Molded dagger board manufacturing technique

Looking at ways to build a dagger board.

Rather than hand shape a core / glass / fair I was considering the following:

Make split mold for expanding epoxy to use as core.

Layup reinforcements dry around this core molded expanded epoxy core.
Insert into a final shape split mold and infuse resin in.

Has this type of technique been used?

Alex

 

Why bother? Look at how a Laser sailing dinghys dagger board is made. Its obviously made in a split mould but is basically a foamed or microballooned polyester core with steel reinforcing wires inset into it to give it the required strength, no glass on the outside at all.

 

Ive built daggerboards and rudder blades in a simple sheet metal mold, a method i learned from the late Malcolm Tenant and used on many of his designs. Basically you have a sheetmetal shop fold a piece of steel or aluminum about 1/16" thick the length you want with a fold in the middle to form the leading edge and open at a 45 degree angle, none of the local shops can fold to the nose radius i want so i run an appropriate fillet, there are 2 more 90 degree folds at the trailing edge where you attatch wood strips to clamp to, so what you have is a female mold in which you layup your laminate then bend in and clamp the trailing edge. As i recall Malcolm laid up a lot of uni at the thickest point and then filled it with a syntactic foam made of epoxy filled with polystyrene beads and pushes it into a jig to set the maximum thickness. I prefer to close the mold around a shear web and leave it empty if the chord id not too long. You end up with a molded gelcoated part with no fairing. I will be doing a pair of rudder blades sometime this summer for a Gemini cat this way, about $60 for the mold.

Steve.

 

Actually the Laser foils in the UK were made from a foaming polyurethane around a steel mesh. I t so happened I ran into the company who made them a few years back. They may have changed the process and or materials since but circa mid 90s' that was the case.

As far as I can work out the moulds for making foils could be pretty much any material. For a 2 off, I'd be tempted to make a glass one, off a pattern, but if you have access to sheet rollers, steel and aluminium might be OK as you suggest. Even coated ply or MFC would work OK with just a local shaped part for the nose (leading edge parabola) joined on. If you have a lot of expanding going on with the foaming core do not underestimate the clamping required to maintain shape.