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4 stroke 8 hp 99 hpWhatbs the difference

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njsct

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"Does anyone know what the dif

"Does anyone know what the difference between an 8hp and a 9.9 hp 4 stroke is. I have an 8hp and could use a 9.9, is it just a difference in the carburetor, or is there more?"
 
"Nelson, if an 8 isn't doi

"Nelson, if an 8 isn't doing it for you a 9.9 or even a 15 won't make an overly noticable difference.

If your rig seems way underpowered, think about a 20 horse if the rating for your boat allows it...."
 
"Graham,
I have a 26 ft sailb

"Graham,
I have a 26 ft sailboat. 8 is almost enough. Hull speed is 6.25, the 8 hp moves me at 5- 5 1/2.

The formula is supposed to be 3 hp per ton. The boat displaces 5400 lbs, or 2.7 tons. 2.7 X 3 is 8.1. I am figuring a 9.9 should do it.

The one knot is not the big deal, it's the propulsion in rough water where I am looking for the difference, like when the prop is out of the water 1/3 of the time."
 
"Nelson, I work alot on small

"Nelson, I work alot on small engines (25 and under) and have compared quite a few - and although not scientific by any means, the difference between an 8 and 9.9 is so small, on a boat 1/10 the weight of yours that it is practically un-noticable.

Is your model the 8 horse high thrust version? 25" shaft??"
 
"It is a long shaft, but I do

"It is a long shaft, but I do not know if it is high thrust or not, it came with the boat. I will look at the serial number tonight to see if that can tell anything."
 
The motor is Model Number F8 M

The motor is Model Number F8 MLHZ. The shaft is 23" from the top of the transom to the plate above the prop. Serial Number is 68T L 302176 S
 
"Nelson, unless you had intent

"Nelson, unless you had intentions of replacing the motor all together, which I probably wouldn't do myself, you may want to investigate if a shaft extension kit is available.

Since you note that your biggest issue is the motor breaking the surface when running in rough water, an extra 5 inches of shaft may make a world of difference.

Aside saving your motor from an early grave, due to lack of cooling water when it sucks air, keeping the prop in the water will obviously make a big difference in forward thrust.

I am not aware of a factory kit to extend the shaft lenght for the 8 horses (have seen them for the 9.9/15's), but Just In Time may know.

Alternately, you could look at simply lowering the mount a few inches (or use an adjustable kicker mount), which could be used as conditions dictate."
 
"Graham,
Thanks,
The issue t

"Graham,
Thanks,
The issue there is that it just barely clears the rudder as it is. Even when it is in the water in rough seas, and strong winds, it could use a little more umph."
 
"Nelson, sounds like you are k

"Nelson, sounds like you are kinda limited then in what you can do with that motor. It really isn't a candidate for a conversion. I believe the overall displacement is different between your model and the 9.9, so maybe nowhere to go in that department.

You could maybe experiment with a hydrofoil (doelfin or the like) which helps with low end thrust on normal applications - but really at a loss of what else you could try...."
 
"Graham,
Thanks for the thoug

"Graham,
Thanks for the thoughts, It looks like I might just be in for a sell the 8 and buy a 9.9 experience."
 
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