small, long-range boat design

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

  1. wavepropulsion
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    wavepropulsion Pirate Member


    Not only people with resources to buy or build a passagemaker has the right to the ocean. Less money is smaller boat till certain limits.
     
  2. Petros
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    Petros Senior Member

    really tiny uncomfortable boats may indeed be a stunt, but I like "pocket cruisers" as a means of enjoying a cruising lifestyle without all the expense or maintenance.

    some people hike the pacific crest trail, some climb mountains, some cross the continent on a bicycle, some sail the oceans in motorless boats. are these all stunts? There are other, much easier ways to get to your destination. Or rather a form of recreation that stretch out physical, mental and endurance capabilities?

    Why do we climb mountains or sailboats? I do not think it as much a stunt as much as a means of planning out of the ordinary adventures, ones that tests our skills. with a boat, it will also test your creative design and building skills as well as your seamanship and endurance. There are not many sports where you can do that.

    You like sailing the ocean in costly 60 ft yachts, have at it. but do not call those that want to design, build and sail their small boat across the oceans a stunt. They are showing much more initiative and range of skill than writing a check to buy someone else's boat.
     
  3. allwet
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    allwet Junior Member

    Seiko da Grindelwald does look like what I had in mind. Well, close anyway, I don't think I'd leave the reading and music behind! It looks like he did achieve 20 MPG, maybe with a bit of a sail and going downwind with the current. Can we can move from "it can't be done" to "why on earth would you want to?" Or do you still want to argue that?

    I may well want to sit in a small boat and do nothing in particular for a year while I tour the North Atlantic, and who's to tell me I shouldn't? Most people outside of this forum wouldn't consider crossing in a 40' motorsailer to be something they would want to do.

    It is a fascinating design problem, or can be if you're into such things. All you people designing boats for rich people are missing it! :)

    Goal:
    a motorized boat capable of crossing Canaries to Caribbean
    2800 miles on 150 gallons (close to 20 mpg)
    average speed of 6-7 kn
    safe and cozy in such storms as one would encounter, self-righting
    capable of carrying one person plus food, water and supplies
    sails optional, as long as it's not a lot of work
    solar optional, as long as it meets the speed and storm requirements
    I guess we need a size requirement, <4000 lbs displacement, 1800 Kg.

    This is upping the bar from what Seiko Nakajima did but hey, it's been 20 years.
     
  4. wavepropulsion
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    wavepropulsion Pirate Member

    Actually much boats in the size you like can do that, but with half the petrol you suggest. Par example that famous FAO boats of the free plans, specially the twoo biggers (decked and with a cabin), and can be a bit inneficient compared to other suitable designs. Can be obtained much more than 20 miles per gallon I believe (from my old second hand two strokes merc 4.5 I obtained 16 mpg in calm conditions). Put "more or less" to my words.
    In your place I not worried about room, will be enough if you like to take a girlfriend, the porta popo and mp4. In two weeks you eat 15 kg.of food, not much more.
     
  5. eyschulman
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    eyschulman Senior Member

    I think a fair approach is to calculate what you have to carry in weight and volume. Then decide on how much leg and swinging room you will need or want. Then fit that to a hull form. You can go short and very heavy displacement say 24-26ft or longer and lighter displacement say 28-30ft. I see no value for going under 24ft especially with so many used boats on the market. I would suggest a sail boat with aux. motor as best fit for long distance in a relatively small boat. I believe sail boats are inherently sounder and more comfortable for ocean use. I lean more toward power for ICW and inland use.
     
  6. eyschulman
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    eyschulman Senior Member

    Please note my words very small boat. For me that means less then heavy displacement under 24 ft. There are many used boats in the 26-30 foot class fine for intended use(predominantly auxiliary sail) and have owned several at that size but never crossed an ocean in anything smaller than a 311 ft DE so can't say what it would be like in a tiny boat. I single hand and like to stand and walk around a bit(at 76 get stiff a bit) so I would want a cockpit and deck that I can move around on and 28-30 foot would be my minimal target.
     
