small, long-range boat design

Discussion in 'Boat Design' started by allwet, Jun 5, 2014.

  1. allwet
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    allwet Junior Member

    I have searched but have not found any boat like the one I'm dreaming of. There may be a reason...

    This would be a small 24' power trimaran, displacement hull, ocean capable, with a cruise speed of 6-10 knots. I don't want to go fast, I want to go far. The goal would be 20 miles per gallon so that with 200 gallons on board I could go 4000 miles or at least 3000 with a reserve. This would give me significant ocean travel capability, maybe with sail as a backup but not a big fixed mast. I am willing to give up comfort and, to some degree, speed.

    This differs from a motorsailer in that the hull is not designed to counterbalance a large sail. This differs from any small motor boat I've seen in that it has a displacement hull. This differs from one of those ocean-crossing rowboats in that it goes a bit faster and is less work!

    I am fairly sure that 20 mpg is possible and may build a prototype to show that, but can I meet my other requirements as well?

    So, 2 questions: is my dream possible? and is there anything like it I could look at?
     
  2. Richard Woods
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    Richard Woods Woods Designs

    I doubt if it was possible, in part because of the fuel weight - 1500lbs? and the space it takes up.

    Go on a F24 trimaran to see what space you have available, check out it's outboard size and fuel consumption from manufacturers data

    My Skoota 20 powercat cruises at 10 knots with 10mpg, but not with 200 gal, our range was about 200miles, not 4000

    And of course the first real question would be "why?"

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. Petros
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    Petros Senior Member

    That kind of range is not possible without using sails. Many have sailed around the world in small sailboats (under 30 ft), some without any motor at all.

    Something that might be more reasonable is an efficen small trimaran sailboat, perhaps with a simple sailing rig to make it easier to sail, 80 gal of fuel (600 lbs) and a small outboard. With both the outboard and a single dagger board to it would be simple to minimize the drag for either under sail or under power.

    at a more modest 6 or 7 knots you would still have over 1000 mile range, with the sail that could be extend as far as the wind blows.

    learn to sail, the wind blows for free.
     
  4. allwet
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    allwet Junior Member

    Richard, I admire your designs and appreciate your comments on this forum.

    The Scoota 20 is closer to what I have in mind than many, but it was still designed to carry a comfortable living space at 10 knots. I am willing to go slower and heavier for more range.

    The question is, could you push a 2000 lb payload through the water at 8 knots using only 5 HP if you designed it for that? I have in mind a 24' tube 3' in diameter, tapered to a vertical bow with minimal outriggers for stability and a fatter section you could live in for a couple weeks at a time. I believe an inboard 10 HP diesel would deliver 5 HP at about 0.5 gallons per hour, if you multiply it all out you get a range of 3200 natuical miles, which would be nice.

    Why? I can't afford a motorsailer that I would trust across an ocean. I thought my floating gas tank would be fairly cheap to build. Also, although I've sailed now for decades I have started to enjoy being able to point my nose in a particular direction and have reasonable expectation of getting there on a schedule. I also believe it's easier to design a small boat that will survive in the ocean if you don't need a mast generally pointing upwards. I don't actually have much experience with oceans to be honest. And spotty success with my inventions!
     
  5. jehardiman
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    jehardiman Senior Member

    Realistically you would starve to death. Payload is way too small for a 30 day voyage.

    See this old thread post for a discussion on how hull type drives load capability. http://www.boatdesign.net/forums/multihulls/canting-keel-monos-vs-multihulls-13511-2.html#post104220
     
  6. Richard Woods
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    Richard Woods Woods Designs

    Well I doubt that you could do what you want. In general boats are heavier than one hopes, and also slower while using more fuel. That's just life...

    Of course the payload isn't just fuel, you'll need water, food and stuff to enjoy life, never mind anchors (2), safety gear, a dinghy... the list is pretty endless if you're living on board and crossing oceans. 3000 miles is going to take you more than a couple of weeks at 6 knots, and what do you do when you get to the other side. If you plan to then get off, why do the trip in the first place?

    Even with a cockpit tent the Skoota 20 has very limited accommodation, I spent enough time on board ours to know that! the 28 is much more comfortable, but even then I'd not cross an ocean in it.

    I've made five Atlantic crossings and sailed to 40 countries. I wouldn't do any more than cross to the Bahamas from the US or to France from the UK on a small powerboat.

    If you don't have much money get a sailboat! Remember the US has some of the cheapest fuel in the world. It is more than twice the price in the UK for example. Even in Canada it is a lot more expensive.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  7. FAST FRED
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    FAST FRED Senior Member

    It takes about 2HP per ton to go at a modest long range speed .

    A skinny very light boat might do even better at 1.5 hp /ton (2240lbs displacement)

    At best An affordable/repairable diesel will create 20HP from 1 gallon of fuel.

    With this very rough rule of thumb, plug in your numbers for full load and light load.

    With the price of a used sailboat , that would be the best option , esp for a low cost Round trip.

    Buy it use it sell it is a round trip.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    I am curious as to the 3000 mile specification, where is this stretch of water that has no fuel refill possibility ?
     
  9. Richard Woods
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    Richard Woods Woods Designs

    Canaries to Caribbean is about 2800 miles

    You can stop off at Cape Verdes as ships used to to re-coal but its still 1800 miles after that

    Richard Woods
     
  10. allwet
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    allwet Junior Member

    Thank you all, I am grateful for the perspectives different from mine.

    Sail seems to be the way to go, as people have been doing for millennia. I am not entirely convinced that a small, low-power, long-range boat is not possible but I clearly have some obstacles to overcome.
     
