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post #21 of 99 Old 07-29-2019
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Re: What Kind of a Keel do you Have

I've got a stub keel with center board on my NAY '23. No problems beaching her in quiet coves.
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post #22 of 99 Old 07-29-2019
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Re: What Kind of a Keel do you Have

Synergy has a moderate draft, moderate area fin keel and moderate rudder design.
PIC00003 by [url=https://www.flickr.com/photos/[email protected]/[/url],

Farr 38 by ,

The pros and cons are that she sails well in a broad range of conditions, has a lot of stability allowing me to carry an efficient sail plan without reefing or furling through an extremely wide wind range, points well, and is shallow enough that she does limit my cruising ability. The difference in draft between the rudder and keel generally protects the rudder from damage. The counterbalanced rudder results in extremely light helm loads which makes use of a vane steering possible and also means that the autopilot uses less amps. While she does not track in the traditional sense, she does balance so she can steer herself or I can steer with the main sheet rather than the rudder (as I had to do when the steering linkage failed)

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post #23 of 99 Old 07-31-2019
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Re: What Kind of a Keel do you Have

Quote:
Originally Posted by SV Siren View Post
can be squirrelly downwind.
In big following seas my boat's squirrelly downwind too. Thinking it's because of the narrow stern?
i have an encapsulated fin that's shaped exactly like a whale's dorsal fin.
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post #24 of 99 Old 07-31-2019 Thread Starter
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Re: What Kind of a Keel do you Have

I don't think a narrow stern should make you squirrely down wind necessarily. My Sharpie has a round narrow stern and she's beast down wind. But, she has two bilge boards and can shift the CLR way aft.

Squirlly down wind is more likely a balance issue IMO.
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Re: What Kind of a Keel do you Have

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I don't think a narrow stern should make you squirrely down wind necessarily.
Squirlly down wind is more likely a balance issue IMO.
The narrow stern definitely contributes to squirrelly behavior down wind especially in conditions where a boat is rolling. When a boat has pinched ends and it rolls, at the extreme edges of the roll the shape in the boat in water becomes a sharply curved wing turning trying to turn the bow of boat strongly towards the side that is out of the water. The rudder correction required to prevent a broach combined with the asymmetric hull form in the water tends to increase the amount of rolling.

This was exacerbated by the large girth spinnakers of the IOR era (and lesser extent CCA era) that tend to cause 'excitation rolling' that greatly increases roll angles. Excitation rolling is caused by the spinnaker rolling sideways through the air and its edges alternately creating aerodynamic forces that pull the boat towards the side and so add to the kinetic forces causing the roll until a broach or death-roll occurs.

If you look at reasonably modern designs from the past 20 years they typically have broader transoms. Those broader transoms do several things that avoid the problems of a pinched stern. First of all, as they roll they develop more symmetrical water lines that tend to move to leeward reducing the rounding lever arm between the lateral center of resistance and the lateral center of effort of the sails. But more significantly they also dampen roll as they increase the form stability as they heel. The result is that they roll slower through a narrower roll angle reducing excitation.

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post #26 of 99 Old 07-31-2019 Thread Starter
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Re: What Kind of a Keel do you Have

Skinny sterns can do great in big following seas, put a sail on them and the dynamic changes. But a boat with a skinny stern and highly variable CLR should do fine. Wind surfers are a good example. As far as that goes, so is my sailing kayak. And my Bay Hen.

The nature of many keel boats prevents you from getting the weight back far enough or the CE far enough forward to make skinny sterns work down wind, but that is not a hull shape issue, it's a balance issue IMO.

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Re: What Kind of a Keel do you Have

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Skinny sterns can do great in big following seas, put a sail on them and the dynamic changes. But a boat with a skinny stern and highly variable CLR should do fine. Wind surfers are a good example. As far as that goes, so is my sailing kayak. And my Bay Hen.

