Gulfweed Keel

[garren]

I was looking at Hanna's Gulfweed plans last night and noticed he designed three keel configurations - two without CB and one with CB. The full-depth keel requires 1100 pounds of outside ballast. His intermediate keel is a foot shorter but requires the same amount of outside ballast.

I'm curious to know how are you able to reduce draft by a foot and not change outside ballast, or apparently anything else, and maintain the sailing characteristics of the full-depth keel?

Thanks - Gary

[frank smith]

There must be different rigs , or different intended usages . That is a guess .

BTY Gulfweed is a pretty little boat , but Imo , the sheer need some work .

[Tad]

Originally Posted by garren

how are you able to reduce draft by a foot and not change outside ballast, or apparently anything else, and maintain the sailing characteristics of the full-depth keel?

You can't..........

[frank smith]

Originally Posted by Tad

You can't..........

Then what would the changes in sailing characteristics be?

[Tad]

frank...

Well I don't know the details so I can only guess.....

Generally the shallower ballast keel will mean less stability, the centerboard may or may not make up the loss of lateral area in the shallower keel....in theory you could build a centerboarder that would be better in some conditions....board up off the wind and less wetted surface, board down on the wind with a deeper and more effective foil......or you could build a ballasted board to correct the loss of stability but it has to be pinned down.....

The intermediate keel will have less stability and wetted surface plus make more leeway......but to most cruisers the effect will be almost un-noticeable......

[frank smith]

Thanks , I also think the decrease in displacement on the shallow keel could be made up with internal ballast . Just a thought .

[garren]

Thanks Tad for your insight. Would increasing external ballast on the intermediate keel reduce the instability? If so, is there a formula to determine the necessary additional ballast?

Gary

[Tad]

Jack Hanna was no dummy but he was human and did make mistakes or adopt odd thinking on occasion......I don't know what his thinking was in this case.....

At any rate we do not know if there is a "instability" problem to fix....and no there is no simple formula to "fix" stability. For the average layman most stability issues are subjective....the boat "feels" tender or stiff....

While I could make lots of modifications to the underbody of the Gulfweed and improve her performance such that she would be a different boat, in general I recommend building as designed (or find a different design)......if there proved to be a stability issue a couple of lead cheeks lag bolted to the keel would help.....but building lighter hollow spars and a foam cored cabintop would do the same thing and make her a faster boat(lower total displacement).

Her actual stability with the various keels could certainly be studied, center of gravity for each model established and that data fed into a computer 3D hull model to generate righting arm and VMG curves. That's what NA's do, but the difference in ultimate stability is probably (for the two outside ballasted versions) something around 5 degrees.......