atriculated shoal draft keels

[philSweet]

Just to throw out some really loose numbers-

suppose leeway is 3^o at 500^# side force and drag is increased by 5% of side force (25 pounds); 6^o at 1000^# side force and drag is increased by 10% of side force (100 pounds). How much additional lift can we get out of those tabs? How much less lift will the hull produce at the new equilibrium, and what will be the new leeway angle?

(I'm playing devil's advocate here, hoping someone will get pissed and throw out some better numbers)

[sandy daugherty]

Yes, it's Chris's 47 I'm talking about. I was first incensed he would even cosider such a thing. I'm part owner of an Atlantic 42 and cherish her ability to point with virtually every boat I've met on the Chesapeake Bay. I also own a PDQ 36, and after talking to Chris for a while suddenly got the idea that I might be able to modify the PDQ's sacrificial LAR keels for a bit better windward pointing ability because I have a narrow river to tack up to get home.

That's why I started this thread, and I'm glad to hear to most recent comments.

[DCockey]

Two ways to judge pointing ability.
1) How close the direction the boat points is to the wind.
2) How close the direction traveled is to the wind.
These are not the same, and only one matters if your concern is tacking up a narrow river.

The one that matters is how close the direction traveled is to the wind. Cambering the keel can improve the first, but may or or may not improve the second.

[sandy daugherty]

What matters is VMG, and getting past that pesky Gemini.

[FAST FRED]

"What matters is VMG, and getting past that pesky Gemini."

This is a far different task than having a fine cruising boat that tacks well and can make progress up wind.

The LAR keels are built to assist the hull in keeping the lee way angle down to about 5deg.

At this point the hull is working well and nothing (unless you are racing) is lost.

If you wish to out point a cruising cat , a lead sled would be a better choice.

FF

[sandy daugherty]

I've owned three LAR keeled cruising cats, and two more with dagger boards or centerboards. The board-equipped boats can outpoint all but the biggest pure racing monohulls on the Bay. The shoal draft keels can almost tack thru 100 degrees. All of them can can slip into the catamaran speed ranges by crackin off a bit. Chris thinks that some part of the lost pointing ability can be made up with flaps on LAR keels.
So the discussion is a matter of degree, much as any other discussion of Yacht Design.

I can count on any number of my Medicare contemporaries to present conventional opinions, but when a successful designer steps "outside the box" I think its time to stop listening to my arteries harden and reconsider traditional truths. Isn't that what brings most of us here?