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Author Topic:   Non Counter-rotating Twins Engines
Plotman posted 02-27-2004 03:43 PM ET (US)   Profile for Plotman   Send Email to Plotman  
Are non-counter rotating twin engine set-ups a big deal? It would seem to me that any propeller torque should be easy to deal with, either by how you trim the engines or with tabs. The motors that are on the boat were not available in anything other than right-hand rotation in 20-inch shaft length, and the guy that put them on apparently didn't want to mess with brackets. Would this scare you off of an otherwise nice boat? [Would twin engines that were not counter-rotating] affect how much you were willing to pay? Is it possible (and feasible) to buy a new internals and make one of the lower units counter-rotating? Thanks

Plotman

lhg posted 02-27-2004 07:37 PM ET (US)     Profile for lhg    
HP and engine brand?
Plotman posted 02-27-2004 11:00 PM ET (US)     Profile for Plotman  Send Email to Plotman     
Larry--1996 Carbed OMC (can't remember Rude or Johnson) 150s. I've always had mercs, but I'm told these were pretty solid engines, and I know this pair is pretty low hours and almost entirely fresh water use.

David

tgrobson posted 02-28-2004 09:27 AM ET (US)     Profile for tgrobson  Send Email to tgrobson     
I have twin non-counter rotating 130 yamahas on my 22 Outrage. I have no problem at all with them. Handling is fine, and any adjustments to trim can be handled by tweaking the engine trim level. I think the only downside might be a slight if at all,loss of top - end speed, however I can't say for certain thats the case.
jimh posted 02-28-2004 10:56 AM ET (US)     Profile for jimh  Send Email to jimh     
I believe the race boat guys have some tweak for twin engine installations where they install them in the opposite side-to-side orientation from the usual recommendation in order to get the last ounce of thrust from them.

I think the normal set up is to put the CW rotating engine on Starboard, the CCW rotating engine on Port.

I have twin engines (not counter rotating) and I don't notice any particularly aggravated propeller torque. That said, my twins are small (70-HP) and their propellers are rather small, too, which may affect the outcome. If you have a big 225-HP engine turning a large diameter propeller, it may have greater effect and become more noticeable.

I also have steering tabs (sacrificial zinc) on the engines and these are oriented to help cancel the propeller torque. I believe that if you have counter rotating engines the normal practice is to remove the steering tabs and replace them with flat zincs. This might improve the propeller efficiency, too, as the propeller aperture is cleaner and does not have the steering tab intruding into the thrust stream.

I found this article on another website that was informative:
http://www.boatfix.com/how/props.html

WSTEFFENS posted 02-28-2004 11:16 AM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     
Plotman:

If the engines are OMC, CR is achieved in the gear case. This was limited to the V6 models. I have a pair of 150's that are CR. You should be able to buy all the parts necessary for the set up. Can't be too tuff as most dealers could service (set up) the gear sets and bearings.

As for non CR twin setups. I had a 22' revenge with twin 115 V4 OMC engins non CR with mechanical steering. It would wear you out. The 25' Revenge with CR and Hyd steering (not power) is steerable with one finger. To me CR (if available) and Hyd steering is the only way to go. You can see the non CR boat in the Cetaca on page #10, second photo.

Best

WLS

mtbadfish posted 02-28-2004 12:38 PM ET (US)     Profile for mtbadfish  Send Email to mtbadfish     
Plotman,

My Dad's 20' Outrage with the Whaler Drive had normal rotation twin 100's and hydraulic steering. They worked great and I recall no torque problems. I don't recall making any adjustments to the trim tabs on the motors. The "toe-in" "toe-out" adjustments were a relatively simple thing. I sat on the transom with my feet on the W/D and adjusted the connector bar in or out, then he would hit the throttle to see the results. We did this until we got it zeroed in.

Good Luck

bwguardian posted 02-28-2004 05:58 PM ET (US)     Profile for bwguardian  Send Email to bwguardian     
Plotman,

I just sold my 25' Outrage with twin non counter rotating Mercury 150 engines utilizing High Five props and hydraulic steering. The only time I noticed they were not counter rotating engines was at 5,000 r.p.m. and higher as the boat wanted to torque to the port side (nothing the trim tabs could not correct). I have owned the boat for eight years and have contemplated re-doing the port engine lower unit to make it counter rotating but always decided why fix it if it aint broke (plus those props are rather expensive).

Calm Seas

peteinsf posted 03-15-2004 08:05 PM ET (US)     Profile for peteinsf    
Plotman,

I have two 25' Whalers both with twin 200HP OMCs. One has CR motors, the other does not.

I don't see any performance difference then some torque steer when the non-CR motors are out of trim.

I wish I had believed this before I reconfigured the now-CR boat, I went to a lot of trouble to set up the counter-rotation...

Pete

Makowish posted 02-22-2010 12:22 PM ET (US)     Profile for Makowish  Send Email to Makowish     
[Revived old thread only to change its topic. This has been moved to a new thread.--jimh]

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