Keel Modification: Increase stability

[C-man77]

As a builder I would not do anything structural without eng. certification

[donradcliffe]

Lead keels can bend, and you are going into uncharted waters. I remember doing the numbers for a Nz boat which got the keel twisted when it was pulled off a reef in the Red Sea. The straightening jig should have worked based on the strength of the lead, but all that happened was the chain kept breaking.

[Ballsnall]

Originally Posted by Capt Ben

Made some design changes. Made cutouts a bit smaller such that the lower edge of cutouts is near lower edge of keel bolts. Hopefully, there's minimal bending...

Have you considered just lowering the keel to give you the desired stability?
You will need to replace the keel bolts for longer ones so cost would probably be higher but structurally should be an improvement over a having hollow sections at the highest stress point.

[AKA-None]

Originally Posted by Capt Ben

Yes, I have been in contact with Mars Keel! While they are fine with making me the split bulb they will not offer me any advice re cutting out sections of the keel to subtract weight...

I wonder what that means?

Maybe they don’t want to be responsible when you make that level of change

[boatpoker]

Originally Posted by AKA-None

I wonder what that means?

Maybe they don’t want to be responsible when you make that level of change

I've been through the Mars plant on several occasions on projects. They do know their stuff and would likely have an opinion for a naval architect but not some guy off the dock.

[malbert73]

I would hire a NA (Farr probably would consult) to design the keel cutouts. Also, the rectangular ones will be susceptible if you have a hard grounding (ie keel would bend aft)? Triangular may be more structural?

[Happ]

Originally Posted by Capt Ben

Sailors,
I am considering attempting to increase the stability of my boat without adding weight. I have consulted w/Farr (the designer of the boat) and had them verify that the keel structure (without mod) could structurally support an addition of ± 800lbs (sandwiched bulb) to the lower edge of the existing fin keel. Additionally, the Farr office has validated the size, positions and material of the keel bolts. BTW, this fall I separated the keel from the hull exposing about 3" of the bolts. They were in new looking condition, and all was as expected.
So, has anyone removed lead from the upper two thirds of their keel and if so have you any suggestions? At this point I'm considering a carbide core drill bit of 3" & 4" diameter cores and a large 1/2" drill (may need to rent something with a stand to drill horizontally into keel in place). Oh, Farr office tells me that if I just added 800pounds as a bulb to the keel that the stability would likely go from approx 107° to about 115°. Unfortunately, I do not want to always carry around that 800 pounds when sailing downwind or upwind in light air. Thus the idea of 'moving' the ballast vs adding. I am considering having Mars Keel build me the (2) symmetrical bulb halves that would be modeled on the mounting face to fit the keel. They have provide me an estimate that seems reasonable.
Any thoughts or advise are appreciated. TIA
Ben

Back in the 1980’s an entire fleet added a 7”keel “shoe to North American 40’s. They were bolted on and micro balloon was used to fair it in. It was not moveable.

In the 2000’s a shoe was added to a Martin 242. It was to bring the boat back into one design configuration as the previous owner had cut the bottom of the keel to make it lighter.

Neither were moveable.

[Capt Ben]

Yep, per initial post, I am working with one of the (2) senior Naval Architects @ Farr...

Originally Posted by malbert73

I would hire a NA (Farr probably would consult) to design the keel cutouts. Also, the rectangular ones will be susceptible if you have a hard grounding (ie keel would bend aft)? Triangular may be more structural?

[malbert73]

Originally Posted by Capt Ben

Yep, per initial post, I am working with one of the (2) senior Naval Architects @ Farr...

Yes, but per your original post they have not addressed what I bring up- whether the cutouts are structurally sound.
They state the original keel can carry extra ballast.
Am I missing where Farr has formally signed off on removing keel material?

[Capt Ben]

Still in the design phase. Initially, Farr thought some removal is an option. How much, and where is still being figured out.

Originally Posted by malbert73

Yes, but per your original post they have not addressed what I bring up- whether the cutouts are structurally sound.
They state the original keel can carry extra ballast.
Am I missing where Farr has formally signed off on removing keel material?

[chrisr]

does anybody know how we can run a survey on who would / would not do an ocean race on a boat with keel modified as suggested ?

don't want to go and start another thread...

cheers,

[Fore and Aft]

Chrisr I hear what you're saying. I can remember working in one boatyard where the owner was making some wild keel modifications. In the end the boss asked the owner to truck the yacht out of the yard. Even though we were not doing the work, just the stigma of having a keel fall of from a boat that had been in our yard was enough to get him booted out.
Cheers

[jtsailjt]

Originally Posted by malbert73

Yes, but per your original post they have not addressed what I bring up- whether the cutouts are structurally sound.
They state the original keel can carry extra ballast.
Am I missing where Farr has formally signed off on removing keel material?

I think that removing material above the keel bolts is very doable with little to no effect on structural integrity. Additionally, I think you could drill a series of 1” holes through the keel below the keel bolts to further lighten the top 2/3 of the keel. Of course all these holes would be filled and faired. Many lightweight materials that could be used to fill the voids are quite strong in compression so any loss in structural integrity would be very minimal.

[rslifkin]

If additional draft and surface area is acceptable, I'd consider building a light weight (relative to lead), beefy spacer (faired nicely to the hull and keel) to just move the whole keel down a few inches. Or you could possibly consider a whole new keel. Getting weight down low would be a good time to use a cast iron keel (which can be thinner for less drag) with a heavy lead bulb at the bottom.

[chrisr]

as i said in an earlier post : don't bodgy about : do it properly - replace the keel completely

cheers,