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Thread: A new motor boat design from Paul Fisher.

  1. #36
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by skaraborgcraft View Post
    Depends on the engine. a 50hp Scandia/ Kelvin/ Hundestad twin would have no issues when fitted with a pitching prop, that most were. Even a Perkins P3 will throw a prop 3ft in diameter with 50hp, and that gives a lot of bite in the water. There was a trading vessel running across the Pacific with a P3 perkins and had it running at lowest possible speed to make the huge distances. I did have friends replace a 2 cylinder 40hp hot bulb engine with a modern Iveco 120hp, the boat didnt go much faster, but the fuel bill did go up quite a bit.
    Ha ha, sorry for your friends but I like that this story suggests a small engine can work well. Why did they get an engine so much bigger?

  2. #37
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by Small boats rock View Post
    Ha ha, sorry for your friends but I like that this story suggests a small engine can work well. Why did they get an engine so much bigger?
    Bigger only in total hp produced, it was about half the size and quarter of the weight of the 40hp engine it replaced. I think a factory rep must have come up with that power requirement based on a limited choice of gearbox ratios for that engine, the new prop was tiny in comparison to the old, but the new engine revved much faster, so they had no issues with docking except for a more pronounced prop walk going astern, which happily worked in their favour given the boats berth.
    The old Sabb 30hp was recommended for workboats upto 35ft and as an auxillary in sailboats to 55ft . Anyone who has seen he conditions on the coast in the North Atlantic of Norway should understand that its not the place to be without reliable power, most people who use a engine as auxillary rarely want to lug around a huge fixed prop, and that is where the lack of bite comes from, rather than a lack of hp.

  3. #38
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    Default Re: A new motor boat design from Paul Fisher.

    So based on those figures maybe the Paul Fisher could be adequately powered with as little as 50hp do you think?

  4. #39
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    Default Re: A new motor boat design from Paul Fisher.

    An interesting innovation with reference to her motion.

    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  5. #40
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by Small boats rock View Post
    So based on those figures maybe the Paul Fisher could be adequately powered with as little as 50hp do you think?
    Adequate will mean different things to different people, and where they are. A Nordhavn 46 as an example at just over 29tons, has a main engine of 150hp, giving a similar hp-ton ratio of 5hp as the Fisher design. But the Nordhaven can maintain 6knots into a head sea and wind using a 28hp yanmar with a small prop, thats less than 1hp-ton.Flat sea cruise revs on the main engine is only demanding 30hp. Admittedly that is a wing engine to back up the main, but if you are not forced to buck strong tides and weather, and do not feel the need to go above hull speed, and are looking for maximum fuel efficency and long engine a life, sometimes working a small engine at 80-90% of its rated duty can work out well. You wont find commercial ships running the same hp-ton ratios of leisure craft, and no, not all of them require or need tugs to dock
    I would rather design a boat around the Perkins 152, but it would not need to be as big as the Fisher design, both in size,length/beam or tonnage. I believe Mr Welsford was drawing up a long range boat around a 3 or 5 cylinder gardner some time back.

  6. #41
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    Default Re: A new motor boat design from Paul Fisher.

    If the day ever comes that I am too enfeebled by age to continue handling sail, I imagine prolonging my seagoing life by changing to a power boat of the displacement variety. This thread does fuel (so to speak) the imagination re such a boat.

  7. #42
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by Small boats rock View Post
    If the day ever comes that I am too enfeebled by age to continue handling sail, I imagine prolonging my seagoing life by changing to a power boat of the displacement variety. This thread does fuel (so to speak) the imagination re such a boat.
    I would and a want to add a bow thruster since this is a single screw, and a staysail to slow down rocking. I'd setup the mast & boom to double as a cargo boom.

  8. #43
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by navydog View Post
    I would and a want to add a bow thruster since this is a single screw, and a staysail to slow down rocking. I'd setup the mast & boom to double as a cargo boom.
    Those are good ideas.

  9. #44
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by PeterSibley View Post
    An interesting innovation with reference to her motion.

    I don't want anything on my boat that sounds like that!

  10. #45
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    Default Re: A new motor boat design from Paul Fisher.

    Quote Originally Posted by navydog View Post
    I don't want anything on my boat that sounds like that!
    I agree but I don't think it's really that loud and once the hatches or covers are in place I doubt it will be heard.

  11. #46
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    Default Re: A new motor boat design from Paul Fisher.

    I have quite a bit of experience of a 22 foot displacement double ender with a 10 hp Bukh engine. It was built as a pleasure boat to the lines of a typical fishing boat from my region though with lighter (means too light) framing.
    I never ever needed to run the motor at much more than half speed. In good weather I cruised at just over 5 knots on one litre of diesel an hour.
    In conditions where all planing motor boats of the same size did stay in port or had great difficulties going to windward I could get home safely at just over idle RPMs. 7 or 8 hp would have been plenty enough. However that extra power was nice to have once or twice when towing something or monouvering in a tight spot.
    For my next boat I will never ever consider a planing motor boat unless I need the speed.

    So I am a decided fan of displacement motor boats but I don't like this Fisher design on open waters. When going into the wind the fat stern and thin bow with very little reserve boyancy would make it nose dive deep into the kind of short steep waves that we have around here taking lots of water on deck. The fat belly would make it roll dangerously in a side wind. Excactly the characteristics you don't want on displacement motor boats.
    Overall it looks like an inshore vessel where I imagine it would be excellent.
    Just my thoughts.
    Amateur living on the western coast of Finland

  12. #47
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    Default Re: A new motor boat design from Paul Fisher.

    I had a Bukh 10 in a 7 ton concrete boat. My experience was similar to yours, rarely needed to use full revolutions, and was economical enough to run for days....continuously. It had enough power to drive us against an Easterly Levanter in the Straights of Gibraltar and a short sea. I imagine in a slimmer motor boat with low auxillary rig it would be more than adequate.

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