Trailer fin placement for twinnie

I’ll be adding a trailer (2.5" stabilizer from Rainbow Fin Co.) to a twinnie I tried to build to replicate the G&S Mini-Fish and wanted to know (1) what’s the best placement, and (2) what will it do to the ride.

Right now I’ve got two FCS “Rocket Fish” fins from Rainbow (not true keels). Specs: one-sided foil, about 7.5" base, slight rake, fiberglass, toed in to point to the nose, 6 degrees of cant, 9" up from tips, 1.5" off the rail… swallow is about 3" deep, tips 7" apart) The board is 6’0" and I’m 6’1", 185 lbs.

Right now it rides a little squirrley for my style. Can’t quite ride it like a true fish… can’t quite ride it like a thruster. Is super fast like a fish, and rides really good on the rail (bottom turns, high line on a steep face…) but if you try to slam a hard turn off the top, the thing flicks around too quickly and the fins sometimes pop out. And if you don’t ease into the bottom turn, it snaps like the fins are too far forward.

I’m hoping the stablilizer will tame the squirrley-ness but still keep the speed and drive. Never tried a small trailer before… Always did true thrusters or true twin fins.

I’ll take any fin advice you can give me, including anybody who’s tried the MR-TFX (?) from FCS that come with or without a trailer.

I have a modern fish with three fins. Forward G5 and rear GX’s. The center trailer fin is placed so that if you drew a vertical line from the back of the tip of the trailer fin, it would coincide with the butt crack of the swallow. It has worked great for me with this configuration. Just one option you might want to consider. Good luck.

hiya NJ !

I basically put the trailer fin at the rear of my back fin box , so that it is positioned like a thruster setup [it helps that the “butt crack” on the prawn is only 3" deep]

the trailer fin is 3 1/4 base , 3 1/2" depth , in the one in THIS photo …

hope this helps , mate !

cheers ,


I am surprised at the lack of replies …I assumed [wrongly ] that more than two people out of “4734 registered users” here would have tried this setup , and would have wanted to help you ?

Yes; I can offer something here. I ride several hybrid fish; a 6’ and a 5’11", both are 20" wide, both are deep butt-crack swallow tails with 14.5" noses. I am 5’10" and weigh 170 pounds.

Favourite setup; FCS FG-3 on the outsides with a GS trailer in the middle - this works great on wave faces up to about 4’. It is like like a 26" skateboard but never slides out.

I sometimes use FCS FG-5 on the outsides with the GS trailer - this makes the board less loose, less like a skateboard, but has noticably more hold on steeper waves. I use this setup on waves I’d normally use my performance shortboard on.

I tried a GX and a G1000 in the middle, being bigger fins I found them too much like a normal thruster setup and not really the intent of the board design.

I hope this is of some use to you.

Trailer placement for a trannie.

I thought this was a surfboard design forum.

Why add a single trailer fin? Splitt it up and make it two on the rails. That gives you good stabilisation in the bottomtunrs. My 5’9" superturtle needed some stabilisation too in the bottomturns, so I made my own twin trailers. Had no chance to test it in 12’faces of real ocean swell, but in Holland it feels perfect in 9’faces. It gets me into barrels too small to fit me in also. Together with 5"flexing twinfins I also made myselve it is a perfect combination. Carbon and flexcontrol make the biggest difference for stabilisation, not fin shape and size! Remember the mold is still there, so I can make them in a few days…


…hi soulman !

welcome to sways , (how’s the weather in Holland at the moment ?)

I have tried both , the four fin , and the twin with trailer setup [and also , with the 5 fin setup , too …]

they ALL feel good , to me !

on different days , in different surf …versatility , in one board …

…fun fun fun !

cheers ,

ben ,

west australia

thanks guys…

looks like Chip does the same thing - trailer tip right over the crack apex. This would cluster my fins closer than the normal thruster setup, but I guess that’s what it’ll have to be. My side fins are only 9" up… normally a thruster would have them 11" to 12".

Also, with the long base length of the Rocket Fish fins, a trailer might not solve the problem. Maybe I should downsize them to normal “twin fin” fins… bigger template than your G3s or G5s, but smaller then a fish fin. Those, with the GS trailer might do the trick…

hi again NJ !

how about narrower based , taller twinnies … like maybe 4 1/4 " - 5" base , 6" depth ones ?

with not much overhang over the back of the side plugs / box ,


the back fin slightly overhanging the back fin box .

Or ,

failing that … why NOT put in a couple of extra back side plugs , for the quad and five fin option ?

it “could” ‘light up the board’ , maybe …who knows ??

