Displacement vs. Planing Hull

-- Last Updated: Dec-13-09 9:14 AM EST --

For SUP that is - standup paddling. Is this guy talking about a SUP being a planing hull full of it or he's got a point? Talking about paddling under your own power (not surfing or strong downwind, which is also a sort of surfing, where the SUP is indeed in planing mode at least some of the time).

http://vimeo.com/2504447 and http://vimeo.com/2504469

Do you think you gain more (in terms of more speed or less effort) from the "lift" compared to what you loose from the inefficiency created by the same lift in terms of "pull" forward lost?

Reading John Winters' articles helps understand some of what makes a hull "plane" (or not). Just curious if by effectively pushing on the paddle down a bit and thus lightening the overall weithg and thus minimizing the displacement needed (for a short moment at least) there is a benefit compared to paddling the "old" way. Canoe paddles are shaped very similarly (they have some angle) but no one I think talks about "lift" in the way this guy is (e.g. in terms of minimizing the displaced water).

The guy is restating many

– Last Updated: Dec-13-09 1:42 PM EST –

misconceptions about planing hulls.

No paddler can put any hull on a true plane, except by launching onto a fast wave and riding the upstream slope, or accelerating with an ocean wave and riding the downslope. A planing hull for paddlers is one susceptible to planing under wave surfing conditions.

SUPs are displacement hulls. They will plane on a wave, but when being paddled under other conditions, they are in displacement mode.

I think what he is talking about something I have experienced with certain of my flattest-bottomed whitewater boats. When I take a stroke in these boats, the bow is sliding up over the water to a small extent, as the water is displaced under and around the boat. This makes for good acceleration, better than may occur in a canoe designed for speed on flatwater. But good acceleration with each stroke does not make for the highest cruising speed.

I notice that the SUP crowd also seem to believe that stability requires a flat bottom, and that a flat bottom means stability. I have one boat with a flattish bottom that has very little initial stability. I have another boat with a very eliptical bottom that has great initial stability.

Planing usually requires a rather flattish bottom. Initial stability doesn't, though surfboard type craft tend to be stable.

Simba, Ungawa!
He misuses most of the technical jargon. Paddles don’t cavitate, they ventilate (big difference). The downward flow he is focused on is not causing planing, but probably just altering the trim briefly as g2d says, to keep the nose above the waves. You could do the same thing by stepping back on the board a bit. He definitely doesn’t understand the difference between a displacement hull and a planing hull. He’s really talking about the difference between a flat-bottomed displacement hull and a kayak or canoe-shaped displacement hull. Except on the waves, of course, where I’m sure they plane away, but then so do surf kayaks. I’m sure he’s correct about his paddle being well-suited to paddling SUPs, I just don’t think he knows why.

Most annoyingly, however, is the way he uses the term ‘efficient’ much the way Tarzan uses ‘ungawa’, which is to say it means whatever he needs it to mean, as the situation demands.

Yeah, my flat-bottomed whitewater boats
feel pretty efficient, as long as I’m not trying to keep up with fast cruising boats.

Plane vs Displace and wakes
A fellow at the club holiday party authoritatively explained to me that the difference between planing and displacement hulls is that on a planing hull the bow wave goes down and on displacement hulls the bow wave goes out to the side.

I know my sea kayak is a displacement hull. I know I experience “suck-water” starting in about 3 feet of water, and I believe that phenomena is related to a down-wake from the hull. Thinking on it, I believe the wake is sent out form the bottom and from the sides.

I didn’t argue with the fellow at the party but decided it was time to move on and mingle with some other folks. I dropped in on this thread hoping to read an explanation.


Actually a very fit paddler in the right hull can get the boat onto a plane for a few seconds. I would have doubted it too and it’s a common thought but awile back watched the video of the guy getting the hydrofoil kayak up on the foils and for a few seconds at least the boat is planning before the foils are going fast enough to lift it up out of the water. Not to say that I can do this :slight_smile:

And no one can generate enough power with a paddle to keep any boat on plane for more than a few seconds, way too much drag.

Bill H.


– Last Updated: Dec-14-09 9:44 AM EST –

I watched these clips on Youtube too - a lot of fun. But that's different as the foils actually generate lift. And it gets out of the limit of the hull's wave generating properties since there is no hull to speak of in the water any more (just the wings).

A flat bottomed hull only has "push", no lift. John Winters explains in his articles that even though strong paddlers can paddle beyond their "hull speed" they are still not planing.

As for Chip's quesiton on the direction of the wave, I've read discussions on this precise topic somewhere. The main wave is generated down I recall even from rounded displacement hulls, hense the suckwater experience.

I've actually posted the same question on a SUP site and it is interesting to see their replies - all the opposite to what I'm getting here from the kayaker crowd -:). Hopefully, I'll learn something from them too.

I'll be paddling my SUP for a first time next week. If the airlines do not lose it on the way there, I'll report if there is any planing or not aside from the airfare part -;)

minimum speed
The hydrofoils have a minimum speed before they do anything other than cause alot of drag. To get up to the speed that the foils actually lift, the boat has to plane for a few seconds at least to go fast enough.

It’s possible to make foils that lift at a lower speed but they would also limit the top speed. That video and that boat were intended to go as fast as possible while paddling.

Bill H.

You are probably right
The boudary b/w displacement & planing is not exactly a sharp line so I would immagine that at some point the dynamic forces that John Winters is talking about begin to increase sufficiently to cause partial planing even without foils. But that can only be sustanined as you mention for a very short time and only by a slilled and strong paddler. At that point, if there is enough speed, the foils may be generating enough lift to lift the hull entirely out of the water.

When I did windsurfing, I could tell at some wind levels that I was partially planing but if I just stood there on the board I would never plane. But, if I pulled on the sail a few times (e.g. paddling in air, sort of), I could increase the speed and decrease the displacement a bit (pulling the sail down a bit effectively lifts the boart a little). That was enough to get the board out being bogged down in displacement mode and into pure planing where the same wind that was not enough to overcome the resistance of the water when the board was displacing was now sufficient to plane me over the surface.

I imagine something similar is happening with the foil kayak. The same thing can happen on flat bottomed boats/SUP too, but since they do not generate enough lift compared to the sustained power a paddler can provide, I think they just dive down again very soon into displacement mode.