Help needed with performance issues during first sea trials 76 foot power cat

[Mark peter]

Hi everybody, I was wondering if anybody could give me some advice or information that can help me to understand why performanse could be so bad during sea trials of a 76 foot cat that I was commissioned to do some basic works to, as the "new" boat was left on hardstand for 6 years before being launched recently. (Boat was seized by the courts untill all litigation issues were sorted out.
Scania motors 860 hp each, zf gearboxes,
I discovered that the left and right hand props were installed incorrectly and boat moved forward when I engaged reverse and moved backwards when I engaged forward position on the Teleflex electronic controller unit.
After swapping out the signal harness wires to the hydraulic solinoids ( F and R ) both engines.
We had the correct response as to direction, but I cannot believe the poor performance in power, handling (inability to use motors in opposite gears to swing the boat around at all. shaking,
no response to the boat when turning the rudders . The list goes on....
could there be a problem running the gearbox oppositly or are the props perhaps not supposed to work in opposite direction? Would appreciate any input or advise no matter how little.
Thanks
Mark Peter

 

[sarabande]

Can you give some indication of your area of expertise in fixing problems on vessels, please ?

Also where the cat is located, what kind of design (commercial/leisure), and information about the litigation as that might have connections with the problems you are facing.

Your use of "left and right hand props" is slightly confusing. Do you mean the port and starboard props, or that one prop is left handed and the other right handed ?

 

[jrudge]

You need to understand what caused fwd to be reverse in the first place.

Electronic controlled engines do not have the same power in reverse as fwd and are rev limited.

find the original problem and resolve. If the props were wrong then fix that and go from there.

 

[Mark peter]

Can you give some indication of your area of expertise in fixing problems on vessels, please ?

Also where the cat is located, what kind of design (commercial/leisure), and information about the litigation as that might have connections with the problems you are facing.

Your use of "left and right hand props" is slightly confusing. Do you mean the port and starboard props, or that one prop is left handed and the other right handed ?

Hi, the props ( gearboxes) are counter rotating, Lh + Rh. From what I can make out is the Lh prop has been mistakenly installed onto the right hand and vice a versa

You need to understand what caused fwd to be reverse in the first place.

Electronic controlled engines do not have the same power in reverse as fwd and are rev limited.

find the original problem and resolve. If the props were wrong then fix that and go from there.

Will swap out the props and return controll wiring to gearboxes as before, and test. Thank you for your time and sound advise

 

[sarabande]

Check the forward and reverse ratios of the gearboxes with ZF. Also it is not impossible given the mysterious background of the boat (answers to the other questions would be useful) that the pitch, diameter and profile are also incorrect. Have you checked these ? The more data you can find and post here, the easier it is for the big mobo owners to help.

 

[SvenH]

Logic when looking from a distance:

Engines probably need to rotate the same direction, right?
So the gear boxes would have different output directions?
Have they been installed on the wrong side?
And are then run in reverse to correct that, losing power in the process?

 

[RichardS]

How was the boat performance when the controls were working in the wrong direction?

If it was OK under that configuration then the solution is clear.

Richard

 

[Whippersnapper]

Aren’t the props designed to perform far better in one direction the the other? So if you have them essentially back to front and are correcting this by running the gearbox in reverse you will be getting astern performance running ahead and therefore that would explain it?

 

[ontheplane]

Does sound one huge botch to me - I wonder if that's why the boat has sat unused from new for 6 years?? - Litigation was mentioned!