That would work if you have the most prop you can run and still plane, but the max RPMs are too high.
I would pay a visit to your local prop shop, as you'll likely have to try several before you find one that is the best compromise.
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Chet, I’ll tell you my story/setup. I’ve got a 1436 jon with the same motor as yours. My boat will go 23 mph with just me and gear, or about 17-18 with passenger. That is always subject to change with weight distribution.
I don’t know anything about your boats weight or dimensions, but on my 14 ft boat I previously had a 15 hp 2 stroke with a fin. The fin made it plane quicker but it plowed the front end through the water if I added any weight up front. Would get about 24 mph on gps with it but it would splash a little. Holeshot was good.
On my new motor I initially bought one, but returned it before I drilled the holes for two reasons:
1) the tail would have been to close to my new transducer on my narrow boat.
2) the modern trim tab that is below cavitation plate on motor doesn’t leave much room for holes.
Can it be done? I’m sure it can, but I elected not to for those reasons. Am I happy with it? Yes, for now I am. It planes slower, but when it planes out it is SMOOTH compared to what it used to be.
My two cents I wouldn’t add anything to it until you break it in and open it up! Then you’ll know what you really have there.
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this is how it goes, after 3 times out with the new 9.9 mercury on my 14ft smokercraft boat model is the big fisherman, i added a front casting deck and it is carpeted, battery up front for trolling motor and battery in rear for elec start, with me any my wife in the boat and our gear i weight 205 and my wife around 130, i feel this is a sort of heavy boat, the first 2 times out i went by the rules not to run it too hard ect. yesterday i did crank it wide open, on smooth water with a little wind help me, the best i can get was maybe 9 or 10 mph coming back into a breeze maybe 6 mph, i do notice that the boat does not seem to increase speed over 1/2 throttle, the RPM's are not there, i guess i will have to get some sort of a tach...and take it from there or take a chance on a prop, but not sure where to start
chet
I'm a big hater of those 10hp limits. Our local lakes claim its to prevent erosion but underpowered boats makes far worse waves which equals worse erosion. They finally upped the limits to 25hp and it's been so much nicer.
I think when it comes to legally running and expecting any type of performance from a 9.9hp motor you need to make sure the hull is adequate. I like a 1442 flat bottom or mod-v for those small motors. Its fairly stable and they are very light bare bones. If you want a deck you can add on easily with aluminum angle and sheet and hardly add any weight. On 25hp outboards and below, I run a U1 size lawn mower battery to save weight there and use a 3 gal tank instead of a 6 gal one. Personally I like the old 9.9hp 2 strokes that you could turn into 15hp motors. I also like recoil start only to save a little weight on the motor and eliminating the starting battery.
Any chance you could post pics of your boat?
I AM A BIGGER HATER TOO, i sold a 25 Yamaha last fall the boat was fast, it flew, then i went with the mercury 9.9 what a waste of 2900 bucks, i will not put it in the river, i don't think the motor will take me upriver in the current, but i will get pics, and this boat by no means is a light weight, fully carpeted 2 big batteries and i added a casting deck. i am thinking of selling everything and start over with a 15ft mod vee hull, a boat similar to Richard Gene's Allweld. the other day with a little breeze in my favor was able to get around 9 or 10mph, going into the breeze, whew this boat was topping maybe 6 or7 mph. will get some pics later
chet
Hey if you find one of the Allweld boats I don't think you will be disappointed. I bought a 98 model 15' Allweld tiller steer boat and put an older 25 hp Yamaha on it a few weeks ago... me and my son went down on one of the limited hp lakes down next to Scout-J-M yesterday and had a blast. My son likes fishing out of it better than my 18' Triton aluminum.
You are asking a lot from that 9.9, for sure.
As for a fuel additive, I am well pleased with Mercury Quickare, an ethanol treatment, fuel stabilizer, and corrosion and gum cleaner. Best price I have found is at Walmart, mix one ounce to 10 gallons of gas. I use it in the boat, pressure washer, weed eater, and two lawn mowers. My pressure washer only gets ran once or twice a year, never a problem at start up. My stuff gets stored with a full tank of treated fuel, works for me.