Road Trailerable Large Blue Water Cruising Multihull

Discussion in 'Multihulls' started by Skint For Life, May 17, 2011.

  1. Skint For Life
    Joined: Jul 2010
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    Skint For Life Junior Member

    Hi all,

    I have started this thread to try to tie together a few ideas I have, I've talked about some here:
    and some here:

    I feel I have written titles and 1st posts that restrict the flow of ideas too much. I also feel I haven't voiced some of the things I would like to achieve in a concept I have so I'm starting fresh with this thread.

    This thread is to discuss and to try and design a "Road Trailerable Large Blue Water Cruising Multihull"


    A cruising multi-hull design (wind powered)
    Within NZ trailer regulations 12.5M long x 2.5M wide x 4.25M high, 3.5tons (trailer and load)
    Max volume and accommodations within the trailer limits.
    Shorthanded sailing ability.
    Comfortable accommodations for four people.
    Safe blue water cruising
    Fully liveable whether in the ocean or parked up in a camp ground (living areas must stay upright).

    I will update this thread with my latest designs, occasionally I may add some of my previous designs.

    I want everyone to realise this thread is to discuss and to try and design a boat to fit the above criteria, said boat doesn't have to be conventional, pretty etc.

    I will probably refer back and forth to my designs, so I'll name them things that are hopefully easy to remember.

    Let the ideas flow :D:D:D
  2. Skint For Life
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    Skint For Life Junior Member

    Kung-fu/Airbag Catri-maran

    Kung-fu/Airbag Catri-maran

    This concept is basically a central accommodation hull with inflatable outer hulls, the central hull is out of the water on flat water, with only the centerboard, rudder and occasionally outboard engine in the water.

    Possible advantages of a boat like this are:

    * Better collision survivability (compared to a light rigid structure hull)
    * Easy storage and demounting of inflatable hulls.
    * Bigger (more seaworthy?) boat for the money and size of trailer it has to fit
    * Less maintenance? Anti foul? Paint?
    * A boat that flexs and conforms to the sea state rather than resisting it.
    * Easily repairable or replaceable inflatable hulls.

    I will update this post with pictures as I think of them. I will post up different design ideas within the overal concept.

    A little bit of inspiration I found on the net: At least there are some people that think sailing an inflatable boat around the world is viable :)

    Attached Files:

    Last edited: May 17, 2011
  3. ProtectTheOcean
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    ProtectTheOcean Junior Member

    Russian Inflatable

    Thanks, Skint, for that link. VERY interesting and inspiring story, even better told by some of the links and subsequent photos. The main hull and amas are amazingly slight in diameter... yet she was capable of sailing the Cape and crossing the Atlantic!
  4. Skint For Life
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    Skint For Life Junior Member

    Is it just me or does the takacat have inflatable "V" sections on the bottom of it's hull tubes?

    Attached Files:

  5. HakimKlunker
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    HakimKlunker Andreas der Juengere

    My other thoughts:

    The question to me is not so much if it can be done or not.
    People have crossed oceans in leather boats, bamboo boats, kayaks and much more. They survived, they arrived - and so they were right.
    The question to me rather is, if the boat will meet all personal expectations, or if something different will come closer to optimum.

    From the transport point of view no one can argue the advantage.
    You can even carry a spare tube on board if things come really hard, and it will not take much space.

    The link to 'Energy Diet' is extremely interesting. I see the major difference to your idea in the absence of any cruising comfort, and in the size.
    The less weight you carry, the easier the vessel will slip off (or away) from an obstruction.
    Flexibility also is embedded in Wharram's catamaran concept. Good: it is much discussed, but these boats are not less safe than others.

    If bigger means more seaworthy, I wonder why supertankers get into trouble sometimes. And how my friend's 29 ft boat made it all the way from Florida to Malaysia. Also 'Energy Diet' makes a clear point here.
    There are also fold-down multihulls around that offer - if not the same, at least - similar advantages ( i.e. Farrier, Dragonfly).
    I wonder how one will perceive assembly procedure: In one case one needs time to set up beams and to pump air; in other cases one is busy with bolts and nuts. On the other hand this is not a daily procedure and in both scenarios perhaps will not count so much.

    From the repair point of view I see not too much difference to GRP: In both cases you need controlled conditions (clean, dry, etc.)
    Compared with steel (or all metals actually): I wonder where I get a welding machine and power plant on a deserted island ... ;)

    I tend not to agree to less maintenance: Any material and especially the man-made type needs care and is subject to '''erosion'''(?) The required methods may differ in amount and/or price, but to my reckoning in each case not too far from each other. I do not really understand why you thing that Hypalon (or whatever you have in mind) is not interesting for barnacles: I have seen inflatable tenders, left in the water, being covered all over - - - emmm: under :)
    I would be very reluctant to remove them with a scraper. On any solid body the scraper would not be an issue.
    From the paint-and-cosmetic point of view you may be right. Still you need some cleaning every now and then. But you said earlier: you would not mind so much if your boat is 'ugly'.

