First fin attempt

Hey Just wanted to get some feedback on my first fin attempt. the fin is for a 5’9 fish that i’m working on ( i’ll do a picture series when I get a bit further in the process) the fin is 8’ 3/4 base x 5’ 2/8 high x 1/2’ thick. It’s obviously a keel attempt.

Go easy, but be honest!


I would foil the back 2/3 more and foil it so the lamination lines are not wavy. I like your template. Is the template wavering or is it the photo? I’ve foiled some really bad ones that have worked well. Check out the True Ames Gephart keels for inspiration and ideas about the width of your bands. Mike

Hi Rooster

I am taking you up on the more foil in the back 2/3 it seems to be the way to go.

I notice that I have a lot of layers, what are the pros/cons of that?

I’m finishing up the sanding by hand and trying to get out the wobbles, it’s not so easy…

Is the bevel supposed to be rounded or more straight? would it be possible to do with a planer? What tools are the best for this work?

Bear in mind that I have nerver held a keel fin in my hand so I’m kinda just going by pics and feel! Up here in cold Denmark there are not too many keel boards floating around!

Thanks for the help it’s much appreciated!

hi moks !

can you take a shot of the base of the fin ? [with the fin lying down flat ], please ?

I ask , because I find THAT perspective in a shot usually helps me to pick up where the flat / straight spots are in my fins , as well as by running my hand over the fin , from the leading edge to the trailing edge [you will feel the areas that need to be rounded more , doing this .]

For my homemade FIBREGLASS fins , I usually use a grinder , then a sanding block , then hand sand . (I am no expert , I hasten to add , when it comes to getting great foils ). I guess with wood , you could use an orbital or disc sander.


I find I just have to keep at it , take my time , and keep putting both the fins together , back to back [if single foiled] , to make sure they are both the same . Again , looking at them , from the BASE up . …

okay , I hope this helps ?



cheers !



I can’t think of any cons for so many layers. The pro’s are it will look really good when done. I’m no expert, either. The bands on mine are roughly parellel to the rear curve of the trailing edge. Not exactly parellel except in my keels with a vertical trailing edge. The wavy lamination line means highs and dips in the curve. Try not to have flat spots. Chip’s suggestion of looking at them from the bottom works well for me, too. I hold the fin in a gloved hand and foil them with an orbital sander. I’ve clamped them to a bench and foiled them, but I have not gotten as good as results. Again, get on the True Ames web site and check out the Gephart keels. Mike


Lay a metric rule on the overcambered side of the fin at the base. Figure where 30% off the leading edge is and put a dot on the fin. Move up about 5 mm or so and do the same thing all the way up the fin. This dotted line is where the thickest part of the fin will be. Some call this the vertical cord, some the draft. I prefer the former. Foil the fin to this line. I prefer a rounded leading edge as its directional transition is smoother and creates less turbulence. To get all the ripples out just take a piece of 1" wood stock about 3" x 8" and wrap a piece of 80 grit around it. You can’t beat block sanding to fair your overcamber out. Get rid of the all the flat spots.

Mahalo, Rich


Suggestions just as Rich says. I’ve done literally thousands of wood keels over the last 30 years…

…I can’t lie, that fin looks like crap. The block might straighten some of those wobbles up. Aft

portion needs more material removal. Show us that you can do a better job.

For flat-sided keels, you may want to go thinner, like 3/8" at max camber thickness.

Definitely use that hard sanding block.

Symmetric and Semi-symmetric foils hold better in sustained turns, but the flat-sided provide more

drive at low speed (as when you “pump” the board to get up to speed). You better stick to

foiling one side until you get your craftsman skill up.

Have fun!

My advice? Listen to Halycon. I’ll be using that method on my next attempt. Thanks Rich! Mike

Exelent advice Rich! I’m at it with the sanding block and the vertical cord line was just what I needed!

I have gotten out some more of the wobbles but need to do some more sanding! I have attached a photo as requested from base up + a progress shot of the wobbely part!

thanks for the honesty and helpfull directors!

Christian [Denmark]


Halcyon would it be possible to see a photo of a fin with the 30% thing you are talking about, from diferen angles?