  7. wavepropulsion
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    wavepropulsion Pirate Member

    My apologyze

    After some time, I'm almost sure now the phrase you quoted of me was originally yours or very similar to your tought. My only excuse not to mention before is I was reading tons about this for years and I forget the original.
    Anyway, thanks master.
     
  8. kerosene
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    kerosene Senior Member

    Agreed of course that people do more extreme things and should be allowed to do so. This can mean more minimalist equipment etc.

    However - not commenting this thread specifically - many on these forums who want to endeavour in crossing oceans with less than optimal gear do not do it from an educated background but have idealized dreams of grandeur and idea that shortcuts can bemade as if nobody else had considered them.

    Comparing to mountains: I have a friend who is a likely Everest climber one day. He has done the highest peaks in Africa, South America, North America and Europe (in that order). He is also out in Sierras almost every weekend, loves and lives the climbing. Respects the risks and the learning and fitness requirements of progressively more challenging adventures.

    Many of the posters who arrive here want to cross and ocean in a self made boat of their own spec even though they have not done the baby steps - which I assume can be of tremendous fun and great adventures themselves ecven if the longest legs were 500 miles instead of 3000.

    I don't think the naysayers are negative for the sake of it.
     
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  9. wavepropulsion
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    wavepropulsion Pirate Member

    You're right under your point of view. But don´t forget that Saint Pierre dorys did what we mean long time ago, and in the worst seas and with less equipment, bad materials, an none was lost. And a race in between Bahamas and NY -not sure if NY but is the same- was repeated much times in the begining of former century with hulls as we mention here. Then when hughe ammounts of hp was used in boat sports the means of a 'powerboat' actually still restricted to rational use of fuels before the advent of this crisis. So I just still refloating old ideas.
    About size some very experienced sailors claim a dinghy is the more seworthy thing. And progress are not restricted to old -in age or experience- people, but generally is the opposite.
    I don't know in other threads, but here nobody I think still dreaming, but exchanging ideas. So please specify why is not possible to a 24 feet powerboat to cross the seas, you can help more than the naysayers with some arguments against that.
    In life exists options, some like to eat chocolate and some pickles, and the market is bigger for chocolate, this not imply pickles can't be ate. Small powerboats offers some advantages and new materiales and engines too. Not ever new ideas are for the sake of it, and history shows new ideas was what take we out of the caverns.
    The less 'rational' boats I know about, was the viking Drakkars, and was the more successfull of that time, cause they tought out of the european box. And was long, light and narrow boats too.
    Not to mention actually sails still each day more expensive, while small diesels each day cheaper. And what will save your life when a 300 feet cargo boat sinks, is a raft 10 feet in lenght or a power lifeboat around 20.
     
  10. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Most seaworthy vessel at sea, is a bottle with the cork strongly driven home.
    But wouldn't want to live in one, even if it were big enough.
    First priority of any boat is keep the water out.
    If it isn't the second priority, it's very high on the list; ventilation.
    Moldy green isn't a healthy environment.
    These two priorities conflict. Other priorities, a list a yard long, also have conflicts.
    Personal choice and preference is about resolving these conflicts.
    The perfect boat is an impossible dream.
     
  11. FAST FRED
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    FAST FRED Senior Member

    Many of the posters who arrive here want to cross and ocean in a self made boat of their own spec even though they have not done the baby steps -

    Crossing oceans , world cruising is one hobby.

    Becoming a boat designer is another.

    Building boats is another hobby , a very complex one to master.

    Seems like each could be done without the other,

    1 crew across an ocean , learn what it like and the requirements do do it yourself.

    2 purchase a naval arch course and enjoy.

    3 Build a rowboat or other vessel and see how the time and effort compare with simply purchasing a used boat , and going!

    For a novice learning all 3 at once would take years!
     
  12. erik818
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    erik818 Senior Member

    The absolute first thing I would do (and did) is to build a small boat. After that you're addicted to boat building/designing and have to continue.

