Which Outboards to power a TinyHouseBoat?

Discussion in 'Outboards' started by Tom Peach, Oct 1, 2020.

  1. gonzo
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    gonzo Senior Member

    It depends on what flag you are registering the vessel under. Spain is a lot more restrictive than the UK.
  2. Tom Peach
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    Tom Peach Junior Member

    No reason other than ease really, because I am planning to construct the first boat in Portugal and I haven't seen many barges in Portugal, plus I thought the ready molded pontoon floats would be quite economical. How wrong I was!!!

    I also couldn't imagine finding many 10m x 4m barge hulls, I just imagined them being longer at that beam width
    Last edited: Oct 4, 2020
  3. missinginaction
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    missinginaction Senior Member

    Keep in mind that you will only be moving your boat at displacement speeds. What a high thrust outboard does for you is provide a lot of torque (thrust) at low speeds. This is precisely what you want in a houseboat or a barge.

    A high thrust engine uses a gearbox to allow a relatively small engine to spin a relative large propeller.

    Keep an open mind and see if you can find a knowledgeable Yamaha dealer who can give you some advice. Better yet find someone who owns one of these engines and pick their brains. You could go larger but for the intended usage of your boat I'd say that a 25 horsepower high thrust outboard would be plenty.

    Good Luck,

    Last edited: Oct 4, 2020
  4. Tom Peach
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    Tom Peach Junior Member

    Well my plan was 39 x PT06 floats (or 36 x PT01), depending on if I went for three or four 'hulls' to make up the pontoon base. Either way it works out about the same cost wise and load capacity wise.
    Sadly the floats from that particular supplier are coming in about 2x - 3x the price I anticipated so I either need to up the budget or consider other methods of construction. The floats are around 8000€ Exc VAT!!! Ouch!!

    Price list attached if you're interested.

    You raise a good point and I am now leaning towards making the pontoon base from timber frame with ply panels and glassing the outside of the hull. What I don't know now, of course, is how does one calculate the load carrying capacity of such a design. Plus I will need to keep the design pretty basic, and square, mainly so as not to challenge my already limited carpentry skills ;-)

    I have sketched a very basic design idea, what are your thoughts?
    I presume I'll need some sort of slope to the bow to displace water more efficiently and avoid water splashing over the deck when moving?

    I am also wondering if there is any benefit, from a flotation point of view, in putting polystyrene blocks in the bottom of the hull? Will it make it more buoyant?

    What is the best method to waterproof the hull? I was thinking glass fibre, but would I need to cover the whole hull in glass fibre mat or just the corners and joints and then just paint with epoxy or polyurethane?

    I'd love to hear peoples thoughts

    Attached Files:

  5. Tom Peach
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    Tom Peach Junior Member

    Is that why you see so many UK flagged boats abroad?
  6. gonzo
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    gonzo Senior Member

    I don't know how it works now after Brexit. In Spain a UK flagged vessel is just another foreign vessel. You should check for import duties, CE compliance, etc.
  7. fallguy
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    fallguy Senior Member

    you really want a barge bottom my friend

    Consider you need structural webbing for any type of flotation. Would you prefer inexpensive flotation and a web structure above it that rusts out in a few years? Or would you prefer a barge bottom with enclose webbing and the locations for fuel, waste, water?

    Polystyrene foam floats and has low water absorption, but how do you intend to connect to it? In loose terms, it cannot support a house without extensive effort.

    Here are fair prices for canal boat hull only that are relatively inexpensive, even for UK.

    Hull Only Narrowboat. Prices and Specifications. http://liverpoolboatco.co.uk/id6.html
  8. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    A barge also give you lots more space and a lower centre of gravity.
    You can make either work but, like Fallguy, I'd recommend a barge hull.

    It doesn't appear you need a motor, and if you do, you only need one.
    But a tow boat works really well.

  9. bajansailor
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    bajansailor Marine Surveyor

    Re the hull shape, just a simple box section with a raked bow should be ok.
    Re glassing the outside, please use epoxy and woven cloth rather than polyester resin and (eg) chopped strand mat (CSM).

    Re calculating the load carrying capacity - first calculate the displacement at a waterline - say 0.3 m.
    I think the boat is 10 m. x 4 m., so at 0.3 m. draft the volume of displacement is 10 x 4 x 0.3 = 12 cubic metres.
    And in salt water (density 1.025) the displacement would be 12,300 kg.

    Now add up the total surface area of the hull panels, and get their volume (by multiplying by the thickness) and then multiplying by the density of the plywood. Make allowance also for the weight of the GRP sheathing.
    Estimate the weight of all the framing employed in the hull in a same fashion.
    Add up the weights of all the outfit items that you know (so far.....) will be going on to the boat, including the engine, furniture, and the fuel and water tanks.
    You will then have an estimate for the lightship weight.
    The difference between this and the calculated displacement will be the load carrying capacity.
    If your lightship weight is more than your calculated displacement, then she will float at a deeper draft.

    Re polystyrene blocks, you would have to 'lash them down' (not very feasible), or fill a compartment(s) with them to get reserve buoyancy in case the boat decides to fill up with water for some reason.

    Re houseboat design, Eric Sponberg has an interesting page on his website about them.
    Houseboats https://www.ericwsponberg.com/boat-designs/houseboats/

    Re your hull form and construction, involving pontoons, here is a left field variation on this theme using discarded plastic barrels as floatation -
    However like with pontoons, you then have the disadvantage of having to design all the tank spaces in above the deck level.
    Last edited: Oct 4, 2020
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