Planing lift and displacement lift in surfboards

 what makes a full nose fish catch waves better than a 5-10 glass slipper ?



A combination of greater displacement lift ( due to greater volume) and greater planing lift ( due to more area)



The two kinds of lift are planing and displacement lift, these occur in varying proportions but both are always present whenever the board is moving.



The board does not have to be 'planing' ie.e leaving the stern wave behind in order to produce planing lift, planing lift will be produced even at paddle in speeds.



Also the amount of planing lift produced by the board will not only depend upon speed but also on the angle of attack, thus more nose rocker for example will produce more lift at a given speed. It will also produce more drag in order to produce that lift, but in reality the greater lift can mean that the board takes off earlier, thus lifting the nose area out of the water, thereby reducing  drag.



So a board with greater area and/or rocker in the nose will have greater accleration on takeoffin many cases. Often we hear about low rocker making the board faster on the takeoff but that's only true in some situations.

Buoyant lift and planing lift

Low dynamic lift surfboards require higher buoyancy than high lift shapes, as they don't produce as much lift at paddle in to takeoff speed.So, a wide board with lots of nose lift ( a high lift shape ) can get away with less buoyancy than a flat and narrow board, as the flat, narrow board needs to make up for its low planing lift with buoyant lift.Shortboard thrusters are usually high lift shapes ( in spite of their low area ) .Of course, a low buoyancy low dynamic lift board can still take off if he wave is steep enough, but the qualities needed for steep takeoffs are not compatible with flat rocker, narrow width, low volume, and lots of length. . . so low buoyancy AND low dynamic lift is a concept better suited to shortboards.Alaia boards are interesting because they are extremely low in volume, and appear to be shapes which are low in dynamic lift until one realises that they gain dynamic lift by bending to increase rocker and sometimes by takeing off sideways which increases span efficiency for higher lift.There's also fin based planing or dynamic lift which can be very significant at takeoff speed if there is enough area presented at suitable angles, so it's not just a hull issueIn the picture above we see a very successful high lift, medium to low buoyancy longboard. When this design is built with a flatter rocker ( as we have done) it needs more volume and buoyancy in order to keep the lift vs speed profile smooth and practical.As mentioned above fin based lift can't be ignored even at paddling speed. Fin based lift is one of our favourite topics and we have been actively researching it for many years.Fin based lift isn't always what one might think. For example, most people assume that a vertical singlefin does not produce vertical lift. This is not the case. With the FP 12 design shown below for example, we have very carefully designed the hull so that in a trim, downwards turning or sideways angled dropping in position, the massive fin is presented at an angle which produces large amounts of lift. . . . thus releasing the hull from much of the lift production burden. This effect can be visualised easily by looking at the picture below. . . there'a a huge amount of horizontal wing area and lift at the trim angle shown. In order to best present the fin at a suitable angle, a particular kind of tail planshape is required, also as shown.