Stern Drive trim rooster tail

Donzi GT250

Petty Officer 2nd Class
Joined
Apr 22, 2011
Messages
110
I just noticed that with my Donzi Gt250 with OMC Cobra 350 and Cobra drive that when I am running at cruise at about 3400 rpm with the drive trimmed in I get a small rooster tail that comes up on the port side of the prop.
If I trim the engine out I get a flatter and more symmetrical rooster tail and also better performance.
I know this doesn't seem to make sense (the asymmetrical rooster tail) as i would think when trimmed in I wouldn't get any rooster tail.
Why do i get a asymmetrical rooster tail when trimmed in?
Any ideas what i am seeing?
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Re: Stern Drive trim rooster tail

I just noticed that with my Donzi Gt250 with OMC Cobra 350 and Cobra drive that when I am running at cruise at about 3400 rpm with the drive trimmed in I get a small rooster tail that comes up on the port side of the prop.
If I trim the engine out I get a flatter and more symmetrical rooster tail and also better performance.
I know this doesn't seem to make sense (the asymmetrical rooster tail) as i would think when trimmed in I wouldn't get any rooster tail.
Why do i get a asymmetrical rooster tail when trimmed in?
Any ideas what i am seeing?

Ayuh,... Is there a transducer or something in the water flow,..??
 

superbenk

Commander
Joined
Oct 27, 2008
Messages
2,022
Re: Stern Drive trim rooster tail

Boat listing some when underway? Anything hanging off the transom (like bondo said)?
 

DuckHunterJon

Lieutenant Junior Grade
Joined
Apr 19, 2010
Messages
1,082
Re: Stern Drive trim rooster tail

If trimmed in far enough, it will be pushing the bow down, and the transom up. I would guess it's a function of the prop's side thrust exiting the water. Just a guess though.

In the end, shouldn't matter as you should be running trimmed for optimal performance (which will vary depending on water conditions, load onboard, etc).
 
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