Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

[Jkrt125]

Hi all,
We have a 2000 Crest Grand Caribbean I/O (V6 Mercr. 210hp) which we purchased last winter, spent the spring chasing the upholstery shop to finish it (another LONG story), and then got it running late last summer.

We noticed that the boat runs great at lower speeds, but when approaching 20mph, would start to experience "cavitation" or prop slip at different loads/distributions/water conditions. We played with trim settings which didn't have much effect.

When we picked up the boat, there were a couple of aluminum plates which were designed to be bolted to the foot of the outdrive (they were removed from drive when we picked it up), so we reattached them to the foot and started experimenting, what we noticed was almost no prop slip or cavitation, but now much more drag on the boat, and top speed is limited to around 22mph, and engine RPM seems bogged down @ 3500 rpm (this engine should "redline" @ 4500-4800RPM WOT). My guess is the plates help isolate the prop somewhat from the turbulence from the 'toons, at the expense of added drag to the boat.
Has any of you with I/O powered 'toons noticed this, does it seem to matter what prop you are running?
I have noticed the newer 'toons, both outboards, and I/O seem to have the engines/drives further back from the end of the 'toons, is this to get the prop cleaner water?
Has anyone else played around with spacing their outboards (or I/o) further back? What would be the minimum distance from the end of the toons to help get cleaner water?

thanks,

 

[rrhodes]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Pictures would help allot. Are the peices you put on actually attached to the lower? It also sounds like you need a different prop. Do you know what size and pitch your current prop has?

 

[jafo9]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

i used to have an i/o on a suntracker. it was the 3.0L. i never noticed the issue you mention, however, it was the carb'd version at 130HP. it was heavy and the boat was limited to a best speed around 22mph IIRC. you didn't mention your outdrive, alpha 1 gen 2? do you have lifting strakes. if you are going faster it could be pulling the prop out of the water. does your trim function all the way in? obviously, if you are down 1000RPM you have a serious issue. have you contacted the previous owner?

 

[Lawnmedic]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

We have a '95 Crest Savannah 25' with a 3.0 I/O we are getting ready to sell. It has 2 flat plates mounted to the anti-cavitation plate. We never have a problem with cavitation on it, but speed is greatly effected by trim. Make sure you have a Pontoon prop on it. Ours has big ears on it. Ours will run 24.9mph on the GPS if trimmed right. It's a little bit of a wet ride, if I trim up to make a dryer ride, I lose several mph...

 

[lmuss53]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

My guess is the plates are a fix for the wrong prop. What prop are you running? I'm assuming you can't give us the wide open throttle RPM because you have to back off when the prop lets go. If you know the WOT RPM what is that number?

It sounds like you have too steep of a prop, which lets go at higher RPM or when you crank on the power. The plates keep it from letting go but then the steep prop can't get up to speed and lugs the motor down. Think of it like trying to drive a stick shift car in 5th gear at 20 MPH.

Use one of the prop selector tools to see what the manufacturers recommend for your boat, my guess is you are way above the recommended pitch.

Get the right prop and I think your cavitation issue will go away. The engine,drive and transom are designed to run configured like they are. I would not use those plates unless every other option had failed.

 

[lmuss53]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

I made a couple of assumptions on boat length (22ft) and drive (Alpha 2.0) and got an 18 to 20 pitch number from the Merc prop selector sight. Use the exact numbers and run it yourself, get the right prop and I bet you'll be golden.

http://www.mercurymarine.com/propellers/prop-selector/#

 

[Jkrt125]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Thanks for the replies thus far. I'm sorry I didn't list the length of the 'toon, it's a 25', two log boat, ~25" diameter tubes/logs. It is fully underskinned, and I would say it's probably on the heavy side for a pontoon.

The prop is a three blade, Stainless Steel, 16" dia x 22" pitch. I'm pretty sure it's a stock Mercury prop.

I'll attach some before and after pics, found a pic of the plates, these are not of our boat, but the plates look very similar. Pics show the "break" facing down, ours were facing up when we tried them last year. I changed them this year to mimic what is pictured in the attachments here.

 

[Jkrt125]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

One more before pic

 

[crb478]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

I think that you might be better off with a 4 blade prop if the turbluent water is what is causing your cavitation issues. That way you will have more blade surface in the water at any given time. I had a simualr issue with an outboard motor on a pontoon and it fixed the problem nicely. You can order one here on Iboats. I did drop in pitch from a 15 to a 13 which took me from near the bottom of my WOT rpm range to the top of it. It is like a new boat and handles much better then before. It also uses less gas.

 

[lmuss53]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

I tried to copy the data from the merc prop selector page. What it shows is a recommendation for 14 to 15 inch 17 to 19 pitch props.

I will say it again, you are propped too steeply. Get the right prop and your engine and drive will work much better for you, probably without any plates bolted on. You need to have that engine running in the recommended RPM range with the throttle wide open. I again made an assumption that you have an Alpha 2.0 drive. You should run the prop calculator for yourself to decide what prop to get. I bought my prop at iboats but I'm not sure what selection aiding tools they have.

I had a 21 pitch prop on the 90 HP Johnson on my boat when I got it, and had the same issues you have now. I now have a Solas 4 blade aluminum 13 pitch prop to get me in the recommended range at WOT.

The good thing about the stainless prop is you can ebay it and get enough to by 2 or 3 good aluminum props for your 'toon .

Reacommended props for your 25 foot pontoon with 2000 4.3 L and Alpha 2.0 drive:

MTL # Blades Pitch Rotation Part number

Alpha 4 Features AL 4 14.5 18.0 RH 48-834852A45

Black Max Features AL 3 15.0 17.0 RH 48-832828A45

Black Max Features AL 3 15.5 18.0 RH 48-11324A45

Enertia Features SS 3 14.2 18.0 RH 48-898996A46

Enertia Features SS 3 14.0 19.0 RH 48-898998A46

VenSura Features SS 4 14.5 17.0 RH 48-825898A48

Vengeance Features SS 3 14.5 17.0 RH 48-16314A46

I looked at you pics more closely and I guess that plate would be OK if you wanted to leave it on. I personally would try that Alpha 4, 4 blade 14.5 x 18 with no plate and I think you will find your boat runs like a different animal. Good luck and enjoy the boat Crest has some well made nice looking boats.

 

[Jkrt125]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Ok, I've got the real prop specs now;

15.75"diameter x 15 pitch 3 blade SS Mirage prop. Part# (on prop itself) 48-19838.

There's not much room to go any bigger, the current prop is close to the cavitation plate.

 

[lmuss53]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

All I can think to suggest is to try a lower pitch 15.75 or a smaller diameter 15 or 13 p. I still think the motor can't turn the prop efficiently. This might get more knowledgable responses if the mods took it to the prop section.

 

[a1nowell]

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

Re: Crest '00 I/O V6 toon prop "cavitation" problem, anybody with I/O toons??

OK, I had the same problem as you are describing and here is what I found.

I decided to put in a new impeller in my lower unit. When I disconnected the trim rams the one on my port side fell apart. It turns out it is held together with 1 bolt inside the ram that had come loose. If I am not mistaken, one ram lifts the lower unit out of the water, the other pushes it down in the water. The port side on my boat pushed and held the lower unit in the water. I reconnected the bolt, replaced some seals and my cavitation problem was gone. I am making the assumption that below 20-22 mph, for me, all was ok. Above 21-22 mph the lower unit under increased water pressure was kicked up to where the prop blade did not get a good bite of the water. After the ram repair the problem went away.

Hope this helps.