Force 50

[wood]

I have a 1991 Force 50 on a Mirrocraft Aggressor, 16 ft. boat. With full gas, two batteries, two adults, and fishing gear, it scales in at about 1100, plus, lbs. including the motor. The outfit is operated at about 4500 ft. above sea level. I installed a #90 carb jet and run an eleven pitch prop. My question is performance. It is very difficult to get the boat on plane and after it does plane it runs about 20 - 23 mph. Am I very under powered or should I get better performance? I have tried a ten pitch prop with poorer results. The motor seems to run well, just no umph. Thanks for any input.<br />Wood

 

[12Footer]

Re: Force 50

You are under powered. This motor was rated 50HP at the powerhead instead of the prop.<br />A Most outboards used to be rated this way, and Force was one of the last to switch.<br />For instance, a 1991 Mercury 50HP will give you 10 more HP at the prop.<br />This makes a big difference with getting on plane and top end.<br />Just one question, what is the RPM at full go?

 

[wood]

Re: Force 50

Thanks for the info - rpm's at full throtle on a good day are 48 - 4900.

 

[12Footer]

Re: Force 50

That IS a tad low. But the 11.5" should give have given you a higher planed speed. I'm not much on props tho, so do get a second opinion on that one.

 

[JB]

Re: Force 50

Howdy, Wood. I agree with 12Footer: you are not getting the engine into its designed operating range. Even at 4500 feet, you should be getting 5200-5500rpm at WOT. <br /><br />My first thought is that you are overpropped for the power you can make at that altitude. . . maybe 30-35hp at the prop. You said you tried a 10" pitch prop but got worse results. Worse in what way? Conventional prop theory says you should go down 2" in pitch to pick up the 400 rpm you need. That would be a 9", awfully short to plane 1100-1200#.<br /><br />I guess there is a small price to pay for living where you do.<br /><br />Red sky at night. . . . <br />JB

 

[wood]

Re: Force 50

Thanks JB.<br />The ten pitch was suggested by Michigan Wheel - The rpm's did not increase and it did not have the power of the eleven. The only way I can get on plane is to trim almost to the point of having the prop too high in the water - it starts to slip with just a slight tap up. The boat is a deep V for its size - would a more flat bottom perform better? I know that altitude plays a big part in performance of all carb engines, but I would like to get the rpm's above the 5000 mark. Any more suggestions would be welcome as you guys seem to really know your engines.