What is better for the Northern Chesapeake: fin keel or wing keel? I'm not interested in a swing keel. They scare me.
Ok, so if you reduce the draft by concentrating in a bulb you need to increase mass of the keel to make up for the shorter lever arm. On the other hand by shortening the fin to make the shallower bulb you've also reduced your lift area affecting pointing. What about that fatter profile for the bulb ? Isn't that more turbulence or at least more wetted surface without lift ? Maybe that is why I've seen some fin keels that taper outward as they go down, to concentrate weight lower like a bulb yet maintain some Bernoulli lift effects.sailingdog said:...A bulb keel can be much more efficient in terms of righting movement, compared to a fin keel. The bulk of the mass is at the very bottom of a bulb keel, whereas it is spread over the entire depth of the fin keel. The bulb can be a bit less draft than a fin keel with the equivalent righting moment. This means that a bulb keel boat may have a shallower draft while having the same righting moment.
You don't necessarily increase the mass of the keel, as the keel's effects are based on the center of mass for the keel, and using a bulb may in fact move the center of mass lower, without a corresponding need to increase the weight.captnnero said:Ok, so if you reduce the draft by concentrating in a bulb you need to increase mass of the keel to make up for the shorter lever arm. On the other hand by shortening the fin to make the shallower bulb you've also reduced your lift area affecting pointing. What about that fatter profile for the bulb ? Isn't that more turbulence or at least more wetted surface without lift ? Maybe that is why I've seen some fin keels that taper outward as they go down, to concentrate weight lower like a bulb yet maintain some Bernoulli lift effects.
If you're not going to increase the keel mass then the profile and therefor lift effects are reduced as mass has to be shifted from the upper keel into the bulb in the shortened keel to move center of mass lower to maintain the righting moment. To compensate some lighter fairing material could be used to maintain the profile but the remaining support structure metal has to bear more load in the thinner upper keel. That is not a trivial engineering exercise. I'm just saying there does not appear to be a free lunch by shifting mass into the bulb.sailingdog said:You don't necessarily increase the mass of the keel, as the keel's effects are based on the center of mass for the keel, and using a bulb may in fact move the center of mass lower, without a corresponding need to increase the weight.