Want to build a catamaran out of 2 identical 24 foot sailing yachts

Discussion in 'Boat Design' started by Tod, Jan 1, 2018.

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  1. Tod

    Tod Previous Member

    Hi all and Happy New Year

    Il start my first post of with an idea i have been dreaming about for 2 years

    I want to build a catamaran out of 2 identical 24 foot sailing yachts

    note: (This Boat Will Never Sail In Open Water)

    As far as i am aware it has never been done because of the weights and stresses would tear the vessel apart in rough water.

    This project will be moored at the top end of a tidal estuary in Cornwall UK
    and will only be used to stay aboard and summer fun.

    one of these boats has a inboard engine which i will leave in for moving into position around the estuary in full tide.
    The estuary is sheltered by a small Vally however during some violent winter storms we can have a force 3 here but as the tide is in for 2 hours max at spring tides and the rough water is very rare.

    I plan to find strength points from the centre keel and connect 2 steel bars across from boat to boat then find some strength points across the decks of the boats for another two steel braces.

    This I believe is the essential part of the build and will leave them connected for 12 months to see if it holds up.

    After this time has passed and the boats are still ok and haven't ripped each other apart i will then build on the top thats the easy bit.

    So I will wait till winter has passed find a level surface and start my project.

    Any ideas or suggestions are most welcome and i hope with the help from this forums we can be the first to build such a vessel..

    Hope your New Years day is great

    Attached Files:

  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    I think your are grossly underestimating the variables involved with this type of modification. First off, the mono's will have a lot of drag if married in this fashion. The strains will be enormous and just taking a guess, at point loading and cross supports usually ends poorly. Lastly, would be the rig and I'd question if you have the understanding to get this remotely close to balanced as well. In short, this can be done on some mono's, particularly if they're on the narrow and shallow side, but the images you've shown aren't appropriate for this treatment.

    I know I've just "rained on your parade", but this isn't reasonable and does need some serious engineering, if you'd expect not to drown someone, as you're working though the issues.
  3. Richard Woods
    Joined: Jun 2006
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    Location: Back full time in the UK

    Richard Woods Woods Designs

    Why do you want to do that??? Do you already have the two monohulls?

    There are good reasons why it hadn’t been done before. Safety, performance and cost being three

    Why not try your ideas first on say two Wayfarer hulls currently being given away by Hayling Island SC

    I assume you have sailed and built boats before

    Richard Woods
  4. Tod

    Tod Previous Member

    But this boat will never be in the sea just made into a houseboat so no rigging or sailing or moving far the estuary is mostly flat apart from vary rare occasions

    Well I'm sorry but I disagree because even if they was a danger to the stresses actually rating it apart which I've already accepted and said this may happen then all I have to do is move the vessel further up the estuary where the full tide never gets deep enough to float her so thing of it more of a houseboat and not a sailing boat that's going to cut through deep water in the open sea pulling 20 nots in open water forse 6 Gale Thanks
    Last edited: Jan 2, 2018
  5. Tod

    Tod Previous Member

    Another ideas i was toying with is build it with movable struts on ball joints and hydraulic shocks so it absorbs some movement. Additionally once it is moored put every mooring rope on shock absorbers for even more dampening of movement.
    The reason i came up with this idea is i did have the two boats tied together tight with tyres in between to absorb any knocks or bangs for well over a year and they never moved or damaged at all. I do understand that separating them two boat withs in between makes them less stable, So I designed a cage in both hulls to act as a skeleton and give extra strength and also i was thinking of using the skeleton as fixing points across the decks. I wasn't just going to put screws into fiberglass i have actually thought about this. Please let me find my drawing and upload this.
  6. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Simular projects are attempted regularly in the Richardson Bay anchorage north of San Francisco. ALL have sunk before competition. Most become hazards to navigation within a month. If they beach then the city of Sausalito pays for removal, submarines raised be the Army Corps of Engineers, and flotsam collected by salvagers paid by the Coast Guard.

    Who is going to clean up your failed experiment?
  7. Tod

    Tod Previous Member

    Yes i have two identical mono hulls, safety and performance is not even part of the equation as this boat wont ever be in the sea Cost is neither a problem for me either. So why don't i just buy a cat? wheres the fun in that. And yes i have built a boat before i made a sailboat into a strong seaworthy houseboat by chopping the roof off and ripping it all out into a shell then raising the roof by 3 foot to enable standing and walking around inside. I made this possible by taking off the mast, and rigging so the extra weight i saved from the wind blowing at the top of the mast projecting all the weight down to the boat. I freed up.
    The thing is yachts are designed to be bottom heavy and in open sea get thrown all over the place and the forces on the mast pushing down sideways onto the boat can reach almost as heavy as the boat its self thats why some yachts capsize in strong winds. But if you take away the mast the rest of the boat has hardly any top weight as they are sleek and built like a submarine with big heavy steel keels so then thy hardy get any movement at all sideways apart from bobbing up and down in the waves.
  8. Tod

    Tod Previous Member

    I wont be ever in the sea or in a bay or moving it apart from at the top of an estuary where maybe on a lovely flat summers day with the tide in i may change her position of mooring
  9. Tod

    Tod Previous Member

    My design for a internal skeleton to take all the stresses

    Attached Files:

  10. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    I see you are asking for specific sizes and mechanical characteristics on back-of-envelope drawings.
    How can you possibly rely on any guesstimates from a public forum ?

    Why don't you just put some old tyres between the two hulls, and moor the two boats together with mooring lines, and just put a removable pod over both of the hulls, with the outer edges resting on strengthened points on the gunnels. You would get a similar effect as those boarding gangways that move as tide and waves move the boat.

    If you really don't get any severe weather, that arrangement would be the least risky.
  11. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    This is bad but exciting idea.... name the boat 'CATastrophe'.

  12. Tod

    Tod Previous Member

    Fair enough I didn't come on here for abuse. <removed>

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