economical coastal cruiser

Discussion in 'Boat Design' started by sandy daugherty, Feb 11, 2010.

  1. Guest625101138

    Guest625101138 Previous Member

    On the topic of efficient boat design you might find this interesting:
    http://www.adventuresofgreg.com/HPB/2008_09_15_archive.html
    read to the bottom.

    With reference to the link that Will provided make sure you read all the way through it. You can see why I persist when the touted experts show so little understanding of the basic principles.

    I can give you many examples of where the so-called experts have shown little understanding of basic principles and prepared to jump in without taking the time to understand.

    Rick W
     
  2. Willallison
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    Willallison Senior Member

    yep... you sure know your pedalboats...
     
  3. Brian@BNE
    Joined: Jan 2010
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    Brian@BNE Senior Member

    u4ea32 - post #323 was great David. Lots of info in a number of areas.

    Lots of people treading similar paths, differences between them not insurmountable by the others, and all in a niche that volume production boats don't cover.

    Good luck with the project, and please, if this thread goes 'other places', consider starting a new thread with info as you progress.
     
  4. Guest625101138

    Guest625101138 Previous Member

    That is a recent interests and lets me build rapidly at little cost to test ideas which I am happy to share with others. It is also a great way to stay fit.

    If you cannot appreciate the linkage between getting the greatest speed from 120W with a 100kg boat and economy in something larger than that shows a lack of understanding of the principles involved.

    Some of the experts here argue that they can get relevant information from models 900mm long that weigh 1 to 2kg.

    On the boating front I have been around them all my life. I come from a family that has been involved in commercial boating for 5 generations. I was only involved at that level for part time work before I started a professional career in areas that paid better.

    I have always been involved in recreational boating.

    Rick W
     
  5. Brian@BNE
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    Brian@BNE Senior Member

    from a different and unlikely thread, but with this sentiment Brent nailed a couple of things for me.

    1. Buy lottery tickets - I need the win to get the boat I want, and I reckon I can stretch the happiness bit out:).

    2. Be constructive and positive in posts - I confess its hard, far to easy to bash the keyboard.:eek:
     
  6. Willallison
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    Willallison Senior Member

    I once read that 70-odd percent of Australians are relying on a win in lotto to fund their retirement.... lot of disappointed old folk out there....
     
  7. Willallison
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    Willallison Senior Member

    Urghh... in keeping with that gentle nudge from Brian, I am going to endeavour (no promises!) to follow the advice of this poster (who, incidentally is a real expert when it comes to props)

     
  8. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Does it follow that 20 HP is about what Sandy has to work with at 12 nmpg (1 gph @ 12 knots)? Then it's a matter of finding a displacement and a length that will allow 20HP to push the accommodations he requires at that speed, yes?

    Note that the current Professional BoatBuilder (www.proboat.com) design competition is for a boat like this. I'd love to see you have an entry in it, Tad. Isn't the deadline about a month away?
    [I've just now stumbled upon this thread and started reading it. If this has already been said/discussed please forgive.]
     
  9. Guest625101138

    Guest625101138 Previous Member

    Fred
    That is the stabilised monohull I have been describing only they sit the bridge close to the water level.

    As you reduce weight the best prop will get smaller. The hull I did earlier was for 3 tonnes. Much heavier than the Oyster.

    Your ideas on the Atkin style hull that I worked for you was one of the prompts for the stabilised monohull. Separating the top of the boat from what is in usual contact with the water is lateral thinking.

    Rick W
     
  10. harry tams
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    harry tams Junior Member

    Is the claim of 30mpg plausible? If it is I can sure see why the 'stabilised mono-hull' would be desirable. Harry
     
  11. Guest625101138

    Guest625101138 Previous Member

    Will
    I see you have not bothered to offer the name of the poster. People are certainly entitled to their opinion. You need to gauge the proven knowledge of the people who express the opinion to gauge its value. Give me the name and I give you examples (privately) of how little they know and why they chose to take that stance.

    You are heading the same way. You really do not understand the physics of props and you are looking for any weak argument that will back your stance taken when I challenged you on something you had not even thought through.

    Have a look at the posts above from Tom and Fred and see if they contradict anything I have offered since I got involved on this thread. Just because it does not agree with your view of how it should be does not mean that there are not others ways.

    Rick W
     
  12. Guest625101138

    Guest625101138 Previous Member

    Harry
    The Oyster is much lighter than what has been asked for as a base case here and that I worked through.

    Long slender hulls are going to be more efficient. A single long slender hull is better than a cat if the length to speed is not overly constrained.

    The yellow one you have been playing with was designed for 8kts with less than 1kW.

    When you have a firm weight estimate for the things you want to put into you can begin to optimise shape for the speed you want.

