Prop size for kicker motor?

500dollar744ti

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I have a 15hp kicker motor on my 23ft boat. Two questions...

Does the prop on the kicker have to extend below the bottom of the boat?

What size prop should I look for to get more thrust from this thing? It's a Sears gamefisher Eska outboard thing that will be hard enough to find a prop for but right now it only pushes the boat 3 mph. I can't imagine that's all I can get from a 15hp kicker?
 

ondarvr

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The deeper the prop is the better it will work, but it doesn't need to below the bottom of the hull for it move the boat.

The lowest pitch prop you can get will work the best, and if you get really lucky a high thrust model would work the best.
 

Sea Rider

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Is your main a long shaft OB or Inboard engine ? The deeper the leg the better assuming you have a long shaft OB and wantt to sit the aux next to it. If a high thrust prop can't be found, getting a lower pitch prop with same diam will do the trick, won't plane the 23 footer, but will better its overall displacement speed than before.

Happy Boating
 

500dollar744ti

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The main engine is an I/O sterndrive. I have a bracket on my swim platform for the kicker to mount. It sits well into the water, since the swim platform is already close to the water, but the kicker prop is not below the keel line.

I would never expect the kicker to plane the boat, but I do want to get a little more displacement speed. I'd be happy with 6-7 mph.
 

500dollar744ti

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I don't know how a plastic prop nut could be so difficult but I had a real hard time getting it off. Anyway, the size that's on there is 8-1/4 x 12p, which from the few props I've found online is about the highest pitch made for that engine.

The best prop I can seem to find for this application is 8 x 7.5p. Should I buy that one? It's the lowest number pitch I can find.

Also, here's what the kicker looks like on the boat, the waterline is visible on the transom. Is this height appropriate?
 

airshot

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Looks about right in the picture, just be sure water pickup is well below water line and it seems to be in your pic. Dropping a lot on the prop pitch is not going to increase your speed much at all but it will save wear and tear on your kicker motor. By running that much pitch you are really lugging that little motor and will shorten its life considerably if used a lot. If you have a propeller repair shop in your area they could make something for your needs, go talk to them, otherwise the smaller pitch would be the way to go. Also remember that the Eska motors do not put out the same hp as a brand name ob. It really only produces about 11-12hp even though labeled at 15 hp. I do know that most jonny/rude 15 hp motors actually produce around 17 hp in tests.
 

steelespike

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If you can find a 7.5 grab it. I'm surprised you can find anything.Have you tried Propco?
 

500dollar744ti

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I ordered the 7.5 pitch prop, there's a place I found on ebay specializing in eska/sears parts and they had a few props available. I did not try Propco. I already rebuilt the carb and replaced the impeller and changed the gear oil in this little motor. It runs great, now if I can only get it to push my boat.

Even if the 15hp is really producing 11-12hp, shouldn't that be enough to push the boat at a 6mph displacement speed? Am I fantasizing in thinking that I can go more than 3mph with this motor.
 

Sea Rider

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If need to get all the ponies outside the barrn will need to install an induction tach to test that 7.5 prop to know it's behaviour and if inside wot rpm range with the amount of passengers or load that will be currently on deck. If between middle to max rpm the better,

Happy Boating
 

steelespike

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The Eska isn't a great choice for your application.The props seem quite primitive and not a lot of choice.
When it comes to making speed you have to keep the outdrive out of the water.I think you need to shift weight forward
so that it isn't trying to climb over any waves all the time.Not easy to balance with the I/O.
 

500dollar744ti

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I'm going to give the 7.5 pitch prop a go and see what it will do. I'm open to trying other kickers but I like the fact that the Eska only weighs 62lbs and since I have to take it on and off the boat a lot, weight is important to me.

I would even be open to modifying it to fit a modern high-thrust prop.
 

Rick Stephens

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My kicker sits just about identical to your picture. I had to drop to a 7 pitch from an 8.5 to get it to quit ventilating so much. With my smaller boat I still only get around 5 mph. Works perfect for my trolling needs if a little under performing for an off shore backup.

Rick
 

steelespike

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I think if you slide the kicker closer to the center line it may avoid venting better.?
 

Rick Stephens

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steelespike, I put it where it has about 2-3 inches clearance from any configuration of the main drive. It definitely would be easier to steer closer to center, but it is what it is.

The Mich Wheel 7 inch prop is marketed as a heavy load prop. For trolling it is excellent. I can control the very slowest speeds a lot better than with the 8.5 stock prop, that's the main reason I bought it. But it also doesn't vent as bad when I run nearer full power. I can still vent the 7 inch if I run hard in chop.

Motor is plenty deep and most of the prop is below hull. However, the kicker is still close to same maximum depth as the centerline of the hull. This is useful, was in a lake just last week where the water level is being dropped so fast that I grounded the hull before reaching the dock. I knew it was very shallow so I had IO all the way up and was running on the kicker. It never came close to the bottom.
 

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ondarvr

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Moving it closer to the centerline increases the chance of ventilation because the prop is higher in relation the hull and further from the side of the boat, this makes it easier for air to be pulled from the surface than water from below. A fin works well on a kicker to help eliminate the ventilation in this situation.
 

500dollar744ti

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I installed the 7.5 pitch prop and now it pushes the boat 3-4mph with much less stress. I still have ventilation issues at anything more than 1/3 throttle. I think a long shaft outboard would be more useful in my application.

Sometimes I can feel it get a good bite at the water then right when it really starts pushing, it begins to ventilate.

I still could move my kicker bracket over about 3 inches and cut the top of the bracket down some so the motor sits about an inch lower. This would stuff it as far into the water as possible.

Do you think moving it over as far as I can to the side will make it so the boat goes in circles or will I still be able to push it strait? I feel like it could get a better bite on the water that way. I would have to examine it and see if moving it all the way over would prevent me from steering the kicker in one direction.

Maybe I should just use it as is and hold out for a johnson or evinrude 9.9 longshaft? Then I can put one of those real high thrust props on.
 

ondarvr

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You could move it over and it would help a little. Putting a fin, or even just a flat plate of aluminum on the AV plate will help a great deal.

Moving it further to the side will affect steering a little, you will be able to turn to the left much tighter than to the right, but for trolling or just getting back to the launch it isn't much of an issue, maneuvering in tight quarters can be a hassle though. It just depends on how much the motor swivels in each direction.
 
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