A fin is a compromise of grip and side drift. It is the device that gives direction and causes most of the lift that generates motion. The waves’ energy is captured on the fin’s surface creating upward pressure. The surfers’ weight in front of this lift is the basic force that causes a surfboard to traverse across the wave. To turn a surfboard, the fin needs to be pushed through the water, but cannot totally release. The surfer’s weight might be a consideration upon choosing a fin. One who is heavy for a given board length might choose a larger volume fin to compensate for his aped force resulting from his weight. The converse applies to a lighter surfer for a board’s volume..
The wider the board is in the tail, requires the fin to be either longer or nearer the tail. Increased volume at the fin base traps more water for lift and drive. Reduced volume above the (immediate) base will reduce turning resistance and in more extreme applications can also create “wag” (see HP fin, below). Increased fin rake (a term for the amount tip that overhangs the base) ads drive, but resists board rotation, but properly applied, can create “wag” (see HP fin, below). Increased tip area reduces tail release while nose riding, but also decreases maneuverability..
With more base measurement it will have more drive. With less base area you get less resistance when pushing through a turn. Increased fin depth adjusts for both tail width and the surfer’s weight. Increased fin depth creates more grip on turns (harder to turn) and decreases premature tail release while nose riding. More volume will also decrease premature tail release.
THE HARBOUR FIN LINE-UP
STANDARD ISSUE FIN (SI)
NOSERIDER FIN (NR)
"R" SERIES FIN
MULTIPLE FINS 2+1
This is the term for one medium sized center fin that is usually 6 to 7.5 inches deep, and the two smaller front fins called side bites. The side bites are normally 3 ½ to 4 ½ inches in depth. Most side bites are in a fixed position, and most center fins are adjustable. Moving the center fin forward decreases the rotational resistance, making turning easier. Moving it too far forward will begin to force the surfer forward to get any lift for motion across the wave plus it begins to get too far from the rail to be effective. When the center fin is increased in size it creates more drive but allows less side drift, which will make the board harder to turn.
ADJUSTING THE CENTER FIN
There is no exact fin location for all sizes and wave conditions, nor is there an exact fin placement for each surfer’s ability. We suggest placing the rear most base of the fin that is exposed above the box at 8.5” from the tail as a starting point (this is not the fin tab). If the board seems to slip somewhat on harder turns, try moving the fin in increments of ¼” towards the tail until the slippage is minimized. To loosen the turn, move the fin in ¼” increments forward. Rarely does the fin need more than ¼” total movement to accomplish a desired ride. And most interestingly, this 8.5 measurement works as a starting point for 2 + 1 set ups too.