I am designing some twin-fins on Finfoil and have lined up to have them CNC routed out of G10.
Obviously G10 is heavier and stiffer because it has more fiberglass in it than a traditional polyester panel.
So, to offset this I am planning on having the fins cut thinner than usual to allow more flex and reduce weight.
Then to offset the tracking effects of going thinner I am intending on shifting the foil further forward (so that the leading edge presents a slightly sharper angle).
I’ve looked over my quiver of old fins and it looks to me like most production fins are 0.25 inches thick (talking only about thrusters, fin box twins and quads here).
I am considering going down to 0.21 inches - which is a small adjustment - and I wondering if people have gone far thinner and could share their feedback?
Anyway, have seen others on this forum post way back about making fins out of G10 and am curious if people have experimented much with fin thickness and foil steepness like this.
The first two prototypes will be a performance style keel with a moderately slanted back front-line and then a large cutaway backside to try and the provide looseness needed for easy roundhouse cutbacks but enough base to hold a high-line.
The second is similar to a traditional 1970s MR style upright but taller and deeper than anything on the market (I’m hoping the thinner fin will allow for a larger overall surface area without creating too much drag) and have tried to keep the outline as smooth as possible to maintain looseness.
Have loved reading this forum over the years and very keen to hear others thoughts and experiences.
Any comments I have would be observational or anecdotal vs scientific, but what is the point of going thinner? I mean, the thickness varies throughout the fin, and tapers to nothing, so what are we talking about here? The thickest point? The surface area at the thickest point is maybe 10% at best, so how much weight are you going to lose by going thinner? And at what point does it become a safety issue?
There are other ways to obtain flex, and weight loss, if those are the real issues. To me, its a practical matter to say that .25 is a limit for a standard thruster or quad fin. I highly doubt you’re going to gain any significant performance advantage from going thinner, but you may have some safety issue with razor knife fins thinner than 1/4"
I mean, if you note a significant weight loss and flex capacity from dropping .04 in thickness, by all means let us know. I’m skeptical. I could probably skip a meal before going surfing and drop more weight than skimming .04" off the thickest part of my fins, just sayin’.
As far as the tracking effects, I’m skeptical about that also, even tho I really don’t know. But if you’re saying a thinner fin creates a tracking effect, then my thinking is just use a smaller fin. Tracking effect is the whole reason we use fins. Yet you talk about wanting to go with a larger overall surface area, which makes no sense to me. I must be misunderstanding something here.
Fins offer a lot of room for personalization and experimentation, a way to tweak a board’s performance without altering the board itself, so I think its a good place to start experimenting with options. I just don’t think going any thinner than 1/4" offers any tangible benefits vs the dangers of hyper sharp/thin fins. And I question whether the weight difference could be significant. And I further think you can get fin flex from other methods than going thinner than 1/4".
That’s just my thoughts, as a non high performance recreational surfer who has had a few painful fin injuries over the years.
Good to test my ideas against some healthy scepticism! You raise some interesting points.
On where the reduction in thickness comes from - you are correct it is at the thickest point. But the thick point is then shifted forward slightly to try and keep the front foil curve similar to a thinner fin.
The reduction in weight will be grams - so it is a small difference - which I’d expect runs to about 140 grams over the weight of the set of fins (I’ll need to check by weighing prototypes).
As small as this difference is, when I use honeycomb keels that are very light I believe I can feel a difference compared to using very large polyester glass keels (it’s a small difference but kicking a board through a snap is a much less natural action than say picking something up in your hands). And I think the various leverage effects fin weights have magnifies these differences.
On flex, I take your point about other materials being more flexible, but what I’m really interested in is flex and then bounce back (ie returning to form).
This is where I see the benefit of G10 as a material in that it should prove both more flexible and quicker to bounce back than alternatives like carbon fiber combined with one or two sheets of glass in a mould.
On fin chop - I don’t think going thinner at the widest point changes this risk at all to be honest. If you look at a set of fins they always taper right down to almost nothing at the rear section and on the tip. That’s the part that cuts you - as it did right through my 5/4 wetsuit the other day.
But the issue there is whether that has been blunted off or sharpened into a blade (obviously we will be dulling down the edges) but the foil curve leading into it will be straighter due to reduced thickness.
Anyway, all sounding a bit defensive now - but again thanks for the points and great to be able to test my thinking against informed scepticism.
If you are using Finfoil, first have a look at the Clark Y aerofoil on airfoiltools.com. which should match your requirements. Drag is directly related to surface area and thinning a G10 will certainly change its drag characteristics and maybe not for the better.