Drive Hull Female Mold & Layup

Discussion in 'Fiberglass and Composite Boat Building' started by jangr, Nov 22, 2018.

  1. jangr
    Joined: Nov 2018
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    Location: Chesapeake Bay

    jangr Junior Member

    Gonzo - my original sketch was for batteries on deck, solar panels overhead, and an electric outboard. Taking the panels down, and mounting the batteries in an easily fabricated pod, would certainly be much, much simpler than adding an actual hull. The issues started to pop up when ran my buoyancy and load numbers. Without the buoyancy of an additional hull, I was left with only 165 lb payload. I'm not a big guy, but as soon as I stepped on board I'd be overloaded, before adding any appliances or product on deck. Even with the current loading, I'm considering replacing the AGM battery pack with lithium ion, which would save ~400lbs.

    Kapn - if I were to go with a lighter battery pack, I could actually cannibalize a canoe for a drive hull. A canoe would eliminate the challenge of a bow section, as well as keel, bow, and stem butt joints, no CAD/CNC required. So instead of building a mould, and laminating a hull, I could proceed directly to the hull stage. I could then reinforce the keel for shaft log and strut, and laminate 'ribs' to provide a foundation for motor and battery stringers. It wouldn't need to be pretty on the inside, and I'd have a nice, fair hull form on the outside. The one issue is height. I need 25" from keel to deck, but a standard canoe is only 14-15" to the gunwale. I'd also have to cut down, or make up, the sheer along the gunwale to end up with a flat flange underside the deck. Thoughts?

    Fall - Very interesting post, thank you for taking the time to include so many details and an image. I like the idea of a bulkhead well back of the stem and a separate stem mould. Makes a lot of sense. That said, it looks like you have continuous planks step to stern, how long is this hull, and what did you use for plank material? Also it looks like you using a batten and foam method to are actually laminate a mould, building up from the inside, using the planks as backing rather than the mould itself. Is that correct? I'm actually trying to do the opposite, using glossy PVC bonded and glassed to frames from the outside, leaving the interior mould smooth and fair from the beginning, notwithstanding the butt joints.

    Wet - Thanks for the clarification, that makes sense.
     
  2. kapnD
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    kapnD Senior Member

    It would be easy to build up hullsides of a canoe, and incorporate flanges into that.
    Remove the rub rail, then screw sheets of melamine to the canoe hullsides that you can layup against.
    Cut the melamine to fit your under deck, and screw on a flange on at the top,
    Add motor stringers, battery supports, and reinforce area where shaft log and rudder will lie.
    On reflection, the center hull need not be a canoe, any small skiff, dingy or sailboat hull will do, and will eliminate the problem you are creating for yourself.
     
  3. fallguy
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    fallguy Senior Member

    The picture I offered was meant for tips; not an end all.

    The picture is a 32' cat hull, with 12mm core and a solid glass vee section forward. The vee section was built using two layers of 3/8" plywood; so I could walk on it as needed. The sides are vac panels. And the entire thing is in a cnc female jig with ribbands/battens.

    All that said, you could so something similar and lay glass into a radiused mould. More than one way to skin the cat, but reducing exterior fairing would be my focus; so female.

    For the picture, we laminated three layers of glass into the vee; the core had a rebate and I laid a piece of plastic into the mould for n aft each side. This allowed for a tape. When we flipped the hull over; we filled any errors and taped the seam and laminated two more layers glass on the outside. The fairing wasn't bad, but I had a high spot in the canoe mould to fill on flip.

    The project has similarities. If you finish short; a 3mm deep tape rebate on the hull and on the nose would be a nice help versus all fairing. 3mm is enough for a couple tapes. The size is also somewhat close.
     
  4. jangr
    Joined: Nov 2018
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    jangr Junior Member

    Kapn, you've opened up a very different set of possibilities here, along with a new set of challenges for me to figure out. You're basically suggesting an economical DIY, e.g a Franken-hull.

    Not sure a flat-bottomed canoe ~32" at the beam is quite the right choice. A buddy of mine was given a free 16' vee-hull runabout, all beat up and cut up inside, no console, someone else's abandoned project. Based on your suggestion, I could get out the trusty Sawzall and carve out the bow and an adjoining keel section to 24" wide x 25" high x by 12' long. I could then form up the hull-sides, transom, and flange. This would also give me parallel hullsides, which will be simpler to thru-bolt to the new rectangular deck framing and hatches. That leaves a few questions that someone here can probably answer.

