New guy-help me figure out what to build...

Discussion in 'Boat Design' started by YotaTruck, Jun 16, 2013.

  1. YotaTruck
    Joined: Jun 2013
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    YotaTruck Junior Member

    I stumbled across this place looking for ideas for DIY pontoons and I'm hoping that I can get some advice on what I should be looking to build so that I can do some research on the best way to build it. I live in between two decent size (about 2000 acres) reservoirs that are limited to 9.9 HP and I want to build something that I use on both lakes just for general boating. I fish a little but mostly I'm just looking to take my wife, my daughter, and the dog out for a nice day on the water and to just explore the shoreline. In fact, the best part of having a boat at either of these lakes is that it allows you to access the far shorelines that aren't easily accessible by trails or other means, so you can have a nice quiet day of hanging out, skipping rocks, and swimming.

    Basically I'm looking to build something very simple and utilitarian that will move people and gear (cooler, grill, etc...) across the water efficiently and safely, but that will also allow us to putter around the lake. Given that, my first thought was to look at some sort of of pontoon/barge type design. Pontoon boats seem simple, but I know that there must be more than meets the eye as far as design. I've looked at a few different plywood pontoon designs (I figure that's the easiest and most accessible material to work with), but I've also looked at a few barge type designs as well. One of my biggest worries working with plywood is weight since I'm limited to a 9.9, but for all I know there is a good design out there that is a compromise between strength and weight.

    It would probably help if I laid out a couple of parameters to help narrow down what design might work best:

    9.9 HP maximum
    5 person capacity/1500 lbs of people and gear
    Tiller steered
    Approximately 7' x 16' platform
    Plywood construction
    Trailerable

    Looking forward to some constructive criticism!
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    There are lots of choices for you to pick though. I'd discount a pontoon style out of hand. They're not very efficient, you have to build two hulls, instead of one, everything is well above the LWL and exposed, etc. Just lots of stuff not to like.

    A 16' boat with a 5 person capacity is asking quite a lot, basically a half a ton, just in crew compliment. This requires a substantial amount of hull volume to support, so a barge, fat sharpie or skiff would be my recommendations. Also with the HP limitation, don't expect to go more then 6 MPH with a barge of pontoon style of boat. A cat might be an option, though we get into the two hull thing again.

    If it was me, I'd accept the speed limitations and go for a flat bottom scow or barge shape. You'll get the most bang for the buck, in terms of room and capacity. I'd want to build from taped seam plywood to keep things water tight and light weight. In fact, in this size range, you'd be very hard pressed to beat a taped seam, plywood build in regard to weight, price, ease of build and strength.

    Try Glen-L.com and Bateau.com, where dozens of designs can be found.
     
  3. gordanm
    Joined: Mar 2009
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    gordanm Junior Member

    My experience with pontoon style boat is very limited, but I wouldn't totally dismiss one design that caught my eye recently: Bateau Pontoon Cat 22 (design is also available in 20 and 24 length). Designer claims much more efficient hulls (less hp required) compared to standard production pontoon tubes. I would also expect speed almost doubled compared to barge style hull (but then again, it might be completely irrelevant to you, YotaTruck).
    Of course, building two hulls require more work.
     
  4. PAR
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    PAR Yacht Designer/Builder

    The Pontoon Cat is a complex build and considerably larger then Yota has asked for. Though it'll take a 10 HP, don't expect it to plane with one. She displaces over a ton, which requires a lot more than a 10 HP. Jacques Mertens has done his usual nice job with this boat, but it's a whole lot more than a 16' puddle jumper.
     
  5. gordanm
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    gordanm Junior Member

    I thought of Pontoon Cat because Yota asked "Approximately 7' x 16' platform " (so in case of Pontoon Cat 20, that's about that). Also, I didn't see requirements for planing (therefore efficient cat hulls will certainly be faster with limited hp).
    And yes PAR, you are right, it's complex build. And maybe to much of LOA. I just fell in love with this design when I saw it so I thought I might share it with Yota (in case his requirements are not "solid as rock").
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    If you are restricted to 9.9 hp, I'd be building whatever you choose around that, you can not expect to be going fast with the load you specify, and the most suitable engine would be a 20 or 25 " with a high thrust gearbox ( greater reduction ratio and larger diameter propellor).
     
  7. YotaTruck
    Joined: Jun 2013
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    YotaTruck Junior Member

    Thanks for posting it. I am only just learning the differences between a pontoon and a catamaran so it's helpful to see such designs. It's giving me a lot of ideas to fool around with on Sketchup. I also found this interesting vessel on Google images:

    http://www.waterwitch.com/6mbuddy
     
  8. messabout
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    messabout Senior Member

    YT the distinction between pontoon and catamaran goes something like this. Pontoons are cyclindrical or box shaped closed containers whose sides are parallel for almost their full length. Designs of that type are not really designs but done that way to utilize the simple, easy, construction from such shapes. Neither of them are very efficient in terms of speed, power requirement or fuel consumption.

