Outboard mounted Midships..yes /no ?

Discussion in 'Boat Design' started by pistnbroke, Jul 16, 2010.

  1. pistnbroke
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    pistnbroke I try

    I am forced to make a boat for the british canal system where the speed limit it 4 mph......stitch and glue about 15 ft long powered by a briggs and stratton 5 hp outboard which I have .....
    Now I could put it on the stern but I thought of putting it about 10 ft from the stern through a well in the centre of the boat ..cavitation plate level with the bottom of the hull ....fixed dead ahead and a drum around it like an old steam boiler with a funnel.....steering via a tiller at the rear....make smoke by putting fogging liquid on the exhaust ....fan to pull air up the funnel as the motor is air cooled...

    can anyone see any problems with steering ....yes yes problem with my head !!

    Wait for Frosty to Comment ....
     
  2. Jeremy Harris
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    Jeremy Harris Senior Member

    It should work fine. 'Dippy's' were configured like this and managed with a fairly mid-mounted prop, see here for some info: http://www.dippy.ca/

    The only thing worth thinking about is the additional draught it would create, but if you can pull it up into the well it shouldn't be a problem

    You could look at recreating a Dippy. I thought very seriously about doing this for my electric boat, the only reason I didn't was that my hull was really too narrow to spare the room for the box, given my large diameter prop.

    Jeremy
     
  3. FAST FRED
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    FAST FRED Senior Member

    Many older outboards were mounted in the aft cockpit in a well.

    They would not pitch out of the water , could be maintained and lines removed with ease, and most were in a fairly well sealed box to lower the noise level.

    A std rudder was used.

    FF
     
  4. keysdisease
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    keysdisease Senior Member

    Mullet Skiff

    A Mullet Skiff as used here in South Florida has the outboard mounted in a well either under the center console or even further forward than that. Underway you can't even tell they are powered differently than a conventional O/B boat although they do have some handling quirks, like docking is way easy.

    Steve
     

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  5. daiquiri
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    daiquiri Engineering and Design

    Do you intend to steer with the outboard, or with an aft rudder?

    Edit:
    Sorry, I've just read that you will steer with a tiller and a stern rudder. I see no problems then.
     
    Last edited: Jul 16, 2010
  6. pistnbroke
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    pistnbroke I try

    thanks for all your help and encouragement....
     
  7. boybland
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    boybland Junior Member

    Not an expert on the topic but I would think it would pretty much prevent planing having the engine well forward like that. Of course with a 4mph limit it probably doesn't matter. Someone who has actually driven a boat configured thus would know better than me though.
     
  8. Jeremy Harris
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    Jeremy Harris Senior Member

    Going anywhere near fast enough to get on the plane is forbidden on all our inland waterways, with the sole exception of a few lakes designated as water sport areas, so this isn't a problem at all for the intended use on the canal network.

    The canal network speed limit is just about a fast walking pace.

    Jeremy
     
  9. keysdisease
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    keysdisease Senior Member

    The mullet skiffs like the one pictured in my previous post have the engines forward so as to not interfere with nets being handled at the transom.

    They plane just like a boat with a transom mounted engine. Underway you wouldn't know any difference to look at one.

    Steve
     
  10. pistnbroke
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    pistnbroke I try

    On consideration I think there is a problem with manouvering at low speed considering the confinded narrow british canal ..the prop is 10 ft in front of the rudder so even with a large balanced rudder you need forward or backward movement to turn...its not like put the rudder over 45 deg and most of the thrust goes sideways.....remembering that the ideas was to build a 1920s steam launch replica with the outboard hiden in the boiler...could be a problem in a lock...thanks for all the advice...
     
  11. Jeremy Harris
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    Jeremy Harris Senior Member

    It couldn't be harder to manoeuvre than a narrowboat, I'd have thought. Plenty of small boats manage fine on the canals without having effective propwash over the rudder. A boat of this size would normally be manoeuvred in locks by boat hook on the lockside chains, or by ropes. No motor/rudder system would hold her steady when the paddles open and start to fill the lock, as the turbulence can be a bit much. To give you an idea of what to expect, here's a photo in a lock taken from the pedal boat version of my electric boat:

    [​IMG]

    The pedal boat Winsome has virtually no propwash effect on her rudder, plus has very limited power, yet still manages very well with just a boat hook and ropes fed through the lock side chains.

    FWIW, I very much like the idea of your mid-mounted, pseudo steam launch. Sounds like great fun.

    Jeremy
     
  12. pistnbroke
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    pistnbroke I try

    yes jeremy I did have conerns about a stitch and glue getting crushed in a lock by the narrowboat alongside ....remember the idea was a replica steam launch so I suppose I could have the boiler at the rear....as you may see from another thread I am working on the electronic steering for the boat at the moment.....
     
  13. keysdisease
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    keysdisease Senior Member

    Just steer the outboard, the boat will just steer a little different but with vector thrust wherever you put the motor it should be responsive.

    You could hook it up with a hidden cable pulley system to a tiller and just make the rudder normal size above the water and very small and shallow below, for show only.
     
  14. pistnbroke
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    I dont want to turn the motor as it should be in a well with the cav plate level with the hull and in a cav plate shaped cut out ...makes the hole in the boat bigger and the fake boiler bigger to acomodate the swing ...I want to use an old british dustbin with wood planking and a funnel....lid on the top ...
     

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  15. DCockey
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    DCockey Senior Member

    I wouldn't count on steering a boat with a mid-ships mounted outboard by turning the engine. The boat is likely to slide sideways more than turn.

    With the conventional arrangement with an outboard at the stern the engine is turned counter-clockwise as seen from above for a turn to starboard when moving ahead. Move the engine to the bow and the boat will turn to port when the engine is turned counter-clockwise. With the engine in the middle the boat may turn to starboard, turn to port, or not turn at all when the engine is turned counter-clockwise. But the boat slide sideways to port.
     
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