    Flexing and seaworthiness:
    I get your idea here; as an approach in itself I do not see it weak or unsuitable.
    On the other hand, any material can be made suitable when the dimensions are correct.
    ("what is heavier: 1kg of steel, or 1kg of bird's feathers? ..." I think you get my point)
    Any deformation will absorb energy. And so we lose propulsion performance. That is not totally important in all conditions, but i.e. with bad weather ahead and a coast to the leeuward, I would feel safer with rather more speed and angle potential than less of it. I consider this too as an aspect of seaworthiness.
    In the case of a 'conventional' rigid hull one will be able to design the right buoyancy, weight distribution and (bow) shape. Here I see neither advantage nor disadvantage. It is just an approach from a different direction.

    Your ideal boat will certainly not be my own ideal boat. So: If it makes you happy, then you've got it just right. I see no major weaknesses in your approach.
    It will be worth while to investigate if other solutions give you more 'customer satisfaction'. If not: Go for it.
  6. Dave Gudeman
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    Dave Gudeman Senior Member

    I love this idea! Here are a few thoughts.

    Make the float with an outer skin hull of non-airtight fabric and use soft rubber air bladders inside the skin hull for the flotation. This has the advantage that you can use any material you want for the outer skin without worrying about air-tightness. Choose something that is highly tear resistant and does not degrade from UV. The skin hull should have chambers to hold the bags in place, but the chamber walls do not need the same toughness of construction as the outer skin, so you can use cheaper material and since air-tightness is not an issue you can sew the chambers in place. You probably do want water-tightness, though to keep the outer skin from filling up with water and getting heavy.

    This scheme is repairable at sea. You can keep spare bladders on board, so if you hit something that tears the outer skin and pierces a bladder, you can make field repairs to the skin and replace the bladder. Or maybe you don't even need to repair the skin -- have the replacement bladders be made out of tougher material so that they don't need the protection of the outer skin --at least for emergency purposes.

    I'd suggest designing the float to be symmetrical to back and front so that you only need two sizes of spare bladders: a sort of cone-shaped end bladder and a single size for all of the middle bladders.

    Of course to do repairs at sea, you need a pump on board.

    For access to the interior of the skin hull, I am assuming that there is a rigid structure holding holding the bag at the top in a circumference with zippers inside the circumference. Does that make sense? Imagine a basketball hoop. Replace the net with a bag attached to the rim in such a way that the zipper is inside the rim but the bulk of the bag hangs down. Now, change the shape of the rim from a circle to a very long ellipse and that's your ama.
  7. Zambizi
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    Zambizi New Member

    Long time lurker, just joined, first post.

    The hull is actually two tubes. Inside the bottom V there is a small tube. When at rest the space between the inner tube and pvc/hypalon V fills with water and has a suction cup type effect.

    As a result have seen a 4m takacat with 5 or 6 divers sitting on one pontoon while the other is still on contact with the water.

    Pretty clever and makes for a super stable platform.

    The water drains once it is on the plane
  8. Skint For Life
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    Skint For Life Junior Member

    Thanks for that zambizi. I had heard about that water stabilising concept somewhere. Can you please include pictures of the design, maybe a cross section about midships? I've seen plenty of pictures of the boat externally, but I'd really like to see exactly what is happening under that skin.

    It got me thinking. I'll post up a pic that I made quickly in MSpaint. Obviously the size of the large and small tube can be altered to a degree, although the smaller the lower tube in relation the upper tube the more "V" shaped the hull will become and the less rounded bottomed it will be.

    I have noticed that the kulikboat, ducky and takacat have tried to create a more traditionally shaped hull in the interests of less slamming, more wave piercing etc. The energy diet tri however appears to still use traditionally shaped round tubes, perhaps it would have been even better with a bow design like newer ducky boats and a bottom hull like a takacat.

    Attached Files:

    Last edited: Jul 4, 2011
    1 person likes this.
  9. Skint For Life
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    Skint For Life Junior Member

    HakimKlunker, Thank you for your input :D

    Exactly, just because it is possible to cover oceans in a kayak doesn't mean it's a good idea. I'm trying to develop a concept, any concept that fits the parameters in the first post. I don't want to design something unsafe, quite the opposite. If the concept were to ever be produced safety would be paramount.

