Prop Issues

[Sixshooter]

Okay all you GURUS out there.

What are some reasons for spinning a prop hub besides making contact with a solid object.

Background: I have an older boat 1978 to be exact. It has a 898 Mercruiser power pland and mercruiser outdrive.

The weekend before Labor Day weekend I was pounding some waves back towards the peir heads and I had a prop spin on me.

For those of you asking what the heck does that mean, props spin all the time that is what makes the boat go forward. Well yes that is true but on my I/O the prop has a rubber type of hub that holds the cog that to the outer prop housing. When I say spinning a prop I mean the prop shaft spins but all the internal guts spin but the actual prop doesn't really spin.

Spun the prop on that saturday and figured oh I was hitting the waves pretty hard and the prop is probably an original. So probably dry rot and lots of load changes from wave up and wave down and that is what happened.

Two weekends later:

Fishing a Caz tourney. Had a spare prop that came with the boat. My guess is this other prop was also probably very old even though it looked pretty new i'm assuming it was at least 15 years old.

Was taking it easy into the waves on teh way back and spun that prop as well.

Getting a little frustrated and more so paranoid about this whole thing.

I'm thinking it was just a whole bunch of coincidence that both props were old and probably starting to dry rot.

I've put a new prop on the boat only it is a little bit smaller than my others while hte others are getting rebuilt. It seems to be working fine except being a smaller prop I run at higher rpms for the same amount of speed I had before.

Any ideas? Is it coincidence and i'm just being paranoid or is there something else I should check.

Thanks

-jim

[Duckman1]

Jim,

Sounds like you are just that unlucky to have both props go on you. From the age I would almost have to say the guts went bad.

I thought I had a similar problem this summer. Mine turned out to be a cap and rotor issue though.

Out on the big water there is very little that we could hit to knock the prop out. I was running in a lake this summer where there are alot of shallow sand bars so I thought I may have toasted the prop.

Hope it all works out well for ya!

[Weekend Worrior]

Ther's probably a good chance that the two props you spun were dry.

If you put a new prop on you shouldn't have any more problems.

If you do you should have it looked at by a cert. mechanic.

Good luck, and always carry a spare.

[Sixshooter]

Thanks Guys.

Thats what I was thinking too...Just a coincidence of bad luck...

[waterfoul]

Yup, coincidence. Old props do dry out. And if you say you are running at higher rpm, how high? If you are over 5000 rpm on your small block you are asking for a lot more trouble than just a spun prop hub. The motor won't last long at higher rpm. Also, your 898 drive (an alpha for the most part) also won't like those higher rpm for extended periods of time.

[Sixshooter]

Yup, coincidence. Old props do dry out. And if you say you are running at higher rpm, how high? If you are over 5000 rpm on your small block you are asking for a lot more trouble than just a spun prop hub. The motor won't last long at higher rpm. Also, your 898 drive (an alpha for the most part) also won't like those higher rpm for extended periods of time.

I was just stating the difference from the smaller prop I have on there now compaired to the bigger prop I had before.

The Engine RPM's don't really run that much higher than they did before based on throttle position. But they are a little higher to say maintain 30mph with the smaller prop than they were when I had one of hte old prop on there.

I don't run the motor that hard most of hte time. THe best cruising speed for the boat is somewhere between 25 and 32 mph. But top end speed with the old prop was in the low 40's.

Although I do loose some power coming out of the hole, and I lose a little bit of speed. I can troll down pretty good, and I'm able to run the boat at a little higher rpm on the troll, which isn't all bad. Keeps the plugs a little cleaner. Bad thing about a carburated v-8 4 to 6 hours of trolling will load up the engine. Have to rev her up once in a while to clean the plugs.

[waterfoul]

A smaller pitch prop should give you more "pop" out of the hole. Are the diameters the same between old and new? Or is the pitch the only thing that changed? Smaller diameter will give less hole shot especially if the pitch is also smaller.

[Sixshooter]

A smaller pitch prop should give you more "pop" out of the hole. Are the diameters the same between old and new? Or is the pitch the only thing that changed? Smaller diameter will give less hole shot especially if the pitch is also smaller.

Both are a 19 pitch prop just one has a smaller blades than the other.

[waterfoul]

Both are a 19 pitch prop just one has a smaller blades than the other.

Ah. This is a subject I have always had interest in. I have a Baja 24 Outlaw that I've probably run 10-12 different props on over the years. Always looking for that performance edge! Blade size, shape, pitch, diameter, aluminum vs. stainless, 3 blade, 4 blade, 5 blade.... all these things add up to different performance from the same boat. I like to call it "black magic" because you might think one prop will work great only to find out it does something totally different than you thought it would.

[Sixshooter]

Got my rebuilt prop back today. There is a sticker on the prop that states to idle the prop for the first 2 or 3 minutes and exercising it forward and reverse several times to make sure it gets a good seating and to heat up the lubricant they use to get the hub inside the prop housing.

Interesting. Guess I will take it easy on this new prop for a few minutes before I try to win the race. haha...

But now I have two fresh props to play with.

[waterfoul]

Got my rebuilt prop back today. There is a sticker on the prop that states to idle the prop for the first 2 or 3 minutes and exercising it forward and reverse several times to make sure it gets a good seating and to heat up the lubricant they use to get the hub inside the prop housing.

Interesting. Guess I will take it easy on this new prop for a few minutes before I try to win the race. haha...

But now I have two fresh props to play with.

You want me to run those prop tests for you? I have a sheet all set that I've used (rpm, speed, handling, time to plane, etc...). Really, I'd love to beat on, I mean drive your boat!! LOL!!!:D

:chillin: