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Old 19 August 2011, 17:11   #1
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a few sr 4 q'uestions from a newbie...

Hello all

i've recently bought a sr4 with a yamaha autolube 3 cyclinder 40hp on it
its got a non original prop fitted (this one s/s and marked up 'vengence' as original damaged), this is supposed to be for 'pulling a waterskier'.
on gps im only getting 20 knots out of it(but this was with me, my wife and 3 small children on board though), so should this be more?
she comes up on plane lovely but seems lacking legs so to speak?

is there an easy way to check my engines rpm?

any got any idea's (in plain english) on how to get more top end?

where do i get bits or how do i fill front air holes in hull? i figure the back ones easily done with s/s plate fitted inside an out then bolted together
from what i gather a lot of people do this, most of my motoring will be low speed in river and v high speed sea so like the idea of not transitioning all the time at 5-6 knots (if this makes sense)

and finally a bit of a silly one - any idea of the mpg i can expect from my 40'?

i'll stand by for help oh and any p-taking or tips as neeeded?

thanks in advance

chris
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Old 19 August 2011, 17:38   #2
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Speed..

Hi Speed with a 40hp 3 cylinder should be up to about 25 knots with that number of people.. depends also on fuel load.
Best way is to go out alone and with said engine should give you around 28 - 30 knots. Also depends on the engine trim.. if you have manual trim then out of the 5 trim pin holes the middle one should be about right.
On mine the difference between top and bottom trim pin holes is about 5 knots.

will roughly burn about 1 litre per mile at full throttle and about 1/2 litre per mile at approx half throttle. Give or take..
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Old 19 August 2011, 17:46   #3
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You are getting on the plane quickly with a big load because of the "ski" prop. It probably has a lowish pitch and hits your max revs at a lower speed. With a big load on board, this might not be the worst thing ever. And you have a big load on a SR4 with a 40hp.! A longer pitched prop should improve your top end, closing the flooding hull will help your hole shot with the bigger prop, but make your boat more unstable at rest. Don't expect too much from the 40hp - I'd guess that properly propped and running light, high 20's is your lot.

The easiest way for you to check revs is probably a Tinytach

Yes, the MPG question is a bit silly. It sounds like you'll be at Wide Open Throttle most of the time, so WOT consumption for a Yammie 40hp is what you need to know!

EDIT: What Badbaws said about trim
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Old 19 August 2011, 20:32   #4
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Don't expect too much from the 40hp - I'd guess that properly propped and running light, high 20's is your lot.
You'd be surprised-I had Whisper's Sr4-same engine, and with a heavy lump like me onboard up to past 30 knots and it was still accelerating.
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Old 20 August 2011, 04:39   #5
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You'd be surprised-I had Whisper's Sr4-same engine, and with a heavy lump like me onboard up to past 30 knots and it was still accelerating.
There's always one. Tell the dude what prop she was spinning.

Why did you stop at 30kts?
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Old 20 August 2011, 04:47   #6
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faster faster..

I had a seagull on the back was good for atleast 45 knots easy and that was at half throttle as was running it in..
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Old 20 August 2011, 05:03   #7
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I had a seagull on the back was good for atleast 45 knots easy and that was at half throttle as was running it in..
That's nothing. I can pull two skiers behind our's by holding up a larke hankie.
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Old 20 August 2011, 06:21   #8
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My brother in law can get 30knots 2 up with his Sr4 & a yami 40 2st on a good day!
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Old 20 August 2011, 10:12   #9
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Our's, 29knts with the BF50.
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Old 20 August 2011, 17:27   #10
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There's always one. Tell the dude what prop she was spinning.

Why did you stop at 30kts?
Don't know on the prop-ask Whisper.

I stopped at 30 knots because it wasn't the smoothest of days and I was in someone else's boat.
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