    If you think there is something already available that fits the requirements then I'm listening :D Although from what I've seen the dragonfly is foldable yes, but not really to a trailerable width. The farrier designs, although brilliant do not have the sort of full time live aboard volume that I would like to incorporate into the concept.

    I was trying to keep the concept part short and to the point. Obviously a big boat can be a good or bad design as can a small boat. I was saying all things being equal a big boat should be more seaworthy than a small boat, I will point out that this is just what I have been told. I'm assuming a bigger boat is better because the bigger the boat the smaller the wave in comparison.

    Thank you for the part about repair and maintenance, all very interesting stuff :) I would think that the cleaning may be easier if trailered regularly enough, deflate tubes, lay out on the ground, wash with a hose and scrub with a broom, all standing up. Less hard work than bending over scrubbing a GRP hull? In regards to a hard scraper, good point. Would the barnacles maybe come off by flexing the hull skin into a tight curve?

    I fully understand your comments about getting caught on a leeshore. Pointing ability is really an important part of a safe boat in this aspect, this is one of the main reasons I am trying to design inflatable hulls that have a very similar shape to conventional hulls. If the hulls are well designed, and so is the rest of the boat I see no reason why speed and pointing ability should be any worse than a GRP boat.

    I know this concept is not going to be everyones cup of tea. I am trying to develop the concept for my own sake. Although I would be suprised if others are not interested in a boat that they could sail the world with, use as a motorhome, trailer whenever needed or park on their front lawn. :D
  10. waynemarlow
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    waynemarlow Senior Member

    Ask yourself what is the one thing that kills multihull speed and usability.

    Tubes are soooooo heavy, one only has to look at the small 16ft inflatiable cats to see how heavy compared to the foam boats they are ( think foam is full of air, tube thickness is full of rubber ) + you still need the structure to support the tubes.

    However in mitigation the small inflatiable cats do sail well.
  11. Skint For Life
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    Skint For Life Junior Member

    Ok, that is not what I expected to hear. My experience with them is that they are lightweight. On that page the very first word used to describe what an inflatable boat is is "lightweight". :confused:

    Does anyone have weights on comparable sized boats made in different materials? Including inflatables.

    I would be very interested to hear more opinions on this. Regarding structure, from what I have seen of inflatable boats structure is added to give the boat rigidity. A concept I am looking into is to create rigidity through inflated parts only, thus allowing for deformation on impact, which a hard skeletal structure (alloy tubes) would not allow.

    Also keep in mind that this boat concept is for a cruising boat, extreme lightweight is not required.
  12. Zambizi
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    Zambizi New Member

    You drawings pretty much nail it.

    As a long time RIB owner I can tell you that the best thing you could do rather than a double skin is to compartmentalise the tube with bulk head equivalents. So that each tube had 3 – 5 compartments, it’s a much lighter weight option than double skinning the pontoons. And provides the same benefit of no deflating the whole tube with a single puncture. Adding a reinforced rub strip to the “keel” of the pontoon might also be a good idea.
  13. John Perry
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    John Perry Senior Member

    I recently brought an inflateable canoe (Advanced Elements Convertible model). Its every bit as heavy as a normal canoe and is not as ridgid even though it is stiffened by an aluminium tube along the bottom. The only advantage over an ordinary canoe would seem to be that you can carry it inside a car rather than on the roof, and that was the main reason that we brought it.
  14. Frosty

    Frosty Previous Member

    The word for this is minimalism. I don't really care what is built my concern is the description "Blue water cruiser"

    Surely "road trailerable large blue water cruising multihull" is an oxymoron

  15. ThomD
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    ThomD Senior Member

    Boats like this already exist so long as one does not expect too much from any one part of the project. It's arguable that only a few boats hit the small, near day sailer, trailerable boat as is, if one wants ease of trailing, ease of set-up, and fairly normal performance. One is talking about a handful of Farrier type things, and variations on the road width catamaran. But if you are talking about boats that can be demounted, and moved, launched, and don't have fabulous accomodations, then you are into a bunch of boats like the 40 foot KHSD tri, Tikis, Some of the seaclippers.

    If you want relative perfection performance wise, accross the board, it can't be done, without a really, really big budget. And even then, I am sure it would not be something I would want.

    To me an inflatible is sorta a joke. Every major system you add is a huge hurdle, so you have the inflatable part, that is going to resonate back and forth, and require everything to be different, more complex, and the end result less useful. Then you need systems to pump it up, etc... You need a lot of your budget to address a boat that is air pressure proof, as well as water proof, and sun resistant. I have a hard time seeing any advantage once it is in the water, and even on the trailer, floppy is not necesarilly good.
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