Converting a Stubby thruster to a single fin?


I had a silly idea and decided to act on it.  I have a Stubby type of surfboard 6’2 x 21.5 x 2.75 with lots of volume and beveled rails.  It’s pretty fun in the thruster set up.  I can get up to the nose a bit but it’s a challenge to hang 5 or to stay up at the nose for more than a moment or two.  I found a great looking longboard fin that was broken where the screw tightens it to the board, so I thought I would use it to make this stubby into a single fin.  I cut it down to 8.5 inches long with a base of 4" and I’m curious how it will work out in the surf.  I made it into kind of a pivot fin so that the rake wouldn’t hang over the end of the tail. It seems like a fun idea because this board looks like a mini long board … but I’m concerned that the fin box is set too far back to the tail of the board.

What do you think?  Am I crazy?  I know if I really want a single fin it’s probably best to remove the center fin box and replace it with a real fin box that will accomidate a variety of fin sizes and positions - but i just had a baby and I’m on a slim budget.  I’m going to test it out the next time there is surf AND I can sneak away from work.  I will let you know how it goes, but I’m open ideas and feed back about making it shorter or giving it a new angle.  I attached a few photos so you can see what I’m talking about.  Thanks!



I did the same to a board I have. It was a 6’4"x22x about 3, maybe? It was a thruster, but I put a single box in. I can cheater five it no problem, and it seems much better as a single. Although I used a 7" fcs dolphin fin, just the plastic one. I ride mine all the way up in the box, which puts it ahead of where the thruster fin was. But I could put it where the thruster center fin used to be if I wanted. I also like really loose boards though. Might as well try it. I mean, it might be better for getting near the nose like that. Mine was. And I suppose you could keep making the fin smaller if it doens’t feel right.

I’m not sure which finboxes your board already has but one thing I’d be concerned with is whether that center box will stay put when that fin gets loaded up duing a turn.  An 8.5" tall fin under load will probably generate a lot more leverage on that box than would the 4.5" fins that normally go in there.  Particularly if the entire load is being borne by the one fin instead of the 2 fins as is normally the case when a thruster set is enaged during a turn.  

A standard finbox is only $10 or $12 bucks (U.S.) at the retail level.  You probably have at least one friend who owns a router.  Or you can use a drill + Forstner bit to drill a series of holes along the stringer and a chisel to clean things up.  Where there’s a will there’s a way.  

I took it out today at lunch time to a beach break that has a few dependable peaks.  I caught a bunch of waves in 45 minutes and had many fast and fun rides.  I haven’t surfed this board this spot before, but it was the only place that had waves that were 2-3’+ waves - it was pretty flat in town.  It seemed to hold up better in the steep and fast waves (but like I said, they were small) than it did in similar waves with the thruster set up.  The waves were too fast to try to get up to the nose today, instead I was just staying focused on making the section and surfing it like a short board.  It felt very natural and comfortable to drop in and carve down the line. I will have to try it out in one of the spots I’m used to taking it to before I decide if it’s a good set up or not.

Hi gdaddy, I was a little concerned about the fin box, too.  It came with DFS fins and fin boxes.  I’ve never heard of them before and I haven’t seen them on another board yet.  The part of the fin that fits into the box is the same length as FCS fins - but it’s one solid piece instead of two plugs.  I’ve used other FCS fins in those boxes before. I’ve attached a photo of one of the fins so you can see what it’s like.  I figure that it’s stronger than FCS fin plugs but not as strong as a single fin box.  I’m not a radical surfer so if I surf it in little waves then it probably won’t break the box - but I know there’s a risk.

Do you have any other suggestions? Little side bites?  My goal with adding this larger/single fin is to nose ride more or cheater five more easily.  I suppose if I really like it as a single fin, I can replace it with a single fin box when I’m sure it’s worth the effort.  … and thanks Drzoidberg for sharing the joy of your conversion to a single fin.  So far it feels good.

If the box holds up then I reckon you’re good to go.  If it breaks or pulls out you can worry about replacing it then.    

