Efficient Displacement Hulls

Discussion in 'Powerboats' started by Karsten, Jan 22, 2006.

  1. Karsten
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    Karsten Senior Member

    My dad asked me on advice what engine he should order for his Nidelv 28 motor cruiser (www.nidelv.com). When I looked at the data I thought that there must be something wrong. It's a 28' boat and weights 3.3t (probably empty) and they offer 100HP engines. He wants to cruise the channels in europe. So there are probably speed restrictions and I guess he will only use the boat in diplacement mode. I worked out that the engine will probably produce about 60kW and use 7.5 - 8 Litres per hour.

    Currently he has a sailing yacht that is 32' long weights 5.5 tonnes and has a 28HP engine. It easily does 6 knots under motor (no idea what the fuel consumption is but it is much less). My advice would be to take off the mast and lead from the keel und put 2000 litres of beer into some tanks to make the hull float on the same lines and then go cruising with that boat. The motoryacht hull appears to be absolutely crap in displacement mode.

    Are there any 30' motoryacht designs out there that are optimised for 6 - 7 knots? I think in the 1930 they produced some launches that would fit the discription but what happened in the last 70 years?
     
  2. Willallison
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    Willallison Senior Member

    Why do you say that the Nidelv appears to be absolute crap in displacement mode? Granted, the shape is hardly optimized for economical cruising, but the flip side of having a wide flat transom and beamy waterline, is that it manages to fit a fair bit of accomodation into a short length - the old compromise thing & you can't have it both ways.....
    Sure it would be more economical if it were a bit narrower and round-bilged, but is the difference really that great? And if it were significantly slimmer, he'd have to by a longer one to fit the same accomodations in.
    I'd also bet that your old mans sailboat doesn't have a nice protected helm and a big comfy cockpit, or nice big windows so he can actually see out of the cabin. The loo is probably half the size and the galley even smaller. Nope - I'd side the old bloke this time Karsten - this looks like a much more pleasant way to tootle through the canals to me.
    However, if all he plans to do is potter along at 4 knots, then I agree, the 100hp plant is way more than he needs. Without doing the sums, I would have expected a 30 or 40 hp engine to be more than enough. Resale with such a donk may be a problem though....
     
  3. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

  4. Windvang
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    Windvang Yacht Designer

    We have plenty of non planning designs in Holland. They are build for the European canals with low speed limits. They handle much better and have better fuel economy than planning boats. Plenty of space and comfort too.

    One example the Kuster 31: http://www.consonantyachts.nl/eindex.htm

    Arthur
     
  5. Vega
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    Vega Senior Member

    Nice interiors, for a 28'. If the sailing boat is not a deck-saloon (with that size it would have to be a motor-sailor), I agree with Williamson. That motor boat will be a lot more enjoyable boat to travel along, looking at the scenery.

    If your father has not yet bought the Nidlev, other option will be to look at a boat that offers the same kind and quality of interior, but optimized for hull displacement speed.

    Take a look at this one (32DS):

    http://www.sirius-werft.de/EN/sirius.html

    If you take out the mast it will be a very nice boat for Touring the canals (I can guarantee you that the interiors are very good). If you put the mast on, it will turn out to be a surprisingly good sailing boat.
     
  6. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I completely agree with Windwang and Vega.
    A boat designed for planing is not very efficient at 6 knots!
     
  7. Karsten
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    Karsten Senior Member

    Thanks guys!
    First I would like to point out that I don't have anything against the Nidelv! It was just a general remark that V-hulls appear to produce lots of drag at displacement speeds which seems to be confirmed by your replies.
    Thanks for your other proposals. Please keep them coming in. The Kuster has a radius of 500 Miles and uses 400l Diesel for that trip. That should be about 4.5l per hour. Not bad considering the boat is 31’ long and weights 7.5 Tonnes! How do you manage to make them that heavy? And just imagine what you could do with a well designed composites boat that should not weight more than 2000kg.
    My dad currently has one of the Swedish yachts with the wide coloured stripes on the topsides. So it’s very comfortable but not quite a motor sailor.
     
  8. BOATMIK
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    BOATMIK Deeply flawed human being

    I don't agree with any of you! :)

    If you think within the framework of a vee bottom boat with conventional displacement and big beam - you are all correct.

    But if you are thinking in terms of absolute truth - I can find an exception to your statements.

    [​IMG]

    The shape is derived from Mr Hickman's Viper in 1905 or thereabouts (18knots with a 12hp of the era - rocketship!!!.

    Because of the straight lines, low displacement, low deadrise :) and narrow immersed transom these boats power nicely through their whole range.

    The remarkable Phil Bolger has drawn up versions up to 50 ft long (150hp and 25knots)

    More info
    http://www.alaska.net/~fritzf/Boats/Sneakeasy/Sneakeasy.htm

    There are also quite a few sailboats with speed in displacement and planing modes. Maybe up to the 20 knot range. Whack a spray suppressing strake up at the bow and you will have something rather nice. Lots less power

    Best Regards to you all!
    Michael Storer
     
  9. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    OK Michael, it seems like I always agree with the last speaker :)
    Of course you are right.
    That's the vertue of light displacement!
    BUT if you want a boat that will be heavy because you are going cruising for a long time, AND it's limited in length and breadth, THEN you want to have the transom out of the water, well you understand...
     
  10. Sander Rave
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    Sander Rave Senior Member

    Karsten,

    7,5t may look a bit heavy, but this type of boats are loaded. In fact I know some people living on them the whole year except for the winter. Their boats are better equiped then their houses.

    Stabillity is not an issue when you have more than a dozen people over for your birthday party and they attack your treasure of 2000L of beer.
     
  11. Karsten
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    Karsten Senior Member

    I love long and slender boats with little displacement. Boatmiks boats should make awesome commuters.

    I also found a boat that would suit my dad. As I expected it's from 1938 and in steel. Appears to be in pretty good nick and has a 50HP engine. Does anybody know if there is something aroud that isn't older than my dad? Does nobody make 10m round bilge motor yachts in fibreglass?

    Cheers,
    Karsten
     

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  12. Windvang
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    Windvang Yacht Designer

  13. Guillermo
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    Guillermo Ingeniero Naval

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  14. marshmat
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    marshmat Senior Member

    Vega, Michael, Raggi- I agree with all of you, strange though it may seem. If you want a boat to have spacious accomodations, be good on plane, and still fit in a marina slip, it will tend to be a pig below planing speeds. Most modern planing cruisers are stubby, fat, heavy and V-hulled. The Bolger sharpies take a very different approach- by virtue of sheer length and slimness you get very low resistance at displacement speeds, while the flat bottom gives good planing and the long hull can span two or three wave crests to give a smooth ride. The downside is that you then have very little room for acommodations until you go to very large lengths, which makes it hard to get into a standard marina slip. The Dashew FPB 83 is another example of such a long, efficient hull (although it doesn't fully plane); despite its eighty-plus feet of LOA it is only a 40-tonne yacht and has the interior room of most production 50-55 footers. So it's a tradeoff between interior space, low speed efficiency, high speed efficiency, practicality at the dock, wave handling, etc, etc. I must admit that I'm a cat fan as far as high-speed high-efficiency goes, although I do have my sights on a number of monos too (gotta fit through the lock somehow!)
     

  15. yacht371
    Joined: Aug 2005
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    yacht371 Yacht Designer

    The most efficient combination of speed and fuel economy is found in power catamarans such as the MC27 built by Bond Yachts in Poland. This boat is as efficient as a sailboat at slow speeds but can do 24 knots with 100 HP. If is built lightly and has narrow hulls. www.motorcat.com
     
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