Motor height or prop issue

[suneshop]

I have a new Crest ll cp3 2755 lbs 3 pontoons with the 250 optimax pro xs.1.75 gear.Lifting strakes.The prop I have now is QA1912X17P. The motor is set one bolt hole up from the lowest setting. WOT is 40 mph 3 people @6000 rpm. That is the same speed that I got with the 15" pitch prop that came with the boat @6000 rpm.It will only run trimmed all the way down any trim up causes the rpm's to shoot up. With the 15" prop it hit the rev limiter 6200 rpm still 40 mph these speeds are with a GPS. It also starts to cavitate when running 5500 rpm and trying to turn.Wondering if the motor is set @ the right height or is it a prop problem.

 

[steelespike]

Re: Motor height or prop issue

I can't speak on the tritoon but a regular toon there is very little trim adjustment,usually just to try to get the least ventilation(cavitation) I would suggest lowering the motor.
You might test it by having the passengers move to the rear one at a time to see if it helps as the stern gets lower.
By the way "cavitation" is an old time term for ventilation. Ventilation is when the prop gets air fouled.
You don't feel cavitation.Cavitation is when the water boils in the low pressure area on the back side of the blades.
Over time will leave scars on the back of an al props blades.Cavitation can be an indication that a prop is working really well.

 

[suneshop]

Re: Motor height or prop issue

I lowered the motor to lowest setting, slight improvement.Still must run trimmed completely down. The anti ventilation plate is about 3" or 4" above bottom of the center tube.

 

[steelespike]

Re: Motor height or prop issue

Being new I would consult with Crest and the Crest dealer.Anti vent plate 3 or 4" above the bottom of the tube seems high to me.
Are you sure the motor mount was installed all the way down?
I hesitate to keep throwing props at it. The Solas Amita 4 blade in a 16" pitch may help.
The Solas props have a good reputation for successful applications.
A 4 blade may also handle better around the dock.

 

[suneshop]

Re: Motor height or prop issue

I have been in contact with Crest and they suggest an Enertia prop before anything I try anything else. I was thinking about a hydraulic jack plate

 

[suneshop]

Re: Motor height or prop issue

I have the 17" Enertia installed, boat still will only run trimmed completely in without ventilating. Ran with 9 people behind drivers seat still unable to trim up at all. I can see 3"/4" of space between a/v plate and h2o while running top speed 41 mph gps. Any suggestions ?

 

[dan02gt]

Re: Motor height or prop issue

I didn't know you could really trim a pontoon. Trimming usually is for lifting the bow on a planing hull. Most pontoons really aren't designed for this so trimming the motor up does nothing but raise the prop out of the water. If you really want to try to get it to trim the jack plate idea is a good one. It will put the motor back from the center pontoon giving it cleaner water to run it and the extra set back with give your motor more leverage to lift your hull. You may also want to have a little cup added to the Enertia.

 

[westcoaster90]

Re: Motor height or prop issue

:facepalm: you gotta get that engine lowered bud. I would start questioning who installed it because 3"-4" above is to high and a very unprofessional installation. I have actually mounted XL shafts a little high on the transom and seen better results then a L shaft bottomed out on the transom. meanwhile it is designed to run an L shaft. I just sold a 15' that originally had a 60 L but I installed a 30 XL just because It had your same issue. thing ran sweet with the 30 but cavitated like crazy with the 60.

 

[jestor68]

Re: Motor height or prop issue

According to the Crest pontoon web site, their larger tri-toons use 25-26" diameter logs.

Measure the transom height. The motor's AV plate should not be that high above the bottom with it mounted all the way down.

It appears that somebody put the wrong motor(shaft length)on there. Looks like a 25" shaft length is required.

Some of the Pro XS models are only available in 20" shaft lengths. Make sure they didn't put a motor on there(TM version)intended for a bass boat.

 

[Rancherlee]

Re: Motor height or prop issue

Mine home built/straked tritoon doesn't like the Cav plate higher that 1" above the bottom of the tube, and that's with a quality 3 blade stainless "big ear" prop. To run aluminum 3 blades at speed I need to drop my motor 1 hole so its level with the bottom of the tube. 3-4" above is way too high unless your pontoon is the style/type that has a bracket that sets the motor back 12-18" away from the back of the pontoon and doesn't continue the shape of the tube all the way back (my transom braket is shaped like the tube)