New 9.9 Bigfoot

[Bronzbackhunter]

Just installed a new Mercury 9.9 Bigfoot & Jackplate on my G31548AW.Boat motor gear & me about 800lbs.
Run the boat 3 hrs brake in, then run the motor at full throttle, top speed 9.8 mph, very disipointed to say the least.

 

[Ranchero50]

Exactly what did you expect out of a small heavy 4 cylinder in a loaded mid sized hull?

Displacement speed of that hull is around 5mph so you just don't have enough umph to get it on plane.

I'd take it back out with the hull stripped down to see what it'll do.

Specs say the hull weighed @ 440, Motor is @100, 5 gallons of gas is 30, etc.

 

[erictetterton]

Yea with that heavy of a boat I wouldn't have looked at anything less than a 25hp. A 9.9 doesn't have near enough power to push that boat on plane

 

[Dyno6942]

I don't know how hard it would be to hook up a tach, but I'd be interested to know how many R.P.M.'s you're getting at W.O.T. Years ago, after spending that much for a new motor, the dealer would lend out different pitch props, so that you could find the sweet spot. You could try to move a little weight to the back, and try to get some air under the front. I hope you get it figured out, because that is a nice motor.
Good Luck,

 

[DrNip]

It's still 9.9hp trying to push 800 lbs. It's going to be slow.

 

[gillhunter]

I have a Honda 9.9, 4 stroke on an Alumacraft 1648 MV because I fish HP restricted lakes. It does 12 mph with my wife and I with gear and 14 with just me. How fast did you think it would go? It's my understanding that a "big foot" has a lower gear ratio, for low speed trolling, than the regular 9.9 Merc.

 

[RustyGoat]

I wish I could get 9.8 mph out my Bigfoot 9.9. I haven't been able to get over 7 with just me in the boat.

 

[grossman]

My 15 gets 23mph with about 650lbs, add a second person for 850lbs and its about 18-20mph.

I think you just need to either play with the weight distribution or trim. If you can get that bow out of the water it'll pick up.

 

[Bronzbackhunter]

Thank's for the input. I bought the boat for HP restricted lakes. I played with the trim a little.This is my first forstroke outboard, the dealer recomended the bigfoot because of the weight. I would like to find some info on different prop pitch.

 

[rickybobbybend]

Good advice above, but by all means talk with your dealer. He has a vested interest in making you happy. Good luck.

 

[RustyGoat]

Bronzbackhunter » 01 Sep 2013, 19:49[/url]"]Thank's for the input. I bought the boat for HP restricted lakes. I played with the trim a little.This is my first forstroke outboard, the dealer recomended the bigfoot because of the weight. I would like to find some info on different prop pitch.

I used the prop calculator on Mercurys website and it recommended a 9.25x11.5 prop, the stock one is 10x7 4 blade. I put a 9.25x11 3 blade on and actually lost 1 mph. I'm going to try to raise the motor up a little more and ad a hydrofoil since the motor still seems too low in the water. I measured the motor yesterday and it's not actually a 20" motor, it measures a full 22". Hopefully raising the motor another 2" and with a hydrofoil keeping the bow down I can get some speed out of this thing.

 

[Gotem]

Put as much weight as you can into the front of the boat. I have a heavy 15 footer with a wood floor for horsepower restricted lakes, but the boat was rated for 30 hp. It originally had a Johnson 6 hp that would do 6 mph. I replaced it with a Johnson 9.9 and it did 9-10 mph. The motor would rev up when there was less weight in the back to get to the 10 mph. I then did the carb upgrade to make it a 15 hp. The speed increase was not dramatic. It now does 12-13 mph, but the weight distribution is not as large of a factor. Decreasing the pitch in the prop from 10 to 8 resulted in a 1 -2 mph increase, but the noise increased dramatically while the rpms bordered its upper limit. I now run the original prop with a pitch of 10. The noise was not worth it. Of interesting note, I did notice that right after ice out with the denser cold water resulted in mph of 14 for the 9.9 and 17 mph after the carb upgrade. As the lakes warmed up, these numbers dropped quickly.

Hope this helps.

 

[FerrisBueller]

I'm guessing there are a few things contributing to the "lack" of speed. One being the fact that it's a 9.9 and it just might not have the power, no matter how you move the weight around, to get her on plane. Second the lower gear ratio of the bigfoot's isn't helping, and even changing out the prop probably isn't worth the money for what you might get out of it.

If you want more speed I'd talk with your dealer and see what they will do for you.