I will be ready to do my cowl shortly. I had planned on doing it via the "Lost Foam" method with finishing resin and 2 oz glass cloth (3 layers). I have been hearing about all the "good" stuff from using water based polyurethane on 3/4 oz cloth for wings - will that work with 3 layers of 2 oz cloth over a foam mold for use as a cowl ? I plan on using a 2 stroke 61 and the engine will be totally enclosed in the cowl, includding the muffler (I will have to cut for air flow and for heat release).

Is this a good idea ? Has anyone ever done a cowl this way ? If it is a good idea (for strength and rigidity) will using gasoline to remove the foam damage the cowl ?

Thanks

The water-based urethane works well for finishing, but I don't think it's as tough as epoxy for structural strength. I have done cowlings with the foam method and I would definitely stick with the epoxy for this. One important thing though. Use denatured alcohol to thin the epoxy over foam, not laq. thinner or acetone, if you need to thin it.