Topic

Speed and RPM 16 Aug 2020 01:09 #106748

The cavitation plate is pretty much even with the bottom of the boat. Should it be higher?

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Speed and RPM 15 Aug 2020 22:10 #106741

You may want to raise the motor on the transom a bit, the early OMC motors are somewhat long.
The following user(s) said Thank You: VinTin, chriscraft

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Speed and RPM 15 Aug 2020 15:12 #106733

That is interesting because I couldn't reach the desired RPMs with any other prop than the 10.5 pitch. I have the 14 and the 13.25 pitch props as well.
Maybe I should revisit them.

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Speed and RPM 15 Aug 2020 13:51 #106728

chriscraft wrote: Maybe a little more but not much. I have a 63 Lark V 40hp with the lowest pitch prop (11.5) which produced around 4,400 rpms and 26 mph.
Manufacturer max rpms is 4,500. I have the motor raised to the third position and it reduces the wetted surface without porpois-ing.


4,500 to 5,000 as per the manual.

Aim for 5,000 with the lightest load the motor would see. That way if the motor sees a heavy load the motor doesn't 'lug'. Lugging is hard on a motor. I was getting 30 mph on a 1958 Vagabond with a 1957 35 hp Johnson at 4,850. The best prop I found was 10.375 x 13.25. The rig has seen 28 or 29 with three people.




.
“Believe me, my young friend, there is nothing–absolutely nothing–half so much worth doing as simply messing about in boats.”
From Kenneth Grahame‘s classic, The Wind in the Willows.
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Last edit: Post by VinTin.

Speed and RPM 15 Aug 2020 12:48 #106726

Maybe a little more but not much. I have a 63 Lark V 40hp with the lowest pitch prop (11.5) which produced around 4,400 rpms and 26 mph.
Manufacturer max rpms is 4,500. I have the motor raised to the third position and it reduces the wetted surface without porpois-ing.

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Speed and RPM 06 Aug 2020 16:50 #106626

I did get the tachometer installed. Haven’t had a chance to test run. I’ll repost when I get a chance to test. Thanks
Ormand Poss

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Speed and RPM 04 Aug 2020 16:30 #106604

The pin location will help too. Did you get your tachometer installed?
Mid 50's to early 60's classic Mercury outboard restorations
1958 Hawk II, 1959 Mark 78A Super Marathon Six

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Speed and RPM 04 Aug 2020 15:02 #106603

Hi Ormand,

You should expect a bit more. Maybe 26-28 or so.
What RPM's are you turning?
You want to prop the boat so that it is turning the top of the RPM operating range recommended by the manufacturer with the lightest load the boat will see.

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Speed and RPM 04 Aug 2020 14:48 #106601

Ok, guys and ladies, need help with what speeds and rpm I should expect. I have a feathercraft vagabond with a good running mid 60’s 40 hp Johnson. Wide open I’m getting 22/23 mph. Should I expect more?
Ormand Poss

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