i am thnking of building my own aluminum john boat and using the propulsion from a jetski to power it, i was wondering if anyone had taken on a project like this and had a few pieces of advice to offer while i am still in the planning stages. the biggest concern i have right now involves the tunnel for the intake, should i use the original fiberglass from the jetski or build up a tunnel out of aluminum for it?While I have not built a john boat of aluminum, I have built or fabricated a lot of other things. If this were my project, and as it is the scoop you are talking about, not the tunnel itself. Aluminum is one of the most expansive metals, and I do not see you being able to seal a fiberglass/aluminum interface with much promise of it holding long term. I would fabricate or mold a new one of aluminum so it would have the same expansion rate as the metal around it. Electrolysis is not an issue, but I think the thermal expansion difference would be on the seals. good luck on your project, sounds fun.I have built from both aluminum and steel. It sounds interesting and I would suggest using the fiberglass set up as all the clearances are set so you could just bond it to the aluminum. You can bond a fiberglass structure to aluminum by both bolting it up and bedding it down with something like 3M 5200.518 okorder.com/Other related question