Water Tank Install is Finished

25 Feb

I posted before about installing the aft water tank but at the time it was just held in place with expanding foam. Now we’ve finished the install with the addition of some plywood and fiberglass reinforcement. This was a simple project which drove home two things for me- first that fiberglass and epoxy resin are almost too easy to work with and second that I really have no idea how to gauge the strength or reliability of the fiberglass work I am doing!

Whenever I have a glassing project I call my father up to talk to him about it and the conversation always goes the same way – I express my doubts about whether it will be strong enough and he scoffs at me and tells me I am overbuilding everything. Still, I find it somehow difficult to place much trust in this stuff. Sure, fiberglass makes sense in theory and I’ve obviously seen it work in practice but when I’m actually handling the materials it’s a different story. The idea that you can take a piece of cloth, saturate it with a liquid and slap it together in all of ten minutes and then expect it to hold up to immense forces just doesn’t feel right. Can a material this pliable and easy to work with really be that strong?

Here is the tank before reinforcement. The blue boards
on either side are glued in with construction adhesive
and the tank is stuck in place with canned foam.
To reinforce it we first added a couple layers of light fiberglass cloth on the outside of the seam where the blue boards are glued in place.  Then I cut some scrap plywood to use as a crosspiece and sort of stringer. These were jammed in place and held in with a couple screws:
Then I painted the wood with neat epoxy to seal it and glassed everything in place with two to three layers of heavy biaxial fiberglass cloth:

This will eventually be hidden behind the engine so I didn’t concern myself with looks, I just focused on getting everything tabbed in. As much as possible I crossed the fiberglass at different angles to increase its strength. This was probably unnecessary since the biaxial cloth already consists of layers of fiberglass cloth at 45 degree angles to each other but it certainly can’t hurt. 
While I was at it I also glassed in the top of the bilge just forward of where the prop shaft goes. It was acting as a trap for debris. This new glass is visible in the center of the photo:
All told this was a quick afternoon’s work. The next day I gave the whole setup a few good kicks and it feels very solid so I guess we’re done with the water tank. I still don’t really trust it though. Certainly it doesn’t help that I don’t have enough fiberglass experience to know whether I’m under or over-building. Or maybe it’s just right?

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


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