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Old 14 January 2012, 22:50   #1
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Rib ran aground

Aloha,

Ran new 15 hr on 50 hp Yamaha Zodiac 500 bay runner onto soft sand and was able to drag rib back We took about 6 inches of water and the fuel water filter was submerged

Boat restarted but was revving and moving very slowly for 30 mts It started running fine after all the water had drained out and the fuel water ful separator was no longer submerged. on land no engine external damage and no water inside engine Have not checked fuel water separator yet

Question is why did the engine rev and boat not move for all most 30 mts

Appreciate any input

Mahalo!

Suri
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Old 15 January 2012, 02:13   #2
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Prop slipping on its bush after screwing through the sand?

Perhaps when the weight of the water was out, the load was reduced enough to allow it to just grip.

If this is the case, if has slipped badly the bush will have been worn down will go again easier the next time. Each time there is less chance that it will grip. Its probably done its job and protected the engine. Time to get it rebushed or replaced.
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Old 15 January 2012, 05:24   #3
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Yes, if you hit the sand while the motor was in gear, then you have most likely done as Richard says. Lucky you - you got away with it. You'll need to get the prop replaced or rebushed ASAP - it will just keep getting worse and let you down some day when you need it most (gunning the engine up big swells, for example).

The fuel system should be fine, but check it out anyway. Those filters are air and gas sealed, so seawater shouldn't get in at surface pressures.
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Old 15 January 2012, 05:50   #4
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Quote:
but was revving and moving very slowly for 30 mts It started running fine after all the water had drained out
I've read this differently from Willk & Richard. I read this as: revving slowly AND moving slowly. They have read it as revving properly BUY moving slowly. Their interpretation is consistent with the prop bush having spun (and saved your gear box). If the engine was revving slowly I would suggest the prop bush is probably fine but you were just asking the engine to try and lift an extra tonne of water onto the plane with you - thats probably something like 3x the load it has to deal with in normal running so its was labouring.
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Old 15 January 2012, 06:23   #5
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Originally Posted by Polwart View Post
They have read it as revving properly
Actually Miss Cleo, I read it as "revving". When ordinary people say "revving" - they mean "vroom vroom". You would probably call this overrevving.

Consistent with our diagnoses.



BTW, my calculations suggest a maximum of 0.5 metric tonnes of water , but I'd reduce that by an E-Factor of 50%.
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Old 15 January 2012, 06:38   #6
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If the water in the boat was about 6" deep throughout the boat then you"ll be carrying over half a ton on water when driving off before the boat empties. Too much to ask of a wee 50hp motor and it's propeller. It's likely the prop just broke away from the water because it couldn't drive that load. The prop had too much pitch for the load you were carrying.
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Old 15 January 2012, 11:24   #7
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Originally Posted by willk View Post
Actually Miss Cleo, I read it as "revving". When ordinary people say "revving" - they mean "vroom vroom". You would probably call this overrevving.

Consistent with our diagnoses.



BTW, my calculations suggest a maximum of 0.5 metric tonnes of water , but I'd reduce that by an E-Factor of 50%.
Willk bloomin eck you like to dispute the minutia don't you! The difference depends on a comma which wasn't present "It was revving, and moving slowly" (i.e. move throttle and get lots of noise but no speed) or "it was revving and moving slowly" (i.e. move throttle and it doesn't get to max rpm). Of course internet punctuation may mean your interpretation was absolutely reasonable.

A tonne was a guess, and 6" is probably more like half a tonne (but still a big load on the engine) but 6" of water wouldn't normally cover a fuel separator so it may well have been more.
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Old 15 January 2012, 11:37   #8
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Some days I wonder about why you know some of the stuff you say, though I do wonder if it's as bad as being drawn into watching zit popping vids on Youtube.
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Old 15 January 2012, 12:11   #9
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Some days I wonder about why you know some of the stuff you say, though I do wonder if it's as bad as being drawn into watching zit popping vids on Youtube.
It doesn't get any better when you meet him in real life either... ...in fact it gets more worrying.
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Old 15 January 2012, 12:47   #10
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Originally Posted by jwalker View Post
If the water in the boat was about 6" deep throughout the boat then you"ll be carrying over half a ton on water when driving off before the boat empties. Too much to ask of a wee 50hp motor and it's propeller. It's likely the prop just broke away from the water because it couldn't drive that load. The prop had too much pitch for the load you were carrying.
I would have thought with half a ton extra load, the prop would have been well submerged and able to grip if it could. Hull was not moving much so it would not have disturbed the flow. Engine would have just lugged if the bush was not slipping, no?

Sounds like the OP did not just strike the engine on the bottom but properly ran-aground (not the only one this week-end!). Prop might have had a good run through the sand.
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