Prop help

Treepro

Cadet
Joined
Jun 2, 2018
Messages
6
hey guys ... I have a 24ft pontoon with a merc 150 outboard . Current prop right now is a 14.5 4 blade 17 pitch . Have had the boat for 2 years now. Boat and motor is 2015 . Wot I’m running around 30mph at around 4800rpm . Problem I’m having is I have to be on pure glass water to get that result . Any type of sharp turns , or if the water isn’t ideal I’m get ventilation every time rpms run around 5k and mph sit around 20-21 . Also happens when I’m pulling tube off the back . I’ve had the motor mounted to the lowest spot at this point . That helped a little . Installed a whale tail on it . That also helped a little bit more . But still it continues to blow out the prop if conditions aren’t perfect ! Any suggestions on different prop sizes or trying something out would be appreciated. I was thinking of going to an even larger diameter prop 16 by 13 3 blade . Rpms should be between 5600-5800 by doing that I believe .
 

89retta

Senior Chief Petty Officer
Joined
Jul 18, 2010
Messages
772
Your right in dropping down to a 13. But 16" diameter might be to big and might have clearance issues. Try a Turning point 14-15x13 4 blade
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
If with suggested prop or any other prop remains same OB sits too high, if OB can't be dropped down any more, there's a slight height mismatch between transom and OB. Check if possible to modify transom height for OB to sit further down.

Happy Boating
 

Treepro

Cadet
Joined
Jun 2, 2018
Messages
6
After looking into some things last night I think my best option would be going with a long shaft extension kit . My OB is as far down as it will mount .
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
Isn't 4800 kind of low?

What is the dealer saying? Hopefully you didn't buy the only one he's sold like that, and he has suggestions regarding what's working for others. .

Pontoon specific prop with larger than normal blades?

How are you loaded? Is the boat sitting level to maybe a hair low in the back? Have seen some newer boats lately where the weight appears to have been shifted too far forward for the engine in use, especially with a few passengers aboard.

A picture, taken from an angle so we can see how the water line, bottom of the transom, and cavitation plate all line up with each other could help a lot as well. If your cavitation plate is several inches above the bottom of the tubes, I'd agree an extension might help.
 

Treepro

Cadet
Joined
Jun 2, 2018
Messages
6
I believe max rpm for that motor is around 5800 . But what I’ve noticed is you can have 2 people on board or 10 prop will still ventilate . I’ll see if I have some decent pics for you guys to get the idea ! I do have to go get the boat from storage next week to get it ready for the lake so I’ll definitely be able to get you some good pictures .
 

Treepro

Cadet
Joined
Jun 2, 2018
Messages
6
At cruising speeds of 10mph or faster that whale tail in the picture is pretty much at water level ! Motor is always trimmed all the way down . If any type of trim up on the motor it begins ventilation mode . Then you have to stop the boat put it in neutral and start over
 

Treepro

Cadet
Joined
Jun 2, 2018
Messages
6
Boat definitely squats in the back when it’s in water . Front is a little higher .
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
That pic does make the engine look like it's mounted high. As soon as those big tubes get moving they're lifting that engine up way too high. If the engine is mounted all the way down like you say, 5" extension may be a good plan.

That pic looks as though the engine is tucked under a little - below level. If so, that's not helping your cause any either. In that position, the engine is lifting the back of the boat up under power, aggravating an already tender situation.
 
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