My Mako - WIP

[Mikey]

Direnc,

The old build was really ghetto. I clamped 2x4 okoume ply boards down with blocks and planks. On the underside I added some carbon I had scrounged and a veneer of wood something (given to me). I used another ply board on the bottom of all that, as the pressure surface. It came out hard as a rock butwith voids between the veneer and the carbon. I slit and filled them with expoxy. All very approximate.

I suggest using this new technique I developed.
Two ways you could do it 1. (if you are happy with the shape and form) try using your real mako as the mold. Get you hands on some 4mm xps sheets and glue laminate them into shape for very little spring back (important). You need lots of glass on that sort of core (not the expert, here).

2. Make a bending /gluing jig with an epx sheet. The jig has three rails; two external (chamfered on top to seat te concave) and one central rail, that is lower by the amount of concave you want. Rails should arc in a constant radius. I used about 5m radius for my rails.
I did 9mm of constant rocker and 40mm of concave (too much). Try 25 - 30mm as the spring back is much less In concave. Brace the rails up and place you ply (2x 4mm poplar non marine) in the jig, weigh down the sand bag dirt or clamp. Go don't try to bend all at once. You need to tease it into shape over a few days.

Pre mold by wetting the boards and leaving them out for a few days (week). And you will find they bend up resonantly well. Then glue laminate with epoxy and clamp straight back down on the rails. Leave for more days (week) You should get about 50- 60% spring back on the rocker. Keep it clamped until you do the glass (helps keep shape)

From there you can do a normal 2 x 125g glass job per side.

Fin and strap insert as desired (look at the other treads on this, as there is plenty of great stuff.

Hope that helps

[Mikey]

Builders,

Plug and inserts done! (Thanks Downunder

Decided to wrap the rails (fingers crossed). For the layup I have 105g and 135g glass. Given the core already weighs 2280g and that I want to keep it as light as possible from here and the inherent stiffness of the rocker / concave combo, will one layer of each (240g total), on top and bottom, be enough?

What are the advantages of 1 layer on top (135g) and 3 layers bottom 105 / 135 / 105?

I like 105 on the outer as it provide a very fine finish for a minimal fill coat.

Suggestions?

[Mikey]

Guys, see above post. Any advise on layup?

Thanks,

Mike

[BWD]

The standard glass skin is traditionally 600gsm over a lighter core.
Plywood forms a tougher core, requiring less glass, if any. Your core is fairly thin at 8mm. But it also is very concave, somewhat making up for the thinness
In my opinion ~400gsm total should be enough.
Incidentally 400gsm is about the minimum needed to give good abrasion resistance for hitting rocks, beaches etc.
If you are massive (100+kg) you may want to go with 600 anyway.
Some may recommend less glass, this may be fine if you aren't heavy, or have less concern with durability.
Having the top layer of glass be a lighter one, e.g. 100gsm, does make getting smooth and even fill and gloss coats easier, not a bad idea.
Good luck!

[rynhardt]

The standard glass skin is traditionally 600gsm over a lighter core.
Plywood forms a tougher core, requiring less glass, if any. Your core is fairly thin at 8mm. But it also is very concave, somewhat making up for the thinness
In my opinion ~400gsm total should be enough.
Incidentally 400gsm is about the minimum needed to give good abrasion resistance for hitting rocks, beaches etc.
If you are massive (100+kg) you may want to go with 600 anyway.
Some may recommend less glass, this may be fine if you aren't heavy, or have less concern with durability.
Having the top layer of glass be a lighter one, e.g. 100gsm, does make getting smooth and even fill and gloss coats easier, not a bad idea.
Good luck!

This is pretty much the weight of glass I just put onto my new foam core board (146x46). Top and bottom layup is the same, from core outwards: 410gsm 0/90, 200gsm +45/-45, 50gsm top 0/90.
It's fairly flexible with a 10mm foam core and 7mm centre concave: 60mm tip rocker goes down to 20mm tip rocker with my 85kg weight on it.

If your wood core with concave is already stiff enough, then you just need to seal the core. If you want abrasion resistance like BWD suggests, and your core is already stiff, then maybe do a +45/-45 layup so you don't end up making it stiffer.

[Mikey]

Thanks guys!

I'd say the core is firm, rather than "stiff", so I'm sure some 0/90 is needed.

I don't do gloss, just fill on the bottom surface and rubed with 200 grit. Top left as glassed

So the consensus is: ????

135g top and 105 + 135 + 105 bottom, all 0/90?

Or 105 top and 135 + 135 + 105 (outer for the finer finish)?

Thanks!

Mike

[BWD]

if you use the same layup top and bottom it nearly guarantees the board will not warp.
0-90 as the outer layer gives more stiffness, +/-45 less.
All your glass is thin and light and should lay up easily, no further advice from me without actually seeing it.
Don't worry it will work out.
Unless you screw it up