Son of a beach !!! I lost 500 RPM

Mark T · **Posted:** Mon May 14, 2012 11:33 am

Finally took the boat we bought last October out for Mothers day for the maiden voyage. Started right up, ran great, handles wonderfully, until we ran aground !! One of my daughters, went into too shallow of an area and as she was raising up the stern drive it got buried in the muck. After fully raising the drive the engine sputtered and did start, but dad ended up hoping overboard and pulled the boat to deeper water. Afterwhich I lost about 500-600 rpm ? did I just trash my impeller ? Prop is now fairly paintless, but minimal nicks and burrs so I don't think that is the cause of that big of a drop in rpm's.

Suggestions ??

scotchwater · **Posted:** Mon May 14, 2012 9:57 pm

Sounds like the prop to me. Doesn't take much to get in out of pitch and lose a few hundred RPM's. If you have, or can borrow a spare, I'd start there.

aguyindallas · **Posted:** Tue May 15, 2012 5:56 am

While its possible you damaged the impeller, it will have zero effect on rpm. After you ran aground, did you notice any new vibration when you drive the boat? This would be an indication of a bent prop.

Mark T · **Posted:** Wed May 16, 2012 8:54 am

aguyindallas wrote:

While its possible you damaged the impeller, it will have zero effect on rpm. After you ran aground, did you notice any new vibration when you drive the boat? This would be an indication of a bent prop.

There was a bit of a vibration, not much, prop has some burrs on it and a couple of dings. Just ordered a 4 blade backup and will try filing down the rough edges before tossing it in the drink again.

ric · **Posted:** Wed May 16, 2012 9:22 am

Mark T wrote:

aguyindallas wrote:

While its possible you damaged the impeller, it will have zero effect on rpm. After you ran aground, did you notice any new vibration when you drive the boat? This would be an indication of a bent prop.

There was a bit of a vibration, not much, prop has some burrs on it and a couple of dings. Just ordered a 4 blade backup and will try filing down the rough edges before tossing it in the drink again.

I went from a 19 dinged up prop that vibrated a little to a 21 and gained RPMS. I actually need a 23 now

Mark T · **Posted:** Wed May 16, 2012 9:44 am

Ric

Company I talked to after asking about pre and post beaching rpm's, boat handling etc has suggested a 4 blade 18 versus the 3 blade 19. Now you have me thinking if it should have been the other way around.

boater · **Posted:** Wed May 16, 2012 2:43 pm

No, the Company has the right plan.
An 18 4-blade should be good on that boat.

Mark T · **Posted:** Mon May 21, 2012 8:11 am

Took the dinged and burred prop off, went at it with a Dremel tool with a round stone grinding wheel. Figured had nothing to loose with new prop on the way. Spent about 45 minutes grinding all the rough edges smooth and evening out the chinks . Tossed boat back into the drink and now I can get 4900 rpm and 47mph with the old prop.

Note, none of the blades were worse than another, so propeller is still pretty balanced after my grinding.

ric · **Posted:** Mon May 21, 2012 8:14 am

4900 you're right at the peak HP curve of a 351. Nice

Mark T · **Posted:** Mon May 21, 2012 8:28 am

ric wrote:

4900 you're right at the peak HP curve of a 351. Nice

Was suprised an 18 year old 4000 lb boat would go like that. Will be interesting to see what new prop will do, ended up cancelling the 4 blade aluminum and ordered a 3 blade stainless after talking to some others. Maybe I'll crack 50 ??

ric · **Posted:** Mon May 21, 2012 8:33 am

Mark T wrote:

ric wrote:

4900 you're right at the peak HP curve of a 351. Nice

Was suprised an 18 year old 4000 lb boat would go like that. Will be interesting to see what new prop will do, ended up cancelling the 4 blade aluminum and ordered a 3 blade stainless after talking to some others. Maybe I'll crack 50 ??

If you went up a pitch, sure

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Son of a beach !!! I lost 500 RPM

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