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Old 05-12-08, 11:22 PM   #1
Hook'em-AND-Cook'em
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Default Jack Plate/RPM ??????

I'm new too the "BIG" bass boats. Recently traded a 16' Alumaweld w/ a 40Hp Yamaha to aTriton Tr-186 w/ a 150hP MERCURY XR6. Both boat and motor are a 2004. Here's my question: The boat has a manual jackplate. First time out on it, the front lifted to over 45 degree angle taking off, took a long time to level and plane out, and it sounded as if the prop came out of the water for a second or two. Took off trimmed all the way the down. Then after plaining, hit a very small wave and the front end came up and down and up and down, etc. Almost threw me and my rider out. Went home and dropped jackplate about 1/2" and it handles waves much much better. The front end still lifts high but not nearly as bad and it still takes a min to plane out, and the prop still sounds out of water for a sec or two. The "bullet" on the lower unit is about a 1/4" to 1/2" below bottom of the boat, motor trimmed down. Is this not below enough and should I lower the jackplate more? Speed tops out about 54-55mph gps. I have around 13 to 15 psi water pressure. And max rpm wot plained out is 5000 to 5100 rpm. I've read this motor should max out at 5600. I believe the prop is a Tempest 23" pitch, which i think is correct for this boat. Any suggestions or info would be greatly appreciated.
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Old 05-12-08, 11:31 PM   #2
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this sounds like a job for 1fastlaser, da zooker, 3d, etc........ tell them all the details about your boat. they can tell you where your jackplate should be to ride the correct way. and welcome to the nuthouse. if you are close enough, check out the get together. it is in the messages post. later and good fishing.
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Old 05-13-08, 08:58 AM   #3
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hmmm sounds like more seat time is needed.

the lower in the water you go the lower your rpm will get..

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Old 05-13-08, 09:21 AM   #4
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Are you trimming the motor allllll the way down to get on plane and are you trimming it allll the way up to get max rpm? If the motor is only 1/4 to 1/2 inch below the pad that seems a little high to me for a stock gear case. But Zooker is right I think seat time and trial and error.
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Old 05-13-08, 03:53 PM   #5
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How close is the plane of the hull from the top of the prop?

Use a yard stick and ruler to figure it out.

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Old 05-13-08, 10:34 PM   #6
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boater, the motor is trimmed alllll the down when taking off and it is trimmed allll the way up at WOT. It ran 54-55 mph GPS, which I think is a lil slow for this boat. And the max rpm at WOT trimmed completely up is around 5100. It was about 4900-5000 the way it was set up when I bought the boat but after I dropped it a lil I gained about 100-200 rpm, but im still about 400-500 rpm short. But if the motor was jacked too high, wouldn't rpm's be higher than normal instead of low??? Is it possible to lower a jack plate that's already too high and gain rpm by dropping it???
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Old 05-13-08, 11:11 PM   #7
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I recommend filling the gas tank up and spending the whole day saturday driving the boat and I bet it starts to run better. new boat and new to bass boats is just gonna take a little time in the seat. At least gas prices are down............sorry.
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Old 05-13-08, 11:12 PM   #8
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welcome to the forum by the way and congrats on the new boat.
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Old 05-14-08, 06:52 AM   #9
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every boat drives differantly. the toon takes time behind the wheel to get it to run right..

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Old 05-14-08, 11:53 AM   #10
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The right set-up for your boat/motor/prop combo should be easy to find. There are lots of them around.

These boats can be a handful to drive and as others have said, seat time is the only way to learn. Suggest you figure out the set-up, probably prop shaft around 2 1/2 to 3" below the pad. If you are 500 rpm below recommended WOT then you are lugging the motor and will eventually hurt it not to mention you are not making all the power you can.

Last edited by foolishone; 05-14-08 at 11:59 AM.
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Old 05-14-08, 05:30 PM   #11
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Appreciate all the responds. This site seems very helpful. The more I take the boat out the more I find out little tricks about it. I'm sure seat time will help a lot. The boat I had before was instable, small, and SLOW, about 25mph max. BIG BIG difference now. If it's not just the jackplate, what could cause the motor to be 500 rpm low at WOT? All I can think of is that's it maybe runnin a bit on the rich side. Oh, the boat had a half tank of gas when i got it too, which more than likely was old. Should have drained it but gas is so damn high. I filled up completely with mid grade 89 on top of the gas that was in it, then put about 1/4 tank of mid grade again alond with Quicksilver fuel system cleaner each time. I'm going to run it all out before I fill up again. Could this be part of the problem? And do you recommend using the 87 or 89 grade gas?
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Old 05-14-08, 05:35 PM   #12
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When you say below "pad", I take pad as the very bottom of the boat at the center, right? When I measured the bullet level, i took a long flexible piece of metal and held it to the centerline of the bottom of the boat, and the top of the bullet was about 1/4 to 1/2 inch below the metal.
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Old 05-14-08, 06:19 PM   #13
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here ya go method of measuring prop to pad

From top to bottom.
1. Leveling the boat using a level on the pad.
2. Measuring the distance from the pad to a level concrete floor.
3. Leveling the engine.
4. Measuring the distance from the center of the prop shaft to the floor. Now just subtract the prop shaft measurement from the pad measurement.

the pad is the indented section on the transome of your boat noramlly found above the plug hole..


