Still Need Input - Questions on Displacement Hull

Discussion in 'Boat Design' started by hershey2014, Aug 10, 2014.

  1. hershey2014
    Joined: Apr 2014
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    hershey2014 Junior Member

    I have had few replies to my original post that addressed my questions. I would like to have some replies and opinions on this particular build.

    I have decided to build an 18' by 8.5' aluminum minitug with a displacement hull. The boat will be used mainly by seniors for fishing and cruising slowly around a small lake (< 2 square miles) and would have a 6 x 7 pilothouse. A 9.9HP engine would be used to power the boat with 5-8 mph maximum speed. I considered a flat bottom knowing this would be easier to build. What would you consider to be the limitations of this design? Other hulls I have seen for such type of boats are vees of less than 5 degrees, modified vees, flat bottom with skeg, etc

    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.

    I have looked at all kinds of plywood plans like the Bo-Jest, in fact all the minitugs and many more boats. I have bought a set of plans and have many study plans. I also know I do not want a planing hull, a pontoon boat, 150HP, plywood anything, etc.

    If someone can give me input into the best hull for this particular boat, it would be greatly appreciated. Even better if someone can give me the pros and cons of each type, so much the better. Does anyone have any suggestions on what would be the best solution? Pictures would be great.

  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You're asking questions that are either extremely complex or so broad that can't be reasonably answered.

    There's no such thing as a "best" hull form. The pros and cons of any particular hull form can be subjective at best and though some generalities can be assumed with each type, but for the most part, especially in this size range, you'll have to accept the particulars and peculiarities of each design. This would be most notably true with an alloy build, where as the material just doesn't have as many offerings as other choices.

    At this point establish a firm set of needs and desires, then focus your search with this in mind. Of course, some level of compromise will be necessary, if only because you'll shop stock designs, but you should be able to find something close.

    I still think you length limitation will make for a very crowded boat with 5 or 6 aboard and a 7' pilothouse. Lets look at some simply math, a 7' pilothouse, leaves 11' available for an outboard splash well, cockpit and foredeck. Lets make the foredeck 3', leaving you with a generous 8' long cockpit, which now has a couple more feet chopped off for the splash well, leaving a 6' long cockpit. Assuming some flare to the topsides and minimal side decks, a 7' wide by 6' long space. Mark this area on the living room floor and have 5 of your friends stand in it and see how comfortable you are with this much elbow room. Sure, some of the crew/guests will be in the pilothouse, but there also will be occasions when everyone is in one or the other.

    Which 18' alloy mini tug have you decided to build?
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  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If this is for seniors, the first thing that comes to mind are physical limitations. A boat that size would be OK for kids with good boating knowledge.
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I think boarding and disembarking can be handled on small craft easily enough, given reasonable thought. My concern is the crew compliment.

    For example an obvious choice would be the Glen-L "Goliath", which is about the right length, a real alloy mini tug, but has a suggested crew weight of 800 pounds. This amounts to six 133 pound crew members or five 160 pounders. At 160 pounds per, there's little accommodation for stores or gear. This isn't a dainty boat, at 4,500 pounds displacement, 18' 6" long, 8' 2" beam, standing headroom, though shown with an inboard, I'll bet a well or bracket mounted outboard could be devised.

    This means Titan at 20' would be a better choice, given the expected load. I think this design is a stretch of Goliath, with the option of further stretching to 21' 6". This boat would handle the load requirement. These Glen-L designs are multi chine, V bottoms and certainly not as easy or initially stable as a flat bottom, but do look a whole lot better.
  5. Russ Kaiser
    Joined: Jul 2009
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    Russ Kaiser Exuberant Amateur

    A barge?

    Have you considered a barge design? If you're limited to 9.9 horsepower on the lake you're not going to be breaking any speed records anyway. You could make the topside look "tug like" and for the cost of building a tug, you could probably build a much larger barge. Five or Six folks fishing are going to want space.

    Is cruising the main function or fishing? If fishing is the main function the more you make the boat like a movable fishing pier the better.

    Is the slip space a concern for limiting size? Permanently moored or launched each time?
  6. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    On that other forum you complained no one was offering suitable assistance yet you refused to explain why you chose 18' as the length of the vessel.
    Care to share with us here?
  7. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    A rectangular punt with high sides to brace the knees/thighs against will do, I don't understand this tugboat business. Perhaps just paint one on the sides ! Like the Irishman who painted a pic of a bus on the side of his greyhound. Just a thought.

  8. Brolga
    Joined: Aug 2008
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    Brolga New Member

    I agree with most of the comments given - you really have to decide just what you want from the vessel and then look for a suitable design. If it is for seniors probably some cover from weather is needed possibly even a small toilet setup. A flat clear area for fishing seems to be needed too. What about a landing craft type vessel shallow draft, broad beam, easy access and could be O/B powered. You could still have a reasonable size cabin and the beam/hullshape to give a reasonable ride and good stationary stability.
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