Installing an auxiliary outboard (9.9)

Discussion in 'Fiberglass and Composite Boat Building' started by missinginaction, Jan 3, 2016.

  1. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    I'm plugging along with my transom project. For those who might not be familiar I restored a 25' Silverton cruiser circa 1973 over the past years and am still fitting her out.

    My question here is pretty simple. Since this is a v-drive boat the transom is wide open as regards the outboard placement. I can purchase a long or extra long shaft 9.9 HT and place the engine right on the center line. She's drawing 15 1/2 inches from the waterline to the bottom of the keel. I can purchase a nice bracket that will get the cavitation plate right where it's recommended to be (Garelick recommends 1" above the bottom of the keel). This placement will put the kicker prop just a few inches behind the boats rudder. I would get some turbulence from the main engine prop, sitting stationary while the kicker was running. I'm wondering if this is something that I should be concerned about at displacement speeds?

    The question is: Is a center line placement preferred for this installation?

    The outboard will be a tiller style but locked in the straight ahead position, steering will be via the boats rudder.

    Every kicker installation I can find has the engine mounted off center as there is something on the center line (outboard/sterndrive) that would not permit an installation there. I don't have this issue.

    I'm probably overthinking this but I like to ask these questions if I'm unsure. It never hurts. Thanks in advance for any advice.

  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    It will make little difference at low speeds. The propeller is probably 2 feet or so forward and deeper.
  3. whitepointer23

    whitepointer23 Previous Member

    If the kicker is in line with the rudder just make sure you aren't restricting flow to the prop when u turn the rudder. It may also send eddies to the prop .
  4. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    I can see your dilemma. I agree with gonzo, I don't think yhere would be much if any affect from the main prop but I can also tell you from experience that it will work just as well off center, not much help I know.

  5. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Thanks for the feedback guys. Steve, that comment was helpful in that it might free me up to do the install off center a bit and use a shorter shaft engine. I'll need to work it out on paper. It's good to know from someone with experience.

    Gonz, I won't worry about the prop as it is indeed forward of the rudder and would be somewhat below the kicker prop.

    As for the kicker prop and the boats rudder I'm starting to think that keeping the two in close proximity might be helpful in docking the boat or using reverse. Based on what I've read those high thrust outboards move quite a bit of water in reverse. That could be helpful when docking. As you guys probably know single inboards without thrusters can be a handful when docking as you have little to no steerage way.

    Now if I can make a decision between the Honda and Yamaha high thrust 9.9's I'll be in good shape. Fortunately I have a little time to think about this.

    Thanks again guys,

  6. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Whether you mount it in the center or off to the side go with an XL shaft. You want the prop as deep as possible and the powerhead as high as possible. This keeps the prop in the water and the powerhead out of it.

    When mounted on a bracket the motor will be exposed to greater differences in water level when the waves and wind pick up.

    For a kicker at low speeds the recommendation on AV plate height is irrelevant. The deeper you can get the prop, the better control you will have, especially in reverse.
  7. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Thanks for the reply ondarvr. The outboard bracket manufacturer's instructions call for the cavitation plate to be an inch above the bottom of the keel. Following your recommendation I could install the bracket a few inches lower and place the propeller directly aft of the boats rudder when in the full down position. This would give me good water flow over the rudder especially in reverse, something I'm currently lacking.
    I'll have to look into this. This boat spends most of it's time on rivers so big seas are not generally a problem. I do plan to get out to the Great Lakes and down to New York. However, if I were in seas large enough to cause difficulty with the kicker I believe I'd be running on the main engine anyway.

    Thanks again for giving me some food for thought.

  8. whitepointer23

    whitepointer23 Previous Member

    I have had a few auxillary outboards over the years . All longshaft and mounted on the port side. They are horrible things on planing hulls in rough weather, they put an incredible amount of stress on the transom. Probably not a worry on a boat the size of yours. I have also mounted a 25 on the center line of an old displacement hull. The rudder post was about 4 inchs in front of the prop and i could not get 3 knots . Chopped the rudder post off And got 6 knots. That is why i mentioned the rudder . It will cause problems. As far as using the outboard to direct flow over the rudder in reverse, no experienced skipper would do that when you can just turn the outboard and direct the thrust where you want. The best auxillary setup i have ever seen was a 30 hp evinrude with its own controls at the helm plus hydraulic steering with a change over tap so the helm could steer the auxillary or main engine.

  9. helluvaboater
    Joined: Jul 2015
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    helluvaboater Junior Member

    I have a 20 foot boat with a single 100HP Yamaha outboard and a 9.9HP Yamaha high thrust kicker. The kicker has a tiller handle and is mounted about 2 feet to the side of the main engine (just close enough that the engines can never hit each other). The kicker will push the boat 6-7 knots MAX, although I like to cruise at 4-5 knots to take it easy on the kicker. The gas prices are ridiculously cheap when using the kicker. I can push the 20 foot boat at 5 knots all day and it will only use a few gallons.

    For steering, I just steer with the main engine and leave the tiller handle for the kicker pointed straight. There is MORE than enough steering by using the main engine. I have taken the kicker several times into rough seas (20+ knot, 6-7ft wind chop) just to test it and the kicker performed flawlessly. I was astonished with how much manuverability the boat has with the little kicker pointed straight and steering with the main engine.

    I highly recommend going for the high thrust version of the 9.9 kicker, since this is torqued lower, has a bigger prop and you are never going to reach planing speeds with the kicker anyway.
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