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Old 24 May 2004, 07:21   #1
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Country: UK - England
Town: London/Hamble
Boat name: Hot Mustard
Make: BWM
Length: 6m +
Engine: Mariner 90
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Engine tones

Hello all!
I have noticed that occasionaly my engine emits different tones and I'm wondering what the cause is. Sometimes when I accelerate from a standstill, the engine produces a more hollow pitch than usual(like a mild version of the noise heard when cavitating). Other times I hear what sounds like a gurgling (hard to put it into words) I've noticed this when close to W.O.T. and trimmed out(again not the same harsh tone as cavitating)

I look forward to hearing your comments.

Regards,
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Old 24 May 2004, 07:34   #2
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Your engine will sound different depending on how much trim you have and whether the prop is ventilating or cavitating. Once you get used to it you can actually use this to trim the boat for optimum performance as well as looking at your trim guage and / or speedo. When I had a DS21 like yours albeit with 150hp I found it very sensitive to trim. In flatter conditions I would trim out as far as I could go before losing speed. I could definately hear a change in engine note at this stage (I think cos the prop was ventilating?). In head seas I would trim right in - the DS21 has very wide hull and you really do want to land on the Deep V part for comfort!
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Old 24 May 2004, 07:55   #3
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Country: UK - England
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Thanks Alan, that's helpful. I am quite impressed with its handling. 34 Kts(GPS) with just me in it. Seems to be alright for 90hp on that size boat.
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Old 24 May 2004, 08:07   #4
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Not bad at all, IIRC we got 42kts flat out with 150hp
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Old 24 May 2004, 09:05   #5
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What is the difference between ventilating and cavitating?
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Old 24 May 2004, 09:10   #6
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See here: http://www.rib.net/forum/showthread....1777#post51777 about half way through.
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Old 24 May 2004, 09:32   #7
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thanks louise
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