How crazy is this design?

Discussion in 'Boat Design' started by Ernie Pantuso, Jul 3, 2020.

  1. Ernie Pantuso
    Joined: Jul 2020
    Posts: 1
    Likes: 0, Points: 1
    Location: Planet Earth

    Ernie Pantuso New Member

    I have zero boat design experience, so the following may seem ridiculous and/or totally outlandish to those of you who do - but I've had recurring dreams about living on this boat so I'd love to know if it's feasible. (I believe this idea found it's way into my dreams because "Kon Tiki" is one of my very favorite books - I'm just replacing the raft with multiple hulls and expanding the little hut in the middle of the raft!) You may laugh uproariously at the ignorance that follows, but I'd appreciate knowing what the flaws are with my idea.

    I'm thinking about a radical multi-hull design in which 6 thick aluminum crossbeams would be laid across and attached to the top sides of 2 (or maybe 3 if necessary) 46' fiberglass hulls. A large cabin (the entire living area of the boat - 30 feet long by 20 feet wide) would then sit atop the cross beams, creating (hopefully) a seaworthy/oceangoing houseboat with a beam of 24 feet.

    There'd be no living space in the hulls - just storage. (Water/holding tanks, and various other items.) There'd be 2 additional "outrigger" type hulls that would expand the boat's beam to 32 feet or so (maybe more). Four of the cross-beams would have an inner section that telescopes outward, extending these "outrigger" hulls out by 10-12 feet to create additional deck space when at anchor - effectively creating our own little private island. For traveling, the decking would be rolled up and lashed down and the auxiliary hulls would be drawn in and secured. One of the primary goals of this setup is to be able to detach any one of the hulls and tow it to a boat yard for repairs/maintenance/bottom painting, etc. Haul outs, I think, would be a lot less expensive. Tow it back, bolt it in place, do another hull a couple months later.

    I am envisioning a solar-powered electric boat, here - not a sailboat. The top of the cabin (including a section that extends back 8 feet over the aft deck) would be entirely covered with solar panels. I think that's enough surface area to soak up all the rays we'd need. (Most of the batteries - in two completely redundant systems - would be stored in the main hulls except for...)

    The motor(s) would be on a separate, detached "propulsion module" (with a few batteries of its own on board). When underway, the propulsion module would be stowed between the main hulls, under the aft deck (out of sight and not easily accessible by dinghy thieves) and secured to the main hulls with thick stainless cables, fore and aft. At anchor, it would still be stowed securely below the aft deck but it could be accessed by hatches in the aft deck, and with the cables detached, it would serve double duty as the dinghy for shore runs. As with the detachable hulls, one of the goals of this unusual configuration is the ability to take it to shore separately from the rest of the boat for maintenance or repairs. (Even if the problem was serious enough that it couldn't make it to shore under its own power, it could still be towed in.) Last but not least, if the propulsion module was designed for speed (when being used as a dinghy), we could even use it as an escape pod in case we had to outrun pirates or if something disastrous happened to the boat.

    All in all, she'd be a very large boat with a 46' LOA and a beam of 32 feet or more. She probably wouldn't win any beauty contests but she'd have plenty of living space and would hopefully (almost) never need to be docked or hauled out.

    Assuming that such a design is even feasible/functional, what I'm unsure about is how seaworthy she'd be. Would she be more likely to capsize and/or sink in high seas? I'm guessing she'd be far less rigid than a well-designed catamaran; is that flexibility a good thing or a bad thing? (It was a good thing for the Kon Tiki.) Is she likely to be slower than molasses in January due to all those hulls? Would the main cabin need to sit midway on the hulls? Or should it sit more forward or aft?

    If you've read this far, thank you. I look forward to your honest, candid thoughts.
  2. bajansailor
    Joined: Oct 2007
    Posts: 3,649
    Likes: 1,593, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Ernie.

    Would you be keen and willing to sink perhaps US$ 500,000+ (maybe a million even?) into building a boat like this, while acknowledging the potential (and probably real) disadvantages that you mention above?
    Not least that if you then decided to sell it, you might get 10% of what it cost you to build. A boat is ultimately only worth what somebody is prepared to pay for it.

    Forget all these extra hulls - even three hulls is probably one too many, when two will probably do.
    And these detachable hulls will play merry hell with your resistance, not to mention seakeeping ability.

    I doubt that she would capsize or sink (except financially) too easily (assuming that she is 'properly' constructed, and has bulkheads to create watertight subdivision) - but I don't think you would make much progress to windward with your electric motors when conditions deteriorate.
  3. trip the light fandango
    Joined: Apr 2018
    Posts: 505
    Likes: 104, Points: 43
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    Welcome Ernie, slide or fold out beams that support nets can really increase living space, possibly a big ferro cement boat because it is hard to damage the resale value being so low ,and they are actually really quite good..but often heavy ..but who cares. I like the increasing area bit of your idea.
  4. Will Gilmore
    Joined: Aug 2017
    Posts: 960
    Likes: 445, Points: 63
    Location: Littleton, nh

    Will Gilmore Senior Member

    I am not a fan of cement boats, but they may have an advantage here. Your slide-out hull idea is just for extra play room when at anchor, sort of a patio idea? However, maybe eliminate the pontoon and just have a slide out frame. The weight of the boat will keep a small group of passengers supported at the end of your extra ten feet or so. Just make sure you have the volume to float them. That's the extra pontoon built into the main pontoon, just slightly more volume.
    You could build a camber into the beams so the whole thing arched down to the water like an artificial beach.

    -Will (Dragonfly)
  5. DCockey
    Joined: Oct 2009
    Posts: 5,229
    Likes: 634, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Why is the LOA fixed at 46 feet?
  6. JSL
    Joined: Nov 2012
    Posts: 811
    Likes: 64, Points: 28, Legacy Rep: 41
    Location: Delta BC

    JSL Senior Member

    sounds like an excellent idea for a dock and with cement pontoons you can donate it to the artificial reef society when finished and use the tax receipt would offset some of your losses.
  7. clmanges
    Joined: Jul 2008
    Posts: 581
    Likes: 145, Points: 43, Legacy Rep: 32
    Location: Ohio

    clmanges Senior Member

    The more stuff you store in these hulls, the less flotation you get from them. If you want them for storage you'll have to include that in the buoyancy calculations.

    I'd think about using fiberglass or just good old wood for the beams instead of aluminum. For the reasons why (waves) I suggest you read J.E. Gordon's two excellent books, The New Science of Strong Materials, and Structures. A "Kon-Tiki"-type raft could survive ocean crossings because of its flexibility. Even mild swells will put repeated stresses on this structure, and aluminum has a rather catastrophic failure mode. Steel might actually be better.

    Just my two cents' worth.
    Will Gilmore likes this.
  8. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,963
    Likes: 176, Points: 63, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

    Not crazy at all.

    this is the Modular concept. | Boat Design Net

    38' trailerable,containerable,modular Work/Play cat | Boat Design Net

    cathull3_PAKpaint_pic | Boat Design Net

    hull showing default hatch openings, and deck-bolts | Boat Design Net

  9. BlueBell
    Joined: May 2017
    Posts: 2,731
    Likes: 989, Points: 113
    Location: Victoria BC Canada

    BlueBell . . . _ _ _ . . . _ _ _

    More crazy than sound, but we've all been there before.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.