Blowsion Tubbie Sponson Install Guide

After getting a good look at several Blowsion boats last weekend at the beach party, I would probably modify my install. It seems that using 3M 5200 would be a better choice instead of an epoxy mix. The downside is that 5200 can take a week or more to cure, but it is much stronger. If you leave the screws in, there isn't really a strength problem, but you might have cracking on the very bottom edge of the tubbie which is really only a cosmetic issue. 
It seemed to me that leaving the screws in without filling and sanding didn't look bad at all, especially with a custom paint job. I also noticed Joe Kenney's boat in particular didn't fair the front edge. Not doing this would save you a lot of time, if you aren't particularly anal about the appearance of this area. They won't flow into the hull and look like an original part, but they will work just the same. 

click on the thumbnail for a larger picture

	Measure from the back and trace the outline of the sponson. It's 36 1/4" from the rear on the Superjet, and 11 1/4" from the front. It's easier to use the rear measurement as your guide as it may differ slightly. The front edge is 1/2" from the bottom of the hull and the center follows the hull shape. The mounting surface needs to be sanded with 80 grit or coarser sandpaper. I recommend taking it down to bare glass for the best possible adhesion. At the very least it needs to be well scuffed in a crosshatch pattern.
	Tack one screw front and back to predrill 1/8" holes at the same angles as the preformed depressions
	Tacked from front and back
	Mix at least 100ml of two part marine epoxy with adhesive filler to make a paste. Lay a bead along the line you traced and along the sponson. Be generous with the epoxy.

	Pre-start the screws through the holes you drilled and screw it down from the back to the front. Tighten till it just pushes out the epoxy along the sealing edge.
	A fat bead of epoxy on the top edge
	Use a squeegee to push the epoxy back along the bead and smooth out the other edges as it dries.
	While the epoxy is setting, grind off the screws protruding from the other side.
	Finished top bead. It's not actually necessary to seal the top, but why allow extra water intrusion?

	Seal grinded screws with leftover epoxy.
	Clean up remaining epoxy with Acetone.
	After curing completely, it's ready for SMC filler.
	You want to fill the front edge so it can be blended in and sanded flush, and allow extra filler along the bottom sealing edge to keep it watertight. Also cover and fill the screws if you aren't going to remove them.
	Filler applied. Use a squeegee to shape the filler before it becomes unworkable. This will reduce sanding time later.

	Finish sanding on the other side.
	More finish sanding. Use any handy spray paint to apply a flow coat so you can see any hills or valleys. Refill as necessary and resand.
	The front edge was filled and extended, then shaped and sanded flush. Use a paddle wheel sander on a Dremel to smooth out the tough areas on the top bead behind the rail.

	Finish sanding
	Front view with one sponson finish sanded and one ready for filler.

I sprayed a flow coat with some flat black enamel paint I had lying around. You can easily see the areas that need to be resanded and/or filled again. Any paint will do for a flow coat. (The paint isn't all the way dry in the pics BTW, so don't mistake the wet areas for valleys)

I'm not going to worry about the upper edge too much as it's not seen due to the siderail and it's very hard to sand there even with a Dremel. I'm mainly concerned with edges and hills or valleys that won't be filled with a primer coat. It looks like the edge line around the lower part of the sponson shaped up pretty well. I did most of that with a 6" Porter Cable D/A sander and 80 grit paper. I'll finish with 150 grit as it's easier to control and not over-sand.

How NOT to install Tubbie Sponsons.