Displacement vs Planning

Mr Efficiency · Sep 29, 2015

sharpii2 said: ↑

There are two advantages I can see for a pointed stern on a planing powerboat:

1.) there should be less of tendency to wallow at displacement speeds, and
2.) the pointed stern would tend to part waves coming from behind.

The second reason is accentuated by the very design compromises needed to get the pointed stern in the first place.

First, there is less buoyancy in the stern, which means the heavy engine needs to be moved forward. Having to do this just about kills the idea of having an out drive. This boat will need an inboard engine, complete with with an external prop shaft and a rudder.

This in turn makes for a lot of drag aft, when hit by a following sea, while at displacement speeds. This gives the boat less of a chance to broach, even without the pointed stern to part the waves.

I suspect there is a top performance price to be paid for this hull configuration, but in certain circumstances it might be worth it.
Click to expand...

Whilst I can see some advantages in the configuration for crossing a bar, if by some chance (engine problem, perhaps) the boat was slowed down to displacement speed, it would be very poor practice to depend on it as a routine method of running the bar, imo, you would come to grief before long.

SuperPiper · Sep 30, 2015

If a straight transom is better than a pointy transom, can that logic suggest that a concave transom is better than a straight transom?

tviveen · Oct 5, 2015

Lifting theory

Maybe this is what you are looking for; lifting theory for monohulls.

http://prntscr.com/8o1o0g
http://prntscr.com/8o1pud
http://prntscr.com/8o1q9l

Cheers!

Tim.

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Displacement vs Planning

Mr Efficiency Senior Member

SuperPiper Men With Little Boats . .

tviveen New Member

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