ultra shallowdraft to seagoing multihull

Discussion in 'Boat Design' started by upstrider, Jan 2, 2014.

  1. messabout
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    messabout Senior Member

    Wetted surface is most influential at low speeds. If you are gunkholing you may be rowing, sculling, poling, or using an electric troller. You will be going slowly and the input effort is largely determined by surface drag. Economy of energy is worthy of notice in those circumstances, especially if your wife is rowing.

    At speed, wet surface is still influential but not nearly so much as form drag or wave making resistance.

    I too am well past the speed craze of my youth. I like silence and tranquility better than all the fuss that go-fast entails.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I was thinking more of the sand-fly swarms that infest shallow estuarine backwaters hereabouts. You are blessed not to have to endure such varmints. :p
     
  3. kach22i
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    kach22i Architect

  4. upstrider
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    upstrider Junior Member

    Mr efficiency is 'on the right track'. How to propel a boat in 6" of water? Stern wheeler, side wheeler, fish fin drive, blades moving side to side, jets, treads, etc? Plus the associated means of steering.
     
  5. pogo
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    pogo ingenious dilletante

    Yepp, three hulls with raked stems, that's where the similarities end. :D

    http://www.gumtree.com.au/s-ad/bermagui/sail-boats/crowther-trimaran/1034378698

    The Nielsen measures 35 x26' , comes in with 1700kg , is single chined out of divinycell sandwich, very twisted flat bottom floats , a flushdecker with alloybeams, centercockpit, 7/8 rigged with selftacking jib, code 0 or genni on 7/8 or top.
    Up to 12kn TW she meanders excellent in only 40cm water, with more wind she prefers 50cm.
    On a beam reach in shallow water(max. 1m) , or deeper courses, she planes very early, groundeffect. Once she planed with 17kn OVER only 20cm , steering with the sails.
    World's biggest skimboard, hahaha, useless for everybody.

    http://m.youtube.com/watch?v=HidIUupvP9c

    Always hand's thickness of water under centerboard's exit !

    Egal....:)

    pogo
     
  6. upstrider
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    upstrider Junior Member

    zephyr

    Thanks for that link. With all the building, launching, sailing, etc no picture survives of mine.
     
  7. upstrider
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    upstrider Junior Member

    POGO magic on your Neilsen

    Here's some in return. Crowther Zephyr 26 had skegs removed, transom mounted twin rudders drawing 2" more than the main hull belly, 36" quadramt pivoting retractable centerboard. Tacking upwind NW along coast of California just outside kelp beds south of Point Conception encountered increasing offshore winds in the evening. Continued closer to shore nearer the buffs approaching Gaviota where there's a pass for more wind. Doing 12+ knots on a beam reach began to hit kelp beds whose kelp was streaming away from the coast. Boat would slow as the centerboard caught kelp then break away sending lightning phosphorescence 100' to either side. Going too fast to track the rocks on the chart we gave up and could see the rocks from the phosphor cloud around them. Broke kelp for hours that night. Did not encounter those conditions again during the life of the boat.
     
  8. Village_Idiot
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    Village_Idiot Senior Member

    I would lean more toward a Panga-style, about 30'-35' LOA with a 60" bottom width, made from aluminum with an eight-foot-long marsh tunnel in the stern. Such a craft would require good piloting skills in rough waters, but is do-able. If concerned about lateral stability, you can always add amas later.

    I run a 2560 flat-bottom aluminum with a six-foot marsh tunnel and a pointy bow. It will run in six inches of water all day long as long as you maintain 20mph to stay on plane (running a 115hp 4s Merc with Baumann four-blade tunnel prop). Find a hole to set down in, and it will jump on plane in 12"-14" of water, in about a boat length when lightly loaded. With the narrow beam, one-foot chop is comfortable, it pounds in 3-foot chop, but I've not had it in big rollers. Not sure about its sea-keeping, as the biggest lake it's been on so far is 25k acres with a steady 25mph wind (resulting in 3'-4' chop, but no rollers).

    However, I suspect you may be looking more toward a cabin-style boat. In that case, I might follow Messabout's lead and design the craft as a single-chine v-hull when the keel bilge is filled with water. Pump out the water and the craft settles into a flat-bottom. Such a craft would require an asymetric hull (think of the cross-section as a check mark), and preferably a movable/tiltable cabin/helm (easily doable with today's fly-by-wire systems).
     
  9. Waterwitch
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    Waterwitch Senior Member

    Don't water striders walk on the surface tension of the water?
     
  10. upstrider
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    upstrider Junior Member

    life returns to this design

    waterwitch: Do you suppose Gerris species could wear "boaty boots" and handle some bigger waves? Have you tried to "swamp them" with waves? Have you seen the narrow legged resting position? Many spiders have the same narrow configuration when resting and that is the flat bottomed boat equivalent while the wide spread is the sea-going equivalent of a very shallow draft vessel.

    villageidiot- interesting stuff...'sleds' are one extreme in the shallow draft world.
     
  11. Waterwitch
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    Waterwitch Senior Member

    Was trying to figure out what features of water bugs you were trying to draw inspiration from, considering they are best known for getting around on the air, water surface tension interface.
    Never played with waterbugs, being more interested in catching fish and frogs then. I read they are covered with hydrophobic hairs so they do not take on water get heavy and sink, which, also traps air for flotation.so I suppose they are unswampable. Scaling up to a 30 ft vessel your boat weighs billions of times more than a waterbug and would not perform the same even in a sea of mercury.
    People use airboats to get around in the shallows too.
     
  12. upstrider
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    upstrider Junior Member

    matters of scale

    A few matters of scale show up in the design of a vessel that crosses the coastal wave barrier and still is extremely shallow draft. Mostly the problem is dreaming of a solution and still bringing in the other side of the brain for balance.
     

  13. upstrider
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    upstrider Junior Member

    closing this thread for lack of interest

    Good designing, building, and boating to you all!
     
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