Every now and then a sailboats prop shaft needs replacing. It can be caused by corrosion, bending or wear at the stuffing box or cutlass bearing surfaces.
On many boats removal of the cutlass bearing can help avoid dropping the rudder. On this boat, an Ericson 34, the shaft just barely slid by the rudder with the cutlass bearing removed. This saved hours of labor time in not having to drop the rudder. To remove the cutlass bearing I used a Strut-Pro tool.
Before the nitpickers come out in full force the word "Cutless®" is a trademarked brand name of Duramax Marine. I therefore use the alternative accepted generic spelling of "cutlass" so as not to infringe on a trademarked "brand name".
From the Duramax Marine web site: "Cutless® is a registered trademark of Duramax Marine® LLC."
03-DEC-2010
Cut The Old Shaft Out
If you know the shaft needs to come out why risk damage to the gear box or gear box flange by trying to press the coupling off the shaft. It is far easier and far less time consuming to simply cut the shaft out. This took all of about 45 seconds to free the 1" shaft from the flange.
I will type this loud and clear so it hopefully makes sense: NEVER, EVER, EVER, EVER use a "Slide Hammer" to remove a shaft from a coupling if the coupling is attached to the gear box! If you want to throw 3k out the window feel free to use a slide hammer, if not, use PROPER procedures for removing the shaft from the coupling such as a coupling press tool.
Only hacks, that don't care about your boat or gear box, use slide hammers to remove prop shafts from the couplings when the couplings are attached to the gear.. Yes it's quick & dirty, and the damage to your gear box can largely goes unseen, for a period of time, but DO NOT be fooled by yard monkeys with slide hammers and do not allow a yard to use one on your boat. Would you go to a dentist who used a Milwuakee Sawzall???? About the same level of stupidity and it is the WRONG TOOL FOR THE JOB.
A slide hammer is essentially a long piece of metal pipe that threads onto your shaft where the prop nuts go. It is about 4 feet long and has a heavy metal weight on it. The weight is slid up the bar to the prop shaft and then thrown or "slid" down the bar until it hits the end and SLAMS to a sudden stop. The idea is it breaks the coupling from the shaft when the weight comes to the suddent and abrupt stop. The reality is it destroys gear boxes in the process.
This destruction is not readily apparent so yard monkeys assume they get away with it and it "works". Yes it works, it works to DESTROY gear boxes. If your boat yard tells you "we do it all the time" please do yourself a favor and find a new yard.
Slide hammers can cause brinneling of the bearings or races in the gear box. This means the shock loads imparted on the static bearings, by the "slide hammer", create FLAT SPOTS in the races or bearings. The gear may work for some time after the slide hammer event but eventually the damage rears its ugly head.
About ten years ago I was at a yard when I overheard the yard boys slamming & slamming & slamming a slide hammer to free a shaft from a coupling. All of a sudden I heard one last SLAM, then a clunk and the sounds of metal bits on fiberglass, then "OH $HIT!"...... You guessed it they hit it so hard they blew the case of the gear box apart and destroyed it. Literally cracked the iron gear box wide open. The shaft, after all the beating that finally destroyed the gear box, was still firmly embedded in the coupling.
Rant over....
18-NOV-2010
Double Taper Shaft
Some shafts, as can be seen here, are a double taper on both ends. Many sailboats though lack the space for a double taper coupling and they are most often a "straight coupling"..
Know what you have before trying to remove it...
14-DEC-2010
New Split Coupling
For tight spaces Buck Algonquin makes a great split coupling. I much prefer a straight split coupling to a straight solid coupling but both work if properly installed fitted and faced.
The nice thing about this model is that it's no longer than a standard solid coupling and is actually a touch shorter than most. The "S" designates "short"...
14-DEC-2010
New "Shorty" Split Coupling
This is the new split coupling from the box above. You can see how compact it is on its overall length.
