FIn boxes and flex

I’m wondering if there is any sense in trying to achieve flex in the tail area of a board that will have a 8.5" fins unlimited style finbox (for a bonzer or widow maker set up). The fin box seems totally rigid and will lock up flex in that area. Further more, say I have proboxes on the rail for a widowmaker, there’s another 4" or so of flex locked up. In the case of a bonzer I’d have 10" of glassed on fins at the rail. How much flex is going on that area?

I was thinking about “pendo” izing my next build. It’s a lot of extra work, ostensibly to get flex benefits. I’ve done one so far and just the cushy feel might be worth the extra work. But I doubt there will be flex benefits.

What say the experts?

you could use an even shorter box in the center (like the old bahne twin fin box, 6"?) and just trim the fin base shorter if need be.  Bonzer center fin is not that big…

for the widowmaker, I guess you’ll need to mold a fin box out of flexible material and not screw down the other end of the fin (ha ha).

where did you get your deck pad material for the one you already did?


Go for it. The hull guys have been riding flex tails with 10.5'' boxes for, what, forty years?

Plus we did some static testing a few years ago that showed the diff in flex wasn't huge. The bonzer runners might be another story, didn't test that...

It depends where the flex is......but I get plenty even with six boxes in.

The box would be on the stringer, so flex patterns changing would not really be an issue, being that the foam flexes around the stringer and the stringer remains the ridgid back bone of the board

Offbeat, interesting board, any more pictures? How is the flex achieved?

ps. That’s not an L5 in the background, is it?

Hi tblank, full report & constuction here -

L5....I wish!........Hoyer about 1955.

Very Cool Offbeat, thanks for the post. Are you sold on this design after riding?

I hoped it wasn’t a Gibson. I knew the pickup wasn’t right. I saw someone ruin a D’Aquisto  by altering it. Love the L5 S too.


This design is all I have ridden since first making it....except for my longboard....but that's only because I haven't made one yet!....but will soon because it is perfect for it.

Getting the flex tension is the key....I now make them so that I can start with a shorter it & increase as required.

I have made boards that I've surfed before I cut the tail at all & every time the performance has been improved by cutting the split in.

I'm working on four new boards at the moment with a more powerful suspension system. could always try a double split & leave the centre section rigid so that you can use a centre fin.....heaps of flex that way & more dynamic than the Pendo [which isn't long wavelength].

I have a cherry sunburst L5-S with the original L5 tailpiece. I had a beautiful ES-175 that I sold for $600 years ago. When I wanted to get another one, they were up to $2000.

nice guitar/amp… oh yeah your board is cool too. Thanks for the pic

Standard FCS offers the best “unultered” flex for a performance board. I’m light and notice long, stiff rigid fin boxes.

Thats what I reckon anyway!