adding freeboard to excisting hull

Discussion in 'Boat Design' started by ASM, Sep 10, 2012.

  1. ASM
    Joined: Sep 2005
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    ASM Senior Member

    Hi all,

    I can buy a very cheap 4.75x1.75 m old polyester sail boat hull (see attached picture). I would like to add height to the freeboard (if that is the correct phrase) , so making the sides higher :D. I think this could be done by sticking all around the perimeter a 20 cm high plywood sheet, and use that as a 'mould' or leaving them permenantly.

    The idea is to convert this little boat in a little ' sloep' , jsut a fun day cruising boat for inland waters by motoring and have good seating possibilities. Yes, I know it is a sail boat and not intended for that, but I do not want to go 10 knots and for sure not going off shore.

    Do you think it is doable or nuts ?
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Why do you need more freeboard ? To keep the water out or the people in ?
     
  3. ASM
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    ASM Senior Member

    To keep the people in... to have good seating possibility with good back support, so halfway of ones back and the knees in normal 90 degrees position.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Might be easier to install a lightweight aluminium rail ?
     
  5. ASM
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    ASM Senior Member

    Thought about that briefly, but I dont like the looks of that. When the freebaord is a low as it is now, it still looks too much like a sailboat. By adding ~ 20 cm, I could use that additional height to add a rope all around or a rubber ' bumper' for monkey proof motoring and cover up the seam.... but anyway, would you think it harms the performance or stability ?
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Some cheap, moulded plastic stadium-type seats, easily bolted-on, would be an easy lightweight fix. Back support problem solved.
     
  7. ASM
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    ASM Senior Member

    haha yes you are right.... but I do want a little more pleasing to the eye appeal.. and yes, I am Dutch, so it must cost not more then 10 cents... but looking like a 25000 Euro boat.... I know, impossible task, but one can try ?
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    At best this little boat can hold 4 adults. Moving around in a boat like this, with that much load will be very uncomfortable to say the least (tippy), so keep the seat height as low as practical. A comfortable seat height would be about 400 mm, less 70% of any cushions installed on them. A comfortable seat back would be about 300 mm, though you can use much less if well padded and shaped, say 200 mm. So, a total height off the sole of 500 mm isn't really raising the freeboard very much and most if not all of this could be done with just an angled combing, forming the seat backs.

    Do some simple scale drawings and vary the seat back height as required to fit a pleasingly shaped combing. This way you don't have to make new, raised hull portions, just install some seat backs. She'll motor efficiently with a small engine.
     
  9. philSweet
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    philSweet Senior Member

    Looks like a good project. I'd shift the seating area forward a foot from where it would be in the sailboat. Powering a boat pushes low and raises the bow. Sailing pushes high and trims the bow down. So you can shift the weight forward some to compensate. The outboard and fuel and battery will weigh down the aft end more than a sailboat kicker also. I'd do like PAR said and just build a comfortable cockpit with lowish seatbacks that form a coaming inboard of the sheer and put a narrow wood sidedeck connecting the coaming to the sheer. A single sheer plank running the length of the boat can keep the sheer looking sweet. Just bolt it to the outside of what you have and install a rub rail on that. I'd probably carry the sidedeck forward as well if you aren't planning to deck over the bow area. The only real issues are ensuring your passenger's knees don't knock together. Sailboat cockpit footwells are sometimes too narrow. I guess they figure everyone will be on the same side of the boat. If you plan to have a folding or removable table, that changes the seat design quite a bit. And be sure to figure any backrest cushions into coaming spacing calculation.
     
  10. ASM
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    ASM Senior Member

    Thanks PAR and Sweet !
    I might electrify the thing and add a keelbox for batteries.... but I for sure will take a good look at positioning the seats. The tip on the weight distribution is good too, never thought of that.
     
  11. jonr
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    jonr Senior Member

    Add inflatable tubes and it could look like an expensive RIB.
     
  12. PAR
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    PAR Yacht Designer/Builder

    Skip the electric stuff and have fun.
     
  13. messabout
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    messabout Senior Member

    Par made the most useful recommendation. Keep the seats low for much better stability.

    There is no accounting for taste but for me raising the sheer will make the boat look clumsy. It is very pretty as it is. You could add a surry top to give it some additional character if you like.

    (surry top: a flat canvas cover above the heads of the passengers, perhaps with some scalloped edges. The whole of which is collapseable for storage and transport)
     
  14. ASM
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    ASM Senior Member

    Yes I will try to keep COG low... I asked for better side pictures and then sketch some additional sheer on it just to see what it looks like.... Am I that stupid in saying that if you ' overload' the boat, she will sit lower in the water and that is all ? (so if sheer addition is watertight, I am safe anyway ?
     

  15. PAR
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    PAR Yacht Designer/Builder

    Simply put, raising the sheer will be a lot harder than just attaching a seat back/coming that offers enough support and effectively raises the freeboard. I don't understand you fixation on raising the sheer. Have you mocked up where people will sit and the seat back heights necessary? It's a lot simpler if you do this on a scale(ish) drawing at the kitchen table, then on the boat.

    The boat was already capable of containing a crew, within it's confines. Again, if the sole is kept low, the need for freeboard would be a matter of a few inches, which can be easily handled with a hunk of 1 by stock, serving as the seat back.
     
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