia and the location of center of mass relative to the center of
buoyancy) is what prevents capsizes.


Phil

Now I'm confused. Marchaj in 'Seaworthiness' has an analysis of dynamic
stability in waves that suggests that boats with long, hopefully deep keels
(large lateral plane) are less subject to riding the wave surface like a
raft (as dinghy hulls do), and thus tend to resist being rolled over in some
breaking or near-breaking waves. But then you risk tripping on your own keel?
So which effect is better?

Ross Faneuf

    The articles I've read suggests that long deep keels cause the boat
    to broach more easily when running in large waves...

re .22:

Hmmmm. Certain designs (eg, IOR boats) with short, deep keels are 
extremely prone to broaching running downwind. What is needed is a boat 
that is directionally stable downwind and one that steers well. A spade 
rudder provides more steering at small rudder angles, but a spade rudder 
stalls and loses effectiveness sooner than a skeg-mounted rudder. A 
long, moderate fin and a skeg-mounted rudder may be an excellent 
combination (eg, Valiants). When the rudder is mounted on the aft end of 
the keel, it may not be far enough aft to provide good steering and 
hence the boat may be more likely to get pushed far enough off course to 
broach. 

re tripping:

This is perhaps not the same as being capsized by a breaking wave. 
Imagine the boat sliding more or less sideways down a steep wave. The 
boat will also want to roll. A substantial lateral area (keel) may 
result in the boat rolling over. If you've ever snow skied, and suddenly 
skiied across bare dirt, you know how likely you are to fall forward or 
sideways very abruptly. You've tripped on your keel, sort of. Capsizing 
can also occur if the deck suddenly digs into a wave as the boat rolls. 

RE:.23 by MLCSSE::BERENS "Alan Berens"

> re tripping:
> This is perhaps not the same as being capsized by a breaking wave. 
> Imagine the boat sliding more or less sideways down a steep wave.  The 
> boat will also want to roll. 

A key point here is not what the lateral area is,  but where the center of
lateral area is in relation to the center of mass.  With most heavy or moderate
displacement designs,  these will be close together,  and the resultant torque
will be small.  If the center of mass is below the center of lateral area,  the
effect is to right the boat!  IOR boats,  on the other hand,  with a center of
mass well above the waterline,  and a deep keep might well get enough of this
effect to matter.


> If you've ever snow skied, and suddenly skiied across bare dirt

That would be more like running aground. 


Phil

I couldn't help but think of this note and a few others in this file when I 
was reading some advertising from Precision Boat Works. The following is 
quoted from letters written by designer Jim Taylor:

Precision 21 - keel/centerboard design

"For small cruisers, a winged keel is more an inexpensive expedient than it is 
sensible design. In order to be effective, the wings themselves need to be 
quite large, which makes them awkward and prone to damage at the launching 
ramp, and when it comes to mud-banks, it is with good reason that they are 
referred to as 'Danforth' wings!"

Precision 27 - 3'7" draft shoal draft keel with end-plate effect bulb

"The standard keel is an external lead casting 3.6 feet deep, (despite claims 
to the contrary, shoal keels with significantly less draft, even if fitted 
with extreme wings, have proven to be poor performers), and it features a very 
carefully developed 'end-plate effect bulb' at the tip. This tip detail is a 
refinement of a well-proven design that greatly enhances upwind efficency and 
stability, is far less troublesome than wings, and closely approaches the all 
around performance potential of the ultimate deep-draft elliptical fin."

- Bob