…IF you do , please report back here , with your findings , as I am always keen to compare notes / findings , with others .

tomorrow , for instance , I am keen to test out my "bushfire fish " ( waves permitting , of course ! ) , with these twin fins …

(They are at 5 " up from the tail tips , with the tip of the fin , only 3 1/2" from the tail tips !!)

I will be interested to feel how they go !

…to be continued …

cheers ,  


Hy Chipfish,

Weather here is stormy, warmer then before, it’s winter here. Yesterday I took the old turtle for a ride again,three years after I shaped it I still love it. With twin and 2.5" center it’s less skateboard then with split centerfin. But everything is depending on the shape of the board, it’s 5’9", 22 1/3" with about 20" nose and tail and very tiny rails to keep it in the turns. Here is some pics from yesterday. My friend is bodyboarding with my nieces 5’ longboard, with the dolfins.

Greetz from Hollland, soulandpower


p.s. - also …

Please feel free , NJ , to use any of those templates on the “twin fin templates” thread of mine …I would LOVE to hear of someone using them , and hearing how they go !

cheers ,


After a fotosession downstairs, some of my homemade fins,they float, 22 grams a piece. Top left 5"and 2.5" quad,top right FCS twinfin for the size, bottom left center 2" gives the board a more loose feeling but stil good drive. Middle 5" experiment, gives great drive but makes the board a bit harder to turn. Bottom right a 3.5" center, gives abit more drive but makes the board harder to turn. But this board has a lot of concaves,very deep which give it stability in bottom turns. On a fatter bottom I need the 3.5" for drive

Just an P.S. you can say.

Have fun with the test tomorrow. Soul


I like the idea of smaller base, but taller twins…

What I’m trying to achieve with the stabilizer is to make it less “loose” or sensitive, and I’m hoping that a trailer will NOT loosen it up any more, but give it a more positive and stable feel.

I’m also hoping that getting smaller but still full template true “twin fin” side fins (less base than the fish fins that are already in there, but maybe the same depth) will make it less flickey and bitey, and more smooth, but still give me the excellent fish-like drive I’m trying to keep.

Let me know if I’m looking for something that’s just not there…

Is it the base or the depth of the fin that makes the larger fins harder to turn?

Well lets get technical. A fin is like a wing of a plane. Ever wondered if they are gonna fall off when they move? That is flex, when the lift get’s too much the tip flexes and the lift gets less, like the suspension of a car. The base don’t flex, so there the lift is only depending on the speed. The tip is where the suspension comes from. When the fin is too straight up is flexes for top to bottom, so losing lift and making more drag. When the tip flexes the rear of the whole profile,the profile changes to lose lift and not increasing drag. That is the thing that feels like suspension. It is not only the outline of the fin, but also the profile and what everybody forgets the materials in the fin that determine the feeling. Windsurfing is on this technique a lot further than surfing in this area because the forces are a lot bigger. A short good performing profile can do more than a long profile (with more drag) at high speeds. I don’t know everything jet and will probably never know it, because there are so many factors. So it depends on the speed and the sideway force what is the best fin. By changing the material it is possible to get a different fin with exatly the same shape. So I hope Ihelped you a bit with understanding, but feel free to aks some more. I hope to learn something too, so my next boards and fins can be better too.

Greetz from Holland, Soul


In addition, when the fin flexes from front to back the turnig will be easier too. when the base is wide turning is harder but drive is better, and you need both for a good turn, so there are many ways to get the same thing…



We’re exactly the same size and so are our boards. Here’s what I did with mine to cut out that slippery/sliding feeling. Works great! The trailer fins are 2" trailers that Clyde Beatty Jr. uses on his Tigerfish. They’re FCS single plugs that are really easy to install.

there’s one more pic…

last pic…

I’m using the F.C.S M.R TFX system on my 6’2"x21"x 14.5"N x16"T x2.5" fish. Best of both worlds, twin fin speed and looseness but that rear Trailer fin gives you that bite when you want to drive hard off the bottom or are a bit slow out the gate on waves that are a bit more hollow or vertical.

Dear senor pato,

I think your fin has got to be bigger because the bottom of your board is flat, For me my 5" is enough because the thick profile of the fin and the concaves in the bottom generate a lot of lift. I’m 6’6" and 185 pounds. I noticed this noseriding a very steep face when my fins just turned out of the water. Icould push them back in with ease, but I didn’t miss them for the drive. In powerturns this is different and that’s where the right flex gives me enough drive and lets the drive deminuish gradually with the angle of attack, so still keeping pressure on the back foot. With the 5" fins my board keeps the skaty feeling on the lip I like so much. The MR TFX are new to me, do they have a thick profile and where is the widest point, on my fins it is at 0.3 from the front. After a few years of only surfing and testing the time is coming again to push development a little further again. You know if most fishy shaped boards are flat underneath? And why?

Greets and hope to get to know some more,