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Peck

Boat Motor Height Setup

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So I've only had the new boat out a couple of times, but it seems to me that it is lacking on top speed and seems to get a little chine walk to it at higher speeds. I'm not as worried about the speed, but I want to fix the chine walk problem.  It is also seems a little slow out of the hole considering it has a 4 blade 23P Tempest prop. I'm here for some advice from some of you guys that have played around with different props and motor height setups.

So here's what I have.......

Boat is a 99 Nitro NX882 with a Mercury 150. It currently has the 4 blade prop but I also have a 3 blade 23P Tempest Plus. I do have a Manual Rite Hite Jack plate. Prop to pad is currently set at 5.25 inches. Top speed was gps 53. 

Just to make sure I measured the prop to pad right here are a couple pictures of that measurement, incase I didn't do it right, boat was level, motor trimmed down level as well :

IMG_20161012_174454372_zps6cfnzt2i.jpg

IMG_20161012_174416973_zpsrdb1wdvj.jpg

Doing some research over on BBC boards, I think I should be more around 3.5 inches or less on the prop to pad dimension, with top speed in the low 60s, with the 3 blade prop I have (not on the boat yet). I didn't really pay alot of attention to what RPM's I was running, but it didn't feel close to being over revved at top speed. Water pressure never dropped below 15 psi at full throttle. The chine walk was my biggest concern, and maybe some of that was driver error....new to me boat, so still learning.

SO my question is should I raise the motor to 3.5 inches below pad with the 3 blade prop and start adjusting from there? Boat also has a whale tale, so I'm thinking they went to the 4 blade prop and whale tale to help get out of the hole, when all along the motor was too deep?  I'm open to any ideas you seasoned professionals may have. I hope to get out this weekend and plan to log some RPM data and water pressures. 

Here are a few other pics just so you guys can get a good idea of the entire setup.

IMG_20161012_174532246_zps20r6o1o7.jpg

IMG_20161012_174537053_zpsklsd5ipb.jpg

IMG_20161012_174545982_zps1ile8ss8.jpg

Thanks for help!

 

 

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Idk much about Nitro specifically, but IMO you're definitely too deep. I'd try the 3.5" mark, and if it improves a decent amount, try going up 1/4" or so at a time from there till you find the sweet spot. Mark your jackplate each time you move it. Make sure when you're doing your test runs that you've got the boat loaded down how you'd typically run it, ie,. all your usual tackle, full tank of fuel, etc. Also, there will be a different sweet spot height for the 3 blade vs the 4 blade, so ultimately you'll have to expirement with both to find your best setup. My guess would be you'll get more top from the 3 blade, and possibly better shot from the 4. But no way to know till you play around with it. Good luck 

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I think I'll move it up and put the 3 blade on there then adjust from there. 3 blade should be more fuel efficient right? I'll definitely mark everything before I start so I can get back to where I'm at. Another thing I failed to mention is that if I trim all the way down at low idle the back of the top motor cover seems to go under water a little.....another reason I think it's too low as is. 

Right now I have the boat on jack stands working on the trailer brakes. If it is sitting on tires I can't trim the motor down level without it hitting the ground before it levels out. 

Edited by Peck

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Yeah it's definitely too low. As for fuel efficiency, there's no cut and dry that one will be better than the other. Like I said, it'll come down to just playing around with both until you get it to do exactly what you want it to. Like if you use Mercury's prop selector, it'll generally give you 3 blade for top end and 4 blade more for fuel efficiency and grip at the expense of top end. But there's no hard rule on any of that. It all depends on your boat and setup. 

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So I raised the motor up to right at 4 inches below pad, still have another inch or so left on the jack plate, but since it was such a drastic change from where I was at I decided to stop there til I got to test it.

Today got out on Cherokee to try it out. Out of the hole there was no noticeable difference, but it's not horrible anyway. Top speed 57.5 mph on the GPS at 5200 rpm and around 15 psi. Top speed was low 50s with old setup. Boat ran much smoother and less sketchy at high speed. It seems I can still come up some on the motor to raise the rpms and probably gain a little more speed. I will probably hold off on raising anymore til I can try the 3 blade prob at this height and see what it will do. 

Cruising in the 40s the water pressure is around 9-10 psi, but wide open it jumps up to 15psi....is this a concern being lower psi at lower speeds in the 40 mph range which is where I will spend more time running?

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Water pressure is PROBABLY ok, but you really need to get the service manual and check to see what it's supposed to be. It varies motor to motor. A Mercury dealer might be willing to look it up for you and make sure you're good. 

And are you saying the center of your prop shaft is 4" below pad, and you've only got about another inch you can raise the jackplate?

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From my experience the pad should be level with the cavitation plate unless running a LWP. Where is your water pressure reading coming from? Meaning where on the motor is the port the gauge is reading from?

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3 hours ago, SteveHTN said:

And are you saying the center of your prop shaft is 4" below pad, and you've only got about another inch you can raise the jackplate?

Correct, inch maybe inch and half to raise before no more adjustment.

