Tri-fin Conversion

DavidM · Post by **DavidM** » Mon Dec 26, 2016 5:37 pm

WD, I have some divinycell if you need some

nanmoo · Post by **nanmoo** » Mon Dec 26, 2016 11:43 pm

Either is probably way overkill. Surfboards have em' set straight into the foam and have way less anchoring surface area.

DavidM · Post by **DavidM** » Tue Dec 27, 2016 7:05 am

wd - answer to your !st question. micro balloon (qcell)/epoxy slurry.

downwind dave · Post by **downwind dave** » Tue Dec 27, 2016 9:23 am

I think it's pretty common to glass under the box and/or divinycell cassette. I just watched a Jimmy Lewis video and that's what he did. a surfboard fin sees nowhere near the load or the duration that a windsurfing fin sees. Think of a long day of sailing, you could be leaning on a fin for hours.

nanmoo · Post by **nanmoo** » Tue Dec 27, 2016 12:31 pm

The idea is to increase the surface area of the box to distribute loads. A base of thickened epoxy or balsa or foam of the same size will spread the load exactly the same. Obviously some options add more weight. The advantage of closed cell foam is if your glass/resin on the surface cracks you might get lucky and prevent a leak to the EPS. Sailboats use the same tech on cored decks where there are inserts that receive heavy loads.

winddude · Post by **winddude** » Thu Dec 29, 2016 8:09 pm

I think the other big thing with the layer of glass is epoxy doesn't bond well to the plastic, so it was an extra layer to prevent any leaks into the eps if the box delams and fully adhere to the bottom lam. Not positive but the delamination from the box may have been a bigger issue with the polyester resins.

After talking to Dave I think I'm going to go the way of no glass between the d-cell and eps. Still debating on shortening the boxs a couple of inches.

nanmoo · Post by **nanmoo** » Fri Dec 30, 2016 3:39 am

Epoxy sticks to everything just about better than anything else. Polyester can't be used directly on EPS because it melts it.

Geoffy · Post by **Geoffy** » Fri Dec 30, 2016 12:09 pm

Actually the glass layer which typically went under the box and then spread flat onto surface was for vertical impacts on fins/mast bases. The glass layer ties the box to the surface laminate so that when hit, the box (even with hi-density foam surround) doesn't press downwards into soft EPS foam and result in microcracks/leaks around the top. Has nothing to do with bonding to the foam itself.

Carbon Art has a nice video clip of box install that shows appropriate thickness of epoxy/microballoons/silica.

Balsa will absorb water, no matter how well you think it is protected (unless you pre-saturate it with resin - then what's the point of using it, right.)

DavidM · Post by **DavidM** » Fri Dec 30, 2016 4:40 pm

Like Geoffy's explanation.

nanmoo · Post by **nanmoo** » Fri Dec 30, 2016 5:10 pm

Because its cheap and easily available in a pinch Geoffy! Sometimes you have a choice... do a reasonable half added job that has a 75% chance of lasting or miss a session. If someone's paying me I'll take the latter but if it's me I'm not missing a session!

winddude · Post by **winddude** » Sat Dec 31, 2016 1:54 pm

After pulling the box I found it was set in a large chunk of Last-A-foam, so I could have kept sailing with a single fin and not worried about water

Tri-fin Conversion

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