If you want to improve your capsize screening formula am I right in thinking ad more ballast?
and of course no adding superstructure like radar and solar.

In basic terms yes but obviously it needs to be done properly else you will create problems. For a typical fin keel the usual method is to bolt a shoe of ballast onto the lower end of the keel - most easily done by making the shoe out of two mirror image halves split vertically, and bolting them on with lateral bolts. There have been numerous successful examples of this using lead shoes onto cast iron or lead fin keels, probably with epoxy glue strength filler between the shoes and keel and to fair it all in including the counterbore holes for the nuts onto the threaded rod. But this will increase the shear and bending moment at the fin keel to hull joint, which may not have enough original design margin to to accommodate it - so the keel bolts and keel floors would not have suitable margin anymore. In a grounding incident - depending on severity - the shoes might become dislodged. Freeboard would be reduced. Re-insurance would be virtually impossible. Best to buy a yacht with an originally designed and built / maintained ballast ratio and stability.

This is an essential read for anyone considering keel modifications: cdn.revolutionise.com.au/site/v2hcrmsgjqpwek7h.pdf

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r13 said..
In basic terms yes but obviously it needs to be done properly else you will create problems. For a typical fin keel the usual method is to bolt a shoe of ballast onto the lower end of the keel - most easily done by making the shoe out of two mirror image halves split vertically, and bolting them on with lateral bolts. There have been numerous successful examples of this using lead shoes onto cast iron or lead fin keels, probably with epoxy glue strength filler between the shoes and keel and to fair it all in including the counterbore holes for the nuts onto the threaded rod. But this will increase the shear and bending moment at the fin keel to hull joint, which may not have enough original design margin to to accommodate it - so the keel bolts and keel floors would not have suitable margin anymore. In a grounding incident - depending on severity - the shoes might become dislodged. Freeboard would be reduced. Re-insurance would be virtually impossible. Best to buy a yacht with an originally designed and built / maintained ballast ratio and stability.

+1 Buy a yacht with the stability you want. Mods on keels are a recipe for problems. You could add some lead in the bilge, but usually for not a big gain.

Making a boat stiffer will also test the rig

I would not use capsize screening formula for any analysis.

The CSF does not consider the hull shape or ballast location.Any two sailboats will have the same CSF value if their displacement and beam are the same. As an example, one could have a light hull with 50% ballast in a bulb at the bottom of an eight foot fin keel, the other could have a heavy hull with 20% ballast in a 2-foot-deep (0.61 m) full-length keel. The stability characteristics of the two sailboats will be drastically different despite the identical CSF value.

en.wikipedia.org/wiki/Capsize_screening_formula

I have also been told that simply adding more weight to the keel in some cases can be counter productive as the boat will sit differently in water and stability provided by the shape of the hull will also change. It will help your screening formula, but may not provide additional usable stability.

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Ilenart said..
I would not use capsize screening formula for any analysis.

The CSF does not consider the hull shape or ballast location.Any two sailboats will have the same CSF value if their displacement and beam are the same. As an example, one could have a light hull with 50% ballast in a bulb at the bottom of an eight foot fin keel, the other could have a heavy hull with 20% ballast in a 2-foot-deep (0.61 m) full-length keel. The stability characteristics of the two sailboats will be drastically different despite the identical CSF value.

en.wikipedia.org/wiki/Capsize_screening_formula

So I am guessing the 8ft bulb has a greater Righting moment ?
so can any one tell me what yacht Has a very good genuine righting Moment ?
i know they use the Contessa 32 as the bench mark , but the Tradewinds 35 on paper has a very low number 1.52 incredible

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Zzzzzz said..

Ilenart said..
I would not use capsize screening formula for any analysis.

The CSF does not consider the hull shape or ballast location.Any two sailboats will have the same CSF value if their displacement and beam are the same. As an example, one could have a light hull with 50% ballast in a bulb at the bottom of an eight foot fin keel, the other could have a heavy hull with 20% ballast in a 2-foot-deep (0.61 m) full-length keel. The stability characteristics of the two sailboats will be drastically different despite the identical CSF value.

en.wikipedia.org/wiki/Capsize_screening_formula

So I am guessing the 8ft bulb has a greater Righting moment ?
so can any one tell me what yacht Has a very good genuine righting Moment ?
i know they use the Contessa 32 as the bench mark , but the Tradewinds 35 on paper has a very low number 1.52 incredible

When I was yacht hunting I looked at AVS.

en.wikipedia.org/wiki/Limit_of_positive_stability

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Zzzzzz said..
If you want to improve your capsize screening formula am I right in thinking ad more ballast?
and of course no adding superstructure like radar and solar.

One of the best places to find the info you require is here.

www.boatdesign.net/forums/stability/

If you search back far enough you will find some of our current and past forum members.

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Ramona said..

Zzzzzz said..
If you want to improve your capsize screening formula am I right in thinking ad more ballast?
and of course no adding superstructure like radar and solar.

One of the best places to find the info you require is here.

www.boatdesign.net/forums/stability/

If you search back far enough you will find some of our current and past forum members.

Thanks Ramona , interesting topic I am surprised at so called seaworthy boats with a high screening number.

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Zzzzzz said..

Thanks Ramona , interesting topic I am surprised at so called seaworthy boats with a high screening number.

Not so surprising, it is a fairly blunt instrument. It was never meant to be anything more than a coarse filter to try and prevent people entering offshore races in boats with poor characteristics. CCA had to do something after Fastnet and it was an immediate reaction. It's useless for anything now we have more precise calculations for stability that take into consideration more than just beam and displacement.