jackshaft: how long???

Hi guys, I need to figure out this:
I have (on paper) a sterndrive wich is 2.7 mt (8 ft 12 inches circa) far from the engine and I would like to use a jackshaft to keep engine under consolle in the LCB area.
The farthest I could move the engine back is 50 cm (20 inches) more than this I would go with an engine placed back in the stern "the traditional way" and I would have to reconsider the whole cockpit.
Do you guys think there is a solution for a jackshaft as long as this one?
A mec. engineer told me yes no problem...I want to be 100% shure...
I know Albemarl use long jackshafts but I think this is going to be longer than that.

 

I think Seaboard Marine has done this before and probably could ship you a package all made up to drop in. Give them a call. Probably would have a support bearing in the middle.

 

Thanks a lot!
Is this the web site? www.sbmar.com

 

That it is.

 

probably they can have a solution: http://www.lancingmarine.com/ and http://www.dbdmarine.com/ but more probably on their own drive systems. Problem will be also to solve the fresh water pickup that usually is trough sterdrive and sometime the exhaust system as well (Volvo sterndrive). Water pickup trough sterndrive is important also for some function of the sterndrive itself, such as the oil cooling. A similar solution with engine on the center and a jackshat to a drive is on the Hinckley 29 ft but the engine is coupled with a jackshaft to a jet drive, exhaust and water pick up are separate. Other similar solutions on many surface drive systems. Engine has to be pre-arranged for an adapter to a jackshaft drive too (in the bell housing and coupling), like showed on the Steir brand web catalogue: http://www.steyr-motors.com/technical/drawings.htm otherwise a custom coupling system has to be realized but in this case will follow for sure a missing in guaranty by the engine company. Definitevely, in my opinion, this is a system that has to be decided and designed in strictly collaboration with the engine company/supplier, if this boat project/production is too important.

 

got more info about

Fede,
I got more info about a jackshaft drive system from my mechanic. The Mercruiser can supply a long shaft with a modified Alhpa drive. The system is coupled to a PRM gearbox direct mounted to the engine. This Mercruiser drive system has a water pick up direct to the engine throug a traditional thrue hull seacock. Acquadrive also can supply a shaft drive system to be coupled to a Mercruiser. But I was not able to find info about this system on the web. Better if You contact Mercruiser. Some info about on http://www.boatdesign.net/forums/showthread.php?t=2550

 

was engineer on a large lagoon cat that ran a jackshaft about 6 feet. shaft was mounted between perkins 4108 and gearbox. had a center bearing and looked just like a 2 piece driveshaft from a car. initial instalation had problems with one set of uj;s as the shaft was too perfectly aligned with engine end and stopped the needle rollers from rolling. after moving the center bearing slightly to one side problem fixed. I think driving shaft before the box is a better setup than after the box as speed is well within shaft capability and the shaft then has to carry much less torque than it would after a reduction box

 

They have solution (for marine use):
http://www.centa.info/
They supply universal "Jack" shaft to coupling jet drive Alamarin to engines.