    How to treat the joint between the existing hull fragment and the new hullsides and transom? Should I feather the edge back with a grinder and overlay glass? What material is best, polystyrene, vinyl ester, or epoxy? Are high-strength fiber fillers useful in all these materials? What layup will give me the strength I need in the hull, particularly at the joint of the hull fragment and also at the flange? Do I wax the melamine or similar before screwing it into the hull, and just peel it away when the lay-up is done? What is the easiest release agent to use?

    Many thanks for this suggestion, hopefully someone can help me with some of the details.
     
  5. fallguy
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    fallguy Senior Member

    If you are doing the Frankenstein thing, only use epoxy for secondary bonding. It is much stronger. For moulds and release, I have never had any trouble with PVA Partall. I use the Partall Paste wax #2 on the mould first to fill any imperfections and then I spray on Partall #10. You can buy a roll on partall if you don't have spray equipment. Someone on the interwebs says to use the wax over the top of the #10 - I would never be able to do that, so I'm not sure how it would be done. My #10 layer is pretty thin and parts readily from the mould if you bump it, let alone rub wax on it.
     
  6. ondarvr
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    ondarvr Senior Member

    People always ask "what's the best" in this case it would probably be epoxy and S glass, but if you're asking what will work and hold up for many decades, plus fit well in the budget, then even polyester and typical glass is fine. Many large commercial fishing boats and yachts get extended (lengthened) every year with nothing more than the basic materials. Using a VE for the initial bond to the old parts would be an upgrade, but depending on the design it's probably not required.
     
  7. jangr
    Joined: Nov 2018
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    jangr Junior Member

    Thanks Fall and Onda. A few pictures might makes things clearer and sour some discussion...

    The barge to be, a freebie I've now stripped to the frame -
    file-7.jpeg

    The donor hull, an unexpected freebie ready for surgery -
    file1-2.jpeg

    Donor hull looking aft, glass exposed -
    file2-2.jpeg
    Here is the process I'm thinking for the Frankenhull, comments welcome and appreciated...

    Flip the hull over and cut out the center portion with a Sawzall, over-sized by two or three inches, say 27" across the beam instead of 24". Flip the remains back up and onto a flat surface, shim it to level fore and aft along the keel, and plumb through the center line. Mark a point on the stem 24.5" tall from the flat surface. Run a laser level across the remains and cut the bow down to the level line. From this point onwards I have some choices.

    I was going to screw in some timber along the new chine to stiffen the remains, and to give me something to screw the mould panels into. Until then it'll be a floppy mess, and if I crack it before I can form it all up, I'm screwed. Then why not epoxy the chine timber permanently with structural fiber/filler, then square up the outside face to vertical? Staying on that thread, could I save a boatload of resin by creating an external frame for foam core and battens, laying up first in the hull interior? I know I wanted to avoid fairing, but I'm thinking a core build would cost less and go faster. Or maybe even a plywood core. Fewer glass layers, less resin, etc, etc. Thoughts?

    My only concern with this donor is that the square chine and flat bottom when I'm done may create some unwanted lift. At 6 knots, is this likely to be an issue, putting upward pressure on the center of the deck and cross frames aft? Should I make the hull narrower than the 23" diameter pontoons, to compensate somewhat? How much narrower?
     
  8. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    There's all kind of splashing going on under a pontoon boat so you'll have to seal up the spaces between the top deck and the top flange of your 3rd hull, otherwise the new hull will fill with water pretty fast.
     
    Last edited: Nov 27, 2018
  9. kapnD
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    kapnD Senior Member

    The donor hull can be anything that floats and will fit between the existing pontoons, I’d not get too carried away with perfect fit and lines here, after all, you’ll be doing very well to even achieve hull speed in this rig, and it seems more important that it floats upright than spending tremendous energy and money on a perfectly dimensioned center hull that is still slow.
    If you’re going to use the hull you show, use the entire hull, if it will fit between the pontoons.
    If it must be cut down, take a section out of the middle, then reglass the two halves together.
    Just glass a flange along the top line, if it’s a little floppy initially, not to worry, it will become very rigid when bolted up to the deck beams.
    The flange can be glassed in prior to cutting down the freeboard, would help the hull to hold its shape.

