Options for driveline replacement

[Salmoneyes]

Im looking at better options for my driveline where weight is my problem.
24 inch and a typical double jointed unit found on most vehicles, with the exception of the tube must be very thick. The thing weighs over 50 pounds.

12M steel ketch (motor sailer)
36k to 4ok displacement
130 HP OM352 (3600 rpm)
PRM 2:1 gearbox
23x15 three blade prop

I know aluminum would be less than half the weight, but aluminum in the engine room is bad (per many experts)

I thought about a lighter weight unit but still made from steel, but hoping there are better options.

I have worked on several boats where the prop shaft was directly bolted to the gearbox....
Other than critical alignment, is there a reason not to do that?

I have an old school stuffing box and interested in replacing the whole works, so I can modify everything for the best set up....

Boat is being completely stripped to bare hull, blasted and rebuilt with all new everything. Im only asking now so we have it in the master plan.

 

[gonzo]

Why is weight critical? Saving 20 or 30 pounds in a 40,000 pound boat is negligible. The cost of a lightweight shaft will be high, and it will likely be less forgiving of damage.

 

[Salmoneyes]

Its a long story, which I have told in another question I posted....

Short version.... She was designed with 4mm hull plateing but built with 6mm. She is going on a needed diet...

I am pulling the stuffing box and shaft today, so I will check my angles... Only reason I can think of for using a jack shaft is, the angles are not right... Which if the stern tube is not on some weird angle, I may be able to compensate with remounting the main...

Still like some alternatives.

I looked at new parts to build a tubeless drive shaft with 1310 series joints and the weight came to 18 pounds. (steel)

 

[Salmoneyes]

Just an update....

The main engine is at the same angle, but is 1 inch offset, and 2 inches lower... I would prefer not to raise the engine to save 18 pounds... Its looking at this point like a jack shaft is a necesitty.

That looks like a potential problem for an upgrade of dripless shaft bearings......

 

[gonzo]

You may have to add a pillow block at the aft end of the shaft.

 

[Salmoneyes]

You may have to add a pillow block at the aft end of the shaft.

You're talking about a solid support on the prop end of the jackshaft? That will allow a dripless install?

 

[gonzo]

Yes. That will take the lateral force.

 

[waikikin]

Im looking at better options for my driveline where weight is my problem.
24 inch and a typical double jointed unit found on most vehicles, with the exception of the tube must be very thick. The thing weighs over 50 pounds.

12M steel ketch (motor sailer)
36k to 4ok displacement
130 HP OM352 (3600 rpm) Seems like heaps of power... thinking 60-80 would be plenty & increase range though working with what you have may be the plan.
PRM 2:1 gearbox
23x15 three blade prop

I know aluminum would be less than half the weight, but aluminum in the engine room is bad (per many experts)

I thought about a lighter weight unit but still made from steel, but hoping there are better options.

I have worked on several boats where the prop shaft was directly bolted to the gearbox....
Other than critical alignment, is there a reason not to do that? Least number of moving parts increases reliability , might be the way to go if the line of shaft & engine height doesn't affect other fit out/sole height over.

I have an old school stuffing box and interested in replacing the whole works, so I can modify everything for the best set up.... Proven & reliable may be old fashioned and viewed by some as "unenvironmental" but a grease filled stern tube works pretty good.

Boat is being completely stripped to bare hull, blasted and rebuilt with all new everything. Im only asking now so we have it in the master plan.

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