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Old 08 August 2001, 02:22   #1
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Country: Greece
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Boat name: SUN KISS II
Make: Nuova Bat 9 Falcon -
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Is it wortwhile ?

I run a Bat 9 Falcon-X with a Merc 115. My max RPM at WOT (trim up), is 4850. According to the manufacturer one must have between 4800 and 5200. Do you think that I must change my genuine 19" Alum prop with a 17", or leave the things as they are ? The above mentined RPM are with 2 adults, 2 kids, the swimming gear for the four, 160 liters of fuel and in a few words a rather heavy boat. Any suggestions ?
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Old 08 August 2001, 04:06   #2
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So the book says the max revs should be between 4800 and 5200. You get 4850 heavily loaded. Sounds just about right to me!

Are you happy with the performance that you get with this setup? You could change the prop to get another couple of hundred revs at the top end, but would you really notice?

This sort of tweaking is worth it when you are racing and trying to get the last few percent out of the setup, but for general use I (personally) wouldn't be too bothered.

John
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Old 08 August 2001, 04:23   #3
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John thanks for the reply. To be honest I THINK that's what the manual says. In your opinion do you think that the numbers are correct ?
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Old 08 August 2001, 06:38   #4
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I would expect WOT to be in the range 5000-5500rpm but thats from experience and received knowledge as I am not an outboard mechanic!

You might try dropping to a 17inch pitch prop - it would give you better acceleration which might be important if say you were into waterskiing. Apart from that if you are happy with performance as it is I'd leave well alone!!

Alan
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Old 09 August 2001, 02:33   #5
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Hi, Alan. I certainly know that the WOT rpm for the Yamaha is 5000 - 5500. But I also know for sure that the WOT rpm for the Mercury 115 is less than 5500. I haven't got the manual in my hands right now, but I pretty sure that it's 4800-5200.
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Old 13 August 2001, 05:19   #6
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I guess to be on solid ground to say that your prop is alright. However before you go into the expensive buying-and-testing-the-right-prop-mode try to get a 17" prop from someone you know or a dealer on temp loan to find out the difference. I own a Bat 5.80 ze and 140 horses and use a 19" Prop stainless steel as well. It maxes at around 6000 rpm with light load. And that is ok for my engine.
Conny
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