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DeoreDX
Member since Oct 2010
2461 posts

Any boat propeller experts on here? [update #3 Pg4]
Put our brand new pontoon in the water yesterday. This one with a Mercury 90HP 4 stroke.

222RS2.0
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When you give it wide open throttle the RPMs jump up to 7k and you hit the rev limiter and the boat doesn't move as the prop totally loses it's bite in the water. You have to gradually give the boat power or the prop loses it's bite in the water, kind of like a car losing traction in the ice the tires (prop) spins fast and we don't move. Wide open throttle range listed in the manual should be 5k-6k rpms. At around 60% throttle we're at 5.5k rpms and any more throttle input and the prop will lose it's bite and start spinning.

Last boat I was in that did this had a spin hub. Seeing this is a brand new boat never been on the water before would being severely under propped spin the prop in the water like that? I think I'm way under propped anyways because I'm already at 5.5krpms and I'm maybe a hair over half throttle. Going back to the dealer today and just looking for some ammo to hopefully get a different propeller.
This post was edited on 7/5 at 2:43 pm


reds on reds on reds
Mandeville
Member since Sep 2013
2007 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Is it a stainless or aluminum prop?


TexasTiger
LSU Fan
Katy TX
Member since Sep 2003
5192 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Prop could be to small, but its likely a rigging issue. Motor probably needs to be lowered on the transom.


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50
DuckManiak
Southeastern LA Fan
Member since Nov 2011
2731 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

When you give it wide open throttle the RPMs jump up to 7k and you hit the rev limiter and the boat doesn't move as the prop totally loses it's bite

quote:

At around 60% throttle we're at 5.5k rpms and any more throttle input and the prop will lose it's bite and start spinning.

Sounds like a spun hub to me. Did you take the prop off to check? A lot of times they'll put boats in the water to test drive.




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20
Barneyrb
Arkansas Fan
NELA
Member since May 2016
1142 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Sounds like either a spun hub or cavitation


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20
hogdaddy
LSU Fan
harvey
Member since Feb 2010
4693 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

Motor probably needs to be lowered on the transom


This would be my first guess.

Also check the weight ratio, make sure you not bow heavy.


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CHEDBALLZ
South Central LA
Member since Dec 2009
13641 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Could be a few things.....

1. Motor is to high
2. Not enough cup in the prop
3. You are trimmed up to high
4. Spun Hub

If I was running a 90 on a 22' pontoon I would run a 4 blade prop. You'll have more hole shot, load carrying capability and control.


KG6
LSU Fan
Member since Aug 2009
8894 posts

re: Any boat propeller experts on here? [update #3 Pg4]
It's really hard to determine that stuff with props. If it is actually prop slippage in the water, you may need more cup, or a 4 blade. May just need a different prop shape. But if you bought it from a dealer, I'm sure they are used to putting at least very close to the right prop on the boat.



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Wtodd
Missouri Fan
Tampa, FL
Member since Oct 2013
26897 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

3. You are trimmed up to high

Probably the reason. I have a 60 hp Merc 4 stroke and it did the same thing. I trimmed it down and all is good.


DeoreDX
Member since Oct 2010
2461 posts

re: Any boat propeller experts on here? [update #3 Pg4]
I did play with the trim to see if it would improve any. Trimming down gave me a better hole shot but the prop would spin at a lower RPM, like around 4k the prop starts slipping and the rpms jump. Trimming up have me better top end but it felt more sluggish off the line.


DeoreDX
Member since Oct 2010
2461 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

Is it a stainless or aluminum prop?


It was black and 3 blades. Haven't looked at it closer. But I'm guessing aluminum since it was black.


Elusiveporpi
LSU Fan
Below I-10
Member since Feb 2011
1610 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Add some cup to the prop. it will bite better


bayouvette
LSU Fan
Raceland
Member since Oct 2005
851 posts

re: Any boat propeller experts on here? [update #3 Pg4]
what are the prop specs?

make sure its on tight first off, but sound like a spun hub.

Figure those 2 out first before messing with blades.

strange for a brand new boat.


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Wtodd
Missouri Fan
Tampa, FL
Member since Oct 2013
26897 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

I did play with the trim to see if it would improve any. Trimming down gave me a better hole shot but the prop would spin at a lower RPM, like around 4k the prop starts slipping and the rpms jump. Trimming up have me better top end but it felt more sluggish off the line.

It could be that the motor was mounted too high. Did you call the dealer where you bought it?


DeoreDX
Member since Oct 2010
2461 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

It could be that the motor was mounted too high. Did you call the dealer where you bought it?


Swinging by there later on in the day. Didn't get any pictures of how the rear sits in the water or any pictures of the rear at all.

Going to suck to have to drive all the way out to the lake house, grab the trailer, drive out to the launch, pull the boat out, then drive all the way out to the dealer. Reason to buy a new one was to put the boat in the water and just ride it and not ever have to pull it out. Guess that ain't happening.


AlxTgr
LSU Fan
Kyre Banorg
Member since Oct 2003
54456 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Trim it down fully. Get up to a decent speed. Trim up a bit. Go back and take a pic of the cavitation plate area and post it.


CHEDBALLZ
South Central LA
Member since Dec 2009
13641 posts

re: Any boat propeller experts on here? [update #3 Pg4]
Get a pen and pad note your RPMS and speed at 1,000 1,500 2,000 all the way through the RPM range. That will help out anyone trying to decide on a prop for you.


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DeoreDX
Member since Oct 2010
2461 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

Trim it down fully.


I actually don't think I ever tried it fully trimmed down. Just going by the trim gauge I was motyl around "level" and went a notch up and down but not anything past that.


DownshiftAndFloorIt
LSU Fan
Here
Member since Jan 2011
48975 posts

re: Any boat propeller experts on here? [update #3 Pg4]
As a habit I pretty much always take off trimmed all the way down and start trimming up as soon as the bow breaks over. Different boats like different things but that generally gets you out the hole the fastest.

Sounds like you definitely have cavitation from the engine being too high, possibly set too high on the transom but most likely from not being operated the way it wants to be operated. I doubt a brand spanking new rig has a spunt hub but it could happen

Trim it all the way down and hammer it. I'm not sure how to eyeball it with a pontoon but the rule of thumb for a regular monohull boat is set with the cavitation plate even with or a hair below the bottom of the hull and tweak from there.
This post was edited on 4/27 at 10:33 am


AlxTgr
LSU Fan
Kyre Banorg
Member since Oct 2003
54456 posts

re: Any boat propeller experts on here? [update #3 Pg4]
quote:

I pretty much always take off trimmed all the way down and start trimming up as soon as the bow breaks over.


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