Yeah, that’s true.  I wonder what the longest/biggest fin is recommended to put into a Future Fin box and feel safe about not pulling out the box … I would guess that the DFS fin box can almost pull the same weight.

My understanding with finbox installs is that the primary cause for box failure is the deflection in the surrounding foam and lamination under load, particularly with light density foams.  Your centerfin box was installed over a stringer so that will stabilize the box in the fore-aft direction but it’s probably still subject to lateral movement in the foam.  My guess is that if/when there’s a failure it will consist of the foam compressing on one side and the lamination breaking up on the other side as the fin attempts to pull the box out of the blank during a turn.


The tangs that go into those finboxes box are only 1/2" deep; little more than half that of a regular longboard finbox.   I think a 6" fin would be pushing it in that box.    With that said, if you like the idea of a centerfin bias you could run a 5"  or 6" fin in the tail and 2 smaller fins on the sides.  The placement of your finboxes looks like that would work.  The side fins would give you some hold during your turns but it would still be the centerfin that produces most of the drive.  

Surf it as is and see what happens.   Personally, I think the fin you’re using has too narrow a base to run it by itself as a singlefin.  But if you like the ride you can always just glass it into the box with some cloth and finrope.  


Second test run today, but with some side fins.  I put the standard size Speedwing side fins in and surfed it in 4-7’ waves at the Hook (in Santa Cruz).  It held up very well in the larger faster waves - again I was mostly zooming down the line to make the sections, but I did get a few decent cut backs in.  Normally I wouldn’t ride this board there when the waves are that big, but the tide was getting pretty high and the waves are harder to paddle into at high tide.

It was not too loose (obviously) and not too tight, either.  With such a wide tail, it was nice to have some extra stability and hold in the steep waves.  If I decide to keep this center fin around, I will probably want some smaller side fins … maybe next time I will try it with some side bites.

It looks like that center box is holding up alright for you.  If the board isn’t too tight then maybe leave the Speedfins in or switch to slightly smaller thruster sides.  

hi mate


  put in a finbox


  so you can alter the fin , and fin positioning ,


  and use lots of different single fin templates .


  you will be glad that you did , in the long run !


  stubbie single fins are the GO , and have been for YEARS !!




  enjoy !!



Hi Ben,

I’m sure I will put in another fin box sooner or later … what sort of fin set up do you think would best for this board?  Currently, it’s my “high tide shortboard” or longboard alternative.  When it’s high tide in Santa Cruz, the waves tend to be mushy and crumbly, so this is great when I don’t feel like taking out a longboard.  I love nose riding and have been hoping to find some nose time on this board, too.  I WOULD like to think of this as my mini-nose rider, but maybe I’m dreaming.

I’m about 5’9 and $160 pounds.  I’m 40 and have been surfing for 22 years and consider myself to be a solid intermediate surfer.  I don’t get too radical or crazy with manuvers, but I seem to catch a lot of waves and have a lot of fun.  I’ve only ridden a single fin a few times before and it was a 9’9 - great board, but I sold it to make room for other boards.  I also rode a friend’s “old school” 60’s or 70’s single fin 6’10 a couple of times.  I had fun on that one, too.  Someday I plan on getting a full-on noserider and maybe that will satisify all my noseriding desires … only time will tell.  I’ve got a variety of boards in my quiver, but in the current moment, this is what I’m working with/on and I’ve only been experimenting with changing my fin set ups for the last year or less.


hi mr. wave sniffer !


  sorry about the delay in reply , my computer weirded out on me for a few days ?!


the fin you have in there may be pretty pivoty


if you are mainly wanting to nose ride this board , you could go with a wider based fin , say 4 1/2-5" , and 7" deep , as a starting place .  Being that it is only a 6’2 being ridden in small waves [yes?] , you may not neccessarily ‘need’ a lot of fin depth…


 and ,  being able to experiment with lots  of fins , and being able to move them forward and back in a finbox , is a plus , you will be able to have one board that is more versatile , as a result.