The nature of many keel boats prevents you from getting the weight back far enough or the CE far enough forward to make skinny sterns work down wind, but that is not a hull shape issue, it's a balance issue IMO.
Its not about solely the stern itself, or that the stern is 'skinny'. In fact traditional life boards were double-enders since the it was thought that doubleenders did well in surf. In the case of a boat with a pinched stern, it is the combination of a wide beam hull form along with the pinched stern that created the problem. The reason that the term 'pinched stern' is used in the first place is to contrast the stern with the beam of the boat.

The reason this is true is that there is a huge difference in the change in shape when heeled between a long narrow hull form like a Kayak, or the planning hull form of a surf board, or the barrel sections of a traditional double-ender, and the pinched transom hull forms of the IOR era.

It is not really a balance issue in the usual sense (keel too far forward or aft relative to the longitudinal center of effort) since the turning moment when downwind is the offset between the center of drag, and the center of effort of the sails times the drive force, combined with the rotational force produced by the shape of the hull in the water.

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Re: What Kind of a Keel do you Have

I think we are agreeing, but I am not sure. It isn't really the narrow stern causing the directional instability. I have no doubt there may be other proportions at play that may be causing the squirley feeling, including the rotation.

Some multi hulls can feel like they are tracking on rails. Multiple, long skinny hulls provide for much of the directional stability. Nearly everybody has sailed a hobie 16. They don't even have boards.

I am not sure what kind of boat Whalerus has, but I wouldn't be surprised if part of the challenge with getting her to track down wind has as much to do with racing rules interfering with boat design as it does the breadth of the stern.

The trend in racing dinghies is even stronger. They have reached the point where they are darn near useless for anything but racing. Which I think might be partially responsible for the resurgence in cruising dinghy popularity. Fine sterns and Lug sails seem to pretty well represented in that category
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Re: What Kind of a Keel do you Have

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Originally Posted by Arcb View Post
Some multi hulls can feel like they are tracking on rails. Multiple, long skinny hulls provide for much of the directional stability.

I am not sure what kind of boat Whalerus has, but I wouldn't be surprised if part of the challenge with getting her to track down wind has as much to do with racing rules interfering with boat design as it does the breadth of the stern.
I don't think we are talking about the same thing. Long skinny hulls do not change shape as much as when they heel as a beamier boat tends to do. When you couple a pinched stern with a beamy hull, the heeled hull form changes really dramatically and as such that the boat becomes much more prone to roll steering. Its exactly the opposite as what happens with something like a kayak or something like a beach cat.

The reasons that modern boats have wide transoms is that a moderate heel angles the shape of the boat in the water is closer to the shape of catamaran in the water and so tracks better and does not roll steer as much. When heeled these boats tend to end up with largely symmetrical shapes that are comparatively narrow in width and low in wetted surface.
Synergy stern by

Although this is too much of a heel angle to be ideal, (sailing into a building wind, and depowering after a mark rounding) I think that the picture above illustrates how narrow the waterline becomes and the shape of the hull in the water (look at the windward side of the boat). When heeled this produces a relatively symmetrical hull in the water with the centerline of the water plane offset to leeward and with the rudder still remaining fully in the water.

By way of comparison, this is a picture of IMP (a Ron Holland designed IOR era boat showing her pinched stern). Imp-flossing her rudder by

If you look at the picture it is easy to see that the windward side of the submerged hull is a fairly flat curve while the leeward side is sharper wider curve, tending to turn the boat to windward.

Jeff
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post #30 of 99 Old 07-31-2019 Thread Starter
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Re: What Kind of a Keel do you Have

Thats sailing upwind I am thinking you like her a bit flatter when running?

I think you are right though. We aren't really talking about the same thing. I am talking about strictly hull form, but with your boat its almost impossible to contemplate your boat without the context of a keel. Its part of the package.

I am thinking more along the lines of maybe a Michael Storer design where the hull itself can be reallistically considered without any board/keel what soever. Long, narrow, hard chines, and very much a modern design.
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