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Old 05-14-08, 06:25 PM   #14
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I agree with foolishone I was always told to start 2.5 to 3 inches below the pad with a stock gear case. center of propshaft to pad
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Old 05-14-08, 11:34 PM   #15
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sorry zooker, i'm still a bit confused about the pad. So i find the indented part above the plug hole and measure from the indention, or measure from the bottom of the boat in the middle of it (lowest part which is the centerline). I fooled around with the jackplate earlier but can't get it into the Ohio river due to high water level and closed gate at the ramp. Boat and motor are about level, held yardstick on centerline of bottom of the hull and pulled out to motor, measured to center of back of bullet to yardstick, and bullet is about 3 1/4" below centerline. About how close is this? Would this be a good starting point or should it be jacked up a lil more to about 2 1/2 to 3" below centerline?
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Old 05-14-08, 11:38 PM   #16
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And could anyone tell me what could cause the motor to be about 500 rpm less than spec at WOT (at about 5100 and should be at 5600)? Prop size should be correct (23 pitch, Tempest prop).
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Old 05-15-08, 07:39 AM   #17
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using a LEVEL jack the trailer up or down till the boat it is level or plumb with the ground. then measure from the indent top to the ground..

using the same level place it on the cavation plate on the lower unit-it's the big fin-tilt trim the moter till this is plumb/level with the ground.REMOVE prop.. measure from the CENTER of the prop shaft to the ground.

subtract the prop shaft measurement from the pad"indent" measurement..and you'll have your prop to pad measurement..

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Old 05-15-08, 07:50 AM   #18
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Sounds like it is too high..

Lets try this a different way.

On the lower unit there is a planeing plate(cavatation plate) above the water pickup area.

Flat wing like metel piece on lower unit..

It should be below plane of boat. In other words if you are flying along at 30 mph the water running off the bottom of the boat will cover that wing like piece.

here is a link that might help..

http://www.ankn.uaf.edu/Publications/VS/lowerunit.html
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Old 05-15-08, 08:59 AM   #19
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Just for grins you might borrow a 22 pitch prop from someone , prop dealer sometimes will let you try one and see if your rpm go up. Also have you experimented with the plugs in the prop? On the hub in front of your blades in the ventelation holes
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Old 05-15-08, 09:24 AM   #20
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Quote:
Originally Posted by Hook'em-AND-Cook'em View Post
Boat and motor are about level, held yardstick on centerline of bottom of the hull and pulled out to motor, measured to center of back of bullet to yardstick, and bullet is about 3 1/4" below centerline.
I think you got the measurement right. Now you need to be more precise. A quarter of an inch can make a surprising difference. Double check the measurement and raise 1/4 of an inch and try it. Keep track of your RPM and top speed, how big a rooster tail you are making, hole shot and water pressure. If you don't have a wp gauge I highly recommend one for your peace of mind and your motors continued good health.

I think your prop is close as you will pick up a coiuple hundred rpm as you raise the motor. Does you prop have holes thru the hub near the gear case ? If so do you have plugs or plugs with small holes ?

As you go up, at some point, you will begin to lose speed and or wp even though the rpm goes up. When you get there, go back down 1/4 inch and you should be pretty close.

The 186 is a quick boat and like all toons it will chine walk if you get much above 60 mph. There are a couple of sites that have good info about what this is and how to learn to driver at speed. Once you do, the feeling of airing one of these boats out is amazing. My TR20X/225 Opti has hit 75 and change ! I don't drive that fast on the highway
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Old 05-15-08, 09:36 AM   #21
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How much offset (jack plate width 4,6,8,10 etc. inches?) have ya got. On that boat ya need ta start with tha prop shaft center line 3 3/4 ta 3 1/2 inches BELOW tha pad (tha very bottom of tha boat). Put tha level on tha bottom, in tha center of tha pad runnin' long ways towards tha front. Put tha level on tha cavitation plate on tha motor runnin' tha same direction. Measure tha difference. Thats just a startin' point. Watch your water pressure guage constantly. You can move tha motor up 'bout 1/4" at a time till ya find tha "happy place", ie: steady pressure and good handlin' and rpm's. That motor needs ta turn up to 5600 ta 5800 ta fully benefit its power. I would say 6000 or more but I'd probably get scolded.......
Like boater says, if got access ta different props, ya might try 'em. Even with a good name brand prop ya don't know what is been through before you got it...........T
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Old 05-15-08, 09:39 AM   #22
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Guess we was postin' at tha same time ........T
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Old 05-15-08, 11:30 AM   #23
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Ahhhhh, the "Happy Place"...
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Old 05-15-08, 06:01 PM   #24
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I'm familiar with most of the boat lingo like cavitation plate and chine walking and porpising. I was pretty sure what the what pad was, just wanted to make sure. I wasn't on the most level ground during those measurements. I just wanted to get a rough idea. I'm gonna pull the boat to where I can find level ground and re-measure. Should be close tho. Even at 54mph at 5100rpm I had some chine walking but not too bad. Ally260, i have a 6" jackplate. The boat rode horrible first time out. Taking off the bow shot up in the air over a 45 degree angle and took a while to plane out. I was trimmed all the way down too. Still trimmed down, a very small wave caused the bow to rise and fall rapidly, making the crappy ride. I should have took it out a couple more times before adjusting it to get the feel for it. But after lowering it plane time was decreased and it handled waves very well. After hearing how to measure correctly, I had it lowered to about 4" below. Its now raised about 3 1/4 below. And the PROP PLUGS were taken out by previous owner. Should there be any in???? Someone said to get a hydro-foil, but that ain't a fix. It's only a band-aid for another problem. I had one on my 40hp and it worked great, but a boat like this shouldn't need one.
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Old 05-15-08, 06:08 PM   #25
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Another thing i was wondering about, does the HOT FOOT have a stop behind the pedal that could stop the throttle cable form opening up the carb plates fully, which in return would cause the rpm loss??? I doubt the carbs have ever been adjusted since the factory either.
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