  Also, you can always go with small sidebites [like 3x3" ] , for stabilisers , for a widowmaker type setup, too…


  fun fun fun


  find what works for you by experimenting mate





(I think)

  1. Most surfers would be happier on a single - thrusters are draggy and don’t know which way they want to go, you have to almost instantly choose a fin to lean on and usually have to change to the opposite one pretty quickly = tiresome. Singles = go straight with less drag, nice stable positive drivey feeling + they teach you about turn and trim / stall and drive in a very ‘learn to interact with the wave’ sort of way that is invaluable to your surfing on a higher level (style + instinct).

  2. Single fins work best with templates / rockers that are single fin oriented. I would not put a single on an Al Maggot Kelly Butthole model any more than I’d put a thruster setup on a Parrish downrailed pipeline gun - the MAJOR difference I see between the 2 is the location of the widepoint. I don’t think its unrelated that the 3’s have a widepoint well back and a wider rounder tail + more rocker, while the singles have a widepoint well forward and a narrow drawn out tail + flatter (generally speaking).

re: your quest / question - IMO boards are what they are and while experimenting MAY teach one a lot (I believe in this 100% and think it is THE way to get the boards you really like), experimenting with crossing apples with oranges may be less fruitful and teach one less.

p.s. That fin doesn’t look right to me. I am no longboard fin expert but I think you want more base and more rake - that small based upright fin looks like a recipe for turning on a dime and promptly having no speed.

Thanks Fins for the fin size suggestions, and thanks OBKali for your thoughts on this, too … but are you saying that this little thruster should just stay a thruster because that is the way it was set up/designed?.. and if I want a single fin mini nose rider, I’m better off just getting one that is already designed that way?


Here’s what happened today:

I rode it at high-ish tide again this morning (in a spot that prefers a low to mid tide) and the waves were 2-4’ - mostly soft with a few steeper moments. Point break. I’ve ridden it here before as a thruster, so I have a better idea how to compare it to it’s original 3 fin set up.   It did pretty good catching the waves and moving up and down the face and I got lots of nose time today - and even did a few cheater 5’s.  I was pretty suprised and stoked at how easy it was and how long I could ride the nose for in slow little waves.  Although it did well with the pivot type turns, it felt really slow in general - probably because the waves were slow and** not **fast like it was at the Hook or at Waddell (first test ride as a single fin).

I was stoked on the nose time and didn’t realize on how slow and stiff this fin set up made it - until I traded boards with my friend towards the end of the session and rode the 5’5 twin fin Mini-Simmons (5’5 x 22.5 x 2.75).  Wow! I guess I was getting used to that crazy fin set up because when I hopped on the Mini-Simmons, it was like I was surfing on lubed up waves!.. so much faster and more playful.  I know it’s not really fair to compare the two boards like that, but it was eye opening.

I think you’re all right about the center fin needing a wider base and not as deep.  I’m going to keep experimenting with it for a while.

Does anyone know by looking at the photos if the side fins are in the right spot to put in some Large Retro Keel Fish Rocket Twin Fins on this board?  Or is a thruster fin configuration way too different than a twin fin?  Do you think this would be a good board for twin fins?

Keels mounted at about 11"?  That’s pretty far forward for a keel.  The twins from the 1980s ran their upright high-aspect fins at about 9".  


But lots of people have run twin+1 setups in wide-tailed boards.  That works and some people like that setup best for such boards.   Because the sides are at ~11" the “smaller” 4.8 x 5.2 twin and a small grom-sized centerfin or a tail dragger or nub could be a good combo.  I don’t think you’ll be nose riding it, though.  

Hey nice guess!  It’s exactly 11" from the tail to the back of the side fins.  I’ve ridden this board quite a bit with the regular side fins and a grom size center fin (but not twin fins).  It’s pretty fun in smaller or mushy waves but slips out sometimes in steeper waves.  It is a little faster than the typical thruster, but not as fast as I was expecting.

Check out this center fin I found on an old Channel Islands surfboard I forgot about … It was from a 7’2 60’s or 70’s single fin.  I wonder if this would work.  Does anyone have photos or images to share as to what kind of center fin you think would be the most fun?  Either as a single fin, or as a 2 +1?