Keel Modification: Increase stability

[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

[SailingHarmonie]

Have you noticed this is the "Cruisers" forum?

You will find more useful information for things like this on more racing oriented forums...

But aside from that, I am curious. Most Farr skippers I know are avid one-design racers. This mod would obviously disqualify you from that part of the sport, and would likely drive your local handicapping people nuts...

I totally understand the sailing reason for doing a project like this, but I don't get the racing reasons? What kind of racing are you hoping to win at to justify the expense?

Explain it to me like I am totally ignorant of racing, 'cause I am...

[Adelie]

Mars Keels have added bulbs, or cut the bottom of and added back a bulb.
Perhaps talk to them.

https://marskeel.com/

[Celestialsailor]

Originally Posted by SailingHarmonie

Have you noticed this is the "Cruisers" forum?
You will find more useful information for things like this on more racing oriented forums...

Having been around a month you most likely have'nt looked at older threads on this forum. A lot of members are former racers. Some are Engineers. There probably isn't any topic that has not been talked about.

[Fore and Aft]

Capt Ben this seems like allot of effort and then you say there are times you don't want the extra 800lbs of ballast. So why not go water ballast then and get the best of both worlds.
We used to put lead bulbs on the bottom of Farr 1220's to stiffen them up for racing. Never cored out the top of the lead keels though. How much weight are you expecting to save as I imagine the keel bolts are going to get in the way and surely you wouldn't want to be drilling right next to them? How does the structure of the keel change if you honeycomb the top half of it? Can it crush or crease when loaded up? Just curious as the loads on keels are enormous and occasionally with a good broach or grounding very sudden.
Cheers

[donradcliffe]

I would just add a sandwiched bulb at the bottom and forget about removing material from the top.

[neilpride]

For me, the best option would be to load the keel on a truck and send it to mars keels.

[Capt Ben]

UPDATE, at this point I have decided to get rid of the hole idea and instead create cut outs via 1" corner diameter bores and then using a sawzall/circular saw to make straight cuts. This method should eliminate ± 600 pounds all to be replaced with a split bulb ± 4'7" long to be sandwiched (through bolted) to the lower section of the keel. Mars will likely make the split halves. I expect to fill the cut outs with a high density foam and then to fill and fair with colloidal thickened epoxy.

[Capt Ben]

Originally Posted by donradcliffe

I would just add a sandwiched bulb at the bottom and forget about removing material from the top.

I was going to do this. However, the down side is that one is always lugging around 4-5 crew members (800#s) at the bottom of the keel. Whether light air, up wind or downwind. IE, the boat will be slower in all conditions except upwind /power reaching in over 12kts of wind. By not increasing the displacement & lowering the VCG the stability should be greatly increased with out the downsides.

[Capt Ben]

Originally Posted by Adelie

Mars Keels have added bulbs, or cut the bottom of and added back a bulb.
Perhaps talk to them.

https://marskeel.com/

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...

[wyb2]

This seems crazy to me too, but 2nd plan looks better. You seem to have an accurate model built and are doing some due diligence with it.

In another current thread where the user is cutting up an unfinished wood/glass project boat, he mentioned some scrap guys cut up its keel with a chainsaw. Kinda makes sense, as lead is very soft. Would go a heck of a lot faster than a sawzall.

[nmuir]

Chainsaw is the way to go.


If you do you will be in good company. I attach a photo for fun. It is Bent Jespersen mid-series modifying the lead keel of Canada II, the 12 meter entry to the 1987 America's Cup in Fremantle. Not a computer model, test tank (or safety gear) in sight.


Things were a bit different back then.....

[psk125]

Cutting out sections of the lead brings up the question of structural integrity. How are the cutouts going to affect the strength of the whole keel? It's seems obvious that if you removed a 6" section of lead from the top of the keel and left a gap between the top of the keel and the bottom of the hull with just the keelbolts showing, that the keel might end up falling off with all the torquing. Will the cutouts act like the "tear here" perforations on toilet paper? Are you counting on the keelbolts holding everything together -- and will they? The lead has a structural purpose besides serving to increase righting moment. How much of a structural purpose does it have, and how much can you safely remove? This is probably not something to take a rough guess at.

[chrisr]

amongst my various race boats, we had 2 on which we did significant keel mods

if you're serious about improving the keel on this boat, throw away the old school delta keel completely. don't waste time and money fiddling with it - fit a proper T keel, with properly designed bulb

righting force is a moment ie weight x distance, so the lower down you put the weight, the less you need. we took this to extremes on a ben lexen designed 30' which eventually drew 9'6" but had a tiny 600lb bulb

there are heaps of design permutations but if you're serious about this, the first one is throw away the existing keel

i would also echo fore&aft...have a look at water ballast. i became a massive fan of this when i had a VO60...doing 9kts to windward in 30kts AWS convinced me !

although you do put the ballast high, you also put it out to the side, and most importantly can add or subtract at will.

but whatever you do, don't go canting !!!!!!

cheers,

[GILow]

Another vote for water ballast if the keel idea runs into too many problems.