Restoring hull stability

Discussion in 'Boat Design' started by silverhand, Aug 19, 2011.

  1. silverhand
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    silverhand Junior Member

    I have a 20' Maxim Hull I have selected for a center console conversion.
    http://19maxumproject.webs.com/apps/photos/album?albumid=12099540
    The stringers look ok. Ill clean them up and give them one layer of cloth and move on to a new deck.

    As you can see the hull cap (whats left of the liner) is not suitable for a center console. I'd like to remove the cap at joint where he rub rail is.
    What I want to make is a rolled guwale linerless boat. I know the cap gives the boat a lot of structural integrity. How can I get this back without a cap?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You really need something to brace your knees against that stops you falling out of the boat, particularly when fishing, apart from the structural aspect, which might see your boat twisting and working in a seaway more than before. You could achieve both by using block polyurethane foam shaped to suit, and glassed to the topsides, giving a box girder effect. And the added bonus of some extra bouyancy in emergencies. I'd be going that way if aesthetics wasn't a big deal, as the finish will be a bit rough and ready unless you go to a lot of trouble.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    .......I should add the foam would need to be fully encapsulated in the glass lay-up, and probably need at least a 4lb/cu ft grade to minimize any future water ingress problems. I'm sure someone will be along to torpedo my idea though. :D
     
  4. DCockey
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    DCockey Senior Member

    You might want to ask the moderator to move this to the Boatbuilding forum. This one "Stability" is generally used for topics relating to how far a boat heels when the load changes and similar questions.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Yeah, stability is not the word for it, maybe "rigidity" is what he means. I'd be interested to know what happens around that outboard well, chop that out and you will have a potential for troubles.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Simply, you can strip off the cap and the liner and build what you want. Tab in a new sole over rearranged stringers (if necessary), then make narrow side decks from plywood, covered in 'glass. These are heavily tabbed to the hull shell and greatly stiffen it. Then drop straight down from the side decks with more 'glass covered plywood to the sole or the hull shell. This area can be opened up a little with access holes to store rods, fenders, etc., but it too should be well tabbed the the hull shell or sole. It should have athwart partitions that attach this vertical wall to the hull shell every 2' or 3', which will keep it stiff for little weight.

    Now you'd have a wide open boat. You'd be best advised to make a raised casting deck forward, possably with enclosed boxes below. The plywood casting deck will help reinforce the bow and it's related slamming loads.

    Plywood, covered in 'glass is the cheapest way to get a stiff, strong and water proof interior. You can use other materials, but costs take a huge jump when all is said and done. Don't use thick plywood, nothing more then 1/2" is required, except the sole, which is probably 5/8" or 3/4". The narrow side decks can be 1/4", but most will feel better with 3/8". Locally reinforce under it where rod holders, steps etc. will live. The vertical wall attached to the inboard edge of the side decks and the sole/hull shell can be 1/4" as can partitions in any built in seating, compartments, bait wells, console, built in floatation chambers, etc.
     
  7. philSweet
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    philSweet Senior Member

    The original fuel tank is gone, and it's going to stay gone, yes?
     
  8. silverhand
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    silverhand Junior Member

    i'd never put an old fuel tank back into a new project
     
  9. silverhand
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    silverhand Junior Member

    Glass on both sides or just the exposed side?
     
  10. PAR
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    PAR Yacht Designer/Builder

    'Glass the exposed sides to improve abrasion resistance and waterproofing, but the inside can just be coated with epoxy. I've assumed you'll use epoxy, mostly because it's so much easier for the novice to employ in this type of thing. The plywood provides strength, the 'glass sheathing just weather proofs it. The inside and side decks of a fishing boat take a real beating and just epoxy coated plywood will quickly get dinged and nicked up, which will lead to issues, so skin 'em in cloth.

    The key to this type if modifications is the tabbing (how it's attached to the hull), which should be stout. The plywood will transfer all loading to the hull shell and/or sole if it's well tabbed, but it'll just break out the tabs if it's not. My point is if you're going to screw something up, make sure you error on too much tabbing rather then not enough. Not enough tabbing, is why most production boats have rotten transoms, stringers, soles, etc. They save money by using just enough, but 10 years down the road moisture gets in and rot starts. You can do a much better job, because you don't have a board of directors to answer too, though the WIC (Woman In Charge) at you house may have issue with this comment, so keep it to yourself.
     
  11. silverhand
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    silverhand Junior Member

    yes its been my exp that while epoxy is a lot more expensive its a lot easier to work with. And very strong. I have floored several boats and worked with making hatches etc but never such a major change. I may salvage part of the liner gunwale but I really like the idea you said about coming to the floor with a piece of plywood. That allows for inserting some nice panels for rod storage etc. Do you think poly resin is ok for the floor skin?
     
  12. PAR
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    PAR Yacht Designer/Builder

    Polyester isn't well suited for coating wood. It's not waterproof enough. It's also not very strong, so you have to bulk it up with a lot of material. When you count everything up, epoxy is not "a lot more expensive". Get your epoxy on line from Bateau.com or other reformulator and save considerably over the major brands.
     
  13. silverhand
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    silverhand Junior Member

    Yesterday I saw an old 20' Mako where they had gone strait from the gunwale to the floor just and you said. It looked very clean and left a lot of space. I think they should have maybe done an insert down the sides for rod storage but still it looked very clean and very strong.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    The part of the gunwale you brace your knees or thighs against needs to be further inboard than where your toes are, or it is pretty useless for serious fishing, IMO. A full inner liner you kick your toes on looks good but I had a boat like that once and the only thing that saved it from being a menace was a heavily patterned surface on the sole that gave a lot of grip. And caught a lot of grime. If it was smooth I'd have gone overboard laying into a big fish.
     

  15. PAR
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    PAR Yacht Designer/Builder

    What I like about hull side made this way is the extra stiffness gained when you triangulate the side decks/hull shell and sole together. In a fishing boat, where athwart stiffeners are not available, this is an easy way to provide it, plus storage, plus cut outs for your feet, etc., etc., etc.
     
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