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Old 12 October 2009, 10:22   #1
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Chine walking Searider 5.4

Does anyone have problems with their SR chine walking? Mine has a Mercury 90hp 2 stroke.
In calm water I can go full ahead (about 40/41kn) without any problems, the engine needs to be well trimmed up to achieve this speed & it appears that the only contact with the water is the engine leg & the aft 2 feet of the hull. Any disturbance on the water will induce chine walking which gets worse with each roll, I guess it is similar to parametric rolling on ships.
The chine walking can be stopped by reducing the rpm & not adjusting the trim or by trimming the engine down & leaving the rpm unadjusted. Obviously both have the effect of reducing the top speed (to about 35 kn).
Is there a solution to this problem while still maintaining full rpm?
The cavitation plate on the engine is just in line with the bottom of the keel.
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Old 12 October 2009, 11:26   #2
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Zub, you might want to have a look at this thread...

http://rib.net/forum/showthread.php?t=32415
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Old 12 October 2009, 16:27   #3
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They all do it with 90's on the back!!
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Old 12 October 2009, 16:32   #4
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So do you reckon there is any point in lifting the engine up a notch or two then or do SR's with 90's have a "critical speed" above which they will chine walk due to hull design?
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Old 12 October 2009, 17:09   #5
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I reckon they all do it once you trim them out too far in search of 40 knots
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Old 13 October 2009, 03:39   #6
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if you can hit 41kts then you have achieved what the hull was designed for!! leave it at that.
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Old 13 October 2009, 05:49   #7
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if you can hit 41kts then you have achieved what the hull was designed for!! leave it at that.
I'd agree, if you want more speed than that in a boat that size, get a different boat! Our 5.4 with a 90 opti did the same. Pushing an SR any faster would be madness. Ribs are mainly for seaworthiness, if you want flat out speed on calm water, perhaps the rib isn't the boat for you? Personally, 41 knots is plenty for all but racing circumstances.
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Old 13 October 2009, 06:10   #8
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My SR4 chine walked like nothing else. Not had the 5.4 do it yet.
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Old 13 October 2009, 06:35   #9
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if you can hit 41kts then you have achieved what the hull was designed for!! leave it at that.
I'd be happy with that
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Old 13 October 2009, 09:43   #10
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Im more than happy with the speed & am not looking for it to go any faster,38-40kn is more than enough in the SR.
The issue is not being able to maintain the speed even in a slight chop without the boat chine walking, it seems strange that a boat designed to carry a 90 hp 2 stroke engine & fitted with a 90hp 2 stroke engine (engine weighs 135kg) chine walks & from what I can gather it seems to be a characteristic of this boat??
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