Pros and cons re: kicker motor placement on Inboard powerboat

Discussion in 'Outboards' started by Northeaster, Apr 10, 2017.

  1. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Hi Folks,

    Hoping to get some advice in deciding to place the more permanent 9.9hp Mercury 4 stroke (on used heavy duty Garelick Hydra assist kicker bracket) on the centerline or off to the side of the transom. Primary power is 4 cyl 150 hp Cummins, so kicker will be used mostly for trolling and in no wake zones as the boat will have a minimum/ slowest speed of approx 5.5 kts at idle with the diesel (once prop is repitched, for other reasons).

    I did have a temporary 2hp outboard on last summer for emergency/ trolling and had mounted off to side.

    Other than asthetics or having the center of stern clear for fishing, etc, how does placement affect performance, and would it better reverse performance with inboard rudder to have kicker on centerline?

    kicker will not be set up to turn...
     
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    The short answer is won't make a huge difference and it will work in any location, but....

    Centerline is better, but for best performance the prop needs to be low enough to not have the flow obstructed by the hull in both forward and reverse, this isn't always possible when mounted in the center. You may need a 25" shaft, which may be harder to find.

    When mounted to one side you will be able to turn much sharper one direction than the other, for simple trolling this isn't much of an issue, for maneuvering in tight quarters it can be.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    The minimum speed at idle of the main engine will be 5.5 knots ? Sounds crazy high to me, I cannot see that being correct.
     
  4. missinginaction
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    missinginaction Senior Member

    I just did a project mounting a Yamaha t9.9 high thrust on my boat last season. I also grappled with the center versus side mount issue. I eventually decided on a side mount position (port). Even with a 25 inch shaft getting the prop deep enough on a center line mount is problematic and I was also concerned with prop turbulence from the main engine's running gear.

    One thing you might want to consider when mounting the kicker is the eventual installation of remote steering / throttle control or a full fledged autopilot such as Garmin's TR1. I found that using the boat's rudder to steer with the kicker locked straight forward was manageable but not as precise as I wanted. Turning the kicker itself (vectored thrust) was much better.

    Here's a link to a post from last summer with a few photos. Good luck with your project.

    http://www.boatdesign.net/forums/wo...swim-platform-1973-silverton-sedan-56033.html

    Regards,

    MIA
     
  5. Northeaster
    Joined: Sep 2011
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    Northeaster Senior Member

    thanks for input thus far.
    - boat did 5kts at idle last summer, but i am adding cupping and pitch to bring rpms down/ load engine more, so i am guessing i will gain half a kt or so. full details are available on this thread. it has a 1:1 gearbox. i did not receive any advice on below thread, so it would certainly be welcome!!!

    http://www.boatdesign.net/forums/pr...weaked-buy-used-one-more-cup-pitch-57177.html

    - boat does have a shaft drive/ full keel and rudder so mounted on centerline the outboard would be trailing all of this.... does that matter though for displacement speeds or only if a larger outboard were used for getting on plane?
    NOTE- this hull does plane, but of course, not with a 9.9hp....

    - I like the kicker mounted on the swim platform, but I already bought a used kicker bracket which will lower / raise the outboard, so I will just mount on the transom.

    - I don't see myself setting up auto-pilot or remote steering.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Put it just so far from the centreline as to avoid the turbulence of the prop/rudder, which is enough drag without having to have your aux working in the "stagnant" water.
     
  7. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    I don't see any problems with a transom mount. If I had a different boat I might well have used one myself. Certainly a kicker mounted dead center is not going to have any steering issues. What I can tell you is that a kicker mounted off to the side isn't going to either. If you mount the kicker on the port side, as I did, the boat might have a slight tendency to track to starboard, but that's easily compensated.
    You're going to be happy once this is done. I use my kicker a lot, great for fishing. I also run on it for at least a few hours a day when I'm traveling. On my main engine I can cruise easy and get between 2 and 3 miles on a gallon of gasoline. With the kicker I'm a "5 knot yacht" but i get a solid 8! So if I'm not in a particular hurry I can save a lot on fuel.

    Regards,

    MIA
     
  8. Northeaster
    Joined: Sep 2011
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    Northeaster Senior Member

    thanks for advise - will mount perhaps a foot or so off center... and yes, looking forward to having a reliable and fuel efficient aux engine.

    Mr. Efficiency - I really appreciate your help in past and thus far - just wondering why you think that 5.5 kts at idle is so high, or what could potentially explain this?

    Engine is 150hp Cummins 4bt (3.9M)
    idle is about 800 rpms
    gear is 1:1
    prop is 15" x 13" - just had measured (i had thought it was a 15 x 14) and currently get 5 kts at idle
    Having a prop shop add cupping and 2-3" of pitch as i can currently hit 3300 rpms in neutral and in gear (at 23kts) when high idle for engine is spec'd at 3100rpms, with an intermittent rating of 2800 rpms and max continous rating of 2500rpms.

    I would like to understand choices/ implications but feel i should have prop reworked to load the engine more, and bring down the rpms approx 400-500, so i can cruise closer to the max tourque/ efficient range of 2200 rpms, and still hit decent speeds...
     
  9. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Mate, if you say it won't go any slower than 5 knots, then 5 knots it is, but it seems to be a minor nuisance that precludes slow trolling or manoeuvring in a marina for example. I agree with MIA that an aux a little off centre won't cause too much steering difficulty.
     

  10. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    It is all used running gear, so i couldn't be choosy like wanting a high end gear box that allows slower trolling, etc.
    re: marinas -not many around here - no big ones to go through. Just leave my dock and go to island beaches or fishing - pass one small marina/ no wake zone on the 0.5 km run down river to open bay.
    that's part of the reason I built the shaft drive/ inboard- or should I say part of the reason I was less concerned about the steering/ lack or backing ability of it...
    thanks for the help!
     
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