Captain Ahab said:
That loosk really bad ***
How about filling them with 2 part closed cell foam? That way the welding would not have to be as perfect?
Yes, that is definitely an option. But I think you would have to have the majority of the sponson welded out, then put the foam in one end of the tube, leaving the last 8-10 inches of the pipe empty, so that when you weld the end cap in place, you're not setting fire to the foam or melting it.
Having the foam in there would also eliminate some of the flex in the pipe, which would prevent it from getting dented, or the paint on the tube being chipped when it bumps a dock.
The way I had my sponsons mounted was fairly simple, too. Just some aluminum angle clips that fit under the outside edge of the gunwale, and rivet in place. I would also recommend backing that up by having a few clips along the bottom edge of the sponson that attach to the side of the boat. I didn't do this with mine.....but it really should be done, to eliminate the risk of up-pressure (like from hitting waves) from rolling the sponson upwards and tearing material at the joint of the clip and the tube....especially given the material thickness of the tube.
As I said, my boat was very stable with the sponsons. Myself and 2 friends stood on one side of the boat, standing on the sponson, holding onto the T-top, leaning as hard as we could, and we never took a single drop of water over the gunwale.
But, again, the low-slung bow of the boat itself was the problem. The hull of the boat has a reverse flare in it, so when you hit waves, the water is directed out and away from the boat.
With the tubes on there, the water would go right over the top of the sponsons at the bow. I filled the boat knee deep a couple of times like this. Never concerned me, though, because of all the foam board installed between the outer hull and the inner deck. But without the sponsons, I can hit the same waves, and hardly get any water in the boat.
So, despite all the time and effort I put into fabricating the sponsons, I reluctantly took them off the boat. I plan to cut them shorter, like down to 10 feet, put a small deck on it, put a trash pump on there, and use it to 'propel' myself in and out of my channel on falling tides, to keep the channel clear (instead of eating up props and water pumps on my outboard to do it)