14-DEC-2010
Coupling Surfaces Made Parallel With Shims
Now the coupling has to be "fitted" to the shaft. These coupling ship a tad undersized for the SAE shaft tolerances. This allows a competent shafting shop to "fit" the shaft to the coupling. The proper fit for a straight coupling is a light press fit or light interference fit. This means it does not just "slide on" and requires some light tapping, or heat to expand the coupling while it is installed over the shaft.. Getting this level of fit can be time consuming.
The two shims are placed in the "splits" to make the bore ID the same at both ends before "fitting" begins.
14-DEC-2010
Rough Reaming Tool
This is the rough reaming tool. The finishing is done with grinding compound or other means of honing the coupling bore.
14-DEC-2010
Flange Is Bored To Fit The Shaft
With the flange held tight in the jaw of the machine the reamer is carefully sized and rotated to remove just barely enough to start to get the perfect fit. It takes some time to make it fit just right.
14-DEC-2010
Inside Finish
The inside of the bore is then honed to get the final fit. This was taken before the honing process.
14-DEC-2010
Should Be A Light Press Fit
Here the machinist is test fitting the coupling to the shaft. A soft lead mallet is used to tap it on. This is NOT pounding but a light "tap fit"... Just enough interference so it won't go on by hand is how it is done.. With a good fit you may need to heat the coupling to make the shaft slide into it when doing the install at the boat..
14-DEC-2010
Shaft Is Cut To Length
For the shafting on sailboats I only spec/use AQUAMET 22. AQUAMET 22 shafting is a high-alloy austenitic stainless steel that offers tremendous corrosion resistance and excellent strength properties. It is some of the best shafting there is.
Here a length of 1" AQUAMET 22 is cut to lengths for machining.
22-JAN-2009
Checking Shaft Run Out
Once the shaft is cut to length it is then tested for run out. A good shafting shop should ALWAYS do this even with a brand new shaft. If it does not meet tolerance then it needs to be made true. This one was out by less than .001 for a 52" shaft.
This shaft was also checked for true after the machining process.
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02-FEB-2010
Machine For Cutting Shaft Taper
Once the shaft is cut to length it is placed in this machine to cut the taper, or tapers, if it is a double taper shaft.
14-DEC-2010
Keyway is Cut Into Shaft
This is the machine used for cutting the key ways.
14-DEC-2010
Spotting The Shaft
After the coupling has been fitted to the shaft the set screw hole needs to be "spotted" into the shaft. The drill press is spotting the shaft in this picture.
Spotting is the creation of a small dimple in the shaft for the head of the set screw to recess into. If your shaft is not spotted for the set screw/screws you have an poorly machined shaft. Some unscrupulous vendors cut this corner.
02-FEB-2010
No Spotting
Here is a prime example of the unscrupulous or sloppy machining. This shaft literally fell out of the coupling and the boat took on water. The coupling was clearly never "fit" correctly to the shaft then the set screws were never spotted to act as a back up. Don't let this happen to you. Insist on a light interference fit and properly spotted set screws.
13-JUL-2010
Properly Spotted Shaft
This is what set screw spotting looks like. You should have dimples in your shaft to accept the set screws..
14-DEC-2010
Facing The Coupling
Now that the shaft and coupling have been "fitted", including the set screw spotting, the flange is mounted to the shaft and placed in the lathe.
When using a split coupling it is very, very important to properly and evenly torque the clamping screws. Not doing this evenly and properly can result in the face being out of round with the shaft. When facing the shaft coupling the machinist will properly torque the clamping nuts so you get a perfect facing with no run out.
14-DEC-2010
Fit & Faced
Just like a brake rotor lathe the face of the coupling is made to rotate perfectly with the shafting.
If you get a new shaft and the face of the coupling does not look, and had not been freshly cut, you've been cheated of a proper machining job. It would be EXTREMELY rare that a coupling would not need to be faced. They need to install it in the lathe head to check it for run out anyway so the 60 seconds it takes to actually cut the face could be a prime indicator the shop never even checked the facing run out.
MAY-2006
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