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Old 30 June 2012, 07:37   #1
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Country: UK - England
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Searider 5.4 with Yam 90 prop selection

Hi guys

This is really a follow on from my prop size mistake on here earlier.

OK brought a new K series 13 X 19 for the yam 2 stroke 90. Took her out in almost flat calm conditions with no wind and 50 litres of fuel. At WOT my engine indicated speed was 5500 RPM and gps speed was 34 knots.

I have researched on here many threads regarding this topic and i assumed I would be achieving closer to 40 knots? I played with the trim until i could get the best speed which as I say was 34 knots.

Whats the general consensus on this - about right or is my motor under performing? There was no hesitation and she felt very strong and smooth running?

Its academic really as top end does not really worry me but just trying to gauge if the motor is performing ok.

Thanks guys
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Old 30 June 2012, 08:18   #2
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I used to get 41 knots with a 13./14 x 19 . Is the hull empty of water
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Old 30 June 2012, 08:48   #3
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Hi Matt

Yep think so. By that I mean at the end of the day when I pull her out and take out the bung - its dry no water comes out!

What sort of WOT did you get out of her? Like I say she feels strong when pulling but the tacho says 5500 and thats the throttle lever all the way forward.

I did pm you a while back with an update on her in case you were interested how she was getting on but not sure if you got it

Cheers Matt

Mark
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Old 30 June 2012, 10:16   #4
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Hi. I used to get 36-37 with a 17 pitch K series and 39-40 with the 19 pitch prop at WOT. The bottom is still mainly anti fouled+ slightly rough, so suppose will improve if/when get the energy to sort that out. Can't remember exactly but the rpms close to 5500.

Even if You don't have loose water in the hull, as the SR contains plenty of wood, there is a possibility that the plywood is wet, adding weight. Lets hope that is not the case anyway.

Check the planning surface of the boat, a rough and dirty surface will dramatically take speed away. Also weight distribution and engine trim, height on transom has its own impact on the speed.

If the prop is OK and You still get the 5500 at that speed, i think Your engine is fine and its something else.
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Old 30 June 2012, 10:29   #5
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if your getting 5500 then thats its max op speed. somehow your losing 5 knots which is a reasonable amount. has the previous owner (plymouth based) lowered the engine at all? check the cav plate height. should be level with bottom of Hull.
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Old 01 July 2012, 02:41   #6
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Hi guys

Thanks for the replies

I will have a look at cav plate height - why would he lower it though I know you set it just right.

C-NUMB - Have cleaned the hull and found a quite a few dings which have been repaired badly - having that all sorted soon via Ribraff in Dartmouth so will see if that has a positive outcome.

Thanks very much both of you for your help.
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