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Opinions On High Thrust 99HP

bkillian

Member
"I have the opportunity to buy

"I have the opportunity to buy a 2000 9.9HP High Thrust 20' shaft for $650 less than a hour of use. My question is my 12' jon only has a 15' transom, any problems beside the depth of water I will be able to run in? I have heard theses are powerful motors. Also will this be too much motor for this boat?"
 
This motor is primarily design

This motor is primarily designed / used on bigger slow moving vessels.It could be used on your boat if you raise the transom and make sure that you put on the CORRECT propellor for your application.Using the prop that is likely on it now will result in damage to the motor.
 
"Brett, the high thrust motors

"Brett, the high thrust motors are really meant to "push" alot of weight as opposed to plane out a small boat.

Most high thrust models "live" on either pontoon boats or in a case such as this motor, would normally be used as a kicker for something up to as high as maybe 8000 pounds of hull weight (cruiser) or a trolling motor on a heavy fishing boat.

It would normally have a very low pitch prop to just move significant weight along slowly. You put that on a nice light little planing/semi-planing hull and it will over-rev and could give you a nice "exploded view" of the interior of a powerhead
"
 
"By the way, I thought I was g

"By the way, I thought I was going to be out about $250 on this motor only dripping from the water coolant outlet, but in one last ditch effort, I went and bought a can of SEA FOAM and sprayed it down the tube from the top of the motor, waited 15 min crossed my fingers AND it started shooting out a stream like a cow p!ss!ing on a flat rock! I was shocked and elated!"
 
"What are planning to put it o

"What are planning to put it on? I can run it through the prop calculator and see what it spits out.

Can't guess at a prop. This being a high thrust model also means that it will be geared significantly (lower) than a regular 9.9...

I will have to look it up, but since Yami made most of the Merc gears in this hp range can give you an example - standard 9.9 gears 2.08:1 compared to 2.42:1...

Now that may not sound like a whole lot of difference but at optimal WOT on this powerhead (about 5800 rpm) that makes the prop rpm about 2788 rpm in the regular model and only 2396 in the HT model.

Almost 400 rpm x pitch = quite a difference. In fact on a very light set-up you may not be able to get a high enough pitch. Most 9.9 model props top out at about an 11 pitch (even in the aftermarket)...."
 
"Yamaha makes a 11-3/4" X

"Yamaha makes a 11-3/4" X 12-1/4", I have a 11-3/4" X 9-1/4" at top end it hits the rev limiter. I figure 3 inches of pitch should bring that down about 1000 RPM?"
 
"Brett, I would figure the dro

"Brett, I would figure the drop to be more in the 600-700 range - but yes, 12 1/4 may do the trick for you for sure...."
 
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