PROP BOIL ? CAVITATION? HELP

[McSkipper]

PROBLEM: My 2000 with a Suzi 50 will be doing 12 -15 mph, w or w/o ballast and for no apparent reason will lose speed and the engine sounds like it is reving. I will slow down and then bring the rpm back up and no problem.
Load is usually the first mate and I with reasonable amount of "stuff". Dealer thought "slipage" in the prop. Had it checked out. Splines are not so much as scratched. Someone said something about "prop boil". My understanding of this is too little power trying to push too much weight.
Is the answer in the prop? Or am I just trying to push her too fast w too little power?

Over the years I've learned alot from lunchtime reading from all you engineers and the resident Sun Baked Florida Lawyer (SJB). All info will be appreciated. I do get lost in the prop/pitch technical stuff.

[Moe]

What prop is on there? If it's the stock 13" pitch that comes with the motor, it's WAY too much pitch, and could be responsible for the symptoms you describe. The stock prop also has a rubber hub pressed into it. It could be "spun" i.e. the splined metal tube broken loose from the rubber, and the splines still look good.

[Bobby T.-26X #4767]

prior to my re-power, i had an '02 suzy 50hp.
it came stock with a 13 pitch.
i swapped to an 11 pitch. the 11 works fine (WOT-6100rpms and 18-19mph) in a average loaded MacX.
however, if you load it down any, you probably need a 10 pitch just to get it to 6000rpm (6500 rpm is max as i recall).

regardless, Moe may be correct in assessing your problem. that is, you may have spun the hub.
as i recall, the Suzy stock and Michigan Match do not have a seperate hub. i know that Quicksilver does have a replaceable hub.

[Sloop John B]

I don't know anything about 'spun' hubs, but did end up with a couple of them (my fast fishing rigs).

I get along okay to a certain point and then 'phlumy'. Crank back down and , hey, it seem okay again until I try to maintain her up on plain, and 'phlumy'. Seems to sort of 'let go'.

This is simple to correct. Have to send prop off to have a giant machine replace rubber gizmo in the prop.

[jklightner]

I've had this problem before and it was related to the trim of the boat. I moved more weight forward, the boat picked up 3 kts and no more over reving.

[McSkipper]

Thank you all for the info. I understand that if I put the engine in gear (w/o battery attached so as to maintain fingers ) and turn the prop and get the motor to crank w/o the prop spining, then the prop is not "spun". If that is the case then I will change to a different pitched prop. Direction to go to the 10 or 11 was understood. Thanks for not confusing me with the how and why which I have gotten lost in such discussions in the past. (Brain damage from the younger years)

Thanks for letting me know you knew exactly what I was talking about SJB -

I get along okay to a certain point and then 'phlumy'. Crank back down and , hey, it seem okay again until I try to maintain her up on plain, and 'phlumy'. Seems to sort of 'let go'.

I've heard about the process of replacing the hub - after I ordered the part

seems like the usual choice - either put up with the "PHLUMY" process and slow down or get a new prop with a 10 pitch - go with it or throw more money at it

maybe use the sail more? so many choices with the

[bwytodd]

You got a lot of good advice in your responses, with one exception, you can't learn anythig about a spun hub by manually turning the prop (unless you can produce 50HP with your hands!). For most people the 11 pitch prop works well, but if your boat is fairly heavily loaded or has bottom paint, then the 10 will be better (10's on all M's).

[McSkipper]

bywtodd,
Welcome to the site and thank you for the info. I do have bottom paint and the problem did start after I put on a few coats of epoxy and bottom paint in response to blisters. will go with the 10 pitch prop.

SJB - I'll let you know if we still go "Phlumy" after the change.

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