Back in 2004 or so, I purchased a 24 or so foot home made pontoon boat and trailer for $750. It worked ok; but eventually sprung a leak. I checked with a marina operator who indicated it was likely not worthwhile to try to patch the steel pontoons as they rust from inside. We recently drug it out and now I'm thinking about converting it to a dock.

I'm thinking about sandblasting it, then JBWelding obvious holes, then injecting that spray in foam insulation and then possibly painting with Rhino or Herculiner. Anyone out there ever done something like that? Would it work?

If it sprung a leak from rust, even if you patch up the hole, that is a sign that more holes are on the way. I'd check the cost of filling pontoons with foam. It could get real expensive, real fast.

Many years ago I bought an old steel pontoon boat ( it's all I could afford) naturally the bottom had pin holes in it so I put a valve stem into each of the vent caps and would pump air into it, sorta like a submarine blowing it's ballast tanks.

It worked ok but the amount of water in the pontoons would change with the temperature so I kept a hand pump on the boat.
If you pulled the boat up on the beach it would let the pressurized air out but as long as it was in the water it worked.

MAYBE.... use a torch to "can-open" the back ends of the pontoons, preferably AFTER locating a sufficient quantity of heavy-duty, sealable, cylindrical plastic jugs, buckets or drums (5-gal?, 15-gal, 30-gal?) that can snuggly stack end-to-end inside the pontoons. Coat the jugs' exteriors with beads of polyurethane expansion-foam before ram-rodding them; one behind the other, into the thoroughly dried pontoons. The poly should expand and "stick" to the pontoons' interiors - displacing even more water, and keeping the vessels from banging round inside the pontoons. Then, close the "lids" of the can-opened pontoons and tack-weld them into their original positions (without melting the last jug). After the spot-welds cool, poly-fill the non-welded portions of the seams to make them water-tight.

Keep it up Kelly. We'll nominate you for the MacGyver Hall of Fame yet!

Good grief Kelly, you're going high tech. I generally just start cramming old soap jugs in and hope they last forever.

I built a floating dock out of old pontoons. My BIL had purchased a set of 24', steel units from the scrapyard. He had them torched in half so he could transport em', then kept the "bow" sections for himself, for a future mini-houseboat project.

I purchased the "stern" sections off of him to use for my dock. I got lucky, as when the salvage yard workers cut them in half, it left an internal bulkhead in the rear sections, where as he had wide open tubes to try and plug up. I just welded a bead around the bulkhead to seal em' up.

I welded a bung into the top of each half, and installed screw in Schrader valves. I kept the existing drain plugs in the bottoms.

It took a long day of welding seams and holes, then pressurizing, then checking for leaks with soapy water, then de-pressurizing so I could weld up the leak. Repeat scenario umpteen times.

When I was satisfied they were as watertight as I could make them, I painted the pontoons with rubberized , waterproof mastic. I figured the black coloration would cause the air trapped inside to expand, helping to prevent water entry. When you depress the schrader valves on a sunny day, air rushes out.

BUT... about once a season, (I pull the dock out in the winter), I end up carrying a portable air tank over and adding pressure to one of the pontoons, then opening the drain to force the water out. At this point the leak has not worsened, so I am content just to keep an eye on it.

I checked on filling the pontoons with foam. VERY expensive.

Very good info. Thanks everyone! Your info plus the additional research it prompted has me considering options like Kelly suggested as well as possibly just using the pontoon boat as a frame for the dock and using other materials (probably either barrels or regular dock floats) underneath it for floatation. Still thinking. Very glad I solicited your advice!

After more digging, I think I will just get an old aluminum pontoon boat to convert and use it as a dock and as a barge to ferry a mower to the island. I can get one fairly cheaply and easily pull it from the water in winter time.

I haven't totally given up on the idea of utilizing that old steel one with either barrels or floats underneath it for something with theory we just take our chances in the winter.

We are using a pontoon boat we were able to get for $500 as our dock. Here is a link to it:

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=269335#Post269335

I found a 30 foot pontoon boat with trailer, motor, etc. for a very good price; but I found it a smidgeon too late and someone beat me to it.

I found another one and wound up buying it for slightly more than salvage value of the aluminum; but front is pointed instead of square and it is in good enough condition that it'd be a shame to cut it up and reshape.

I'm still looking. There is a good buy up towards Peoria IL of a pontoon boat converted to floating dock; but that is a fairly long drive. Still looking...

Jeff, what's wrong with pointed ends for a dock?

Would like to use the boat as both a dock and as a barge for getting a riding mower to / from island. Therefore, I'd like to mount a fold down ramp on the front to act as walkway from bank and also as a loading ramp.

Re-reading my post. It is the deck that is pointed. Probably better that way for fishing; but not for mounting a ramp.

OK, I see. You're wanting it as a combo dock and barge.