So i bought a very cheap 2nd hand 70cm fin to try and get going earlier in light winds.
I noticed it had some very small lumps on the surface (1mm diameter?) More on one side than the other. I assume it must be some sort of minor delam from being wet all the time? (The fin was soaking in its case).
So i decided to sand them off. Feels much smoother now, but ther are very small arc shaped notches left on the surface where the lumps were.
My question is, what should i do about them. Should i try and seal the notches (also how to seal them?) or just let them be and go windsurfing?

What board are you going to use? Is it a Drake?

Yes its a drake fin. Using it on a jp slw 168l 2016. Taken it for one run pretty powered up with no issues before sanding it down. But it did feel a bit draggy (compared to my 56cm stock fin) hence the sanding..

i do not see how small bumps or divots would cause drag
if you want it smooth ...
i use MarineTex epoxy and then sand it down level

joewindsurfer.blogspot.com/2012/03/fins.html

I wouldn't be to worried unless doing over 30 knots? not as ugly as some of me reef biting fins

maybe wet and dry sand paper 600 will smooth it out ,

you will never sand flat by hand - use a block and wet sand to 400.

But as to whether it matters....? I'd suggest not. That minor fault is nothing like the mm of variation in your board or the fact your mast is 3mm longer or shorter than others in the batch, or the angle of the dangle on the day

I think this may be paint reaction. The epoxy remedy, would need to adhere to the surface , not paint.
1. Remove offending area or all, then epoxy, I think 2stage Of Gorilla or such would be ok.
2. Leave it alone as suggested.

i would probably remove the paint at least I think what it is, skim coat epoxy, probably repaint. That's me.

Thanks for the replies guys!
I think i will try and fill them with some epoxy, maybe a bit of graphite fill. Mostly i'm worried about water getting into the cracks and possible consequences.

I would not fill with epoxy as it is harder, and when sanding back then the paint will sand off easier, and you will still not have a flat surface. Squirt of hi build primer and sand back. Advantage is its grey too!!!

That fin will always feel draggy if you are powered up because it is too big. I have a similar rrd light wind board and can use an 11m sail with a 54 Formula fin reboxed. It is still plenty of fin, so I can imagine what a 70 would feel like.

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Mark _australia said..
I would not fill with epoxy as it is harder, and when sanding back then the paint will sand off easier, and you will still not have a flat surface. Squirt of hi build primer and sand back. Advantage is its grey too!!!

Any bigger flaws that the primer won't fill, use a bit of spot putty. Dries quickly and sands easily. If you use epoxy, you'll send a lot of time waiting for it to cure and sanding off all the gob that went in the wrong place.

Thinking about those comments on epoxy, they are right to a degree. Adding a sandable additive would help.
3M , make a Marine Putty, be just the ticket. Only have seen it in a large tube .

regards blob , this should be a skim application.

Thanks for the input guys. I ended up putting a thin coat of epoxy filled with graphite and glue powder and sanded off before it went fully hard. First run yesterday fully powered up with 9.8m sail and had a blast!

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sun fisher said..
Thanks for the input guys. I ended up putting a thin coat of epoxy filled with graphite and glue powder and sanded off before it went fully hard. First run yesterday fully powered up with 9.8m sail and had a blast!

what was the wind strenth? Im thinking about a 70 too

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BSN101 said..

sun fisher said..
Thanks for the input guys. I ended up putting a thin coat of epoxy filled with graphite and glue powder and sanded off before it went fully hard. First run yesterday fully powered up with 9.8m sail and had a blast!

what was the wind strenth? Im thinking about a 70 too

Im about 97kg, but not very good at pumping yet. I think i easily got going in 15kts maybe a bit less and it was gusting around 20kt later in the arv and was still controllable - ish