Stability curve by heeling

[steelfloats]

Has anyone made up a stability curve for their yacht by heeling it and measuring the force on the heeling line? I recall reading about this in an article about Uffa Fox, but cannot find the article. It should be possible, the maths do not look to daunting, any thoughts?

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[Roberto]

I did it once, we wanted to improve rough weather wave handling by reducing longitudinal moment of inertia trying to keep an honest righting moment: we ended up slicing away a bit of the keel and replacing it with hardwood to keep the same lateral plane area, and adding lead ballast in the bilge

I needed to know at least an approximation of the existing righting moment before doing anything, so we basically shifted a known weight atwarthship at a known distance, measuring the heeling angle with a thin rope hung from the ceiling and brought into a bucket (to smooth movement), then computing righting moment and center of gravity position

If you run a search for "inclining experiment" you will find the methodology involved

As you say, maths are quite simple, just repeat it a few times to get an average measure, possibly measuring port and starboard righting moments..



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[PeteMcK]

Unfortunately, to make up a curve, you also need to know the displacement of the boat and the height of the centre of buoyancy. The latter moves, especially as the immersed shape changes with substantial amounts of heel and it's calculating this incrementally which makes the process so tedious. If you have a lines plan for the boat, it's all do-able. A naval architecture CAD package would speed things up enormously. See http://www.naval-architecture.co.uk/links/showlinks.asp?Topic=software . I've used the free download of Vacanti Prolines quite successfully for this. Best of luck!

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