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  How do YOU operate your twin? How do you trim your engines?

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Author Topic:   How do YOU operate your twin? How do you trim your engines?
Morocco posted 09-03-2002 03:55 AM ET (US)   Profile for Morocco   Send Email to Morocco  
Any advice for someone who has never had more than one engine to run before?

My 150s (87 Johnson 150 GTs) run great, but it seems that my boat is happiest with the starboard engine trimmed nearly all the way in (down) while the other engine is noticably more out (up) -- seems weird to me.

I always start with both engines all the way in (down) and then trim up together -- but the nose drifts right until I do the above.

Any pointers?

JoeyP posted 09-03-2002 06:02 PM ET (US)     Profile for JoeyP  Send Email to JoeyP     
Do you have trim tabs on your boat?
Morocco posted 09-03-2002 07:37 PM ET (US)     Profile for Morocco  Send Email to Morocco     
SSCH posted 09-03-2002 09:23 PM ET (US)     Profile for SSCH  Send Email to SSCH     

My twins don't work like yours. Are the 150's counter rotating? Which Whaler?

My guess is that your engines are not CR and need trim tab adjustment to compensate for steering torque. I run mine trimmed the same. Just as you described, I start with both engines tucked under the boat, then trim out together as the boat begins to plane. Since my rig has CR engines, I've got both tabs set at center.

Tom W Clark posted 09-04-2002 01:03 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Your pair of 150 GT's are not counter rotating and thus the propeller torque is causing the boat to list. This is why the differential trimming is necessary.

Morocco posted 09-04-2002 02:53 AM ET (US)     Profile for Morocco  Send Email to Morocco     
Tom et al. --

Yeah, they are definately not CR -- I had the wife crank them up while I watched this evening. Funny, the guy I bought it from wasn't even sure, but he was smart enough to trailer the boat to a great mechanic every spring like clockwork. So far they really hum.

I guess the REAL question (sorry Jim, sometimes it just takes a while for it to reveal itself...) is whether operating this way has any downside other than perhaps lower efficiency since one has to expend energy to counteract the listing forces rather than pushing the boat forward. Doesn't seem like it.

On point of theory, does the trimmed in (down) starboard engine exert more torque (or p-factor) than the trimmed up one? Or does it act to counter the forces of both engines turning the same way?

Either way, it looks weird but sure is fun.

kingfish posted 09-04-2002 08:55 AM ET (US)     Profile for kingfish  Send Email to kingfish     
JoeyP asked the key question, in my opinion - unless there are other extenuating circumstances (I don't know what hull you have), your condition sounds perfect for trim tabs. You can differentially lower the tab on the listing side to compensate for the torque, thereby relieving your motors from working against each other. Differentially trimming your motors does have at least some negative effect on performance and fuel efficiency, so there's something to use to justify the outlay for tabs if you need anything.


jimh posted 09-04-2002 09:29 AM ET (US)     Profile for jimh  Send Email to jimh     
The listing you are seeing could also be the result of the Whaler leaning into the wind--a tendency these hulls have. It is quite common to see the boat lean to windward when underway in a cross wind situation. If you still have a list when going downwind, then it is probably related to propeller torque.
Morocco posted 09-04-2002 01:22 PM ET (US)     Profile for Morocco  Send Email to Morocco     
Sorry, the boat is a 25 revenge, and it does get a lot of wind effect with the cabin enclosures up.

lhg posted 09-04-2002 01:47 PM ET (US)     Profile for lhg    
Morocco, you have your engines trimmed the opposite of the correct way, to counteract only prop torque.

The Starboard engine should be trimmed out a little, thereby pushing down on the starboard side of the transom. The Port engine should be trimmed in a little, thereby lifting the port corner of the transom. The effect will be to level out the boat while underway.

Steering torue is something else, and you need the trim tabs on the cavitation plates adjusted to fix that condition.

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