Thread: Planing is bunkum - New article on storerboats website

Sometimes the obvious needs pointing out.
Including when the king has no clothes...

Hi MIK, I really like your 'theory' posts, and this is a good'un.

I've sometimes wondered about the fascination with 'prismatic coefficient' in boat design, and why it should increase for boats intended to be faster, and your 'traditional methods of beating wave drag' explains that nicely.

I also like the "equal and opposite reactions" approach to looking at wakes in your post - that the hollow behind the boat indicates that the water must be doing some 'pushing up'. It makes it easy to visualise how steeply rising buttock lines might 'suck' a boat's stern down, too - now I'm looking for images of 'bulging' wakes to see if I can find that illustrated.

Cheers, Jack

A classic example of sucking a boat's stern down is what happens to an OzRacer or PDRacer when it goes faster. The more the curvature of the bottom the more you can see the effect. Every burst of speed the bow goes up high.

Dave Gentry in PDR Kwik Kwak at Mt. Storm, WV - YouTube

But compare with the Goose ... same depth of rocker, spread out to 12ft rather than 8 and it behaves completely differently. Same weight, same sail area and a fraction of the wind.

PD Goose sailboat gently planing. Homebuilt boatbuilding plan - YouTube

bow doesn't pop up and it can travel through the increase of drag at "hull speed" much more easily. But the OzRacer/PDR speed jumps all over the place. The goose would be screaming along with high unchanging speed in those conditions.

I was quite stunned by the difference. Particularly because it is very close to a full scale controlled experiment.

MIK