Busted Daggerboard....

I like the Uni's idea. I get the whole "don't mix carbon and eglass" thing. Is this possibly a good application for some 12K carbon tow uni? I happen to have some of that.) It means more grinding, but what the heck, winter is here. Might as well....

I still want to do the horizontal column to tie in the sole and the other side of the hull. Yeah, it'll be a tripping hazard, but it should resolve the crushing issue for good. I ground it out yesterday and am letting the glass dry out for a while...

 

If it was me I'd be going further up the case and having that floor out, uni would be ok sandwiched by double bias that is +45 -45 stagger the layers to have max build up in the join. Glass against the case with carbon over to finish.

 

Drying out the glass?

When you say drying out the glass, was it wet with water? That is a worry. I would be more worried about the core.

If you have problems with water you need to protect the core (or at least check it). This means getting the angle grinder in again and digging away at the glass. It does not look too nasty. I would bevel a 45 degree angle of the hull core so that the inner laminate of glass touches the outer hull laminate before turning upward to the case.

Doing the part of the case next to the hull will be a bummer - reciprocating saw from the outside? Airtool? Lots of swear words and skinned knuckles often does it.

I would not remove the floor or do a vertical bulkhead for support. The floor is a lovely beam lying on its side. It is stiffer in the horizontal plane than the equivalent section of Veed hull would be. So use it for stiffening properly. Attach the DB onto the floor and use the floor to distribute the case load away from the case.

Your little bulkheads do not have to be vertical - they will be in compression or tension. So lie them flat ONTO the floor. The floor will stop them going out of column. Visualise the forces on the case and then use unis to fan out the forces onto the floor and DB to consolidate. Engineering will be done by saying - That looks bloody strong.

The loads on the floor side of the case are easy. To get the load from the case pushing on the outer hull side I would make a little beam on this side and attach it to the bottom of the case. You have a shelf that is probably too high to take the case bottom loads. Put some 20mm spruce or similar fit to the case and hull skin. Lead it forward and aft of the case and mount it as low as you can. Its job is to take the case load and push it forward and aft. You could even tie it to the floor on the other side of the case with unis and DB to consolidate. Visualise the forces on the case. I think about how I would tie the item on with rope and do the same with uni.

Having another look it seems as though the side NEAR the floor (the side nearer the hull centreline) may have let go through tension rather than compression. If that is the case then maybe only the core on the floor side is compromised. You can dig that out easily. If it is a tension failure, because the other side was too flexible, putting the small beam in down low should help.

As to mixing carbon and glass. We don't usually do it because the elastic moduli are so different. A bit like reinforcing steel using rubber. It is often done when you want to increase the carbon's toughness. Carbon sea kayaks often are made from a carbon/kevlar hybrid. Carbon is great but will snap catastrophically in thin laminates so kevlar is added to keep the hull together when after large impacts . I would use glass uni myself but if you have carbon use it here. No one really knows the loads, the load paths, the stress increases due to corners. It is all a guess so use whatever is available but personally I would save the carbon for some chainplates later.

Remember - Use the floor Luke. Use the floor (with apologies to Obi wan)

cheers

Phil

 

Use the floor

I agree with Phil about the floor, when I said I would have it out I also should have been clear that I would be putting it back after glassing and yes put a layer of Db over it.