Conference unifix::sailing

    Better for what? Common wisdom indicates that a full (now semi-cut
    away fore-foot) is more directionally stable, slower (more wetted
    surface/displacement) and requires less work at the helm than a
    fin keel. On the other hand a fin is faster (less wetted surface),
    more maneuverable and requires more helm work. Fins are found mostly
    on 'racing' types and semi-cutaway full keels mostly on cruisers.
    So it depends...
    
    Ed-a-wood-semi-cruiser-fanatic

    THis is gonna be a fun one !!!!!!!!
    
    I've read in several places that full keel (let's agree up fron
    that we're talking cutaway forefoot full keel??!!) designs of BIll
    Luders are very fast boats, even in light air, so don't assume
    full keel boats are slow. 
    
    I would have to consider myself well-qualified for this discussion
    as the owner/operator of both a fin keel boat and a full keel boat.
    
    I swore when we sold the Pearson 26 (fin keel, balanced spade rudder)
    that I would never buy a fin keel boat again. She could turn on
    a dime and accelearated very quickly out of a tack. However, you
    could never leave the helm because she had very little directional
    stability. we were able to get her so she'd sail by herself if it
    was flat calm. And then you could move arounfd the boat because
    weight distribution changes changed the balance of the boat and
    off she would go..... Off the wind, she'd fly but she was a bear
    to steer downwind. I learned how to rig a preventer real fast!!!
    
    My Sea Sprite 23, Alberg designed, is a much more comfortable boat
    to sail. She doesn't turn quite on a dime or accelerate as quickly
    as the Pearson. She tracks better than the Pesarson and doesn't bounce
    around as much. She gets up close to hull speed fairly quickly so
    I think she's pretty fast, or as fast as a boat of that waterline
    is going to be. Off the wind she's a joy because she tracks so well.
    I don't know what she's like with a spinnaker cuz we didn't get
    to try ours last summer. 
    
    Jumping in with the compromise school of naval architecture, I'd
    hav eto say that what I'd prefer would be a boat with a big fin
    and a big skeg in front of the rudder. Tom Gilmer's designs come
    to mind, also Pacific Seacraft boats. (JR, don't the Sabres have
    big skegs?)
    
    Alan, don't be bashful!! :-)
    
    Ed
    
    I would say that if you want to spend all of your time  

    Ed mentions three of the biggies in full keel yachts-Alberg, Gilmer,
    and Luders.  I agree with all that he said and can add one more
    reason for liking their designs-the boats they draw are beautiful
    to look at.  
    
    In addition to the question of directional stability, there is the
    issue how comfortable the motion of the boat in a seaway is.  Comparing
    cruises on a C&C, Beneteau, and Hunter (fin keels) vs. my own Cape
    Dory (full), I much prefer the less quick, less bouncy motion of
    the full keel boat.
    
    And what do you really give up in speed?  It is measured in seconds
    per mile generally, so at the end of a long day you might arrive
    at Catalina, Block Island, or Camden half an hour later than a fin
    keeled boat of the same LOA.  That might be significant in America's
    Cup racing, but not in cruising.

    RE: .2
    
    Sabre's skeg is quite tiny, in fact if it wasn't for their
    literature I could have won an argument with my know-it-all son
    that there was no skeg at all.
    
    This discussion could be expanded to include CB's. My Sabre 30 and
    34 were fins while my 38 was a keel/centerboard combination. Except
    for the normal differences that you'd expect due to size, they all
    seemed to handle exactly the same. The CB did require more attention
    to the mainsheet in heavy air as there was a tendency to head up
    in a puff. Normally though, it would sail perfectly balanced, hands
    off for long periods of time.

Full keel more directionally stable? Not necessarily. I think it really
depends on the details of the hull shape. A boat that does not develop
much more (weather) or less (lee) helm as it heels will likely be quite
directionally stable, ie, it will not need constant rudder changes to
stay on course, regardless of the keel shape. For example, our boat has
a long fin keel with the rudder well aft on a large skeg. Once with the
tiller lashed, the boat stayed within 5 degrees of the intended course
for about 15 minutes in a 15 to 20 knot breeze and a 4 to 6 foot chop.
In the gusts the boat would head up (more weather helm as the angle of
heel increased) and in the lulls would head off. 

(By the way, self-steering works much better on boats that are
directionally stable.) 

