keel worth to be modified?

[nemo]

I'm thinking about modyfying a 31 feet IOR keel by adding a small lead bulb. The heeling of that boat is too much as the wind strenghtens, the efficiency of the hull and the sails drops, so the boat cannot be competitive nowadays. But on the other hand, adding a bulb can have two consequences: it increases the wetted surface, and can increase loads on the mast.
I still haven't designed anything so I haven't got any drawing or calculation.. but what do you think about it?

[Tim B]

I presume that the IOR is a regulated class like the IRM and IRC classes. If that is the case, then make sure that you will not breach class rules by modifying the keel, otherwise you won't be able to compete. The other word of caution is to make sure that you don't over-load the keel. You can do a (very) rough sum on it quite simply, without the need for anything fancy like FEA. The basic formula is f=1/(2*PI*SQR(m/k)) where k=mg/d and d is the deflection of the tip at rest in meters, m is the mass in Kg, and f is the natural frequency. If f is much less than 2Hz I would'nt bother. I don't think anyone has yet seen a keel oscillate in bending and break, but I dare say it's possible. As for the rig loads, they will go up, but the shrouds should be able to take the load. If the rig looks to be flexing excessively, back off, instantly. Most rigs are designed to withstand high transient loads, but high steady loads may not be in the design, your best bet is to talk to your rig manufacturer.
Hope this is of some help.

Tim B

[nemo]

The boat now competes in IRC class, so it's allowed to have such a bulb, it just needs changings in the certificate.
I think static loads are to be considered before any oscillating or fatigue load. So first of all I could get empirical datas to build a stability diagram (placing known weights at a measured distance from the centerline and reading the heel), then estimate the weight to place at the bottom of the keel, then calculate the new stresses on the hull. But how can I know if the disadvantage of adding wetted surface will be counterweighted by the better stability?

[Polarity]

I guess that depends on how much wind you regularily sail in...
If you are a light wind racer then WSA I would think is more important, in stronger winds with plenty of driving power then its stability. One of the many trade offs of yacht design!

However since you have said
" so the boat cannot be competitive nowadays"

What are your other options?

[Polarity]

Here's another thought, I assume you are talking about a fin keel, could you make the bulb also end-plate the keel to make it more efficient?