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I recently purchased a 1993 13' Sport with a 1994 Mercury 40 HP 4 cylinder motor. The prior owner stated the motor has less than 100 hours on it but no way to verify. From reading several posts on the forum, I was expecting to run in the high 30's MPH. I am only getting a WOT of 31 MPH. When I purchased the boat, the motor was sitting all the way down. This motor bracket has 5 holes, so before I put it in the water I raised the motor to the 4th hole (2nd from the highest). It originally had a hydrofoil on it which I took off. The prop is an aluminum 17 inch pitch. The number on the prop is
48 73144 40L 17P. I don't see a manufacturer name on it. I ran the boat with just myself in it (190 lbs), 12 gallons of gas under the rear seat. The problem is that I do not have a tachometer on it so I do not know the RPM's. There is no power trim on it but I have experimented using different positions of the trim bar and 31 MPH is the best that I have achieved. There are 2 layers of bottom paint on the hull. Any suggestions on how to increase the speed or is 31 MPH the most I can expect?

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Your top speed seems within reasonable limits. A better prop may give you a few more MPH, but as I think you probably know you won't know what to switch to until you know your RPM range at WOT.

John K.

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12 gallons of fuel is a lot for a 13' to carry.

Yes, the bottom paint will knock a MPH or two off. But, as what was mentioned above, you're within the max mph for that boat. You'll definitely need a way to determine your RPMs or else it's just a crap shoot trying to figure out what prop you might need.

A 17p does seem a little much for your motor.

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Your running a Merc Black Max aluminum prop 17p.
I would bet your not hitting the max RPM at WOT but without a tach you will never know. The first thing I would recommend is to get a tach, even a temporary one like tiny tach will let you know what your RPMs are. http://www.tinytach.com/

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31 MPH is w a y too slow That boat should do 35-37 MPH with that motor. Yes, the bottom paint can have a profound effect on the boat's speed but motor height and propeller selection do too.

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I agree with Tom. Should go 35+ mph. I think you need the 15" pitch prop. I had two different 50 Merc's on my 13 Whaler with bottom paint. The old 50 merc's put out about 45 hp at the prop which was good for 38 to 40 mph. I ran both a 15" and a 17" prop. I think the 17" prop is too much pitch for that set up but you need a tach to be sure. I would buy the 15" prop and keep the other for a spare.

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What is the weight of the hull? Water in the hull? If the engine and prop are correct this could be the problem...Good luck

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Tom Blinstrub, I would think that a 15" prop would get me on plane faster but would not increase the top end. I guess without having a tach I can't really tell what's happening with the motor. I guess at some point I will have to add one. That mini tach looks pretty nice for a small boat like the 13.

Contender, the boat appears to be in excellent condition and from what I know about the history, it was not left in the water much. I don't believe there is water in the hull, at least there are no oblivious signs. There interior has no holes and has all original gelcoat. The bottom has paint but there are no obvious places for water to enter. I haven't weighed the hull but if there was a lot of water in it, that would definitely be a cause of the slower speed.

Tom Clark, I know that you are the expert on these matters and I thank you for your reply. Do you feel the 4th hole is the right height for this motor? Could the bottom paint result is a 5 MPH or more decrease in speed? Is the 17" pitch prop the right prop for this setup or do you think I should go down to the 15" prop? Again, without a tach these answers would just be guesses but I'd like to know your best guess. Thanks.

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48 73144 40L 17P is the 10" x 17" Mercury BlackMax aluminum three blade propeller, the least expensive prop Mercury offers. If you are not experiencing ventilation with this old aluminum design, I think it is safe to assume the motor is certainly not to high. I would leave it where it is until you get things sorted out and once you do, you can experiment with raising it that last set of bolt holes if you like.

Yes, bad bottom paint can have a profound effect of boat speed. I do not think most people realize how much speed can be lost from a bottom that is foul.

There are certainly better propellers out there than the basic 10" x 17" Mercury BlackMax, but before we start stabbing in the dark, can you tell us what the recommended WOT range of your motor is and what the gear ratio of the gearcase is? With that basic information, we can a little math and see how you are doing now with the propeller that is on there.

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Tom, I checked with my Merc dealer and found that according to specs the max WOT should be between 5,000 and 5,500 RPM's. The gear ratio is 2:1.
I had it out today in some heavy chop and did notice it the prop ventilating as higher speed.
What can you tell from these numbers?
Thanks

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OK, if you are only going 31 MPH with 2:1 gears, and a 17" Black max aluminum propeller, then we also know that motor can't be turning more than 4000-4300 RPM which, as you can see, is w a y too low.

My suspicion is the motor is not running right because otherwise, you would have to drop more than four inches of pitch to get your RPM up when that boat/motor combination should really be running a 15" prop, depending on model (or something close to it).

Have you checked all the simple and obvious things first? Verified the motor is not running on only three cylinders, for example?

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Hi, sorry to jump in on this thread, but I may have a similar issue. I have a 2001 13sport with a mercury 2010 40hp 4EFI on it. It runs at 5800rpm with a 13" 10.25 black max prop but i get 29-30mph.

Is that normal or am i slow? From this thread it seems slow, do i need a different prop? How would i know if the hull has water in it? How can you get it out if there is?

Thanks,

Sam

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Sam -- You should start a thread to discuss your boat and motor's performance rather than resurrect an old thread about a different boat. The 2001 13' Sport is a completely different boat than a 1993 13' Sport.