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I have just put my 15' Sport in after 3 years of overhaul. I have a 1992 60 hp Merc intsalled with a 5' setback plate. My first try out was on calm water & the engine & boat worked better than I imagined. Today I took it out with 2 to 3 foot swells. I stayed close to shore & went very slowly. When I tried to increase the throttle the engine started to come up to speed & then seemed to slip (the prop seemed to over rev with no push). I tried this a couple of times & had the same result. I packed it in & motored back to the marina. Is this due to the swells & turbulent water & is there something I can do to prevent this? Note: I had the motor trimmed all the way in at the time.

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What you experienced is ventilation. The motor is too high. Though it may be OK for smooth water, it is too high for the rough water you experienced on your second trip out.

You may be able to control ventilation with a different propeller instead of lowering your motor. It depends on what prop you have now.

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Thanks Tom, I checked on the prop & it is a stainless Quicksilver with the numbers 48 79792 A5 12P.That is the prop that came with the engine as I had purchased this engine 2nd hand.

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The 15' sport does NOT like a prop that is much less than "Perfect", if the prop get's slightly damaged or worn a bit, it will "Ventilate" as soon as full power is applied, and the nose starts to lift, then a big air bubble gets blown around the prop, dropping the nose, and running away with the RPM, slow and medium performance is fine, full power even works when applied slowly, it's when you apply full power (hole shot) it does this, you either need a new prop, or have the wrong prop on the boat, I'm betting that it's slightly worn, due to my own experience with the 15 sport, over the last 17 years.

mw

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Hey Sporty,

Before we jump to conclusions. Few things. Is your engine mounted high off the set back? If it is 3 or 4 inches high or even less that may do it particularly if you are in rough water and prop catches air. Engine height is something one needs to adjust a little at a time. Also you need to be certain that it getting water for cooling... BTW a 12-inch stainless will definitely bite the water although it does seem small. Others who have this model boat can comment on pitch and diameter.

The set back itself will help as it moves the engine further away from turbulent water behind the transom.

Your problem may also be the rubber hub. May have been spun before you purchased it and after 3 year of non-use… it may really dry out make it weak. (I think this is what MW means as worn, I think he has a boat like yours with a 50 HP) Maybe compare notes...

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Thanks for the replies MW & Jon,
I installed the setback plate to spread out the engine weight load more than for performance reasons, as this boat lived a hard previous life & I also have upper & lower transom savers to beef up the transom. The engine is jacked up 1" higher then the standard. The prop does seem like it has some hours on it as it does look a bit worn but not that bad.
MW: When you say "worn" does that mean the prop as a whole or the rubber hub? Should I rehub or just buy another new prop? Can I rehub on my own with this model? Is this a good pitch for the engine /boat combination or should I be looking at something else? I am looking for more stability & power rather then more speed.