Offshoreonly.com - Mercury CNC props Bblades MRI scan

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kvogt

07-17-2019 07:31 AM

Try a different set of props. See if they have the same rpm problem.

payuppsucker

07-17-2019 10:19 AM

One drive is chain driven, the other is gear driven (to change rotation). The gear drive box is less efficient than the chain drive and will extract more power but I wouldn't think it would 15%. Do you know which side the gear drive box is on?

14 apache

07-17-2019 04:39 PM

You might be able to put synthetic oil in the slow side gear box.

Tmaddox4x4

07-17-2019 06:34 PM

https://cimg8.ibsrv.net/gimg/www.off...0bf8bd5b4c.png

Quote:

Originally Posted by payuppsucker (Post 4697181)

I believe the ZF 280's are gear only. Basically one is in reverse and one in forward. Typical three shaft transmission with an input, a lay, and output shaft. The side that's down on RPM is the one that has more gear contact to rotate same as the motor. I can't imagine it's 15% though.

payuppsucker

07-17-2019 06:39 PM

Quote:

Originally Posted by Tmaddox4x4 (Post 4697289)

https://cimg8.ibsrv.net/gimg/www.off...0bf8bd5b4c.png

I believe the ZF 280's are gear only. Basically one is in reverse and one in forward. Typical three shaft transmission with an input, a lay, and output shaft. The side that's down on RPM is the one that has more gear contact to rotate same as the motor. I can't imagine it's 15% though.

Agreed, 15% is a lot.
What horsepower are you making?

payuppsucker

07-17-2019 06:46 PM

Hold on, let’s back up a bit......
I am talking about the ASD8 drives, not the transmissions.
So are you saying the counter rotation is accomplished in the transmissions rather than the drives?
I am not well versed on the ASD8 but assumed it was similar to the ASD7 which uses gears to reverse rotation on one drive and a chain/sprocket combo on the other drive.

Tmaddox4x4

07-17-2019 06:48 PM

Quote:

Originally Posted by payuppsucker (Post 4697291)

Agreed, 15% is a lot.
What horsepower are you making?

They are the 480HP 950TQ rated motors. I just had the the first 250 hour service done on them. We checked the valve lash and injectors, and a few other things. I'm really leaning towards the props, it makes the most sense. My only experience with surface drives is with RC boats. I do know that a very small change in prop makes a huge difference. Granted, that probably not the best comparison.

Tmaddox4x4

07-17-2019 06:57 PM

Quote:

Originally Posted by payuppsucker (Post 4697292)

My Arnesons don't have a gear box. They are connected straight to the trans output. My trans are 1.118:1 ratio, basically direct drive. My motors sit incredibly low and the transmission takes care of the drop. The output flange is also at a 7° down angle.

payuppsucker

07-17-2019 07:16 PM

Ok, well excuse my ignorance and I learned something here.
If you have #6 props I have a spare set if you’d like to try them.
They are considerably smaller than what you are running though.

14 apache

07-17-2019 08:41 PM

Last thing I can come up with is one intercooler is clogged with soot.

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