EcoSmart, an efficient motorboat

Discussion in 'Boat Design' started by HJS, Mar 9, 2022.

  1. HJS
    Joined: Nov 2008
    Posts: 483
    Likes: 130, Points: 43, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    A summary of the most important parameters for creating an efficient motorboat is presented here. This basic data applies to all sizes of semi-planning and planning boats. In addition, an example of the application of the reported parameters is presented.

    Halved power requirement compared to normal planing boat with the same total weight, load capacity and interior space.






    Persp fuu.jpg
     

    Attached Files:

    Last edited: Mar 9, 2022
    bajansailor likes this.
  2. fredrosse
    Joined: Jan 2005
    Posts: 439
    Likes: 81, Points: 38, Legacy Rep: 56
    Location: Philadelphia PA

    fredrosse USACE Steam

    This thread is particularly interesting to me as I am currently building an oil fired flash steam plant (12 HP @ 1000 RPM) that will eventually be fitted into a hull with very similar dimensions you have stated. I plan on a typical plywood/glass/epoxy hull to be built soon. Of course I will have a conventional inboard arrangement, but that should probably allow a more ideal propeller size. Picture below is initial trials with steam plant stuffed into a converted 14 ft O'Day Javelin, only pushing to 4 HP presently while design parameters and operating details are worked out. Thanks for starting the thread. Rosse Oil Fired Steamer.jpg
     
    alan craig likes this.
  3. HJS
    Joined: Nov 2008
    Posts: 483
    Likes: 130, Points: 43, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    In addition to what has been said in the compilation, certain parameters that are related to speed also apply.
    This mainly applies to the area and the depth of the transom below the waterline. In addition, the position of the total center of gravity and the center of the waterline area must be matched in relation to the optimum speed.
    Do not guess, calculate ..... ;-)
    JS
     
  4. tlouth7
    Joined: Jun 2013
    Posts: 282
    Likes: 100, Points: 43, Legacy Rep: 10
    Location: Cambridge, UK

    tlouth7 Senior Member

    How does a long, narrow hull reduce planing drag?

    You seem to have counted the benefit from flat vs V bottom twice?
     
  5. messabout
    Joined: Jan 2006
    Posts: 3,381
    Likes: 527, Points: 113, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Help me understand how an "interceptor" causes the unit pressure on the involved bottom area to increase. Does such a device increase the velocity of impact at or near the stagnation point. Velocity is thought to influence unit pressure. In elementary impact theory the term V square is involved as in rhoV^2/2. Forgive my failure to understand how a barrier to normal flow can accomplish what you have described. I am open to further understanding of this concept.
     
  6. wet feet
    Joined: Nov 2004
    Posts: 1,461
    Likes: 463, Points: 83, Legacy Rep: 124
    Location: East Anglia,England

    wet feet Senior Member

    Its a nice looking hull and I hope we see some reports in the near future to confirm that it behaves as predicted.With the recent sharp increase in fuel prices,it could have a strong chance of being popular.I can just about visualise why an Interceptor would increase the pressure on the bottom and thus produce more lift.I also expect there is a drag cost involved and presumably the challenge is to gain the most lift for the least drag penalty.As is immediately clear from the results for speed/weight/power building light is always going to be important for a planing hull.Good luck with the project.
     
  7. Will Gilmore
    Joined: Aug 2017
    Posts: 960
    Likes: 445, Points: 63
    Location: Littleton, nh

    Will Gilmore Senior Member

    A fascinating paper and I like the concept, however, the weight to length argument for efficiency might Miss the point a little. That is, if cargo weight is part of the equation. If we just want a boat of a certain length without load considerations, then yes, long and skinny might be more efficient.
     
  8. HJS
    Joined: Nov 2008
    Posts: 483
    Likes: 130, Points: 43, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    Will Gilmore
    Payload is always included in my calculations.
    This is what I call total weight.
    JS
     
  9. Will Gilmore
    Joined: Aug 2017
    Posts: 960
    Likes: 445, Points: 63
    Location: Littleton, nh

    Will Gilmore Senior Member

    Then you are saying that a boat of 3:1 length to width ratio is less able to plane with a gross tonnage equal to a boat with 4:1 ratio while carrying the same maximum payload?

