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Gearcase ratio 2.38:1 is what is listed for both lower units. So should be the same. I wouldn't think there would be much loss in gearing to reverse rotation.

we do have separate fuel tanks and indeed when matching rpm the counter rotating outboard uses more fuel. The Mercury electronic Vessel View uses the on board computer in each engine for RPM and fuel consumption feed back.

So I have a 24' TomCat with twin Mercury Command Thrust 115hp Out board engines, starboard engine is counter rotating. I use Mercury VesselView mobile for electronic engine feed back. When on step I usually match RPM but noticed the counter rotating (starboard) engine uses a lot more gas than...

Well 2020 boating is here, tried out the new PowerTech 15x16 props. RPM came up to 5600 RPM, Speed 30 knots WOT. So better... but the old 14.5x17 aluminum props actually did better. Both speed and RPM (32knots WOT at 5800 RPM) Kind of disappointing.

Well finally got the replacement 15.25 x 15 PowerTech SS props on and did some testing. For my application the 15 pitch is not enough, Rpm was over 6000 and only 28 knots. Will trade them out for next size 15.25 x 16. That should pick up my speed and load my engines about right. So season is...

A giant thank you to all for the information. Especially liked the referral to the PropGod. He was very helpful and open with information. I have a set of Powertech OFS3R15 and OFS3L15 on order and will report back after I’ve tried them out. Thank you all again. Great forum for information.

I called Ken at PropGods. He had great advice. He recommended Mercury Enertia 15x15 SS with hub to reduce vibration at lower RPM. He also recommended a OFS3 15x15 SS includes hub. About $1500 for Enertia with hub & shipping and $900 for OFS3 with hub & shipping. Now I’m wondering if the...

I’ll follow up on that thank you.

Not much in the way of prop shops up here in Alaska. Local C-brat dealer unresponsive and Mercury outboard dealer not knowledgeable on Props. So kinda hangin out gathering more info before we change over. Currently running 14.5” x 19P peaking at 5200 rpm. Aluminum.

Hello all, I’m looking for some advice specific to prop size. I have a 1998 C-Dory 24’ TomCat repowered to two Mercury 115 command thrust out boards, approximate boat weight with passengers and gear is about 6200 lbs. The mercury engines design spec for top end is 5800-6000 rpm. Looking at...