Trailer Sailboat Conversion to Motorboat

Discussion in 'Boat Design' started by doogymon, Mar 18, 2012.

  1. doogymon
    Joined: Jul 2006
    Posts: 27
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Ontario

    doogymon Junior Member

    Hi

    A Slipper 17' GRP, 18" shoal keel has a fairly flat bottom being a trailer sailer.

    Could a guy plunk a motorwell in behind the keel or bend on a

    offshore bracket with floatation so that a larger motor could

    push her up past hull speed?I'd like to add a windscreen, pedestal seats and

    helm.

    http://sailboatdata.com/viewrecord.asp?class_id=6473
    Sorry if details are sketchy.
     
  2. whitepointer23

    whitepointer23 Previous Member

    tunnels has done this. send him a pm if he doesn't post a reply.
     
  3. PAR
    Joined: Nov 2003
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    Likes: 477, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It's quite unlikely you'll get much more than a knot over her hull speed, given the shape of this boat. Simply put, 6.5 knots (about 7.5 MPH or 12 KPH) is about all you'll get without a several hundred HP and some way of holding the bow down.

    [​IMG]
     
  4. tunnels

    tunnels Previous Member

    I just used a HD rise and fall spring loaded outboard bracket and didnt try ever to steer the boat with the outboard just used the standard tiller and rudder but not all the way down . We never changed the boat at all ! still had themast and sails and everything plus the cast iron keel and everything else . The boat was Was reasonably flat in the area of the hull behind the keel so it planed well with the family in the cockpit .
    Was really funny one day coming home late afternoon and tide in and getting near the top of the tide with the channel running quite fast!!!, so pulled into a small sandy bay to drop the mast stow all the gear and kids to have a rom and blow off a little steam . As i came rounded the corner quite quickly! almost planing and into the bay a lady saw me and fanticly came running down the beach waving her arms shouting the bay is to shallow for yachts and to stay out or i would run agound !!!!! ,so as i got a lttle closer I dropped the bow anchor and swung the boat stern to the shore and then reversed the out board till i had some momentum and the lifted it and backed completely up on the sand and jumped off into the dry sand , She had a completely bewildered look on her face as mean to say how the hell did you do that ? after the family got on shore i payed out the stern anchor and then pulled myself out into the bay into couple of feet deep water and stayed there till all was ship shape and stowed then let go the bow anchor and pulled myself back into the shore and everyone got back on board again and we stowed all ropes and the anchor and powered off and planed all the way back to the boat ramp
    The boat only drew a very small amount of water and with the cast keel as the lowest point we used to go speeding across the shallows and not bother following the channel . Had a couple of smart power boat guys try to follow me once but we left them sitting on a sand bar miles from any where The joys of boating are many !!:p
     
  5. tunnels

    tunnels Previous Member

    The outboard id be looking for is the older 15hp omc !! its a powerfull little beasty!! same as the 9 hp but a little more grunt !! wow that little boat would simply fly !!. .
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 477, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The stern of that boat has a pretty tall "tuck" angle. It's all in the buttocks (as it should be) and she'll pretty much just squat, once over 5.5 knots. A "Dolfin" on the ventilation plate will could help this to a small degree, but asking her to climb very far up the "hump" is just a futile effort. A planning surface could be added at the LWL aft, to permit semi plane speeds, but you'll max out at a little over 8 knots (9.4 MPH, 15 KPH). Just too much tuck and not enough volume distributed aft, to do much better.

    I've made a few of these "putt-putt" conversions and they work well if you're interested in economical, low speed operation, not so much if you want more then semi plane speeds.

    Lastly, do yourself a big favor and rig up steering for your outboard. You can use a slave rod to the rudder/tiller, cables and pulleys, remote helm, what ever, but the maneuverability is so much better then with just a rudder, that you'll never go back to a rudder once you've tried it.
     
  7. whitepointer23

    whitepointer23 Previous Member

    even if it got 7 knots par, he could cover a lot of ground on a day out.
     
  8. doogymon
    Joined: Jul 2006
    Posts: 27
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Ontario

    doogymon Junior Member

    You folks are are amazing....

    I was thinking of bolting on a portside motor bracket identical to the

    starboard OMC type bracket. Then I would strap (bolt) a short 2 x 8 across the stern

    attached to the brackets. This would clear the rudder and provide a solid perch for a

    larger motor I'm thinking. My centre board is glassed up inside the keel...not used.

    Was hoping to get 10 knots.

    Doog
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 477, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    7 knots is a wish, 10 knots, frankly a dream that's not going to come true. Just the wrong set of shapes on this hull. With a "whale tail" type of device and lots of power, you might get close, but these types of hull alterations are often a hit or miss type of thing, with trial and error as the only method of making it work, which sounds frustrating and costly to me.
     
  10. tunnels

    tunnels Previous Member

    Without dreams about boats we might as well be married with kids !!

    :idea:You could just make a glass exstension with no back just a new shaped bottom and sides to make the hull shape that would give you the best of both worlds !!,Let the water flood the exstention and when you move forward it will empty and get up and go using you out board ,Nothing is impossible !! :(
     

  11. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Why not get a 18ft Boston whaler and install your accomidations on it?

    It will be fast , seaworthy (with not too much house) and is trailerable.

    Might even have a resale value if the cabin comes off.

    FF
     
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