Trail-able 'no-fold' Catamaran 7.5 x 3.6 coastal cruiser

Discussion in 'Multihulls' started by Itsallaboutthebuild, Nov 10, 2017.

  1. Itsallaboutthebuild
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    Itsallaboutthebuild Junior Member

    Thank you for the feedback, just to clarify some presumptions, It is a sailing cat (1350kg) and the trailer/rotary frame has been completely costed/weighed and comes in at 1490kgs. the 'bearings' are actually hardened pins and bushes, similar to heavy earth-moving equipment.
    In Queensland the Transport Department allow a 2.5 wide and 4.3 high trailer to be towed without extra permit, providing the tow vehicle is licenced for the weight (most 4wd vehicles these days are good for 3.5T).
    Having said that, the other points raised are certainly ones that I also have pondered over.
    I definitely wonder what it would be like to tow.
    The packing/unpacking will be extra work, but in the overall scheme of things, not a reason for abandonment.
    I think the lack of assembly time as per the de-mountable hulls more then makes up for the pack/unpack.
    Richard Woods folding cats are a great idea and end up with a wider beam, but no easy step entry into hulls from the saloon.
    The complete outfit is most definitely not a daily drive, but rather a solution to ownership of an affordable coastal cruising catamaran that can be kept safe at home for the majority of the year, then towed to the coast and moored or berthed for a season of sailing. With the benefit of a good beam to length ratio that will be more stable then the normally towed cats, good accommodation for 4, full standing height in the hulls where galley and separate shower/head are located, and comfortable sitting in the saloon.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Side winds , especially on high bridges, e.g., will be a real worry. You'd have to pick a calm day before doing anything like that !
     
  3. fallguy
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    fallguy Senior Member

    Pins and bushings is definitely the way to go. Bearings = trouble.

    The Skoota 32 demountable cat doesn't have step entry from the salon into the hulls either. You can enter the hulls via steps from outside to gain two single bunks. But it is a two trailer or semi transportable boat and rather large to move without some crew or mechanisms. I see the separate entry as a plus for privacy. Only thing is I will need to make sure no one can fall overboard from the singles.
     
  4. hump101
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    hump101 Senior Member

    I've towed similar sized loads quite a bit (7.5m long x 4m high x 2.4m wide). Similar mass too (3500kg), but with a lower centre of gravity than your proposal. Side wind wasn't the biggest issue, even though you would think so, and it can get scary in a big gust. The biggest issue is sudden changes in camber causing rapid rolling forces, which can put enormous side forces on the structure and could overturn the trailer in the extreme. The way to overcome this is to look way ahead as you drive, and go slowly over camber changes or round bends to reduce the roll rate. If you know the route you'll be taking and can safely reduce speed when required, then this should be do-able. I would engineer the pivots so the cat can be dropped as low as possible once on its side (separate suspension units?). I would agree with Guzzi3 that the trailer weight seems excessive, so you might want to revisit your structural calcs on that one.

    However, I have to ask why you aren't looking at a tri instead? For the same material you can build a 10m tri which will sail better, give 3 separate sleeping areas if you have an aft cabin, and act as a camper when on the road. Easy to engineer folding or removal of the floats with a custom trailer, and the CoG when towing will be half as high, or less.
     
  5. guzzis3
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    guzzis3 Senior Member

    What hump101 said. ^^^

    I'm a mechanical engineer and while I haven't calculated your job properly 1400 kg is about twice what it should be. Bushes will be fine, rolling element bearings a disaster.

    Consider carbon epoxy and resin infusion. If you want to swing a bridgedeck cat about in the air and run it down the road the significant weight savings are well worth while and the cost isn't ridiculous.

    Mr Woods clip on cabins only give 5' headroom in the hulls of sango, but you could make higher ones for 6' and still be under the silhouette of the cuddy cabin. Ok you have to leave the central cabin to enter the hulls but you've got a 25' x 15' boat that launched in maybe an hour sails like a demon trailers ok and weighs 900kg. It too uses a mechanism on the trailer but it's not as difficult as what you are proposing. I understand the advantages of full bridgedeck cabins but in that size they are always claustrophobic, and of course the 3 separate cabins give real privacy like you absolutely won't get in any other config in that size.

    Demountable tris might be worth a look, the folders require extra work, and tris are not everyone's cup of coco...you would need 30' plus to get the sort of accommodations you want and they don't come cheap...

    Anyway whatever you decide best of luck.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    No way you are going to have a 25' boat trailer with the extra complications involved here, that weighs anything like 700kg.
     
  7. fallguy
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    fallguy Senior Member

    A 25' Venture aluminum base trailer here in the states is listed as 1050# with a cap around 5925#. But the turning apparatus would probably need to be fairly beefy, so I am thinking he can probably get close to the 700kg number, but doesn't this require hydraulics and battery or gas hydraulic engine, etc. Might be a bit more than 500# add on for the parts. But add in trailer reinforcing; I'd say he can still get it done within trailer limits; even if you are right.

    I still don't like it very much as it seems super tippy to me. The first time you hit a curb with that thing; you're gonna need a change of underwear. To be fair; there is probably an engineer around that can tell you just how high one side can be versus the other before it flops over, but that would include any side grade, etc. Then add in a force for speed, wind, etc.

    I have seen boat trailers here in the states that lift one side of the boat with hydraulics to get some beam, but usually those boats have low head height.

    I'd opt for a different cat.
     
