Which way does the crevasse behind that crack run Leo? If it runs vertically I wouldn't worry about it. The buried part of the foil is intact, it's just a fin box within a fin box.

If the crevasse goes horizontally I'm surprised it's not already broken. Especially if the crack was there when the fin was longer and had more leverage about the base.

Gday mate !!
hope your well the cracks seem to be running into the box but i need to have a bit of a scrape back to be sure an safe.
the strange thing is that the crack are pretty much identical both sides !!
is this a common thing?

Ian K said...

Which way does the crevasse behind that crack run Leo? If it runs vertically I wouldn't worry about it. The buried part of the foil is intact, it's just a fin box within a fin box.

If the crevasse goes horizontally I'm surprised it's not already broken. Especially if the crack was there when the fin was longer and had more leverage about the base.

doesn't look like the fin has cracked it's the base giving way, and it does look like it's an old repair, my guess is who ever did the last repair didn't clean the surface before before filling in, i'm with you just cut the base away till its solid

If I was sure the fin bolt nuts are solidly in the fin, and if there's no movement between fin and base. I wouldn't worry about it, my only concern would be if it's loose and the nuts aren't securely in the fin, the fin could drop out.

That looks like just the base material cracking, not the foil itself. It's not uncommon to see this in many fins if you have a close look. There is a stress point where thin fin comes out of the base. Other fins that have the fillet removed, show this up as a slight de-lamination between the foil and base.

I would probably just leave it, at most sand out the fillet. If the cracks get bigger, the only real way to fix this properly would be to grind the old base off, and mold a new base on.

Hey Chris
yep i got it wen i bought the Sputnik a few years a go now.. it is a great fin
I think its a Lavell design
hope ya well mate hows the new boards?

slowboat said...

No wonder you like the fin with the top cut off- its an old CNC northshore custom. They were pretty well machined from memory. The base profile should be pretty sweet. But the bases were pretty cheesy- they all cracked after a while.

Leo the fin looks great hope you get the speed you are looking for, all this fin making is making me think about giving it a go. Just need the time.

Great work Leo, good to see that my repair kit finally got put to good use.

I've got fingers crossed for a good NE'r so we can pace that fin!

Edit: Just checked the forecast...Woohoo

Forecast for Sunday
Winds: North to northeasterly 10 to 15 knots becoming northeasterly 15 to 20 knots during the afternoon then increasing to 20 to 25 knots by early evening. Winds increasing to northeasterly 25 to 30 knots later in the evening.

lelos12345 said...

leo is the spray putty high build or a one coat putty primer did you try sanding it dry with a kitten scourer , i tend to think you would use a flat block on a flat surface, i found the 3M fine sanding pads the best you can use them dry and then finnish off with water and detergent, the pad or scourer will follow the shape or the foil rather than a flat block these pads arent 3M but simular

brad1 said...

Can I ask why the spray putty then take it all back off? You're not changing the shape, it would only fill any pin holes in the laminate.

The spray on putty is just a layer to see where the peaks, troughs and divets are in the surface.

ITS SPRAY PUTTY HIGH BUILD
I NEEDED TO CHANGE THE PROFILE A BIT JUST DOWN THE TRAILING EDGE
NOTHING ELSE IT SHOULD BE THE SAME BUT NO WHISTLE ... FINGERS CROSSED
THE PROFILE LOOKS MUCH BETTER THAN IT WAS NO FLAT SPOTS .. SHOULD FIND OUT TOMORROW HOPEFULLY !!
THANKS FOR YA HEP KEEF LOOK OUT FOR THE POST TOMOZ

keef said...

lelos12345 said...

leo is the spray putty high build or a one coat putty primer did you try sanding it dry with a kitten scourer , i tend to think you would use a flat block on a flat surface, i found the 3M fine sanding pads the best you can use them dry and then finnish off with water and detergent, the pad or scourer will follow the shape or the foil rather than a flat block these pads arent 3M but simular

What's the trailing edge like? About .5mm flat (not rounded at all) is how I usually finish mine. Razor sharp is faster, but you (or somebody else) can pay a big price from unwanted contact, (just ask slowy).

I've read but haven't tried it, that if the rear edge is at a slight angle in stead of square, that will stop humming.

a sharp trailing edge shouldn't hum unless the rear surfaces are coming together at a steep angle.
The flows from either side of the fin will cause turbulence when they recombine. It's better to have the last part of the rear surfaces as close to parallel as possible, that's why there is a hollow at the back of most good speed fins.

Check the rear of your fin with a straight edge, about the last third should be straight, a hollow at the rear is better.

I'd always recommend, not having a sharp edge, human flesh is just too soft.

i cant see why not, just make sure its clean before painting,the only paint i wouldnt use is acylic appiance paint you cant sand it