Twin df140s, cat lists to port when at speed

[zx7king]

Hello all,

I wasnt sure where to put this post since it deals with a few different areas of the boat but my initial feeling is the engines so I am starting here. I apologize if it needs to be moved. I searched and I found numerous posts on lists but I didnt catch any with a multi-hull and twin OBs.

Anyway, I have a 22 CC Prokat with twin DF140s. The issue I am having is that when at speed, it lists to the port side quite a bit. I can counteract this (as you do with a cat) by working the tilt/trim independently. The problem is that the tilt of the stbd engine to counteract this is pretty extreme (not to cavitation extreme, but close).

The port engine is a 2002 and the stbd is 2007... dont ask The specs show the two motor weights to be the same so i dont think that is the issue. I did notice that the vertical trim tab on the lower unit of the port engine is deflected much more than the new engine. I dont have any issues with prop torque regarding steering but am wondering if that could be the culprit?

I have also seen posts regarding the height of the engine affecting some v-bottom boats so I plan on measuring that precisely when I get back to the boat this weekend. (cavitation plate in relation to transom bottom)

Due to hurricane Hanna it is out of the water right now so this is a great time to investigate this.

Other facts:
- Boat sits level when at the dock
- Boat does not have horizontal trim tabs
- For the life of me I cannot remember if it was as bad before the new engine was put on
- New engine has prop from previous blown engine so it is the same as the other
- Looking with the naked eye, engine heights look the same (again, i will measure precisely this weekend)

Anyone have any good place to start to troubleshoot this or anything else that might cause this? Wanted to head to the boat this weekend armed with things to try .

Thanks in advance,
Charles

 

[zx7king]

Re: Twin df140s, cat lists to port when at speed

Hi,

This is not a bump, but an actual follow-up question ...

I will be going down to the boat this weekend and from my original post wondered if anyone can answer whether the difference in deflections of the vertical trim tabs on the lower units could cause this? (these are NOT counter-rotating props) I guess it is no sweat to go ahead and deflect the newer one to the same angle and give it a shot, I was just trying to get clarification since i dont have any steerage torque at the moment.

Thanks,
Charles

 

[gsyfishy]

Re: Twin df140s, cat lists to port when at speed

The difference in reflecting water could very well be causing drag on the port motor, hence slowing that side down. Can you not bump rpms on the port motor to compensate for the pull? The difference in the year of each motor individually could also be a culprit, due to torque specs. Being that it's a cat hull, and the motors are further apart than on a V-hull, I would concentrate on the differences of the anti-vent plates, and the drag caused by it.

 

[zx7king]

Re: Twin df140s, cat lists to port when at speed

Thanks gsyfishy..

Sounds like you would first relax the deflection of the one on the old motor to match the newer, correct? I was thinking the other way around but this makes more sense.

Thanks,
Charles

 

[ctales4]

Re: Twin df140s, cat lists to port when at speed

Charles,

This may seem like a simple question, but are the engines counter rotating or are they both left hand rotation? If both props are spinning in the same direction,you may be suffering from prop torque causing the boat to lean to one side. I have a similar problem on my 21 mako when I wind her up. The hull leans to the left due to the prop torque.

 

[zx7king]

Re: Twin df140s, cat lists to port when at speed

Thanks for the tips..

I tried removing some of the deflection on the port side to match the stbd and that definitely helped if not cured. I didnt get to test extensively cause i ran back into my fuel starvation problem on the stbd motor.. thread.

ctales4.. these are not counter-rotating.

Thanks again,

Charles

 

[gsyfishy]

Re: Twin df140s, cat lists to port when at speed

Being that your motors are probably around 3'-4' apart, the prop torque issue is not a factor, engines that are mounted right next to each other have more cause for prop torque issues when not counter rotating.
You may need to play with this a little bit more to get it closer to perfect.