Bill has been kind enough to share with me the details of his Pre-fin design. All credit goes to Bill here…I brought nothing to the table on this one except for that I made the fins. Both are his templates and design.
The main fin is a 7 5/8’’ fin that is the template he used for the most recent big wave board that Bird Huffan had Bill shape. The fin is made from (30 layers) 7.5oz Volan with yellow tint to give it this ugly yellow poop color.
Here are some notes from our conversation which led to the making of these fins.
Pre-fin is held in place by the main fin
Pre-fin is 50-60% the depth of the main fin
Pre-fin can be used with thick foiled main fins
Pre-fin base 1.25'' to 1.5'' wide
Match the trailing edge of the Pre-fin to the leading edge of the Main fin
Slot between the two fins must remain constant width
Slot width is between 5/8'' and 3/4''
What makes the Pre-fin so effective is the very high camber, in relation to the fin chord. That and the gap between the pre-fin and main fin.
This fin is heading to a fellow Sway and hopefully he will give us a ride report one day.
…I see the errors from here in the longboard surface; you should sand it better next time…so for the guys here that always talking about 1/8 or like that of tweaking here and there, bear in mind that a bad sanded board is another variable.
I surfed for about 3 years with a board with inline fins in ´97; also I put here few photos of other boards that I made in the past with in line fins; in Aussie land lots of boards with in line fins in early to mid 90s but most were glass on, the only thing different seems the wedge in the base of smaller fin.
That style fin was all the rage in windsurfing for a few years. They held insane. But ultimately faded away because they were a tick slower. For nose riding it might be the ticket.
The benefits would be felt anytime you executed an abrupt change of direction on a wave, as well as generating increased speed in trim. The function is much like a leading edge wing slot, on an aircraft, or the jib on a sailboat. In nature, it is similar in function, to the Alula on a bird’s wing. In all cases it improves flow on the main foil, at higher AoA’s, preventing stalls and loss of speed. Chest to head high may well be the best functional range, simply because more extreme maneuvers are attempted in that size of waves.
I’m probably going to make a fin to try this out. I’ve been doing a smaller trailing fin in my traditional style single fin longboards, and love the extra hold and speed in certain sections of the wave.
Have you determined the ideal distance to have between the fins?. I found with a smaller trailer, 2 5/8" to 2 7/8" separation feels best to me.
For a pre-fin, I want a space of at least 5/8th to3/4th inch between the trailing edge of the pre-fin, and the leading edge of the main fin. I don’t have any experience with trailing fins, so can not comment.