  8. hump101
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    hump101 Senior Member

    My 3500kg twin axle 8m trailer weighs 550kg. 700kg without my supports but plus the OP's stuff is a bit of a stretch, but no way is it going to be double. 800-850kg sounds about right, without doing any calcs.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    No point in trying to lighten it anyway, with the "high rise" load, some "ballast" down low is an asset.
     
  10. hump101
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    hump101 Senior Member

    Agreed, but you don't want to calculate the load lateral stability assuming a trailer of 1400kg, and then actually drive with it at 800kg.
     
  11. massandspace
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    massandspace Junior Member

    Do not think that you will be able to "launch" in 30 minutes....??? And the engineering/loading is problematic.....

    Seems making a cat "easily" trailerable is not "easy". Noticed threads on a smaller "demountable" power cat recently that was meant to be disassembled for "easy" transport, but instead was trucked full beam for a non-local trip.....I also tried and failed to make such a cat many years ago....not really sure it is possible...
     
  12. fallguy
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    fallguy Senior Member

    Yes, this is all valid. The part that gets tricky is lifting the cabin up. If you can get lift assistance from a trailer, the Skoota cabin can be lifted without a crane. But if you have to count on a crane service; suddenly you are on someone else's schedule. And despite the owner's desire to not fiddle with the demounting part; the boat is still technically demountable for transport. And avoiding a wide load permitting process across the 3000 mile US is a big deal. The person you mentioned lived in the PNW and if they moved the boat to FL; the rates for a wide load would have been rather high. I believe they moved the boat to Texas and water hopped the rest to save money on the haul. If they got a good deal moving the wide load versus moving the demounted boat; why not? If you put a value of $1000 on dismounting the boat; you try to win that in budgeting, right? Why would you not move the boat wide if it only costs you $900 additional dollars against the value of $1000?

    For my Skoota build, I already plan on using electromechanical gear and shift so I can unplug a wire to move the boat. The steering is quick connect hydraulic.

    There is nothing easy about moving demountable catamarans, which is why I suggested the folding 24.

    However, I got a quote from a reputable marine hauler to move a 5 meter beam boat from Minneapolis to San Diego and I got the corporate move rate. $55,000 ! They assume my company was moving me and my personal belongings and could name a price, so it wasn't shopped, but had a bit of reality.

    Consider for a moment, a guy like me who wants to do the Inside Passage someday. I can arrange for my vessel to be transported via semi to a port on the West Coast and arrive there to oversee the put together and spend 8 weeks running up and down the coast. Then if I live in the Carolinas, I can go home and so can my boat. It was all still cheaper than renting or buying a boat. I get my systems, my fuel economies, etc.
     
  13. massandspace
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    massandspace Junior Member

    It's all about the costs...financial, timewise, emotional, etc.

    But in the end why build a boat that "costs" the same to demount (however you wish to define the term "cost") as it does to trailer it wide???? And having the ability to move from the cabin to the hulls is almost impossible with a demountable...

    Electromechanical gear/throttle control for outboards available only in the larger size engines.....I did a lot of research on this....not available for smaller motors, unless homemade....but that also would cost a lot and be prone to saltwater intrusion into the components which would most likely be made for non-saltwater use....

    Anyway, I too failed at an earlier attempt to build a "demountable" cat, so I cannot claim superiority....I just think it is impossible to build an "easily" demountable boat in the size range being discussed.
     
  14. fallguy
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    fallguy Senior Member

    I already agreed and said it wasn't easy.

    The demountable cat I am building is the Skoota 32 DM by Richard Woods.

    If I demount to move it two times in its life; it will be a success.

    i7700 seastar is an actuator that will reduce the work involved in setting up cables, but the cost is horrid at $4800 it approaches the motor costs, I still plan to use it. I am going to install them inside a box and rubber grommet it out to protect it from the elements.

    there is no electronic steering for cats that makes sense in the smaller motor range I am using~F70 Yamaha.

    I doubt my build will fail; there is only one issue that is bothering me on the entire build right now. Richard is supposed to be looking at it. As for whether we demount it very much; that will be another story. Was the design your own when you failed?

    I guess you can pm me if you like. This is becoming a hijacking by accident.
     
    Last edited: Nov 12, 2017

  15. guzzis3
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    guzzis3 Senior Member

    A DEMOUNTABLE boat in this size range is certainly doable and has been done many times. That problem is sorted. Racers as long as 12 meters/40' have been built slim and long and trailered.

    A FOLDABLE catamaran in this size (25' the OP) has been done and is well proven.

    Where it gets tricky is when you don't want to do any assembly and insist on a full width bridgedeck cabin. The cabin btw can be made 8' long, detached from the hulls and rotated 90 degrees but then you've got an assembly problem again.

    The problem with the origional post was a single structure at all costs and the solution to that is the 90 degree rotation. If you compromise on the lines for a 45 degree rotation to get within width most of the problems go away. That is what KH is doing with the 8 meter, a boat at least as big as the OP suggests which can be trailered at 45 degrees. A very nice solution and well worth watching.

    Everyone wants a trailerable cat, and much thought and work has gone into them. EVERYTHING has been thought of. EVERYTHING is a compromise somewhere. Pick your poison...

    As for the trailer weight as I said I hadn't done the sums. Maybe it won't be 700 kg but it won't be 1490 kg either. That is ridiculous. You may choose to use hydraulics or whatever, but it's a simple leverage problem. You don't need speed, it needs to be waterproof if it goes in the drink. It needs to have enough leverage to lift the weight. Every lever problem has the same issues, it's trivial. A 45 degree lift is orders of magnitude easier. You can probably do that with a trailer winch.
     
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