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Old 15 January 2012, 12:48   #11
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Help! Help! The Admin Team are picking on me!

I would like to take this opportunity to correct my usage of the E-Factor. It is a "multiplier" and so should have read E0.50

You'll see a bit more of it over the coming months:

For top speeds in RIBs it's generally E0.85
For sea state experienced by RIBbers it's usually something similar
For fish that got away it can be as low as low as E0.20

A rough rule of thumb for the Exaggeration Factor is the amount that you feel tempted to embellish a story recounted down the pub...

BTW, I've covered fuel filters on my old transom, maybe 8 inches, and kept my feet dry at the controls. The water gathers there.
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Old 15 January 2012, 13:01   #12
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Thanks everyone!
To clarify revving at 3500 rpm and was moving at 9 mph for 10-15 mts then slowly gathered speed to 20 mph at same 3500 rpm without me touching the throttle. I was able to rev to 5000 rpm and obtain top speed of 30 mph after that

No external prop damage Hit sand at lowest speed before shutting engine off manually Also 6 inches of water was taken in and I estimated about 20 gallons maybe?

Where I live it may be cheaper to buy a new prop
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Old 15 January 2012, 13:07   #13
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Hi,

That just sounds like the weight of the water* onboard holding you back off the plane.


* E0.15
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Old 15 January 2012, 16:22   #14
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Quote:
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The difference depends on a comma which wasn't present...
...which can be quite fundamental sometimes. I recall a book on the subject called 'The Panda eats, shoots and leaves'

Quote:
Originally Posted by Wikipedia
A panda walks into a café. He orders a sandwich, eats it, then draws a gun and proceeds to fire it at the other patrons.

'Why?' asks the confused, surviving waiter amidst the carnage, as the panda makes towards the exit. The panda produces a badly punctuated wildlife manual and tosses it over his shoulder.

'Well, I'm a panda,' he says, at the door. 'Look it up.'
The waiter turns to the relevant entry in the manual and, sure enough, finds an explanation. 'Panda. Large black-and-white bear-like mammal, native to China. Eats, shoots and leaves.'
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Old 15 January 2012, 18:50   #15
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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?
But it doesnt work that way. The prop is under maximum load when the boat is stationary and the throttle is opened. The load reduces as the boat accelerates. The faster you go, the lower the load on the prop blades.
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Old 16 January 2012, 01:42   #16
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But it doesnt work that way. The prop is under maximum load when the boat is stationary and the throttle is opened. The load reduces as the boat accelerates. The faster you go, the lower the load on the prop blades.
That's bollard-pull condition, the design point for tugs.

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Old 16 January 2012, 01:57   #17
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The maximum load on the prop (or torque on the bush) would occur when the engine is delivering the most power - which would normally be at high revs for an outboard. Exception might be for very dynamic load changes such as changing from turning in water to hitting sand or rock. If the power absorption of the prop at the given water speed and shaft speed is greater than the power output of the engine at that shaft speed then the boat will not accellerate and the engine will not climb up its power curve.

We normally don't have much excess power at low speeds and therefore are not much use as tugs despite our relatively large engines.

I would have thought a proper tug would be set-up to deliver its maximum power at a much lower water speed. You presumably don't use all your available power at your maximum speed when not pulling anything.
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