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PVC Pipe Pontoon Boat

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Homebuilt pontoon boat / double-hull kayak
made from
PVC Pipe, foam insulation and vinyl siding.

 

Design goals (not necessarily in order):

Cheap, simple and fast to build
Stable, safe, easy to re-mount from the water
Zero or near zero maintenance
Better hydrodynamics than 1-2 person pontoon bass boats on market
Propel with paddle, electric (12v) or gas
Able to evolve -- easy to modify in future

Design basics:
Dual hull kayak with deck between hulls
Frame - PVC pipe, 3 inch diameter
Floatation - pontoons made of 2 inch insulating foam cut to shape and stacked
Deck - 4x8 ft x 1/2 inch exterior plywood (heavy, but cheap)
Length = 10 - 11 feet
Width = 4 feet
Propulsion - double paddle, 12v trolling motor or small gas outboard

 

Drew rough plans modified over several months for strength and construction simplicity.

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Cut 3 inch PVC pipe to size with power mitre saw. Fitted and glued pieces flat on concrete driveway for reasonably decent alignment.

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Bow and stern crosspieces were glued to elbows flat on driveway and allowed to dry completely before joining them to pontoon frames. This insured that all vertical pipes would be acceptably close to square (90 deg from horizontal). Vertical pipes are spaced to allow 3 on each side to catch 8 ft long deck.

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Deck holes were cut extra large to allow easy fitting and plenty of wiggle room for alignment later. Plan is to fill gaps between deck and PVC pipes with epoxy / glass / putty once deck is installed and aligned.

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Cut cardboard templates from discarded boxes and assembled them with hot glue. (Note: hot glue is HOT not warm; on skin, think arts-and-crafts napalm.) Templates were made 11.5 inches wide to allow four pieces to be cut from 48 inch wide sheet, since some foam is lost to soldering gun.
Pattern was transferred to foam sheet by tracing template with felt tip marker.

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Pontoon layers were cut from sheets of foam insulation using an old yard sale soldering gun. This was slow, tedious work as soldering gun didn't seem to get very hot.

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Stacked cut foam pieces in place after applying silicon caulk to surfaces of each layer to help keep them in place. Filled space in oversized holes around each vertical pipe with spray foam. Strapped layers together with strips of fiberglass epoxied in place (note brown vertical stripes). Cut excess spray foam around vertical pipes flush to surface after it dried.

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Made deck from 4x8 ft sheet of 1/2 inch exterior plywood painted with white roof paint (water resistant, UV resistant, cheaper than house paint). Reinforced it with aluminum box tube bolted to plywood with 1/4-20 galvanized bolts.

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Put deck in place and completed pipe frame. Sanded paint from bottom of deck where it contacted foam pontoons and applied epoxy resin to contact area. Filled holes in plywood around vertical pipes with epoxy resin mixed with cooking flour to form thick paste, then applied several layers of fiberglass strips soaked with resin.

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Detail of fiberglass & resin collar around vertical posts through deck.

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Used sheet metal snips to cut plastic (vinyl, PVC?) siding to approximate shape of pontoon points. (circular saw, bandsaw or jigsaw might've worked better, since snips didn't steer well in this material.) Ragged edge is ok, as fiberglass tape / epoxy will cover flaws.

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Good new is, just happen to have a stack of scavenged "slightly used" plastic (vinyl / PVC?) siding. Bad new is, the edges of the layers of foam making up the pontoons are too rough / uneven to allow the epoxy resin to form a good bond to the siding. Need something that'll adhere well to both the foam and the siding, that won't drip or run, and that will easily fill gaps between the uneven foam and the smooth siding.
Looked into construction adhesives (Liquid Nails) and glue specifically sold for foam (PL Foamboard Adhesive) but both carried warnings against immersion in water. Checked out the roofing department of Home Depot and found a few adhesives that claimed to be waterproof, but they all said not for use on foam or plastic.

The closest thing to a foam / plastic safe waterproof adhesive seems to be silicone caulk. Not sure if it'll work, but applied lots of caulk to inside face of siding then tacked them in place with nails and bits of wire (that's what all those holes are for) until caulk cured.

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Applied strips of fiberglass with epoxy resin to seal joints between pieces of siding. Added additional layers of fiberglass & resin, averaging 3-4 layers for most joints, more where abrasion from launching and landings might be an issue.

Note: used epoxy, not Bondo, as Bondo melts fooam.

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Added PVC molding to joints in areas where abrasion seemed likely.

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This is during the process of glassing all the joints. Also applied lots of "putty" made from resin and cooking flour.

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Bottom view of the completed pontoon boat. Repainted top & bottom of deck with white roof coating. Painted pontoons with roof coating too, mostly for cosmetics, as epoxy resin had turned brown for some reason.

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Bon voyage!

 

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