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Old 01 June 2010, 22:18   #1
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Country: Australia
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Prop choice and shallow Water - any advice?

Here in Oz, I'm finding I'm using the boat mostly in really shallow water - typically 1.5m to 3m with a sandy bottom.

As a result, top speed is often down from 38knots to 32-33 using a 13x17 prop. It also tends to cavitate or loose grip more in turns. There just isn;t enough water to push along at full speed.

Is there any general advice about prop (or setup/engine height etc) selection for shallow water? Am i better with a slower turning bigger pitch or a higher revving low pitch?

I don;t want to fully sacrifice deep water performance (whale spotting season's just started!) but i do lots of hours in a bloody ditch!
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Old 02 June 2010, 03:25   #2
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I doubt whether the depth of the water has anything to do with it unless you're very close to touching - and a change of prop wouldn't help you out anyway - all IMHO of course!
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When a boat looks that good who needs tubes!!!
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Old 02 June 2010, 05:55   #3
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I'm not sure there is a way around it though I'm surprised you are feeling bottom drag at 3 metres. The wave that issues to the side of the boat also exists under the water right around the hull and it's the interaction between this and the sea bed that causes the drag.
I suppose, just like any speed problem, you need to pitch the prop so you can reach maximum power at the engine. One prop for the ditches and one for the ocean, maybe.
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Old 02 June 2010, 11:19   #4
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I run in shallow water when going for abalone. It's a rock bottom, though, so I usually (well, OK - always) replace the SS prop with aluminum. Cheaper when the skinny water runs out.

Don't know about top speed, as I usually slow (way) down when water gets thin. Then again, I'm not running over sandy areas, either.

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Old 02 June 2010, 12:18   #5
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buy cookees jet rib
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Old 02 June 2010, 17:33   #6
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buy cookees jet rib
and turn it into a sandblaster
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Old 03 June 2010, 03:44   #7
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buy cookees jet rib
Funnily enough we have done a version of the same hull with a Mercury 115EFI - the same as Hove Russ's engine and was sold to a member on here!
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