drive line

hi,

would like to ask best drive line option for my newly built twin 360hp diesel x 140 pax, 65 feet x 24 feet steel hull catamaran boat.

Details:
17'-3" horizontal distance from transom to tranny
23" vertical distance from keel to tranny coupling (center) @ engine side
6" vertical distance from keel to shaft @ transom side
36" horizontal distance from transom to propeller

im using to double universal joints with spline ( sequence: propeller connected to 7' x 2.5"D 304 ss shaft - double universal joint with coupling- 11' x 2.5" D toll steel- double universal joint with coupling connected to tranny) my problem is the drive line angle. would it be possible to use the zero degrees angle to get optimized speed and no resultant thrust or take the 9 degrees down angle to get the straight shaft from propeller to tranny?

Thank you,
seacat

 

Firstly, are you saying you built a commercial vessel and didn't design the powerplant yet? There is no way to answer your question without a set of lines with construction details, specifications for the engines, etc. The structure and layout will determine engine placement, which in turn will limit the installation. If you are going to use U-joints, it makes more sense to install them as a jack shaft so there is no need of complicated thrust bearings, pillow bearings, etc.

 

sir Gonzo san, the powerplant twin 360HP intercooler diesel engines and already mounted in the engine bay. the boat lightship 22 tons and loaded displacement of 32 tons. transom mount drive system seafury concept though a hard water propeller 28"diameter x 34" pitch 4 bladed. my concern is the vibration and the optimize shaft angle. the thing im concern with is the resultant thrust for the 9 degrees down angle or the ventilation for the zero degrees angle. a prototype catamaran design wave piercing hull.

akihiro watanabe

 

WOW. If you are concerned about vibration, you might have a problem with your drive line, mounts, framing in the hull. The transmission. The engine itself. Most often universal-joints cause the vibration problem. But, it can be just about any mount, or connection in your drive train - even the propellers themselves could be out of balance.

At what speeds do you notice the problem?

A 14 year old Catamaran? Yes, it could need new u-joints. But, it COULD be something else.

Good luck!

 

Through Seafury concept or Seafury drive system.

You mean you copied a Seafury Surface drive?

Post pics.

 

Frosty,

Look at the photo on his profile.

 

He has'nt built it yet.

 

Read the name on his catamaran in his profile photo ....

 

its not a photo --it an artists impression.

 

You might be right.

But, I think he needs new u-joints.

 

@ frosty san- sir not copied from seafury, the concept is at transom mount. will post pics asap.
@ El_guero san - sir thats my worries now, the vibration, the optimized angle, and the resultant thrust - the boat is already done, last thing to fit are the cooling system and the drive shaft. Engines are already mounted inside the engine bays. - i have in hand are double universal joints with spline ....

 

Looks like your committed far enough to give it a try. I have to admit I dont understand your transom mount drive.

Fit your UJ's opposing each other , that may help in cancelling out vibration.

But where is the thrust going if you have a spline?

Im gonna need some pics.

 

@ frosty san- posting pics now for the stern tube with flange to be mounted at transom, together with cutless bearing, lignum vitae bearing, shaft seal... theres are thrust pad with thrust bearing (7 tons dynamic thrust load capacity) fitted at the shaft between the shaft seal and the uj's.

 

Seacat, why are you so concerned with vibration? From an engineer's point of view you've done everything by the book. Let the U-joints enjoy a small angle, just enough to keep the needle bearings occupied without causing noticeable variations in angular velocity.

If any vibration is transmitted to the hull it will be through the engine mounts. Because there is no thrust force, the mounts need only cope with torque, so they can be very flexible.

 

CDK, thank you very much for the vital info regarding vibration and u-joints job. originally the set-up was 9 degree down angle. though im thinking and asking your expertise sir CDK, what would u recommend, zero degree angle or 9 degree angle as engineer's point of view. ? thank you sir in advance...