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Old 21-02-2012, 14:07   #1
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Shaft Extensions - Good Idea?

Hi Please could someone advise if there is such a thing as a shaft extension used in lieu of a new longer shaft? Are they recommended and are there in fact pro's and con's?
Would you need to, or is it advised to then also use two flexible couplings, one on either side of the extension?
Really appreciate some advice as our new engine is way smaller than the huge old cast iron Ford we had and will sit too far aft, in fact into our aft cabin cupboard...
Thanks Greg
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Old 21-02-2012, 14:15   #2
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Re: Shaft Extensions - Good Idea?

compared to a new shaft, the extensions if they even exist for such a small shaft, would cost more than a new shaft.
Think of what the shaft needs to do.
1. transmit all the prop thrust to the engine/hull
2. pull the whole boat backwards when in reverse
3. run true without wobble

You could always put a thrust/pillow block at the end of the existing shaft, couple a cv type of shaft to it and the engine and go with it, but I think the cost would outweigh the benefit.
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Old 21-02-2012, 14:30   #3
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Re: Shaft Extensions - Good Idea?

Thanks Sailmonkey, please advise what is a thrust pillow, cv type of shaft etc...
do you have any internet links we can look at?
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Old 21-02-2012, 14:38   #4
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Re: Shaft Extensions - Good Idea?

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Originally Posted by Greg Debi Josh View Post
Thanks Sailmonkey, please advise what is a thrust pillow, cv type of shaft etc...
do you have any internet links we can look at?
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Old 21-02-2012, 14:39   #5
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Re: Shaft Extensions - Good Idea?

I second Sailmonkey's suggestion. If you have room, fit a CV drive. Quieter, no more alignment worries less vibration etc. You will make back some of the money it costs by not having to buy and fit a new shaft, and also not having to do more than a very approximate engine to shaft alignment. The one we have is an Aquadrive but is 25 yrs old now so the name may have changed.
Regards,
Richard.
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Old 21-02-2012, 14:40   #6
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Re: Shaft Extensions - Good Idea?

you could coble something together here

McMaster-Carr
McMaster-Carr

or purchase the complete setup here

Welcome to Aquadrive
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Old 21-02-2012, 14:47   #7
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Re: Shaft Extensions - Good Idea?

a pillar bearing and drive shaft i had on one of my yachts
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Old 21-02-2012, 15:42   #8
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Re: Shaft Extensions - Good Idea?

Shaft extentions are used on power boats with shafts over 10 - 15 ft where they can connect together using a long coupling.

I agree with the others that a fixed bearing at the end or near the existing shaft and an Agua drive CV joint (Constant Velocity Joint) would be a better araingment. You would need to glass in a mount for a "Pillow block" bearing that has thrust capability. Which is to say one that has tapered bearings.

A short shaft with a CV joint at each end finishes the connection. CV joints are used extensivly in automotive applications. Just look at the drive train on most front or rear wheel drive cars with independent suspention and you will see CV joints used.

If you have a 6 mm allen socket wrench You could pick up a CV joint at the local commuter Park & Ride but you might have to fight with the folks stealing Catalictic Converters. Think BMW 3 series. LOL
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Old 21-02-2012, 16:07   #9
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Re: Shaft Extensions - Good Idea?

Quote:
Originally Posted by Greg Debi Josh View Post
Hi Please could someone advise if there is such a thing as a shaft extension used in lieu of a new longer shaft? Are they recommended and are there in fact pro's and con's?
Would you need to, or is it advised to then also use two flexible couplings, one on either side of the extension?
Really appreciate some advice as our new engine is way smaller than the huge old cast iron Ford we had and will sit too far aft, in fact into our aft cabin cupboard...
Thanks Greg
"Shaft Extensions - Good Idea?" NO!

More chance of whip.
More chance of bad alignment.
More chances of it working loose.

Like the others say go with a Pythondrive or aquadrive. your motor will thank you for it! >>> Pythondrive The ideal flexible and vibration-free drive unit
As much as Yanmars shake the drives absorb the movement and torque.

.
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Old 21-02-2012, 16:57   #10
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Re: Shaft Extensions - Good Idea?

http://cdn.cruisersforum.com/forums/...1&d=1329865668

Del, I just noticed a problem with your install......
The shaft seal seawater supply is on the wrong side of the vented loop. It stands the very real possibility of flooding the engine.
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Old 21-02-2012, 17:30   #11
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Re: Shaft Extensions - Good Idea?

Quote:
Originally Posted by Sailmonkey View Post
http://cdn.cruisersforum.com/forums/...1&d=1329865668

Del, I just noticed a problem with your install......
The shaft seal seawater supply is on the wrong side of the vented loop. It stands the very real possibility of flooding the engine.
I guess I need to tell that to the motor. It already has 200 hours on it w/o quirk. I don't see where it would matter. When the motor shuts down the water drains out thru the PSS to sea level, which is about where the head sits on the motor.
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Old 21-02-2012, 18:31   #12
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Re: Shaft Extensions - Good Idea?

Obviously it works, but then why bother with the vented loop?
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Old 21-02-2012, 18:44   #13
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Re: Shaft Extensions - Good Idea?

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Originally Posted by Sailmonkey View Post
Obviously it works, but then why bother with the vented loop?
When the boat heals over under sail it changes the sea level. Plus......per instruction!



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Old 21-02-2012, 19:48   #14
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Re: Shaft Extensions - Good Idea?

Exactly, sea level changes from the perspective of the shaft seal also. If the line coming from the shaft seal is below sea level at any point the water will run straight into the mixing elbow without having to rise to the level of the vented loop first.
Just trying to help, not being nitpicky.
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Old 21-02-2012, 20:17   #15
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Re: Shaft Extensions - Good Idea?

The PSS hose in question is not a water supply line, just a vent to allow the assembly to fill with water after a haul out.
I ran mine straight up to deck level on the centerline and left the top open (not that that matters on a multi).
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