Planing Question

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Big Al1

Seaman
Joined
Dec 8, 2002
Messages
68
I've read many times on this forum that certain boat hulls do not plane off in the water. What makes a hull able to plane off? Does it require a certain amount of surface area contact with the water or just a sloping hull? If it is designed to float and move forward, then it will plane off. A pontoon boat will plane off if fast enough. The resistance of water is much greater than the resistance of air. Think of an airplane wing. It is the friction of air under the wing that builds pressure under the wing to lift the plane up. The friction of the water is pushing your boat upward. All boats have a sloped hull that allows water to push the boat upward. The hull can be flat as long as the front of the hull slopes upward. I’ve been told on this forum that my 14ft jon boat will not plane off. All I know is that at 15mph, I have a very large wake for a small boat. But when I gun it to about 20mph, I can actually feel the boat lift up out of the water and I then have a wake that is about 1/3 the size as before. The angle of the boat never changes. If that is not planing off then what is?
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Planing Question

You have it right, Big Al.<br /><br />Your Jon is a planing hull.<br /><br />But there are hulls that are not intended to plane. They are called displacement hulls. Tugs and trawlers are the best examples I can think of. They commonly are deeper in the center than at the stern.
 
B

Big Al1

Seaman
Joined
Dec 8, 2002
Messages
68
Re: Planing Question

Very good site. I now understand that not all hulls are planing hulls. Some are rounded at the bottom allowing them to move about the water more efficiently without planing. I guess they could possibly plane off but they would have to be going pretty fast.
 
S

Solittle

Fleet Admiral
Joined
Apr 28, 2002
Messages
7,518
Re: Planing Question

Big Al - You got the idea. A nuclear powered aircraft carrier will do in excess of 35 knots but one could hardly say it gets up on a plane. <br /><br />On your airfoil analogy - Actually it is a vacume that is formed by the passage of air over the top of the wing that creates lift not the pressue under the wing. An airplane flies when there is sufficient thrust from the powerplant to propel the aircraft through the air with enough speed to overcome drag and generate enough lift to "overcome" the weight of the plane.
 
magster65

magster65

Commander
Joined
Sep 1, 2002
Messages
2,573
Re: Planing Question

There is something missing from that site. It takes very little power to achieve displacement speed. It's not uncommon for a single diesel powered 34 footer to cruise along @ 9 knots (11 mph) and use a 2 gph. Pretty impressive really.
 
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