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Old 31 May 2007, 15:40   #1
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Wave Crest Phenomenon

Whilst mucking around in the Solent today I became very aware of a phenomenon that I had come across before but not really thought about. I was following a large tug in to Southampton water and riding on the waves it was producing. Just practicing a little throttle control. However whilst doing so I became distinctly aware that after sitting on the crest for a while when I wanted to just accelerate away forwards and drop in to the trough my engine really struggled to make any increase in speed. However if I turned right or left then accelerated the engine would act normally.
Anyone any idea what causes this ?

This has happened to me on a couple of boats. Its like your boat gets stuck to the top of the wave.

NR.
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Old 31 May 2007, 19:59   #2
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I am only guessing but would it be because your prop was in the wave crest as in airated water?

I am sure one of the Royal College of Physics will be on so I will get out of the way>>>
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Old 31 May 2007, 20:01   #3
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I am only guessing but would it be because your prop was in the wave crest as in airated water?
Aidan this is our initial thoughts but as you say lets see what the bods from the Royal College of physics come up with.
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Old 31 May 2007, 21:24   #4
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It could be down to the speed of the wave you are sitting on. You may think you are doing 20kts but the wave may well be doing more.
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Old 31 May 2007, 21:33   #5
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I don't think we were doing 20 knots. The tug was doing about 15 Knots. But try as I might I couldn't get the boat to accelerate off the top of the wave. It was almost as if I had a massive trim that had my boats nose pointing vertical. Full throttle only gave me about 4000 revs but no increase in speed.
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Old 31 May 2007, 21:59   #6
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What I've noticed is that while sitting "on top" of a wave (not a tug's wake, but an actual wave), I'm actually slightly short of the crest. The boat is riding a bit nose up, and I'm playing the throttle to stay there. To accelerate over the top, you have a little bit of uphill to overcome before dropping off the leading edge.

Might be what you're seeing. Might not.

jky
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Old 31 May 2007, 22:49   #7
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It could be down to the speed of the wave you are sitting on. You may think you are doing 20kts but the wave may well be doing more.
Our waves go a little faster over here Cod..so we don't have this problem...
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Old 01 June 2007, 07:33   #8
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I've noticed this when following one of our company's launches and riding the wake, it will go over but there feels as if there is a lot of drag. I don't know what it is but if it was aeration the prop should cavitate?
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Old 01 June 2007, 07:44   #9
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I have had the same effect from riding on an actual wave, the tug was just an example from yesterdays outing. jyasaki seems to have a good idea of what is possibly happening. It is a big power killer though.
I don't think its cavitation just because it doesn't sound like cavitation.
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Old 01 June 2007, 07:53   #10
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Does this occur when most of the boat is hanging in mid air? I'm wondering if it's not something to do with the engine having to hold the boat in that position?
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