Keel Modifications

PDQ issues applicable across all PDQ Yachts (or if you can't find a place for something, it probably belongs here for now)
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thinwater
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Keel Modifications

Postby thinwater » Mon May 04, 2015 6:32 pm

Following on the tacking thread, has anyone ever modified the stock keels? I would love to slice them off and slide them back 2-3 feet, but that's not happening. But I'm sure there are more subtle mods. The last boat I had was a Stiletto, and MOST of them were modified.

I've toyed with the idea of adding a little area on the trailing edge by simply extending it back to a sharper finish. Easy. I would not want to go deeper for obvious reasons. Same for wings (grounding).
* COE moves back a little. Reduced affinity for irons.
* A little more weatherly and faster when close to the wind.
* A little slower turn-in, but more speed entering the turn.
I have noticed some improvement in turning from extending the transoms; though you might expect the opposite, the extensions make the end smoother when sweeping sideways. It is more obvious backing, of course.

Not much you can do for the rudders. They can't go deeper (grounding). The leading edge needs to stay blunt because of the sharp turn-in for tacking. The trailing edge is already reasonably fine, and experience and theory tell me that very fine edges require more careful steering than I care for, even on a steady track.

Pete Weis
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Re: Keel Modifications

Postby Pete Weis » Tue May 05, 2015 8:47 am

thinwater wrote:Following on the tacking thread, has anyone ever modified the stock keels? I would love to slice them off and slide them back 2-3 feet, but that's not happening. But I'm sure there are more subtle mods. The last boat I had was a Stiletto, and MOST of them were modified.

I've toyed with the idea of adding a little area on the trailing edge by simply extending it back to a sharper finish. Easy. I would not want to go deeper for obvious reasons. Same for wings (grounding).
* COE moves back a little. Reduced affinity for irons.
* A little more weatherly and faster when close to the wind.
* A little slower turn-in, but more speed entering the turn.
I have noticed some improvement in turning from extending the transoms; though you might expect the opposite, the extensions make the end smoother when sweeping sideways. It is more obvious backing, of course.

Not much you can do for the rudders. They can't go deeper (grounding). The leading edge needs to stay blunt because of the sharp turn-in for tacking. The trailing edge is already reasonably fine, and experience and theory tell me that very fine edges require more careful steering than I care for, even on a steady track.



The likely best answer to make any meaningful upwind performance improvement, in a practical way, is to add outboard dagger boards per the design of a qualified designer. However, not everyone might like the look of them.

"Tahini 50 Catamaran - The owner of this Wharram designed 50 foot catamaran came to VGYD with a balance problem. After some consultation and a rigorous study of the boat's sailing characteristics, we determined that a set of dagger boards would have the greatest effect and would not be detrimental to the flow around the keels. The trunks, made of plywood and fiberglass, were positioned to the side of the hulls with minimal impact to the interior volume. The 8.7 foot long foils were fabricated from fiberglass with a wood and foam core."


http://www.vgyd.com/Appendages.html

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thinwater
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Re: Keel Modifications

Postby thinwater » Tue May 05, 2015 2:25 pm

I put dagger boards in A Stiletto once; yup, quite a project, thought not to tough to design. Major cabin refit.

The real problem, in the Chesapeake where we sail with just inches to a few feet under the keel for miles at a time, is what happens when you plough into the bottom at speed. With the mini-keels, you feel the boat slow and turn, and you quickly change course. With dagger boards, they dig deep, the stress is VERY concentrated, and the odds of breaking something expensive are material. Do it a few times, and problems with jamming become common place... and maybe become common place anyway, due to stuff growing in the trunk. If there is enough space for movement, in sloppy seas they talk to you (whoomp, whoomp).

Yes, they will have you going to windward like the hammers of hell and spinning on a dime, but at a price.

And they are also in the way, both in the cabin and on-deck. And you've got to grunt them up and down.

Personally, I think they make little sense in cruising boats, and by the look of things, most builders agree. So we tweak what we have, and from what I am learning, the PDQ has a good bit of tweaking room for small $$.

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Re: Keel Modifications

Postby Pete Weis » Wed May 06, 2015 4:14 pm

I hear ya.


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