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Old 25 March 2008, 08:16   #1
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Post test sanity check - Max RPM

Finally got the "new" toy out for a test run yesterday. Managed to clock an indicated 6500 RPM at WOT (in the short length of "flat" water I could find that would allow a long enough look at the instruments without stuffing it or going airbourne! )

Now, the only reference I can find to my generic Yamriner 2 cyl 2 stroke is on a scan of a Mariner 55 "Marathon" Microfiche. It says I should have topped out at around 5500.

So, Does anyone know if the marathon was purposefully "maxed" at 5.5K, or better still does anyone have access to paperwork that might tell me what my theoretical max should have been. ('79 vintage Yam 55 2cyl 2 stroke) It was literally screaming when it happened, and sounded "normally WOT" when throttled back to 5500, so I think I may have too low a pitch on there! Mind you, 2 - stroke Yams are always rev - lovers, so maybe 6.5K isn't that unrealistic?


Apart from that it was a good trip, only other big problem was my knee against the fast idle lever. This weeks job is going to involve moving the remotes up the side of the console by about 6".........
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Old 25 March 2008, 08:34   #2
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My book says 4500-5500rpm. WOT.
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Old 25 March 2008, 12:57   #3
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Thanks for the quick reply. I had the nagging feeling you might say that! On the plus side, I still have all the pistons I left the marina with!

So, anyone know of any 13 spline 10& a bit inch diameter 15" props going a begging?

Or anyone round this corner of the world have one I could borrow for half an hour at a suitably convenient time?
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Old 25 March 2008, 13:06   #4
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Hi What Pitch are you running at the moment?
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Old 25 March 2008, 14:49   #5
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Thanks for the quick reply. I had the nagging feeling you might say that! On the plus side, I still have all the pistons I left the marina with!

So, anyone know of any 13 spline 10& a bit inch diameter 15" props going a begging?

Or anyone round this corner of the world have one I could borrow for half an hour at a suitably convenient time?

Is that the same a the K series prop?
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Old 26 March 2008, 06:45   #6
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Ashby, 12" - probably spec'ed for the 9 bods it was rated to carry by D.O.T 25 years ago. Hole shot is awesome!

Nos, Haven't a clue.......
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Old 26 March 2008, 07:17   #7
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Ok 12" to 15" will loose you about 600 RPM for the same boat configuration. May be woth looking @ 17" this will drop 1000 RPM for the same load.
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Old 26 March 2008, 07:54   #8
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Ashby, 12" - probably spec'ed for the 9 bods it was rated to carry by D.O.T 25 years ago. Hole shot is awesome!
Maybe. Before going off to buy props, give us some figures because with a 5.5mtr boat and just 55hp I would have thought 12" pitch wouldn't be far wrong. Revs, speed, gearbox ratio.
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Old 26 March 2008, 08:31   #9
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Managed to clock an indicated 6500 RPM at WOT (in the short length of "flat" water I could find that would allow a long enough look at the instruments without stuffing it or going airbourne! )
I was going by the Numbers already supplied!!! about 1000 revs over max!!!
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Old 26 March 2008, 08:53   #10
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I was going by the Numbers already supplied!!! about 1000 revs over max!!!
Yeh, I know. There was no critisism of you intended. It's just that a 5.5mtr with 55hp on a 12" prop at about 5500 would give around 25mph and that doesn't seem far off to me. But I don't know the gear ratio so I'm gessing.
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