might end up just buying a silicone water jacket so the tubes don't exit straight up
Be prepared for a boat full of water. Every silicone jacket in our club boats leaked like a sieve after a short time, even with plenty of bathtub caulk around the edges. Better to plug the existing jacket holes and re-drill for the nipples below. That way you can put them in the right places - exit high on top, inlet as low as possible.
I don't know what the thread is on the water jacket but check these out. Scroll down a bit and there are several 10-32 90 degree and swivel fittings. .http://www.mcmaster.com/#standard-ba...ttings/=if9hjn click on the brass fittings on the left and scroll down.
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