The design features of recent boats that generally improve boat speed
seem also to make the motion of the boat more uncomfortable in a seaway
and to reduce directional stability. I think that the hull shape has
more effect on motion and directional stability than the keel design per
se. 

Take a look at the underbody of almost any recent racer-cruiser.
Generally, bottom of the hull is quite flat, the turn of the hull at the
waterline is quite abrupt (hard bilge), and the curve of the bow into
the bottom has a sharp knuckle. Often, the beam at deck level is much
more than the waterline beam. Finally, the shape of the waterline plane
is quite asymmetrical -- pointed at the bow and wide at the stern. Each
of these design features affects directional stability and motion in a
seaway. 

My understanding is as follows:

The directional stability and steering balance of a boat depend, in
part, on the shape of the hull at the waterline. As the angle of heel
increases, the waterline shape of the hull in many designs changes quite
significantly. If this shape change is such that the asymmetry increases
(or decreases), then the balance of the boat will change. The usual case
is that weather helm increases, causing the boat to round up if the
rudder position is unchanged. (This is one reason wheel steering is so
popular -- the steering effort remains low even with large increases in
weather helm.) If the change in balance is small with a change in angle
of heel, then the boat will probably have good directional stability.
Note that weather helm, by itself, is not a cause of directional
instability. Rather, it is change in balance. Here is where the 
stiffness of the boat plays a part. The angle of heel changes much more 
for tender boats than for stiff boats for a given change in wind force. 
Thus the change in balance is greater.

Note that recent hull designs tend to have much more asymmetrical 
waterline hull shapes than older designs. The Colin Archer-type designs 
(eg, Westsail 32) are nearly symmetrical.

The motion of a boat depends too partly on hull shape. If the immersed 
volume of the hull increases quickly as the hull sinks, then the motion 
will be abrupt (eg, the boat will pound). Pounding is one characteristic 
of boats with flatish bottoms (eg, our first boat, a C&C 26). If the 
volume increases slowly as the hull sinks, then the motion will be much 
less abrupt. V-shaped bottoms with a gradual curve of bow into bottom 
will be more comfortable (this is the case with our current boat). 

However, asymmetry of the waterline shape is important. If the waterline 
shape is symmetrical, the boat will pitch or hobbyhorse badly. The stern 
needs to be much fuller than the bow to dampen pitching. But the stern 
fullness still needs to have a relatively gradual increase in volume 
with increased immersion. (The hull shapes of the Valiant 32 and 40 look 
almost identical. However, the stern of the 32 is much fuller than the 
stern of the 40 to reduce pitching on its shorter waterline length.)

The nature of the motion of a boat in a seaway is more important when 
cruising. Gentle motion is much less fatiguing and is much less likely 
to throw crewmembers off balance (and maybe over the side). 

Boat speed is certainly increased by minimizing wetted surface area, and 
this is exactly what fin keels and current racer-cruiser hulls shapes 
do. But as always, compromises are necessary.

By the way, Bob Perry's designs (eg the Valiant 32 and 40) tend to long
fin keels, skeg-hung rudders, and V-shaped hulls. The Valiant 40 has a 
PHRF rating around 132 and is considered (by some) to be the best cruising 
design in the last decade. 

Alan

Please, bashful I'm not, at least when writing notes. Opinionated, 
maybe, though I prefer to think of myself as a holder of definite
opinions which do change from time to time.

    
    Has anyone experienced, or heard any type of feedback about the
    new "winged" keel boats?  I wonder if wings add some noticeable
    stability to the fin keel?

    Tom--

    C.A. Marchaj has just published a book ("Seaworthiness") which treats
    this subject in technical, exhaustive, and fascinating detail. I
    have only skimmed the book, and will try to pass on a few items
    without gross misrepresentation. I'd wait, but the topic is here
    now...
    
    Alan's comments match well with Marchaj's analysis (a combination
    of tank tests, mathematical modelling, and consideration of full-scale
    observations). Marchaj points out the crucial importance of adequate
    roll damping, created by adequate lateral area, in dynamic stability
    of boats in a seaway. He claims that the modern fin-keel racer which
    relies on form for much of its initial stability is more likely
    to roll all the way in a heavy (survival) seaway, and more likely
    to remain upside down, than a traditional full-keel hull form. This
    opinion is reinforced by an extensive technical analysis. Alan's
    observation's about deck beam being greater than waterline beam
    reflect form stability. The boat is shaped so that as it rolls,
    more hull at a greater distance from the centerline is submerged
    in order to resist rolling - the wide, flared form of a racing dinghy.
    
