Don I just put my hull on the scale (not the most accurate not digital) it came in a 8.5oz but I molded in a 3/4 inch lip on the top so i can bond it to the deck as well as I have to trim the stern a little, with that I would think that I am fairly close right? whats a few oz. between builders.
Vacuum bagging has to be good for something. It’a a lot of bother if it isn’t lighter. I guess no pin-holes will make it worthwhile.
Don
Don, I am going to be trying to vacuum bag my deck, once I make the mdf mold. I was given a vacuum from a friend getting out of the fridge repair buisness. For my hull I actually used 4mil poly and tightly wrapped it and stapled it to the underside of the mold. I think next time I might even try using that clear poly wrap that they use to bundle wood at the lumber yard with. It is the type that comes in a 4" or 12" roll then you wrap it a few times and it clings to it self, the product write up says the more times you wrap the tighter it gets, almost like a tenser bandage (hey maybe that will wok as well?).
I am not sure that you understand one of the advantages of vacuuming - removing excess resin from the layup.
To hand layup a hull inside a small female mould - it is virtually impossible to squeegee ( a soft rubber “scraper”) excess resin such as you would be able to over a male mould. Hence holding down a layer of material into the mould that will absorb the excess resin is one of the aims of vacuuming. This layer has to be removed from the new hull and thrown away - hence Don’s plastic layer with the holes in it so resin can pass from the new hull, through the plastic to the absorption material.
Vacuuming will considerably decrease the thickness of the layup - the hull will be much more “oil can” like, but much lighter. The throw away material will contain more resin than the hull!
I have been vacuuming 4’ - 6’ hulls for some time, but when I try to vacuum a IOM hull using the least amount of resin to (almost) wet the layup, the discarded resin is still much more than what remains in the hull. Since a lot of resin is removed from the layup, there are pin holes EVERYWHERE with 1 or 2 layers of cloth , many with 3 layers etc. You need a “gel coat”, primer or similar, as well as brushing the thinnest coat of resin into the finished - warm- hull BEFORE removing from the mould (otherwise the resin flows throught possible pin holes destroying your outside finish)
My current IOM hulls have the thinnest coat of resin in the mould (as a “gel coat” - I use about 30 grams) then a fine weave cloth (about 100grams) then a bi-directional cloth (400 grams) and then the final resin coat inside. Weight is normally under 250 grams (can just get complete boat under weight). Decks are identical layup (200 grams total weight). The hardest part for me is seperating the hull from the discarded layers, particularly in the bow section (a nylon bleed cloth, a layer of shade cloth, and another “fluffy” absorption cloth absolutely saturated with resin sometimes!). Rough guess for panel thickness is less then 1/32".
Very time consuming, lots of material discarded.
Jon
I thought one of the advantages of vacuum bagging was no pinholes. If I have pinholes in this hull I might not vac bag next time. I’m not sure the weight loss is worth the hassle(all the plastic and crap in the bow). I could soak up most of the excess resin with rags befor it goes off. On the other hand I think I have an idea to solve the bow mess. If there is a next time I’m going to cut the front off the mold. It already has a flat bow for a bumper. I’ll just remove the flat part. Then the mold will be more like a trough and the breather, soaker and vac bag will lay nice and smooth. It will come out of the mold easier too. After I’ve popped it out I can push it back in the mold and epoxy in a bow piece or just sgeeze the sides together and epoxy them.
Just thinking out loud
Don