    I must reiterate that in any hull configuration, including just the original two pontoons, it will handle like crap with a low powered single straight shaft/spade rudder configuration.
     
  10. jangr
    Joined: Nov 2018
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    jangr Junior Member

    Agree. Fore and aft the drive hull will be sealed below deck, while new framing above the flanges (in orange) will seal the motor and battery/shaft log compartments. Both compartments will have watertight hatches at deck level. Hope that makes sense.
    Pontoon Drive Hull 112718.jpeg
     
  11. kapnD
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    kapnD Senior Member

    Another full hull is being added to an already very buoyant craft, the displacement numbers have been crunched, all good.
    This is not an ocean going yacht, sealed decks?
    There should be plenty enough electricity onboard to power a bilge pump that will easily handle splashes!
    I would not waste one drop of epoxy on this, polyester is more than adequate.
    Are you guys are intent on draininG the OPs wallet?
    There are discussions on this forum that talk about hi speed, hi tech, lightweight futuristic craft, but I don’t see this barge as fitting that category.

     
  12. jangr
    Joined: Nov 2018
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    jangr Junior Member

    The donor hull will certainly need to be cut down. I was going to try and retain the keel and bow intact, then glass up new hull sides and a transom from the inside against a vertical mould surface. A little target fixation on my part, wanting to keep the production bow shape intact, and not considering the labor and material needed to fabricate new hull sides.

    You suggestion leaves a single seam along the keel, which could be reinforced the same way I was going to treat the two chines. This could be done practically by propping the hull up on it's side and marking my cut lines either side of the keel with a laser level. It'll still be a trick to get two identical halves, but I should be able to get close. I can fix the gunwales to each other with temporary stringers while I glass the inside of the mated hull along the keel. The mated hull should then be stiff enough to flip, then mount the shaft strut, cut the shaft log entry, and fill/glass/fair the new keel line up through the bow stem. Last step would be cutting the freeboard down to size, leaving the flange surface for last. Does that sound right?

    Lastly, would you please help me better understand the issue of using a fixed shaft & rudder vs outboard or I/O, both of which are now in use on pontoons? Pontoons handle like crap under the best conditions, how is it any worse with a fixed shaft and rudder? I can't imagine it's a power issue. These boats came standard with a a 35 or 40HP back in the day. Low speed maneuver dockside or otherwise is just above idle RPM, no more than 10HP (if that). My RPM/torque/prop spec will deliver 300 lbs of thrust for 3000 lbs displacement, which seems adequate to tool around at 5 or 6 knots, or to maneuver and land with reasonable control..

    If the issue is how poorly pontoons track in general, I could add a narrow 6" or 8" keel fore and aft of the shaft log, without creating too much drag. Would that be useful? What is it about redirecting thrust with a rudder that is so different? I'd really value your insight, and any mitigation that might be possible, assuming this remains an electric boat and that I'm limited to 5-7Kw of power, outboard or inboard.
     
  13. jangr
    Joined: Nov 2018
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    Location: Chesapeake Bay

    jangr Junior Member

    Thanks Kapn, I appreciate the interest on $$$, especially since the 'electric' part of an electric boat is always pricey. I'd like to keep the remainder of the build reasonable. That said, I inherited an epoxy-bias from my dad, though it was a religious discussion in my family generally. I suppose I could use polyester just as easily, I just don't have much experience with it, some anxiety there. And I should clarify on the hatches, I'm not going to be installing Bowmar hatches here. Thinking just a 4" x 1/2" strip of coosa around the edges with a plywood and glass cap. Or even just a removable section of 3/4 deck supported by a stringer around the edge.
     
  14. jangr
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    Location: Chesapeake Bay

    jangr Junior Member

    And yes, there will be a bilge pump. Never met a shaft seal that didn't leak or fail at some point.
     

  15. kapnD
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    kapnD Senior Member

    The issue with the rudder is not so blatant at cruise, but it will be ungainly at slower speeds, esp in a crosswind.
    The biggest drawback is control in reverse, where there’s no prop driven flow over the rudder to push the boat in the direction you need to go, so it will prop walk until enough speed is gained for the rudder to have some effect.
     
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