Always been curious about the design of the US fin box and fins.

Question:
With highly designed bottom shapes on boards (ie mm perfect rocker, vee, concave etc), and highly designed fin shapes (reflected in price!), do the following compromise these designs:
1/. Open slots in the US box either side of the fin.
2/. Fin base not sitting flush with the board.
3/. Daggy fin bolt not flush with the board.

Do these things not matter as waveboards are designed to perform on their rails?

Seems a "clunky" part of an otherwise highly engineered bit of gear.

I dunno just curious.

I'm with you. I've always wondered about this.

Hi Rox,

Originally used on surfboards, then taken across to windsurf boards because it was (almost) the only thing available.

Its thin design allows use in current wave boards which continue to have a thin tail.

Powerbox etc are considerably thicker: not good for waveboards (can you imagine a waveboard with a tuttle/deep tuttle box?).

Not used where high speed race/slalom etc. is required, so the design limitations you have wondered about simply don’t matter in its primary application (waves).

Others may wish to comment.

I'm thinking that US and the Euro boxes came into windsurfing fairly early on and there were not many alternatives besides either moulding or glassing the fin in.

The problems you have listed became more apparent as people were sailing faster and with bigger fins. So Mr Tuttle developed his bolt through box and the big manufacturers responded with the Power and Trim Boxes along with Tiga's conical box.

The bolt through boxes have overcome the problems of the US boxes plus allow bigger fins to be used.

However for whatever reason wave boards have stuck with the US fin box. It used to be something like put the fin forward for manouvrability and back for speed.

Perhaps the problems listed are considered to be less than the need to be able to tune the board for speed or manouverability.

Perhaps its due to bolt through fin boxes needing thicker boards than US Boxes.

Perhaps its a fashion thing.

Those bits of dagginess must make a difference but I have never heard of anyone going faster or reducing spin out by tidying them up. Still, I was thinking of using a wave board as an occasional speed board and so I guess I will pay some attention to it just out of anal-ness.

Hi Tom, I guess that the hydrodynamics are not as critical as for a speed board doing around 80km/hr. When I recently got an old wave board with a US fin box for bay bashing, after being used to power and tuttle boxes, I was a bit amazed at the flimsiness of the arrangement. But on asking the same question as you I was told that because wave riders often/usually sail where there can be reefs and rocks that it is better to have the fin break off than rip out the fin box - thus the flimsy system.

i've been shoving a slither of surfboard foam into the slot before and after the fin and trimming it flush with the surface, and i think it makes some difference to early planing and top speed on the waveboard. u can see how much cleaner the flow of water is passing from under the tail of the board

it made a significant difference filling the slots on a tri fin i had, when only using the middle fin

i found i had to shove it all the way down into the bottom of the slot then trim it flush, otherwise landing jumps forces it to pop out

Well I dunno how many of Rox's points are valid anyway

- there is no gaps at the side of the fin, if there was it would wobble.
- the fin sits flush with the bottom of the board unless it is one of the ones where you sand off the tab that sits in the bottom of the box (like a DIY depth controlfor first time you fit it)
- and yes the bolt sits up a bit, but if it worries you that much you just run a 8mm ish drill bit onto the fin about 2-3mm deep and it sits flush.

add haircut's suggestion to mine and it is as flush and hydrodynamic as a powerbox or tuttle