Marrying Lifeboats Up - The Push Me Pull You

Discussion in 'Fiberglass and Composite Boat Building' started by BoatRenovationPeople, Aug 26, 2021.

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  1. BoatRenovationPeople
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    BoatRenovationPeople New Member

    Hello folks, new to the forum.
    I'm sure it's been covered but I'm interested in the possibility of taking two GRP 30ft life boats, slicing them up into 1 hull. Have people tried similar things, obviously there are major structural considerations, buoyonancy and weight distribution at play. Feel free to tell me I'm a fool.

    I've rebuilt boats from composite core in the past, it's more the other elements. Use would be a live aboard, occasional cruiser, coastal.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You mean splice or slice ? What are you proposing ?
     
  3. BoatRenovationPeople
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    BoatRenovationPeople New Member

    It would have to be chopping the bow of one and chopping the stern off the other. You'd loose overall length but you'd still end up with an ample base for a live aboard.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Do you have a picture of the boat ? You would need parallel lines to join together cleanly.
     
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  5. BoatRenovationPeople
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    BoatRenovationPeople New Member

    I could deal with some slight discrepancies but ultimately they'd need to marry up well yes. I'm just in the research stage - just seeing if its viable. Have the access to space, cranes etc and a good amount of experience with composite. I can imagine the pain in the *** would be cutting through a keel.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I think the joining is more difficult than the cutting, if you have something that has a long constant hull section it might work out, otherwise not.
     
  7. bajansailor
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    bajansailor Marine Surveyor

    Lifeboats are usually quite tubby things, so would it be feasible to simply chop one in half amidships, and then add a length of parallel mid-body?
    This would give you more room inside, and also make the boat effectively skinnier, with a higher L/B ratio.
    Would you keep it as a motor boat, or would you want to put a sailing rig on it?
    Be aware that for the cost of buying a lifeboat and the cost of the materials and labour to do the conversion work, it would probably be much easier / cheaper / less stressful in the long run to simply buy an existing boat that hopefully comes close to what you want your boat to be capable of achieving.
     
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  8. Mr Efficiency
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    Mr Efficiency Senior Member

    The typical lifeboat isn't designed for much in the way of long distance motoring, just safe custody of people abandoning ship. They are quite stubby-ended which helps with internal room and overall stability. I guess if they are built with a long constant section, it lends itself to grafting two together, better than most boats, but the end result is always going to be not quite ideal for purpose, unless the purpose is not too demanding. Perhaps you should define the intended use.
     
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  9. gonzo
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    gonzo Senior Member

    The sides are not quite parallel and the bottom isn't horizontal. Joining them will let you with a useless piece of bow and stern, and a lumpy hull. The longer hull will have increased stresses that may exceed the original design. Further, it will cost you more than buying a 40 foot boat ready to cruise.
     
  10. DogCavalry
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    DogCavalry I aim to misbehave.

    In the absence of a sizable parallel midsection, splicing boat to increase LOA is not theoretically possible.
     
  11. TANSL
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    TANSL Senior Member

    I assume you are talking about the longitudinal strength of the ship-girder. If so, keep in mind that boats of such a small length are very unlikely to have problems of this type. That would probably not be a reason to discard the job. The modulus of the main transversal section should be checked and, if there is such a problem, it can be solved by adding some longitudinal reinforcement. It has been done many times.
    It may be possible but, probably, it does not look very pretty.
     
  12. DogCavalry
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    DogCavalry I aim to misbehave.

    Actually TANSL, I'm referring to the joint itself. Imagine joining 2 eggs to make 1 longer egg. The connection can't be made fair or strong.
     
  13. TANSL
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    TANSL Senior Member

    Not fair but strong, why not?
    In any case, I would like to see drawings of the boats to give a more authoritative opinion.
     
  14. DogCavalry
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    DogCavalry I aim to misbehave.

    I'm visualizing an unmanageable concentration of stress at the sharp concave intersection. I suppose with enough epoxy and cabosil it might get a large enough radius to survive, but it seems a bad idea.
     

  15. TANSL
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    TANSL Senior Member

    I would like to see drawings of the boats to give a more authoritative opinion.
     
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