    If you look around you will see lots of interest in the stabilised monohull and quite a few examples under construction or actually in use. The Oyster is one of the smaller ones. The LCS Independence is one of the biggest ones.

    The people building these things are doing it for a reason - economy at speed.

    We have determined that 3t at 12kts and 1gph is feasible. Getting 30mpg would need to be quite a bit lighter but it is feasible.


    This thread is a bit messy now. You should start your own thread and get into focusing on your needs as i suggested a few weeks back. David, Erik and Brian are looking for something bigger. Although Erik is likely thinking less than 3t.

    The one given is that the stabilised monohull will give the best result for economy at speed.

    Rick W
     
  13. fcfc
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    fcfc Senior Member

    Marketing technics :p

    The real fuel burn curve of an engine is not a curve, but a MAP. It is dependant of two parameters : rpm and load. Load can be expressed as % or torque.

    Otherwise, why would genset manufacturer would give you fuel burn at different loads ? (genset run at constant speed). Why the fuel burn at 50% load is not near 50% of fuel burn at 100% load ?

    Also, why do they give figures for 100,75 and 50 load, and not 25% load. Easy, as you reduce load, fuel burn figures tend to be embarrassing to publish.

    Now, for marine engines.
    Both Vetus and Sole are triyng to cheat you.

    Vetus gives you the specific fuel comsuption gr/Kw.h of the engine, but it is only a curve, not a MAP. So I fear it is for 100% engine load. Wich is the BEST curve to publish.

    The absorbed power curve of a propeller is something like a cubic or exponent between 2.8 and 3. You need something from 2^2.8 (6.9) to 2^3 (8) the power to spin your propeller twice faster.
    You know one point on that curve. At max power, you spin your propeller at max rpm if it is correctly sized.

    If you look at Vetus spec m3.28, max speed 3600 rpm. Vetus give you the fuel burn at 2600 rpm. At 2600 rpm, you are at (2600/3600)^ (2.8 to 3) Roughly 39% of the max power.
    Now, on the power curve, at 3600 rpm max, you have 20 Kw. 39% of this is less than 8Kw. But if you look at 2600 rpm, you see around 16Kw. You are using less than 50% of this. The engine load driving a prop at 2600 rpm is less than 50% . Ie more or less throttle position at 50% of the range.

    And now, the fuel burn curve that was given for a 100% load is not valid at all, since you are under 50% load. It is where they are cheating you.

    Now, for Sole.

    They give you a comsumption curve in l/hours for an engine loaded with a propeller. But nowhere they specify you what is the propeller absorbed power. As sated above, range can be from 2.8 to 3, but again, nowhere written.


    More serious are Yanmar and Volvo.
    They give you a comsumption curve in l/hours and they give you an power proller curve. But it is still on tiny graph.

    Ultimate and truly professional is Volkwagen Marine.
    That only gives you map, but also tabulated data.

    But the big drawback is :

    Soles prices < Yanmar Prices < Volswagen marine prices.

    In short, you get what you paid for.

    And for the chinese diesel, I fear they perfectly fit in the scheme above.

    Since chinese prices < Sole prices, I leave you to draw your own conclusion. Being cheaper does not mean the quality has been traded off, but whatabout other things like weight, or service interval, or fuel burn or ...

    PS:
    For diesel weigh vs outboard weigh, you forget an important point : Soundproofing. It is heavy to have a correctly sound proofed diesel engine. Especially if there is a cabin. An outboard will always be outside. It is likely an inboard engine have interference with cabin. And if you want to allow acces to cabin while engine running, better have some serious sound proofing.
     
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  14. fcfc
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    fcfc Senior Member

    Why are you cheating for half a quart of fuel burn between 40 or 100 hp diesel or outboard ?

    At the end of the boating season, you will not be able to fill half the tank of your F350 with the difference. :p


    EU regulations are clear. Under 7700 lbs (3500 kg) it may be a car or car trailer. Anything above is truck or truck trailer, and subjected to ALL commercial trucks constraints and licences.

    Hummer H2 sold in france have reduced payload to fit car regulation, and cannot legally tow anything above 7700 lbs. You need to register them as trucks (and truck = commercial) to do so.
     

  15. fcfc
    Joined: Feb 2005
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    fcfc Senior Member

    Stabilised monohull are tried since over 20 years. : You probably know : http://www.hiswasymposium.com/pdf/2004/Nigel Irens.pdf

    People interested in this kind of boat only want to establish world record, or try to draw media attention for their sponsors or their ideas.

    It seems to be of strictly no other interest for general boating public. Drawbacks far outweights fuel gains.

    NB: The rangeboat idea has already lead to bankrupty 2 french companies. It simply does not sell.
     
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