    An old rule is that you need 1 -2 hp per tonne, so moving a 3 tonne boat with 5 hp isn't unrealistic. Another rule is however that economic speed in knots isn't much faster than the square root of the LWL in feet. Setting the length constraint to 24' makes your task more difficult.

    Specific fuel consumption for a modern small diesel inboard is approximately 0.2 kg/hp/hour, or 1 kg/hour @ 5 hp. Assuming you only achieve 5 knots with 5 hp, you will need 2800/5 kg diesel = 560 kg diesel for the 2800 NM strech from the Canaries to Bahamas.

    My own old traditional lapstrake double-ender is 7 m long (23'), displaces about 1500 kg and moves at about 6 knots with 5 hp. Maximum speed with the 7 hp I have is marginally more. Downloading it with 560 kg extra diesel would reduce the speed to about 5 knots. I've tried when transporting concrete. The boat is reasonably comfortable for two married persons without leading to a divorce.

    As for supplies, my backpacking experience is that you need less than 1kg/day/person in consumables, water excluded. 1 kg / day includes everything except water: food, toilet paper, whiskey, washing detergent, soap, fuel for the cooking stove etc. All personal and camping equipment if you exclude the backpack and the tent weigh less than 10 kg/person. Excluding water, you don't need more than 50 kg/person for 30 days in relatively good comfort. Weight isn't a reason to do the trip alone.

    It's the length constraint of 24' in combination with the speed requirement that makes the design goal difficult. You need to keep the length/beam ratio high if you want an economic speed beyond the square root of LWL. The displacement for a boat with the payload you need will be minimum 2 tonnes. A 24' and 2 tonnes boat won't be narrow enought for the efficiency you need at the speed you require. Remove the length constraint and the rest of your design goals will be easier to meet. A stabilised monohull with e.g. an LWL of 30' and a BWL of 3' might fit the bill. Stabilisation could be in the form of one or two outriggers.

    Erik
     
  13. wavepropulsion
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    wavepropulsion Pirate Member

    Assume the boat has 10 hp engine to round the numbers, at 3800rpm max. and consumes 0.5 gallon per hour. If normal cruising revs are 3000 rpm ( 80% of max ) the power developed 80% X 80% X 80% = 51.2% of the maximum. Because the decreasing in rpm affects at cube the hp.
    ie 0.51 x 10 = 5.1 hp , the fuel consumed is 0.25 gal per hour
    Calculate the half of this for the 5hp. This is 300 liters or 250 kgs. (this numbers are round to simplify)
    Therefore by reducing the engine revs from 3800 to 3000 you have halved the fuel consumption. & most probably only reduced the speed from say 6kn to 5kn. And while advancing the trip less hp and revolutions will be needed for the same speed. Is not the ideal for confort but some people suggest to have two propellers: one to run heavy and another to run lighter, and I just mention this to remark the changes in weight and rpm. But the rpm running normal can be at half of the total, so more economy can be expected and if a variable pitch propeller is used much better yet.
    About the hull weight I think can be lighter than 1.5 tonnes. And somebody needs to play with the stern shape, cause a double ender is very efficient at lower Froud numbers but this advantage decreases at 1.0 or less, and the bottom shape is also of importance. I'm not very sure, but in a boat with a lenght beam ratio of 1 to 4 a bit of lift in the stern can be of advantage at higher Froud numbers and don't need outriggers. Some boats have a sensible less beam at waterline also and is better to consider this relation at waterline. The boat for power needs to be designed for power.
    The route mentioned is cause the trade winds and current, being pessimist in the good seasson half ot the trip can be done with the downwind sail while the boat remain as a simple powerboat design.
    Read my post as suggestion, I don't know if I'm right.
     
  14. eyschulman
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    eyschulman Senior Member

    So here is an extreme idea. Get hold of a aluminum coffin(pretty dam water tight) and mount it on two pontoons with coffin out of the water. Use a long shaft ob and fill the pontoons with fuel. If things go really south well you are already in your final resting place.
     

  15. wavepropulsion
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    wavepropulsion Pirate Member

    Good idea, I already have the mast.
     
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