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Originally Posted by ancora
There has been some discussion about adding ballast to improve vessel stability. By adding ballast the vessel must ride lower in the water with more wetted area leading to a higher fuel burn. Am I correct in that assumption?

Yes, adding ballast increases the total weight (displacement) of what you are trying to push through the water. If the hull form remains the same; almost the same length, beam, entrance angle, and transom immersion, the fuel consumption will increase. The tricky part is that you could increase displacement a lot by cutting the boat in half and adding 10'. Then your fuel consumption will go down. But transverse stability will stay almost the same.
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Would adding ballast to a semidisplacement hull be selfdefeating?

Probably. It depends what exactly you are trying to fix. Adding ballast (down low) will not appreciably change the low angle stability (that from say 0 to 15 degrees of heel) because low angle stability is mostly dependent on your waterplane area(a cut through the hull at the waterline). So adding sponsons will be more effective than adding ballast.
Highangle stability becomes more center of gravity and displacement dependent so the added ballast will help at 254565 degrees of heel, but modern powerboats rarely heel that far. And when they do there is big trouble.