I have had a look at the true Ames website and they are beautifull, but it’s hard to see what I need…

Second photo: much better. Starting to look like a fin. Remove more off the rear half- move the

stripes up forward a couple cm more. You might want to read re-read what Rich wrote…

hi Christian

I was told [a while ago now] that when you put the two single foiled fins / keels together back to back , that the combined profile ‘should’ resemble a cross section view of an aeroplane [‘airplane’] wing , if the foils have been done ‘well’.

hope that helps ?



Thanks plus one!

I have actually discarded the fin now as I could see that the starting point was way off the target, I trying again!

The idea of the airplane wing really seems to vlear up the points to go for! Thanks!

Thanks for the help! I’ll keep you updated on progress (if any)


My advice is to not throw it out. Save it for comparisons. I have some that I look at now that are hilarious. They are so thick I could get two fins out of one if I was good enough on a band saw. Some of my ‘bad’ ones worked really well,too. Your first is way better than my 3rd or 4th. Keep it. Mike

I have made a new attemt at the fin and I think I’m getting nearer to the thing I’m after! I have taken all yor advise onboard and tried to effectuate it through my hands, I hope I have some level of succes! I’m not quite done yet but I hope I’m moving in the right direction!?

Thanks for the help guys :slight_smile:

That looks 100 times better Moska, I would make the lines in the wood follow the curve of the back of the fin a little more myself.

Lay a metric rule on the overcambered side of the fin at the base. Figure where 30% off the leading edge is and put a dot on the fin. Move up about 5 mm or so and do the same thing all the way up the fin. This dotted line is where the thickest part of the fin will be. Some call this the vertical cord, some the draft. I prefer the former. Foil the fin to this line.

This is what Rich wrote. Define the max camber line. Make it the wide point on the fin. 25-30% is a good safe place to start, I don’t think you will EVER want the wide point to be further forward than 20% or further rearward than 40%. Further forward is drivier and slightly higher drag, further rearward is lower drag and less drivey. I use 20% on thruster rail fins, but would use 30-35% on a keel fin because they just are not gonna get that drivey with that fin outline. Old school keels were not even foiled, just smoothed out the front and rear edge, and 90% of the fin was flat foiled. And they worked out with the occasional hum…

You new foil comes a lot closer to a modern foil, by eyeballing it I am guessing the max thickness of the foil is close to 20% from the leading to the trailing edge. And it that’s what you’re after, that is good.

Here’s one I foiled at 20% in glass. This fin template was far from optimal, but you can see the steps I used to foil it from the successive photos.

I like the soundtrack …but it got cut short ?

got any shots of the finished fin and foil please Dave ?

[especially the profile , from the base looking to the tip of the fin ?]



That foil was finished, all I did was finished sand with 220 grit by hand and hotcoat and polish…

But that template didn’t work, it was part of discovering why the base width of a rail fin needs to be the longest chord on the fin, they just lacked drive, so I trashed the fins after 3-4 rides when I made the replacements, a true elliptical planshape that did work as planned. Actually recalling back I made them with too much cant and had to reset the cant first, then discovered the lack of drive. On the next ones the chord length increased with the square of the distance from the tip, to give an elliptical load profile…holy cow…super drivey and best release EVER, unfortunately the hold suffered some as the tip was minimized…pointy actually…then I had a holy revelation, straight from the great spirit…the extended tip on a thruster fin is there for a good reason, it is not about drive, it is about hold. The base does most of the drive, the tip does most of the hold…that’s an exagerration, but it is no exagerration that the role of the base width in drive is 5 times that of the tip, and the role of the tip in hold is 5 times that of the base…armed with that knowledge, it became quite easy to design fins for all conditions…the base rake is constant…smaller waves get more base width and no tip,…larger waves get less base and more tip…of course I could make the base width pretty wide without incurring a drag penalty because the rail fins rotated…so 5 inch base width was as fast as 4 and had loads more drive…

Hi Blakestah, with the RFS, is it partially intended to reduce lateral pressures on a standard 3 fin setup ( see pic). This is a basic pic, sorry, but is this the way you see it? or not? or what?

And is the role of the base (for drive as you said) diminished by the lesser angle ? Or maybe increased with all bases facing the (approx) same direction? Regards, Brett.


the rail fins rotated…