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I was replacing mind proactively ( hadnt seen cracks but had broken back beam) and as i undid the last bolt it buckled in front of my eyes due to seagull striker tension. It was well f&cked and the last sail i had we had been giving it death, nearly hull flying with masthead kite. After that i kept a very close eye in things...

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i'd agree it's the lack of sleeving that did it

 

on multis all those wracking loads are at the corners

 

and the strength there needs to be at least double the mid-beam 

 

so with alloy beams you can either use a simple section, that's far too strong-heavy in the middle

 

or find a way to get double or triple the strength at the ends

 

any bicycle with pretensions of light weight - high performance uses butted tubing for exactly that reason

 

carbon ones would tend to have 4 - 5x the carbon at the corners than at the middle

 

when capricorn was out we found that after 10? years of thrashing there some minor cracking around the rear beam to float join

 

nothing on the front, presumably as the front beam is twice as thick so spreads the loads better

 

ground off the bog 

 

gallery_1988_37_508071.jpg

 

and laid down lots of carbon in all directions, over a much bigger area

 

gallery_1988_37_235524.jpg

 

but yeah, alloy beams that aren't telegraph poles in the middle

 

are going to need to be about twice as strong at the ends somehow

 

sleeving being the obvious solution

 

sure you're getting far better advice from others but you could buy the same beam extrusion and sleeve it with 1mtr? bits of the broken beam that had a correctly sized 1mtr section cut from them

 

the problem would be compressing them down

 

or you could cut these 1mtr sections of the old beam in half to use as half molds, wax the inside, and glass in a few mm of boat cloth 1 mtr long, half-cure with the tubes strapped shut and some blown up wine bags against dry? cloth? forcing the wet cloth to shape, then deflate and remove bags to lay 900mm carbon strips inside that, half-cure again with the bags, lay more 700mm carbon, half-cure 600mm etc

 

try and bake your final mold  on a the dash of a closed up car on a hot sunny day, (reaches about about 50C), all day

 

crack them open the next day to remove your glass insulated carbon sleeves, ready for sanding rough, latering in an epoxy, adhesive mix and slipping into new beam ends

 

not going to be quick or pretty but the end result won't be seen and can be as strong as you want it

 

start begging carbon scraps

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Not sure where you found cracks, and apologies if stating the obvious, but you need to ensure the stainless straps do not touch the ali at all or the corrode out real fast. I sleeved my front beam when i did it, prick of a job to get them in there. So when i did my main beam, i got john at sparloft to sleeve for me.

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