What makes a boat plane?

[gonzo]

Narrow double enders have hulls speeds of up to 3xsquare root of wl.

[Wynand N]

A displacement hull won't plane. Planing hulls have rather straight buttock lines and the structural integrity to take the pounding at high speeds.

Hi Gonzo

Sailing dinghies that are sufficiently light-weight will usually plane even in light to moderate winds.
Nonetheless, for a large portion of it's sailing life they perform as displacement craft which they are.

Grumman Canoes had 2 hull styles. Flat bottom for sport speed use, and a rounder bottom for camping or as they called it back then- "freighter use"- 16' and 18' rated for 2,000 to 3,000 pounds of cargo. They were very deep and wide hulls that were used as " freighters ". All had a stern out board bracket because the average side breeze would kill the best paddelers in a short time.

[tonyr]

Gonzo, how narrow is "narrow" in that context? Putting my w/l beam at 3 ft, and the w/l length at 16 ft, that gives a w/l ratio of better than 5 to 1 length to beam. Any way to guess at where the critical speed might lie in a hull of this shape and proportions, where "planing" however defined, starts (given as the multiple of the sq rt of w/l, not knots)?

Tony.

[gonzo]

All planing hulls can move at displacement speeds. If they are designed for planing they will perform efficiently at high speed.
Tonyr:
I think that hull fineness is a better reference because a very narrow but deep hull will have a low maximum speed. Also the shape has a lot to do. Easy sweeping lines with the beam about 55-60% aft seem to get higher speeds. Straight buttocks help streamline the waterflow and create less turbulence.

[grob]

Tony

An international moth is a planing boat and is relatively narrow . I think over 10:1

For a simple rule of thumb to predict planing speed use

velocity = k * LCG / SQRT (B)

k = Constant 4 for ft 7.2 for metres
LCG = Distance from logitudinal C of G to transom
B = Beam

see the following.

see
http://www.hydrocompinc.com/knowledg...aningSpeed.pdf

another interesting online reference is http://www.mothboat.com/USMMCA/Building/hull.htm

All the best

Gareth