round bilge vs chine

what are the advantages/disadvantages of round bilges or hard chine in semi-displacement boats?

 

Co$t.

FAST FRED

 

Better speed potential with hard chines, more comfortable ride with round bilge.

 

Less roll with hard chines.
Less ponding with rounds.
Better fuel economy in displacement speed with rounds.

 

Less roll with hard chines? On plane I assume.

 

Of course, static roll stability depends on the dimensions. The fairest comparison between a round hull and a chine hull would be to match the static stability curves as closely as possible. In that case, I would expect the chines to resist roll dynamically.

 

The chine acts like a bilge keel.

 

Prefer raduis chine. Best of both worlds & easy to build.
Has the stability of a hard chined hull with the aesthetics of a round bilge hull.

 

thanks, so there are advantages to both.

 

Design is always a compromise.

 

As others have noted, a squared-off transition gives more roll stability, easier planing. A rounded transition gives smoother ride, more efficient in displacement mode.

If you begin to push the envelope with roll moment, the square profile will have greater initial stability, but then an abrupt transition to full capsize that will occur so quickly you won't be able to counteract, while the rounded transition will smoothly and gradually increase roll angle, allowing you to detect the issue and redistribute weight so as to prevent capsizing.