Why glass wooden box fins?

So this may be a dumb question, but I’ve previously foiled a wooden fin, which I glassed onto my longboard.

All perfect, was happy with the result.

I am looking at foiling some more fins for fun, but to go into fin boxes, and have been going all the way back to basics and asking myself why should it actually be glassed?

Is adding a wood waterproofer/treatment and a thick layer(s) of varnish not enough? Or does it HAVE to be glassed? (Obviously has to be glassed to be glassed onto a board, but I’m specifically checking for boxed fins).

Looking at old boats made out of wood, thats all they had and they sat in water for years and years, without much going wrong.

May seem like a dumb question, but thought I’d ask as I am new to this.


Also where can I find a template online for the thickness and height etc for the actual box connector top bit of the fin, with the screw etc?

Actually you do not need to glass them like you say.

A glassed fin just doesn’t require any maintenance (reapplying varnish, …) and makes them more durable.

But a nicely foiled wood fin without any fibreglass will surf great!

Here is an example of a board with just varnish (no glass), and a wooden fin that was not glassed-on.  Like hans said, varnish requires maintenance.  I built the board in 2007, and haven’t surfed it for a while because it needs to be re varnished.


Bloodwood with teak oil:

I removed it after every surf as I was afraid the wood might swell and bust open the plug.

Then I worried I was going to widen the box or strip the grub screw threads from constant removal/ insertion

Then I went back to a regular thruster set up


I made  a 7.5 inch Koa wood fin, unglassed in a FU box,  break during a turn.

Now I just Glass them all for the strength and lack of maintenance required

Thanks all for the advice.

So I’m guessing its possible just glass the fin with resin and leave the fiberglass off? I guess you see where I’m going, in that I find that showing off the wood, which is so beautiful, is pretty rad.

Throwing all the fiberglass on can slightly hinder the appearance, but I guess if its necessary, then so be it. Thought I’d just check in for some knowledge from Swaylocks to see what you guys thought :wink:

If you are not putting on glass, you are not glassing :wink:

I’m going to word this more strongly than the previous posters: pretty much any wood fins that are going in a fin box (and even glass on for that matter) should be glassed, unless you want to snap them off. Wood has many magical properties, but for the common woods you would use for fin making (i.e., relatively lightweight woods like cedar, redwood, mahogany, walnut, cherry) they just don’t have the strength to withstand the leverage placed against the tiny area held in the box, the grub screws will chew them up, etc. Some really dense exotic woods might hold up for a while, but why give yourself the headache? 3-4 layers of 4 oz cloth on each side will not hurt the natural color of the wood, but will give you sufficient strength for regular use.

And anyway, a good varnish job would take much longer and be much less durable than a fiberglass and epoxy layer. Would you rather go surfing or spend your time stripping and reapplying varnish?

I would fiberglass it.  Wondering what kind of glass / resin he is using that doesn’t allow the wood grain to show?

Making wood fins that are fiberglassed is a big process but not one that can’t be accomplished.

There is one guy who does what you are asking about and does it well.  I don’t know his technique but since his fins look good I am assuming it is harder then it looks.  However I believe that he uses a resin or epoxy to waterproof the fin.






Anyone remember camplus? Now those were some wood fins!

I read the title wrong and thought you were asking about wooden fin boxes… I suppose you could laminate them from scraps of veneer and glass offcuts. Interesting idea anyway…

Made hundreds of 'em over the years…only three main concerns if they are to go in a slide box = strength at the base , grain orientation and TOTALseal , to prevent water intrusion…all in all , glassing the fin is by far your best option…and epoxy wins hands down if any degree of flex (whatsoever) is required.

I’ve made my share of wood fins and glassed them and have had issues with the cloth hiding the wood grain underneath.  Usually this is from old cloth that has abosrbed too much moisture and poor lighting and working the epoxy too much with the squeegee instead of letting it soak slowly through the layers.


This is one such fin:

  See how the trailing edge gets lighter where I foiled off some of the obscuring glass when refoiling.  This fin has a very lively flex and I am always surprised at the projection on a back side bottom turn.


Here is a smaller fin that I only used 2 or 3 layers of new 4 oz per side. But the larger cutaway above it also suffers from older 7.5 oz cloth and bad technique



I want to get some finer lighter cloth for future projects rather than using E cloth that I’ve had for too long and stored…improperly.