    The skinnier boat should sit deeper in the water at rest, or it would have to be a longer boat, which defeats the weight savings. Do your calculations disagree with this?
     
  10. HJS
    Joined: Nov 2008
    Posts: 483
    Likes: 130, Points: 43, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    Last edited: Mar 12, 2022
  11. Will Gilmore
    Joined: Aug 2017
    Posts: 960
    Likes: 445, Points: 63
    Location: Littleton, nh

    Will Gilmore Senior Member

    I am very sorry, HJS, but your point went completely over my head. I wasn't comparing V-hulls to Flat-bottom hulls. I was comparing the wider length to width ratio of a hull vs the narrower length to width ratio and the ease of moving vessels of equal displacement.

    Assuming planing is more efficient than non-planing headway, the most efficient vessel would be the one that planes the easiest (earliest, fastest).

    I believe that would be the wider hull because, for a given tonnage, the wider hull, up to a 1:1 ratio, would be the shallower hull in the water and the one that presents more planing surface to begin planing sooner (more efficient from the beginning). Bow shape would have an effect, since the bow wave is a big factor in planing. A bigger bow wave, the harder it is to lift the boat to the top of it. But that is also not part of the length to width equation.

    The closer a vessel's length to width ratio is to 1:1, the greater the buoyancy for the tonnage. It would suit higher in its lines. This is why I think the statement about skinnier boats are more efficient because they are lighter is not necessarily the point you want to concentrate on.
     
  12. sharpii2
    Joined: May 2004
    Posts: 2,254
    Likes: 332, Points: 83, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    My understanding of planing powerboats is that wider is better, up to about a 0.40 Beam/length ratio.

    The wider boat gets on a plane sooner, because it has a wider aft surface for the boat to plane on. This means it gets adequate lift with less bow-up pitch.

    Once it gets on a plane, the theory as I understand it goes, the fuel consumption rises a lot slower. It may even fall some.

    The narrow powerboat semi-planes instead, meaning it doesn't climb over its bow wave. It extends its stern wave instead.

    This, combined with a sharper bow, makes it much more economical to operate. This way, it can power considerably past a 1.34 speed/length ratio, while using a smaller engine for its weight.

    But, for the same horse power per weight, once the wider boat has adequate power to plane, the wider boat will be faster.

    If you go for a big enough engine, you can get the narrower boat to plane also. But it's not as efficient.

    But there is a lot to be said for a 20 ft boat that motors at say 10 to 12 kts, instead of 5 to 6 kts.

    The real advantage, in this case, is the range of speeds in which the boat will work reasonably well in.

    The wider boat, with its full depth immersed transom, suffers greatly at sub-planing speeds. I know this from experience, trying to keep a 19 ft one going in a straight line at between 3 and 4 kts.

    If the threat to either tax fossil fuels to the moon, or even ration them, ever comes to pass, these wider boats (over say 20 ft) will quickly become obsolete.
     
  13. HJS
    Joined: Nov 2008
    Posts: 483
    Likes: 130, Points: 43, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    Will Gillmore
    Show us your calculations in the form of charts, no guesses or speculations. Remember that a wider boat weighs more than a narrower one.
    JS
     
  14. kerosene
    Joined: Jul 2006
    Posts: 1,285
    Likes: 203, Points: 63, Legacy Rep: 358
    Location: finland

    kerosene Senior Member

    why would it weigh more (if length is reduced and not only beam extended)?
     

  15. HJS
    Joined: Nov 2008
    Posts: 483
    Likes: 130, Points: 43, Legacy Rep: 288
    Location: 59 45 51 N 019 02 15 E

    HJS Member

    Of course, I meant boats with the same length but different widths. In my compilation, the boats have the same weight, interior space and payload. The data I have reported are calculated and tested in model and full scale.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.