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RANT: fin boxes with twin fins

Hazrus

Hazrus

Nep status
Sep 23, 2016
602
503
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Within the last 6 months, I've had 3 separate fin box issues on twin fins without hitting anything; just from surfing. Two of the boxes just cracked and were loose, needing a reset. The other one just ripped right out while doing a bottom turn.

Two were Futures boxes, the other was FCS2. All different board manufacturers, two PU/PE and one PU/epoxy. All were using upright fibreglass twin fins.

Is this a common problem? I've never had any issues like this with thrusters or quads.
 
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Aruka

Aruka

Tom Curren status
Feb 23, 2010
12,136
23,024
113
PNW
it is fairly common with twins. especially with standard 444 glassed PU/PE in my experience. bigger fins means more leverage on the box. i've bothered Futures about making a better box with a larger footprint for this reason but they didn't seem to think it was a problem inherent to the small footprint of the box and suggested "more glass".

I do think more glass is helpful but it's more of a (pardon the pun) patch than a long term solution. i think denser blank material helps, whether it's heavier PU or Varial, etc. maybe even a good EPS? my banjo fish keel was EPS and never cracked around the boxes.

surprised to read that the fcs2 boxes failed. there was chatter on here that perhaps they were a better option for big twins.
 
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oeste858

oeste858

Phil Edwards status
Sep 11, 2017
7,007
17,443
113
San Diego, CA
Yeah, common problem. Been a couple threads devoted to it past year or so.

Consistently blowing out twin fin boxes

I’ve blown out a Futures box on my 6’6 Christenson Nautilus Twin. I’ve blown out a Futures box 3 times on my 6’2 Christenson Nautilus twin. And I just blew 1 out on a Twinsman. I love surfing twins but I’m starting to think the concept just isn’t functional. This always happens on a big...
forum.surfer.com forum.surfer.com
IME futures are the worst with twins (just too much torque for a lot of builds), which sucks because they definitely have the most selection of twin fins.
Album Matt suggests stronger alt builds for those worried about it: Dark Arts, Varial, XTR.
GG will say that fcs fusions are the strongest fin system.
YMMV
 
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sdsurfrat

sdsurfrat

Michael Peterson status
Jun 2, 2008
2,585
765
113
Hazrus said:
Within the last 6 months, I've had 3 separate fin box issues on twin fins without hitting anything; just from surfing. Two of the boxes just cracked and were loose, needing a reset. The other one just ripped right out while doing a bottom turn.

Two were Futures boxes, the other was FCS2. All different board manufacturers, two PU/PE and one PU/epoxy. All were using upright fibreglass twin fins.

Is this a common problem? I've never had any issues like this with thrusters or quads.
Click to expand...
The main fins on your "thrusters or quads" is likely 4.5"- 4.75" tall (depth)

Your Twinny fins are likely 5.25"+ that is your issue!

Yes, I've blown out over a dozen Twinny fin boxes and it's par for the course.
 
SixtyGrit

SixtyGrit

Gerry Lopez status
Oct 3, 2015
1,015
1,226
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SD
Happened with my twinsman (futures).

Can someone link to that dowel reinforcement construction?
 
Hazrus

Hazrus

Nep status
Sep 23, 2016
602
503
93
Thanks all for the replies. It's good to hear that I am not alone, but surely this is something that both the fin and board manufacturers should address...

Slightly different question - - - have any of you blown out the fin boxes with keel fins? Or is it more an upright twins thing?

If fin box breakage is biased towards upright twins, I wonder if it is because they are normally in boards with more "HP" tendencies and are surfed that way. For me, my boards with keels are surfed in a more cruisy manner.
 
silentbutdeadly

silentbutdeadly

Duke status
Sep 26, 2005
33,727
23,528
113
Tower 13
this one is weird and I think it may have to do with glassing. I've pushed really hard on boards where this fins stayed in tact solid as can be. had a stu twinzer with fcs2 that he said was supposed to be stronger and that box blew out so easily it was ridiculous.
 
Aruka

Aruka

Tom Curren status
Feb 23, 2010
12,136
23,024
113
PNW
Hazrus said:
Thanks all for the replies. It's good to hear that I am not alone, but surely this is something that both the fin and board manufacturers should address...

