Install height in relation to trim..

[tahoetech]

Hey guys,
We are rigging more and more high performance pontoons every year and we are always fighting motor height. For one, to get clean water and two, for traction in the turns. Recently we have been experimenting with top end speed, propping and height. Today we have found the best prop available for our situation but have noticed that we are in excess of 90% trim at wot to get the desired number. We still have about 2" available adjustment with motor mounting holes without going to a plate. Does higher mounting normally equal lower needed trim angle? I know the style of prop really helps with lift, we have found that the 17" Rebel is about 5mph faster than the Viper of the same pitch in our application. (23' triple toon, 250ho Etec.)

[nitro_rat]

If you are having to trim up excessively, I would think you need more setback to help carry the bow. Makes sense since a pontoon is a barge...

I've never looked at a "high performance pontoon" before, but I don't know if there is enough structure back there to hold a big motor with a lot of setback.

An adjustable jack with say 10-15" of setback would be what I would try. Then you can mess with your motor height easily too.

[tahoetech]

In a perfect world we would have an awesome plate that the customer could put anywhere he needed. But cost, simplification and confusion all play a part in these 'toons. The customers need "set it and forget it"... The trim is automatic *itrim* and contols / cables too short for the setback required. I guess I was just wondering if height could help the trim situation. Kind of an oxymoron, right... "high performance pontoons". They may not be super lightweight tunnels or Vees, but they do perform.

[FORBESAUTO]

Hard to say on toon, but I have experienced with my setup the higher the motor the less trim it takes to get max speed and is usually faster but does depend on prop. Some props just liked trim, the higher raked props seemed to run better level and high.

[David - WI]

How fast & what rpm's are you seeing?
Also, have you tried with the iTrim disengaged?
Finally, do these ETEC's run in "break-in" mode for the first so many hours?

[transomstand]

Does higher mounting normally equal lower needed trim angle?

Not usually.

[RIVERRUMMER 70]

I found the merc revolution 4 to be the best perf toon prop ever produced.
sounds like your over trimming to get more rpm for more speed .....
which leads me to believe the pitch may be to much.
put a 15" pitch rev 4 on it and go test, if it hits the rev limiter with a lite load test it with a few people and full tank of gas.
if you prop it to run unloaded it will be a turd when you get everyone on with gear and fuel. what is the normal load when using this boat? 5 people? 10 people?
what gear ratio is the lower? what rpm with the 17" pitch. what speed? what test load did you run with?
if you cant pull full rpm without overtrimming the prop pitch is to much.
common mistake when trying to go faster with a barge.
better off banging the rev limiter with a lower pitch, than lugging the motor to try and get more speed.
50 mph should be realistic.

[FORBESAUTO]

That makes sense with my experience. The higher the motor the more it frees up thus took less trim. Never thought of it like that. As long as you have a prop that'll stay hooked up as you raise. Also like stated before setback would have to help.

[tahoetech]

Itrim is pretty good from a customer standpoing, and we can tweak it, but the max speed isnt seen until I override and go from about 75% to 90%+. All of my lake tests are set up for maximum given rpm to forsee any load in the future. I have tried about 5 different props and this one performs the best all around and give me 49.5mph gps at 5900 - 6000 rpm. We also change props if the customer wants something different that what we are set up for. My boats are built a little different than what the builder usually sends out, different strake design, placement and tube size. So, the builder / evinrude performance reports get close but not right on. Evinrude props are a crazy good deal right now from our rep to make the boat show deals close, so I will prob stay with them. I do have a Rev4 I will try later this week to see if that changes anything.

[RIVERRUMMER 70]

if your overtrimming to get max rpm thus max speed unloaded, whats gonna happen when you load it up?
doggggggg!
overtrimming to get max rpm = props too big.

if you raise the motor it will slip more and you wont have to over trim .
but you'll be running in a constant high slip factor and you'll
loose bite in turns, less bow lift =turd.
correct setup would have that motor on the rev limiter wot with only you in the boat and not overtrimed to get rpm.
so when you put 5-8 people plus gear and fuel it stays near 5800-6000.
i think you can pull the motor up one hole and put that rev -4 on and see the diff...bet it smokes all those other props .
maybe even be able to pull a 17" rev -4 then.

[tahoetech]

I guess I am trying to just get the boat to perform. If hanging it out is what it takes to get the extra 4-5mph, then so be it. What I really want is to not have to push it this hard to get the result. So... Why does it take so much trim? How can we get the same result without finesse and "tricks"? I know these are hypothetical questions that you guys really dont know the answer to, I think you know what Im getting at. Consistent and easy. LOL Huge setback will be thought of while rigging the next one. (longer cables etc). I'm excited to see the results.

[RIVERRUMMER 70]

i told you twice why it takes so much trim but you dont get it.
i gave you solid advice you must not comprehend.

HOW ARE YOU TESTING , WITH A FULL BOAT OR JUST YOU IN THE BOAT?
FULL FUEL AND GEAR ?
I DONT UNDERSTAND WHAT YOU MEAN BY PUSH IT THIS HARD?
RUNNING WIDE OPEN REQUIRES ALL SHES GOT SO WHAT DO YOU MEAN
BY PUSHING IT HARD?
THATS WHAT WIDE OPEN IS!
USING 90 % TRIM TO GET 5900 RPM TELLS ME PROP IS TOO MUCH PITCH, UNLESS YOU HAD 5-10 PEOPLE WITH YOU.
IF YOU WERE ALONE WITH NO GEAR AND LOW FUEL THEN THIS IS A NO-BRAINER.
MOTOR SHOULD BE ALL OVER 6200 RPM WITH THE BOAT EMPTY.
YOUR NOT HANGING IT OUT TO GET LAST FEW MPH ....YOUR SLIPPING THE PROP TO LET THE MOTOR GET FULL RPM.

[tahoetech]

Thanks, River.. Yes, I do get what you are saying and to be honest I just didn't want to prop down . But I do have a handfull of props on their way for more trials. This particular boat was tested with 3 200+ lb guys and a full tank (60gal) of fuel. By "running hard" I meant manipulating the boat to run what it did. Playing with the trim and throttle in a way that maybe most customers wouldn't. Yes, I want a simple throttle down and go! Thanks again! I'll update results soon.