Questions on a Displacement Hull

Discussion in 'Boat Design' started by hershey2014, Aug 8, 2014.

  1. hershey2014
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    hershey2014 Junior Member

    I want to build an 18' boat with a 8' 6" beam. The hull would be a displacement type. The boat will be used mainly by seniors for fishing and cruising slowly around a small lake and would have a 6 x 7 pilothouse. A 9.9HP engine would be used to power the boat. I considered a flat bottom knowing this would be easier to build. What would you consider to be the limitations of this design?

    I would consider something other than a flat bottom. I want to maintain stability but make sure the boat is not tippy when fishing with the motor off. I also need to keep draft to a minimum. Does anyone have any suggestions on what would be the best solution? Pictures would be great.

    Thanks
     
  2. DCockey
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    DCockey Senior Member

    How small is the "small" lake?

    What has determined the dimensions and pilothouse size?

    How many "seniors" to be carried?
     
  3. hershey2014
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    hershey2014 Junior Member

    Reply to DCockey

    Lake is < 2 square miles. The boat will carry 5-6 people max. Pilothouse size determined by width and length for 2 on cold and wet days. This pilothouse size is an estimate and may change a little.
     
  4. DCockey
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    DCockey Senior Member

    Would a pontoon boat with a pilothouse added work?
     
  5. hershey2014
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    hershey2014 Junior Member

    Reply

    I am not interested in a pontoon boat. Thanks
     
  6. DCockey
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    DCockey Senior Member

    Do you have a particular design you are considering? Or have you seen a picture of a boat you think would work with some modifications?

    Are you planning on designing the boat yourself or are you looking for plans?

    Does the boat need to have a pointed bow or would a square bow be acceptable?

    What type of construction - plywood on frames? welded aluminum?
     
  7. DCockey
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    DCockey Senior Member

    18' length x 8 1/2' beam and minimum draft implies either a flat bottom or a shallow V-bottom.
     
  8. hershey2014
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    hershey2014 Junior Member

    Shallow Vee

    It was suggested to me 5 degrees for a shallow vee would be fine. Any thoughts?
     
  9. hershey2014
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    hershey2014 Junior Member

    The boat would be aluminum, with pointed bow. I have seen planing boats this size that I like but they are pretty tippy for a mobility restricted senior. Some are available from Liquid Metal, Ironwood, and Silver Streak amongst others. Too much boat for my use and very costly. I want to have some options when I get a quote from builders. There are no aluminum plans out there that are commercially available. Just custom builds.
     
  10. DCockey
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    DCockey Senior Member

    Without more information about the design, a shallow V of X degrees will probably be fine as long as the chines are submerged for most/all of the length of the boat. If the shallow V continued to the stem I'd keep the chines submerged to the bow to avoid slapping in shallow waves.

    I had a look at some of your previous posts. Are you interested in "micro tug" appearance?
     
  11. hershey2014
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    hershey2014 Junior Member

    MicroTug

    Yes, I am looking at a variation of the mini tug I previously posted about. I like the look. There are number of wooden tug plans available but all seem to have a different hull. No consensus hull for that length and beam of boat.
     
  12. PAR
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    PAR Yacht Designer/Builder

    The added complexity of a V bottom doesn't offer any advantages to offset the additional build effort and materials, plus it would be as initially stable as a flat bottom. 5 - 6, particularly if well fed adults is a hefty load for such a small boat, especially if swinging rods and tackle around, worse with a pilothouse eating up nearly half the boat's length.

    Can you post some pictures of similar size boats that appeal to you?
     
  13. rwatson
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    rwatson Senior Member

    Attached Files:

  14. messabout
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    messabout Senior Member

    A flat bottom with hard chines has a tad more initial stability than a vee bottom of the same breadth. If built of aluminum, then some structural considerations come into play. The flat bottom will need a little bit more framing than the vee bottom. The vee bottom offers almost no advantage for a slow moving boat other than that.
     

  15. PAR
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    PAR Yacht Designer/Builder

    The HB-18 from Bateau is a good option, simple to build, hefty payload, standing headroom in an enclosed pilothouse for those cold weather days, good static stability, etc. Not very pretty, but functional. It's a tapes seam build, so fairly high in goo factor and has a pretty large plywood requirement in it's BOM (31 sheets) for an 18' boat. I also think the 12 gallons of goo requirement is significant for a craft this size.
     
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