Slightly different question - - - have any of you blown out the fin boxes with keel fins? Or is it more an upright twins thing?

If fin box breakage is biased towards upright twins, I wonder if it is because they are normally in boards with more "HP" tendencies and are surfed that way. For me, my boards with keels are surfed in a more cruisy manner.
Click to expand...
I've actually seen more problems with keels than upright twins. I figured because they were even bigger there is more leverage :shrug:

Heavier glass jobs help but I think the weak point is the small footprint of the box.

Hopefully one of the two fin companies will figure it out eventually and actually make a box appropriate for large twins.

In the meantime I advise you cut back on your squats/deadlifts, lower your TRT doses and limit your scrotum tanning and joe rogan podcast listening to once weekly.
 
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nicholas hanover

nicholas hanover

May 9, 2018
26
65
13
Posted this a while back but i thought id repost it here, A solution to repair correctly but doesnt address the fact that futures and FCS need to address the issue with a bigger footprint to take the forces associated with large area fins;

"
Ive had three futures boxes go on my dhd twinny. contemplated selling it and lucked into talking to a mate that shapes quite a few boards for our local crew, majority been twins. He said he has had the same issue when he started shaping so shifted to doing glass ons only. He did come up with a cool hack to stop the issue through years of R&D. So far 4 months later, surfing solid waves and big fins, not a single blow out or hair line fracture around them. His method is to create a slightly larger well for the box, drill two holes through the rail, and pour resin then feed through wooden dowels all the way to the outside of the box. the leverage of the fin is then offset by the surface area gained by the dowel. works a charm.


217400891_1149204138824448_2429947372971035814_n.jpg
 
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C

claw87

Legend (inyourownmind)
Jan 30, 2017
388
1,395
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My twins have an extra patch of glass in the fin area and fcs 2, no issues so far. I would think that fcs is less prone to fin plugs ripping out as the forces are introduced in the blank / glass job via peanut shape as opposed to futures where there's just a straight line (almost like a predetermined breaking point in engineering terms).
That being said I have my first twin with fcs ii and channels arriving soon and am already worried haha
 
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GromsDad

GromsDad

Duke status
Jan 21, 2014
54,755
16,626
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West of the Atlantic. East of the ICW.
nicholas hanover said:
Posted this a while back but i thought id repost it here, A solution to repair correctly but doesnt address the fact that futures and FCS need to address the issue with a bigger footprint to take the forces associated with large area fins;

"
Ive had three futures boxes go on my dhd twinny. contemplated selling it and lucked into talking to a mate that shapes quite a few boards for our local crew, majority been twins. He said he has had the same issue when he started shaping so shifted to doing glass ons only. He did come up with a cool hack to stop the issue through years of R&D. So far 4 months later, surfing solid waves and big fins, not a single blow out or hair line fracture around them. His method is to create a slightly larger well for the box, drill two holes through the rail, and pour resin then feed through wooden dowels all the way to the outside of the box. the leverage of the fin is then offset by the surface area gained by the dowel. works a charm.


217400891_1149204138824448_2429947372971035814_n.jpg
Click to expand...
The footprint of the box flange is not the issue. The flange attaches to the surrounding glass and resin. The addition of glass microfibers into the resin used to set the box along with additional glass on top of the box makes for a bulletproof install. Resin alone when setting the box into the foam lacks strength and is brittle.
 
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R

rowjimmytour

Tom Curren status
Feb 7, 2009
11,534
5,831
113
54
No problems "knock on wood" both running large twin sets in fiberglass..
Alpha Omega, 6/4 6 pu/epoxy S, FCS Fusion, pure glass, True Ames twin set fiberglass
It 2win, 6/4 6 CFT medium, Future, Fins Unlimited 2win twin set fiberglass
5150, 6/4 6, DFT, Future, Fins Unlimited 2 win twin set fiberglass Fins Unlimited S1 rears fiberglass
 
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R

rgruber

Miki Dora status
May 30, 2004
3,624
1,347
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I think Simon Jones anchors the fin boxes to the outer stringers of Torren Martin's triple stringer boards.
 
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