Hi all,
I just bought a used mid-size board the other day (8 x 21 3/4 x 2 7/8) and wanted to see if I could 3D print a single fin with tabs to fit into the old FCS 1 center fin box, so I could in theory switch from a thruster to an 8’ or so single fin without having a different board or replacing the original fin boxes. Are there any problems with this? Any information would be greatly appreciated.
cheers
ross
For fin, the small 2 tabs will not resist long to pressure from a big single fins even more if it’s 3D print plastic, must be make with full carbon to hope it work.
For plugs, it can work if there are well installed in board: well connected to deck via the stringer and to a strong lam with a chanfrein under, all glue with fiber reinforced resin.
That’s funny. Because FCS makes an adapter that goes into a longboard box. The main idea behind the adapter is to make a 2 +1 into a Thruster. If I really wanted what you are talking about, I would put in a center longboard box and use the adapter when I wanted a Thruster.
I agree with Lemat. Those small tabs will not hold up well on a fin with a lot of surface area, especially a 3D printed one. But, I suppose the cost on your end will be pretty low so when they snap you can just make more. 
FCS1 tabs can barely support a large twin fin, this is why removable fish keels are often three tabs.
This might actually prove to be just the inspiration you need though! It’s been mentioned that the usual way to achieve this would be a standaed FU box at the back… but that’s more work than might be necessary.
You might be able to get the strength you need for a fibreglass fin by simply adding a third FCS box ahead of the two existing centre boxes; 3D printed fins though? Jury is still out on how achievable reliable strength is from consumer grade 3D printing, even with a full FU base.
Hi Ross,
I’m gonna agree with everything that’s been said, unless the center plugs were put in really well I don’t think they’ll hold up versus the much bigger and deeper fin. Chances are, they weren’t.
So I’m thinking you maybe want to put a couple of slots in the tabs of your printed fin, so it will break away rather than taking out the plugs Or plan on the repair and installing a Fins Unlimited type box down the line.
hope that’s of use
doc…
Print the fin with a couple of extra tabs. Then install a couple of FCS plugs to correspond in the board. I’m sure that would help, but still not as strong as a single slot box and fin.
In addition to the other comments, the placement is not going to be very good for a single fin. Too far back.
Another option you could explore is an in-line single. For this, you would install a regular single-fin box just ahead of the where the leading edge of the center thruster fin lands. Typical spacing would be to have a couple inches between the trailing edge of the larger single fin and the leading edge of the smaller rear fin, although it’s honestly a very flexible setup. You don’t see it a lot, but it’s been around for decades.
Hopefully this link works, if you’re interested in knowing more:
https://www.swaylocks.com/forum/41662/line-and-fin-designat-last
Thank you all for the information you’ve provided, I’ll weigh up my options and figure out what I’ll do. I may even shape a replica board and muck about with fin placement/boxes on that as well. If I end up with anything decent ill keep this thread updated.
cheers
ross
hi all,
Would it be possible to have a hydrodynamic base plate integrated with the fin to prevent movement and damage from the larger surface area, as I realize it won’t take much to rip the fin boxes out. Also, what should I also take into consideration when designing the fin to match the board? I don’t know much about fins bigger than 5 inches and have been reading other threads on longboard fins, fin systems, shapes, and sizes, but am still unsure what to go with.
My other current plan is to go with the breakaway tabs idea from doc, and see how they fare, if these don’t work ill route out the old boxes, put a regular single fin box in and buy that adapter McDing is talking about.
cheers
ross
Hi Ross,
Would it be possible to have a hydrodynamic base plate integrated with the fin to prevent movement and damage from the larger surface area, as I realize it won’t take much to rip the fin boxes out.
Huh. Damned good idea. Your stresses on the plugs then come down to little more than shear. You might even get a smidge less drag, considering. An example of similar base form would be the sails/conning towers on the latest generations of subs.
Also, what should I also take into consideration when designing the fin to match the board? I don’t know much about fins bigger than 5 inches and have been reading other threads on longboard fins, fin systems, shapes, and sizes, but am still unsure what to go with.
I’m not that familiar with 3D printing, so I’d go with something easy to model/program/fabricate within the limits your machine can do. Dunno if there’s an easy way (preprogrammed library stuff, let’s say) to do things like NACA airfoil shapes but one of those, essentially mirrored as a cross section, that would work, ‘centered’ on something like a segment of an inverted hyperbolic curve? Shrink it by something for every iteration/layer?
If that made sense, there ya go. Otherwise, I’d find a standard fin and copy it, scan it if you’re set up for that… Or look around ( library code again) for something you can adapt.
There have been a gazillion fin shapes and cross sections and so on, all with their fans who swear they are the best thing since canned beer. And zilch for any real data. Me, I like beer in bottles and again, I’d suggest something easy to do.
hope that’s of use
doc…
1
Yes placement would be of by at least a couple of inches.