Long & lean vs. short & beamy

Discussion in 'Boat Design' started by makobuilders, Mar 1, 2014.

  1. makobuilders
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    makobuilders Member

    I know that I'm re-visiting an often debated subject, but I would appreciate some opinions as to the merits regarding seaworthiness, comfort of motion, cost, etc between the following two designs with a similar SOR (full displacement power cruiser, steel construction):

    Design 1) 33'0" LOA X 29'8" LWL X 11'1" beam X 3'10" draft, 11.0 tons
    Design 2) 49'3" LOA X 39'6" LWL X 14'0" beam X 4'0" draft, 11.1 tons

    I assume the following:
    1) Interior volume is slightly greater (but not a lot more) on the longer design because of the long overhangs, versus short overhangs on the smaller one;
    2) Since displacement is the same, engine power (40hp) would be similar;
    3) Material costs would be more on the longer version, but this cost would not be significant over the life of the boat: steel, paint, ground tackle and windlass, port lights and glass, etc.

    Besides the obvious greater costs of haulouts and moorage, what would be advantages / disadvantages of the two?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Design 1 is significantly shorter, narrower, and not as deep, but weighs the same ? How so ?
     
  3. makobuilders
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    makobuilders Member

    Design 1 is double chine and very full (round) in the bottom. Design 2 is flat bottom.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Any drawings that would explain this ?
     
  5. makobuilders
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    makobuilders Member

    Can email to your PM
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Better to put them on the open forum, that way you will get more helpful opinions. :D Even if the boats were of similar length, it is hard (for me, anyway :rolleyes: )to see how two boats of similar draft can weigh the same, but one be that much wider.
     
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  7. makobuilders
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    makobuilders Member

    The longer one, with flat bottom, has shallow hull draft and then the keel/skeg brings it to 4' draft.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    OK, but the round bilge narrower boat draws less, which means the skeg must be deeper on the flattie ?
     
  9. philSweet
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    philSweet Senior Member

    It would help if you listed the purpose of the vessel, how many hours it would operate each year, the level of fitout, and where it is operating. It's hard to compare costs without that info. The powering suggests a bit less wetted surface than on the longer version, unless you plan on having a crew of young, attractive girls scrubbing the hull down daily. It which case, the more surface, the better.

    There is so much more hull plating on the longer one that I think it would be difficult to get it out at that weight. The short one sounds about right. Could be a foot longer LWL. Unless the SOR is restricted to short jaunts on very restricted waters, you'll want more power. You can get away with some overhang on very low powered boats, but overhangs are generally frowned upon for sea boats. If you want either of these boats to operate above 5 knots, loose the overhangs. 11 tons is about as small as I would want to go in steel. And it would tend to push the design towards the short and tubby end of the spectrum. I believe steel is a premium price option in that small a displacement, but others would know better than I do.
     
  10. parkland
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    parkland Senior Member

    I think the power is going to need to be greater for the shorter beamier boat for the same given speed.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I am still trying to work out how the skinny round bilge boat draws less water at equivalent displacement.
     
  12. FAST FRED
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    FAST FRED Senior Member

    Remember in the hunt for low cost boating Marinas and boat yards charge by the foot of LOA.

    I would always prefer a long skinny boat , but as a liveaboard for 20+ years, I built a 33 instead of a 41 and saved big for 2 decades.

    About 25% cheaper everything.
     
  13. Jacques B.
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    Jacques B. Junior Member

    Roger that!

    I've got a roomy 62 x 13, and not only is dockage more expensive, it's getting harder and harder to find.
     
  14. parkland
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    parkland Senior Member

    I wonder why that is?
    It seems like the money charged for moorage, there would be more competition...
     

  15. Jacques B.
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    Jacques B. Junior Member

    Well, in this northern Florida neck of the woods, there doesn't seem to be much competition for long boat docking. Most marinas with finger slips seem to prefer squeezing in more short boats that require less "turnaround room" (channel) to get to them.
     
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