Semi-displacement
Semidisplacement or semiplaning vessels are identified by three factors.
The shape of her run, the underbody aft, secondly, her displacement length ratio and third is a combination of her other abilities like sea keeping, strength and comfort.
Although hulls with very light displacements for their lengths can achieve higher
SL ratios
than 1.4, true planing hulls require flat underbodies aft for planing surface.
It is primarily the flatness of a vessels run that determines weather more power can be used to push her past theoretical displacement hull speed of 1.4.
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