Design Question

[BigAssHam]

For no particular reason, I would like to know if hard chined boats have more induced drag than round bottom boats. Just something I've always wondered. If so, is it noticable or negligible?

[Jeff_H]

Yes, hard chined boats have more drag both because of increased wetted surface and because of turbulance that forms at the chines. In theory the chines could be laid out to match water flow if the boat did not have leeway, but of course boats do have leeway and it is the cross flow of water across the chine that creates turbulence.

If the boat is low performance, and carefully modeled, the induced drag would not be noticable, but on a reasonably high performance, displacement hull, chine drag would be large enough to be significant. Losses in speed due to chine drag is less significant on a planning hull once it is planning.

Jeff

[deniseO30]

I think it's argued by Ruel Parker in his book about sharpies that hard chined boats have less wetted surface when heeled. of course that woudn't apply to power boats I guess.

[Jeff_H]

It may be true that a hard chined boat heeled over has less wetted surface than it would when level, a hard chine boat will have more wetted surface than a round bilge boat when heeled. For any given volume, half a cylinder will have less surface area than any other geometric shape. The closer you are to a cylindar the less surface area for the volume. In terms of surface area to volume, a triangle is pretty inefficient in that regard.

Jeff