MS25S Volvo Penta Saildrive-Changing Rotation

[Kodac]

I would like to change my port propeller to a right hand drive. This would leave me a starboard left hand drive and a port right hand drive on our catamaran. I do not know if the MS25S saildrives are happy driving in any rotation or if forward direction always needs to be a left hand drive.
Thanks for any advice.

[ggray]

I'm curious as to why, or how important you think doing this would be? Especially as with saildrives there should be no inclination to the shafts.

I understand for dual outboards on powerboats, it is helpful, and the benefits are different whether the props rotate toward each other at the top or at the bottom, but this is a lot more horsepower much closer together.

But you may have thought of something I haven't!

[skipperpete]

Originally Posted by Kodac

I would like to change my port propeller to a right hand drive. This would leave me a starboard left hand drive and a port right hand drive on our catamaran. I do not know if the MS25S saildrives are happy driving in any rotation or if forward direction always needs to be a left hand drive.

Thanks for any advice.

I can’t give you an answer from hands on experience but I suspect the answer is that port and stbd props need to be LH despite the fact that Flexofold list a left AND a right hand prop on the website ( RH is for shaft drive). There is only mention of Left hand rotation in the service manual.

[Kodac]

The boat is located in the Med where one is frequently backing stern to a dock or stern tying to shore. The prop walk is very useful in helping manoeuvring while backing up. If the props are set as noted the starboard prop will pull the stern to port, and port engine in reverse will pull the stern to starboard.

[skipperpete]

I think thats just the way cat’s work regardless of prop walk.

[Snore]

Originally Posted by Kodac

The boat is located in the Med where one is frequently backing stern to a dock or stern tying to shore. The prop walk is very useful in helping manoeuvring while backing up. If the props are set as noted the starboard prop will pull the stern to port, and port engine in reverse will pull the stern to starboard.

With all respect you are trying to run a cat like a monohull.

When backing a cat, secure the wheel and use the two engines alone. Think of it as driving a track driven vehicle like a bulldozer or tank.

Much more effective using the engines and a spring line than trying to prop walk the boat.

[Kodac]

Originally Posted by Kodac

The boat is located in the Med where one is frequently backing stern to a dock or stern tying to shore. The prop walk is very useful in helping manoeuvring while backing up. If the props are set as noted the starboard prop will pull the stern to port, and port engine in reverse will pull the stern to starboard.

I guess I asked for it when I said “any advice”. Yes cats are easy to back up by locking your wheel and reversing on two engines. Yes with both engines with left hand props cat be dragged in both directions. But until you try it you do not appreciate the difference. Try keeping the cat in one plays while backing on your anchor while your spouse is swimming in for the shore lines and you get hit with a side wind. Try backing down a tight finger and notice how much easier it to pull the aft end to port vs starboard. I already have the above left/right hand prop configuration, I notice the difference. I just wanted to know if I am doing any long term damage to the port saildrive. Please no more reversing catamaran lessons, make it a separate thread. Does anybody know MS25S saildrives and amI doing any long term damage?

[skipperpete]

Originally Posted by Kodac

I would like to change my port propeller to a right hand drive. This would leave me a starboard left hand drive and a port right hand drive on our catamaran. I do not know if the MS25S saildrives are happy driving in any rotation or if forward direction always needs to be a left hand drive.

Thanks for any advice.

I’m puzzled here, you already have a right hand prop fitted????
One thing that might be an issue is the direction of rotation and the direction of the threads on the various components.... is a RH propeller more likely to come loose on a right hand thread in continuous operation?

[Kodac]

Originally Posted by skipperpete

I’m puzzled here, you already have a right hand prop fitted????
One thing that might be an issue is the direction of rotation and the direction of the threads on the various components.... is a RH propeller more likely to come loose on a right hand thread in continuous operation?

I have Max Props. Simple change on the prop, and then reversing the gear cable on the shifter.

[skipperpete]

The introduction of Max props makes the “left hand-right hand thread” suggestion more relevant, I’ve fitted maxprops to Yanmar saildrives with the proper shock absorbing hub on the vertical shaft, those props don’t play nicely with saildrives and although I’ve never seen em on a volvo saildrive I suspect that the shock loads still exist so the potential to release threaded connections that would normally be tightened by OEM rotation should still be a consideration.

[ggray]

Perhaps your experience is different, but from Sail Magazine online:

"Also known as “asymmetric blade thrust,” prop walk affects most single-engine vessels. It occurs when a prop and its shaft are not perfectly parallel to the water’s surface."
And
" An offset shaft may alter the effect, and when a shaft is parallel to the water’s surface, as in a saildrive, its prop doesn’t walk at all."

[tbird24]

unlike other replies, i think i understand your question/reasoning. i don't know this drive, yet, but the basics will apply. if the transmission were of the automatic style, it would be bad to let it freewheel because of no fluid flow (engine driving torque convertor), thus no lubing the moving parts.


on the other hand, in a standard drive, freewheeling will lube via splash/submerged parts. no harm, just added hours on parts. this brings us to your concerns. usually there will be one extra gear to allow reverse. along with that the reverse gear ratio is likely to change. we'll say the forward ratio is 2.41 to 1. in the same unit, the reverse maybe 1.91 to 1. from the units i've seen, that extra gear is located in the upper half of the case. if oil level is low, you can run the risk of no lube there and well.... the gear ratio, if my numbers are right, would be an increase in load if used for forward. fuel consumption, at the same rpm as the other engine, would be more but move you a bit faster. a prop guy suggested engine load, with the right prop, should only allow, at full throttle, 80% of rated RPM. then cruise at 75% of that.



i hope this is enough food for thought to help you understand what your change can make down the road.

[tbird24]

i just downloaded a workshop manual for that sail drive. it is NOT as i described in my first post! it is very similar to your typical outboard drive assy.



i am new here, so i need some time to learn how to add a pic to show you how it is. i'll send this along for now.

[tbird24]

see the attachment....

[Tupaia]

I doubt it will make any difference given the shafts are horizontal. Since you already have max-props that can be set to either direction and the sail drive is a matter of reversing the gear change lever, try it and see. On power cats with big engines and big props outward rotation is the convention.