FCS inside foil fins & tolerances

[collnarra]

Picked up a set of those blue FCS fins (FG-5) with "inside foil." They've also got a slightly different toe angle and cant to the standard fins. This is accomplished by offsets in the lugs that fit into the FCS plugs.

When I put the fins into my board I noticed that there was a gap of perhaps 0.5mm between the fin base and the bottom of the board on both the outside fins. So I undid the grubs, took the fins out and reseated them. Same deal.

So I surfed the fins while I was up north over the last few days and thought that they had extra drive (but this could just be me being suggestible). What I don't know is whether the fins are supposed to have that gap or not...

I could take them back to the shop - the owner said if I didn't like them he'd sort something out - or I could just sand the 0.5mm off the base of the lugs. Or leave them as is, but being able to see light between the base of the fin and the board just doesn't seem right, and I am sure I detected a slight hum.

I am tilting in favour of just sanding the bottom of the lugs.

Thoughts?

Col.

[booter]

Every set of the blue F-series fins that I have seen (prob 8 sets on 8 diff boards) didn't sit flush with the board.

Makes f*ck all diff as far as I'm concerned - don't sand the plugs man, just surf and forget it

[collnarra]

But why don't they sit flush with the board? Is it just bad manufacturing (which reminds me: why are there numbers handwritten on the base of the fin lugs?) or are they designed that way? And if they're designed that way, why doesn't it say so on the packaging?

I'll have to surf 'em a few more times, but they seem like a good fin - I'll hafta ride some of those H2s, too, and see where the millions of dollars have gone - but the poor fit makes them look shoddy.

col.

[bro]

These fins are not quite as an exact science as the carbons or the composites in their production. I would avoid sanding them due to the fact that they are a hollow construction and that you could weaken the tab (these aren't that strong in these fins to begin with). Have a look and see if there is a build up of paint on the tabs either near the base or on the bottom of the tabs that you could sand. Mine do the same but have found the tabs vary in size which is frustrating as i hate the gaps as well. If you can and i know it's a hassle but go thru a few sets in the shop to find a pair that the tabs are more regular and buy those puppies, hope this helps.

[collnarra]

Thanks Bro. As an aside, how would you describe the difference in performance between these fins and the regular fins?

Col.

[booter]

In terms of performance - I have ridden normal plastic g5s, the blue fseries g5 and also own a set of kelly carbon lites

I originally thought that I would have never noticed a difference between these fins but I can assure you there is a big big difference in each of these fins.

The main thing that I notice is a HUGE increase in speed.

The plastic fins seem to be a bit looser than the kellys but the kellys are much much much faster. Notice it mostly in fat mushy waves. With the Kellys I seem to maintain speed out of a turn but with the plastics I bog.

I can never go back to plastic fins.

The blue fseries g5 seems to be somewhere in the middle...

[Hawkeye]

Hi Coll,

If the ENTIRE bottom of the fin sits up off the board, I'd sand the bottom of the lugs LIGHTLY. I doubt there will be any structural problems. Your main concern would be crushing of the lug from the grubscrew, so I think it's a safe bet that this part of the fin is solid glass/resin.

I have a set of these fins as well, bought a few months ago. With mine, the base of the fins was curved, so that the middle of the base sat clear of the board but leading and trailing edge were in contact. I have left these as is.

The number stamped on the bottom was "0104", so maybe it was an early batch.

Performance-wise, the difference is dramatic. More speed and drive, especially in turns. I put the old G5 plastics back into compare the other weekend, and the board felt rubbery and boggy in the turns, and lacked drive. The FG5's are back in now.

Haven't tried the kelly carbons, but am keen to ty the H2's.

Stiffness makes a dramatic difference to drive. I have a foil plotting program on a CD somewhere at home, and some lift/drag charts for some of the foils, so I'd like to try making some fins with even more concave just to see what the difference is.

Some pointers on moulding techniques would be handy, if anyone can point me in the right direction.

[tootr]

i have had this 'problem' before

it may not be the fins so much but if the particular board has deep concave or accentuated rocker (or a combo of these two) around the fin area than it cannot sit completely flush as the fin base is made flat

no biggy IMO

[collnarra]

It did occur to me that the concaves could have something to do with it... although I asked my shaper to tone the single -> double down this time around. They were starting to look like icecream scoops...

The strange thing is that the conventional G5s I had it in before sit perfectly flush.

Thanks for all the feedback everyone. I'll keep you informed how these fins go.

col.

[bro]

Col, in terms of the performance of these things the most notable thing is their directional change due to what you pointed out the increased tow angle which of course makes the board want to turn rather than go in a straight line. My first reaction to these fins was that on take off it took a split second before they 'reacted' like they kind of stalled but only for a split second and then they went. Like all fins i have felt they have worked in some boards and not in others i have only just gone back to them after using Greg Trotters Soar fins with FCS tabs.

The H2's now that is a whole different story ask Nick Carroll on that one as he was one of the test pilots.