kayak, glass repairs and modifications. an engine!

Discussion in 'Fiberglass and Composite Boat Building' started by headsmess, Dec 24, 2014.

  1. headsmess
    Joined: Dec 2014
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    headsmess New Member

    howdy all :) first post. oh no. a newbie!

    man all lifeboats! flee!

    erk. lets cut to the chase here.

    i got an old fibre kayak. pretty ratty, but for the price (free) it suits my purposes.

    one. a small 4 stroke engine.
    two. a selection of the largest RC props i could find and afford at the time.
    three. lots of sanding and glassing to get the engine attached.

    all be inboard, glassing a box in just behind the seat with a lid, and a flexible 1/4" shaft out the bottom.

    therell be a kitchen rudder for control. gives me steering and reverse. rudder bar up front for the feet, throttle/reversing link up where handy but not obtrusive...

    the glassing side of things, that i got down pat. ill be putting another two layers of thin cloth over the bottom, where its all worn out and tired looking. maybe more. couple of bulwarks for floaties, and some reinforcement here and there. as long as i use enough catalyst in each batch:rolleyes:

    the thing is, mounting the prop-shaft, and engine mounts. what materials?

    a bit of research is telling me to mould a prop tube in glass, a fair bit bigger than the stainless tubing ill use. i glass that into the boat, and either silicone or epoxy the stainless shaft in afterwards.

    that make sense? due to expansion contraction and vibration...dont try glassing the tubing straight in?

    as for engine mounts... itll be rubber isolated, but...i guess i just lay up some heavy sections of glass and use large SS screws/bolts n washers? dont try glassing any steel into it? i guess that goes for all fittings, like pivot tubes etc?

    NOW! for the pundits that will gripe and grouch and say an RC prop is useless...:p this things a KAYAK. i have a 1.5 hp engine. im not expecting to break records. im expecting to go check out some of the local creeks and waterways without having to paddle :) and spun up at 5K... these things really do move some water! they load up enough that i seriously doubt the engine will actually pull much faster than that. theyre also running fully submerged and ducted with the kitchen rudder.

    i can get up to 82 mm, and if thats not enough...i got a 4 axis milling machine ;)


    cheers for reading. hope someone thinks of a few lil points i may have over looked. im sure theres plenty more! for now the main concern is to get the glass part done, and done once!


    oh! other than an orbital sander...how to strip gel coat? i tried sandblasting. eat holes in concrete in a flash! strip rust away instantly! think it would even mark this gelcoat? i sat there for two minutes and got a square centimetre off...
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    First question: what is the RPM of the engine when it produces 1.5HP?
     
  3. headsmess
    Joined: Dec 2014
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    headsmess New Member

    ahhh, sounds like the first pundit has arrived :)

    about 6500, much the standard for lil 4 strokers. probably what it will do when moving. stuck in a bucket of water, best i can get is 5k until it sucks in some air... then its free spinning up to the 10k redline... wee! max torque is the 5k mark.

    yes. i know theyre intended for 12k+. i know theyre usually surface type props. i know diameter is important and these are tiny. (though 72mm is pretty freakin big for an rc boat... they arent terribly common,and the 82 is even harder to find.)


    cant see how thats relevant to glassing foreign materials into a hull and how to prevent future trouble, ie cracks at joins and leaky bits?


    buuuut...at least someones interested :)
     
  4. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The RPM is relevant to the choice of propeller and shaft diameter. This will also drive the size of the shaft tube.
    Second question: what is your target maximum speed?
     
  5. markstrimaran
    Joined: Dec 2014
    Posts: 291
    Likes: 6, Points: 28, Legacy Rep: 28
    Location: usa

    markstrimaran Senior Member

    gas motor

    Blocks of wood bonded to the fiber glass. If your mounting it inside the hull cooling will be a problem. Ever see a go devil type motor mount. Surface drive straight shaft. Easy to mount. And readjust.
     

  6. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Is the engine a horizontal or vertical shaft?
     
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