    The round pontoons are a bit better for very slow running but a pretty awful design for running at speed. The flat bottomed box is a little better for speed and horsepower requirement but less efficient at low speed. Not enough less efficient to matter much however.

    A catamaran has hulls that have a curvy shape when viewed from the top. They are pointed in front and sometimes, but not always, in the back. Catamarans are displacement boats that are capable of mid range speeds with modest power input. They are far more efficient and sophisticated than pontoon types.

    Whether pontoon or cat, you are limited by dimensions for the amount of weight they will support safely. fifteen hundred pounds on a 16 foot length is not a happy combination for either cat or pontoon.

    A 16 foot monohull is much more practical for hauling the 1500 pounds that you suggested. If decently designed it will go along just fine with the 9.9. Not fast though, not with that much weight. If the mono was designed correctly it could go quite briskly, 20 plus MPH, but only if lightly loaded with all up weight of 500 pounds or less. A different design would be needed for heavy weight operation and you'd be looking at maybe 6 MPH but with very modest fuel consumption. In such a boat you would not be flogging the little 9.9. With the fast boat you'd be using the motor pretty hard.

    The difference in the monohull design involves the way that the back half of the bottom is configured. Viewed from the side, the aft bottom would be curved upward toward the waterline for the burdensome boat. Yes, that is counter intuitive but that is the way this deal works. For the fast, and not so burdensome, boat the bottom would be essentially straight from the front to back. That is about as brief a description of the differences that I can muster.

    The aluminum work boat in your link is strictly a work boat. It is ill suited for family cruising. It is, however, very good for its intended purpose which is pulling weeds or removing trash or detritus from the water.

    Continue to ask questions if you like.
     
  9. YotaTruck
    Joined: Jun 2013
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    YotaTruck Junior Member

    This was helpful, thanks. I should note that hitting 20 MPH isn't what I had in mind. If I could put around at 6-7 MPH and top out at 12 that would be more than adequate. I still have a lot more research to do.
     
  10. miamitech
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    miamitech New Member

    what to build

    does it have to be built? how about a 16ft RIB, that is a rigid inflatable boat, should cover all your expectations, wieghs under 400lbs and will move by 9.9hp outboard plus you can upgrade johnson/evinrude 9.9 to a 15hp carb or buy a 15hp and renumber the cover to 9.9. rarely would you get checked.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Building a RIB, certainly doesn't fall into the criteria he's listed as desirable, not to mention isn't a very cost effective entry level project.

    Assuming a 14' LWL, you're looking at displacement speeds of 5.8 MPH (at 1.35 S/L ratio). To see 12 MPH, you'll need to be on full plane (3.2 S/L ratio), so power verses weight and a really efficient (to plane) hull form is necessary, hence my recommendation (earlier) for a flat bottom skiff like set of shapes.
     
  12. YotaTruck
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    YotaTruck Junior Member

    So after much searching and asking questions over on the Bateau forums as well I think I'm going to settle on the GF16 Garvey/Jon Boat. It's definitely simple enough to construct as a first timer and with a 5' 2" beam it's certainly going to be large enough to meet my needs. I have a few questions regarding capacity, forgive me if they're fairly elementary for these forums, but I'm just trying to make sure that I understand things for safety's sake. I had mentioned that I wanted the ability to carry five people (including myself)-given the specs of the GF16, is this possible/safe?

    Draft at DWL - 5"
    Hull Weight - 165lbs
    Displacement at DWL - 1310lbs
    PPI at DWL - 250lbs


    I take this to mean that when the combined weight of the hull, motor, accessories, passengers, gear, etc...is 1310lbs, that the boat will be sitting at DWL. Is that correct? If so, than the following should be true:

    1310lbs - Displacement at DWL
    - 165lbs - Hull weight
    - 85lbs - Approximate weight of outboard
    - 250lbs - Miscellaneous gear
    -----------------------------------------
    810lbs - Crew capacity with boat at DWL


    However, given what I also understand about PPI at DWL (and please correct me if I'm wrong), this means that once the boat is at DWL it would take the addition of another 250lbs to cause it to draft an additional inch? If so, given the fact that there is so much freeboard to begin with on this particular boat, I don't think it would be unsafe to add a 5th passenger for a total crew weight of 1060lbs. That of course is assuming that I understand these terms correctly. It should also be noted that I'll be adding enough foam to make the boat unsinkable.

    I do realize that the boat will certainly not plane nor move swiftly, but again, that's not of much concern. Perhaps down the road I would consider a clandestine upgrade beyond 9.9 HP and opt for a 15 or even a 25, but from what I've heard the rangers (the reservoirs are under the purview of the State Division of Parks and Forestry) are wise to that trick and will check serial numbers stamped in various places on the engine if they suspect shenanigans.
     

  13. miamitech
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    miamitech New Member

    outboard

    Smart rangers they might be but they won't take apart a 9.9 just to see IF the carb has been replaced with a 15hp carb. Enjoy your new boat.
     
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