    Unfortunately, in large waves, these boats tend to follow the wave
    crest very well, so that if the wave is big enough and is breaking,
    it easily carries the boat right over. That is, the deck tends to
    stay parallel to the wave surface, and if the surface curls...
    Traditional designs do not exhibit this behavior.
    
    Similar comments apply to yaw stability. I haven't read closely
    enough to comment on that.
    
    Perhaps a reasonable design compromise is the large fin keel - with
    a root which approaches 30-40% or the waterline length. Such a fin
    exhibits at least twice the lateral area of the more extreme fin
    keel, and may offer a useful mean between the stability problems
    of the fin keel and the high wetted surface of the traditional design
    (and its easier to build). Of course, I'm prejudiced; I'm building
    a boat with this type of keel, and I certainly hope it has only
    virtues...
    
    Ross Faneuf
    

    RE: .6
    
    I have been sailing a patented form of winged keel, called the Scheel,
    after its inventor.  It has been around for years, and used on Tartans
    since around '78.
    
    It is much less radical than the current trendy keels, like on the
    O'Days. In fact it looks a bit like a moderately long deep fin which
    has been dropped, resulting in the lead at the bottom mushrooming
    out and the draft being reduced about 1.5'.
    
    It performs very well (the whole boat performs nicely) as long as
    you keep the average angle of heel down. Below 25 degrees heel the
    leeway is negligible. It increases from 25-30 degrees and beyond
    30 degrees there is more leeway than I like.  Since our boat responds
    better to the helm and is much more comfortable to cruise with the
    angle of heel below 25 degrees anyway, we sail accordingly.  
    
    Oh. The ballast/displacement ratio is 44%, and the hull form is
    modern with moderate overhangs, beam and long relative waterline.
    She displaces 10,000 lbs on a 29' LWL and 34' LOA  which makes her
    a modest D/L, and she goes like a bat_______ in light air, and still
    reasonably comfortable in a seaway.
    
    Nice setup for a coaster. I would tend to favor a higher D/L boat
    if we regularly sailed in strong air offshore.  

    
    I wonder about the Australia II type wing setup on a cruiser though.
    The reduced draft without performance penalties is nice along the
    coast, but pot markers might be a bitch.  Also getting unstuck when
    running amuck might be akin to getting a plumbers helper off a wet
    vinyl floor.

    
    RE: my druthers
    
    Like any design option, I am sure there are as many good as bad
    examples of full keels as fin.  There will likely be a rash of
    poor winged keels in the future which will tarnish that configuration
    as well. The choice of keel needs to be made in light of the owners
    expected uses and the performance/security tradeoffs of the whole
    package.  
    
    I prefer a somewhat light boat with good performance for the sailing
    I do. I also like a comfortable boat, which is what sold me on the
    Tartan.  I have a friend with a full keel Oyster 39 ketch, which
    was super crossing the Atlantic. His sailing is now coastal and
    all that security has become extra baggage (he now sails more with
    me because he cannot get anywhere on a day sail). 
   
    Walt

    Can someone help me understand the function of the trim tab used
    on big keel boats? I can think of three possibilities:
    
    1. Used to gain lift at low speeds at the expense of some additional
    drag, which is ok if there's plenty of wind. In this case I would
    expect to see the tab adjusted at mark roundings, tacks, and other
    situations where the boat is not up to speed.
    
    2. Used to approximate an asymmetrical foil on upwind and reaching
    legs. In this case I would expect to see the tab set to a certain
    position for beating and reaching, and set to neutral for running.
    
    3. Used to adjust helm balance. In this case I would expect it to be
    adjusted depending mostly on wind strength and also depending on the
    leg.
    
    Which, if any or some combination, of these is it?
    
    Doug.

Definitely 2.

Option 1 sounds good in theory, but on the 12 meters, which all had trim
tabs, it was adjusted by the helmsman, and I doubt if he had enough time
to do this during mark roundings.

I think some of the twelves had a linkage between the trim tab and the
rudder, which meant the tab provided some extra turning ability, and it
was possible to steer them by the tab alone if the rudder mechanism
failed.

Option 3 doesn't sound too likely. Racing boats should adjust the helm
balance using the rig, not by inducing extra drag, which is exactly what
you are trying to prevent in the first place.

    Thank you. This has had me wondering for quite a while...
    
    Doug.