Having absolutely no moulding experience (apart from trowelling tons of car body filler into the roof and a-pillars of my first car) i realised how much work would be needed when i started dimensioning and generally surveying the existing blade.
This was the beginning of my interest in West Systems Epoxy, according to older brother Rik he recommended this on the basis of its strength and ease of use to work and the fact that there is an additive for every application.
By this i mean whether you are filling some surface scratches in the gel coat of a dinghy to rebuilding a yacht with the side torn out of it; Wests make additives that get mixed into the basic epoxy resin to give a different chemical composition depending on the application required.
I'd found out to make the plug of the rudder i'd need a mix that could be sanded and shaped fairly easily but still retain its strength. Whereas the making good of the keels would require a high density filler (but more about that another day).
Being as i make things with my hands for a living i approached it logically and drew both sides of the rudder blade out 1:1 scale on half sheets of MDF.