  11. Tiny Turnip
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    Tiny Turnip Senior Member

  12. wavepropulsion
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    wavepropulsion Pirate Member

    I think is absolutelly possible to have a long range in a powerboat. I have an idea very similar, but using a sampan like boat of the same lenght. But the petrol is limited to half of that in my tought and in the passage from Canary Is. the trade winds will help with any kind of sail or kite if going in the same direction of the wind.
    I think makes more sense than sails if the boat is well designed.
    As new boater I learnt not to ask to conservative people with great success in ther specific area. If you have a new idea go and try is your own risk.
     
  13. Petros
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    Petros Senior Member

    here is the issue: are you trying to prove it can be done by motor, muscle. wave power or wind power? all have been done. all suffer various disadvantages. but in all cases for small boats, the primary means of moving the boat is the ocean currents. people have rowed and kayaked across oceans, but most of their movement was by virtue of the ocean currents. muscles, wave power, or a low powered motor are not powerful enough to go against these currents, so you have to go with them.

    If you want to prove a new means of crossing oceans, than have at it, do something new. You will still have to plan around the winds and currents, just like a sailboat. but if your motivation is to enjoy ocean travel using minimal fuel consumption, than go with proven technology: sail power. That is highly refined and humans have been at it since before there were written records. the story of Jason and the Argonauts is from the bronze age, it was only good down wind, and why it had a crew of oarsmen.

    A real efficient hull design, strong enough for the open ocean, and with enough capacity for self contained long distance travel (water, food supplies, etc), is going to be rather heavy anyway. Most muscle powered ocean crossings us a weighted keel to make them self righting. If you have that you might as well put a real efficient sail on it and use the wind officially, since you will be using both wind and current anyway.

    What actually might be an interesting and low fuel consumption demonstration boat might be a 16 or 18 ft sailboat with a retractable bicycle-like device to drive a prop using your legs rather an oars or a paddle. You can add a small 5 hp motor and a more modest fuel supply for motoring long distances as well. With some solar panels to power your radio and navigation gear you could be self contained in a relative comfort, with several alternative means of moving the boat along.

    Those rube Goldburg devices posted by Tiny Turnip are interesting but not only way too costly, they are way too complicated. Almost certainly most of that electronic crap on the boat will not be working more than a week or two into the trip. A long distance boat design is best when there is nothing to remove from it, not when there is nothing left to add to it. The more you depend on "technology" and complex devices, the less time traveling and the more time you will be stuck trying to get it fixed. Simple is better, the fewer things to break the fewer things there are to break down.

    Long distace minimalist sailors Lin and Larry Pardee (who have sailed around the world several times in a 24, than a 27 ft, simple motorless sailboat) tell stories of retired couples in the "dream" (become nightmare) yacht stuck in some remote island having to fly in repair specialists and parts on special charter float planes to get things fixed like electric winches and desalinators fixed because they could not even get their anchor back in the boat and they did not have enough fresh water storage to make it to the next island! all those fancy "accessories" ruined their dream trip and drained their retirement funds.

    If you want to travel long distances, keep it simple and reliable. Use what works.
     
  14. wavepropulsion
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    wavepropulsion Pirate Member

    I agree with Petros in most things. In first I designed my boat to use the waves as propulsion, was efficient just in ideal conditions -3knots-and I used just the shape of the hull, no fins. Then I added a 4.5 hp outboard (bring me 7 knots) and a small jib, 1.5 sq.meter for a 18 feet boat. Last times I used a sculling oar under Slieve MacGalliard asessment and also Douglas Brooks, it works very well but the crew have not experienced with that as a muscle propulsion device, works quite well. Just bring you around 2 knots in the long range but never fill tired.
    For energy I used a very small solar panel, 10kw, and after trying I change a 55 amp.battery for a smaller one. GPS, handy and compass.
    Ever I consulted the weather as a sailing boat, and tidal and currents also.
    For water you just need two liters per day-more in summer-, and you can add till 20 percent of saltwater. If you found a manual watermaker from a raft is better. Deposits for fuel and water not built in, but in containers.
    The Pardeys bought an engine lastly, cause the strong currents. Ever a sailor needs an engine in coastal conditions, and most of them travel very slow heading to the wind.
    A powerboat can be more shallow, I take the coastal surf several times with no problem, no big skeg or rudder to break.
    I trust in light boats to ride over the waves, cause this the sampan shape is better to me, because the beam sea doesn't affect and wieght also doesn't affect much. Weight can be a bigger problem for multihylls? I don't know. But cross winds are a problem indeed till you begun to know your boat and know how to accomodate the boat shape to wind and waves. In my next boat I like to change the bow profile.
    The engine must be diesel, cause safety, torque and economy.
    Sailing boats I think are slower, sails are expensive and hull design more complicated. What you save in petrol you lose in sails and docking.
    I have not much experience, just a few years, I'm new and accept I can be wrong. But I tryed and works. Before some crossings the anglers laugh at me, then after the crossings they bring me cigarettes, pay my drinks and tells me they was joking, they know that way can be done. So, sails can be efficient, very well I know much boats under six meters do the Atlantic crossing every year, and I consider the first one in crossing west to east in a dory was considered a bit crazy. Same with powerboats, now boats in the 30 feet range are doing great passagemaking, why not a smaller one? In a 24 feet boat with 200 liters of diesel and 100 kg of water I still light yet.
     

  15. rwatson
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    rwatson Senior Member

    I enjoyed your insights WP. Thanks for posting

    I particularly empathised with your observation ..

    its like the old saying

    "The fine art of getting wet and becoming ill, while going nowhere slowly at great expense"
     
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