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36 minutes ago, tnriverrat1975 said:

From my experience the pad should be level with the cavitation plate unless running a LWP. Where is your water pressure reading coming from? Meaning where on the motor is the port the gauge is reading from?

Looks like my cavitation plate is slightly higher than pad. And I have no idea on where the reading comes off the motor from. I'm not sure what I'm looking for under the cowl.

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If your cavitation plate is in line water pressure should not be an issue for you. As far as chine walk goes it's one of those things that seat time fixes. 

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5 minutes ago, tnriverrat1975 said:

If your cavitation plate is in line water pressure should not be an issue for you. As far as chine walk goes it's one of those things that seat time fixes. 

So is around 8-10psi bad around 4500 rpms? WOT at 15 I think is ok. From what I can find online the Mercury Optimax motors are low pressure high volume. I think I'm fine I just want to be sure lol. No chine walk today, so either raising the motor took care of it or another day of wheel time and I didn't do something I did the first time out. The 150 has a lot more power than the 90 I had before, plus I've been behind a bow rider for the past two years.... completely different driving a bass boat lol.

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FWIW, water PSI on Merc outboards is gauged at idle and at WOT. There is no set number in between....too many variables.

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5 hours ago, Mountainman said:

FWIW, water PSI on Merc outboards is gauged at idle and at WOT. There is no set number in between....too many variables.

10-4. I'm good at idle and good at WOT.

Thanks for all the advice so far.

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with all the stuff you have already done to the boat it would be cheap insurance to replace the water pump IMO

  • Like 1

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30 minutes ago, country said:

with all the stuff you have already done to the boat it would be cheap insurance to replace the water pump IMO

It was replaced this Spring before I bought the boat

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+ 1 on 3.5" as a benchmark.  Your plan to ease into it from 4" is sound.  No two hulls are the same.  Will take a little time but you'll find the sweet spot on yours.

 

5200 rpm at WOT sounds low.  Should be 5800-6000 at dead-nuts wide open.  57 mph at 5200 is terrific for that set-up.

 

Your water pressure gauge is probably analogue.  Not the most accurate when trying to discern the exact pressure reading at any given time.  Digital gauges will give you more accuracy, precision.  I use the water pressure gauge to note water flow thru the motor.  I have a SmartCraft digital gauge right next to it - I keep it set on engine running temperature.  That's a better (IMHO) measure of how your big motor is doing at any given speed.

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I got a 1988 Winner Tournament 2000 with a 200hp Evinrude 2 stroke... I've only had it a few years & haven't had it out in 2 years due to physical & mental (PTSD) issues. The boat seems to run great & very steady at WOT but it doesn't seem to stay on plane at lower speeds. This may just be the way bass boats operate & my lack of info & experience makes me think that it should stay on plane at lower speeds... seems like I can only crawl along before the front of the boat starts lifting up. I've only had 2 boats in my life & the first one was a pontoon so I just don't know. 

Edited by Marine
forgot to add words

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At low speeds (-30mph) you pretty well have to be trimmed all the way down to keep it on plane. Otherwise you end up with porpoising issues. Even then, a lot of boats have problems at low speeds. 

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^^^^ what he said

When night fishing I stay around 30 or so for safety, and generally leave the motor trimmed all the way in the entire night. 

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So basically anything slightly above idle will start to bring the front end of the boat up?

Also, why would you not have your motor trimmed all the way down once you are on plane?

I know these are rookie questions... but they are questions coming from a bass boat rookie! :wacko:

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Anything a little above idle generally will start to raise the bow. As for why you don't keep it trimmed in, it creates too much drag. You want just the back third or less of the bottom of the boat touching the water when you're running higher speeds, IN MOST CONDITIONS.....I say that because taking waves you sometimes want it down to slice through the waves. But generally you wanna keep the bow up off the water, without getting so high that you lose control or thrust. 

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marine, next time you're out on the water: trim all the way down and take off. Once you are on plane, start trimming the motor up in small increments. Then you will know exactly why most of us don't leave the trim down all the time. You can leave it down if you prefer, and it will give you better turning capability, but when you start trimming up you will go faster because less of the boat hull will be touching the water. You can hear it get louder and go faster with each touch of the trim button

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4 hours ago, rusty50576 said:

marine, next time you're out on the water: trim all the way down and take off. Once you are on plane, start trimming the motor up in small increments. Then you will know exactly why most of us don't leave the trim down all the time. You can leave it down if you prefer, and it will give you better turning capability, but when you start trimming up you will go faster because less of the boat hull will be touching the water. You can hear it get louder and go faster with each touch of the trim button

I guess that might explain why I've seen boats shooting a rooster tail up in the air as they passed by.

How can you tell when you've trimmed too high that it is no longer effective... besides trimming it all the way out of the water... I think that would be pretty obvious! :lol:

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You will hear it sucking air, then trim it back down. I have a 50 hp so be careful trying that with a 200. Just trim up in small increments and you will hear when it gets too high. Someone with a

larger motor may know a better trick but that's how I find the sweet spot on my motor 

 

Edited by rusty50576

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