I have had an experience that I want to share with the group . After motoring approx. 30 hours over a period of about two weeks , in Aug. from Toronto to Belleville and back , without incident, there was no wind to even motor sail by , at 6 knots ,or more at times. I noticed a lot of black soot around the bottom of the transmission area that I could not account for. to make a long story short the key joining the coupling and the prop shaft was so beaten up I found it in two pieces . What was keeping the prop shaft from slipping out the back were the two set screws in the coupling , which appear to have not been set into the shaft but only compressed against it . The only reason it didn’t go out the back is because I was going forward all the time and only in reverse briefly a few times . I am astounded that the only mechanism keeping the prop in place were these set screws.The end of the prop shaft has been badly chewed up by the loose key and the set screws , which accounts for the black soot . I am thinking the shaft is going to have to be replaced along with the coupling . This time , I am going to have a bolt hole drilled through both the shaft and coupling and install a bolt and dimples set into the shaft for the set screws to fit into . I tried a temporary fix by installing a zinc anode on the shaft between the transmission and the stuffing box but it vibrated loose . My seasons over , but consider my self lucky , there could have been some wind where I would have put up the sails and turned the engine off and zip the shaft could have slipped out the back. So maybe it would be a good idea to check your propeller shafts . Any advice would be appreciated , like where do I get a new shaft and coupling ?
Sounds like your engine and shaft are seriously out of alignment. You may even have a broken engine mount or a bent shaft. I suggest that you get a good mechanic to have a look at the problem. You shouldn’t need anything more than the set screws and a proper key but the saft and/or the coupling flange may be damaged beyond repair. Putting a bolt through the shaft could lead to even more carnage if you don’t find the source of the problem.
Sounds like your engine and shaft are seriously out of alignment. You may even have a broken engine mount or a bent shaft. I suggest that you get a good mechanic to have a look at the problem. You shouldn’t need anything more than the set screws and a proper key but the shaft and/or the coupling flange may be damaged beyond repair. Putting a bolt through the shaft could lead to even more carnage if you don’t find the source of the problem.
These shafts should fit to what is called an interference tolerance.
You need to heat the coupling and cool the shaft to get them together
or apart. This tightness holds it in place and the set screws are
simply a back up they do not serve to hold the assembly together.
I suspect like others have mentioned you have a alignment issue.
Loose engine mounts, engine / shaft alignment, or other alignment
balance issues that have caused the shaft to move in the coupling.
You will have to remove the shaft and coupling. Most likely the
coupling is shot. A machine shop that works on propeller shafts will
be able to machine the new coupling and old or new shaft to the
correct tolerance. They will check the trueness of the propeller
shaft at the same time.
To assemble the coupling and shaft I have used a map gas torch and a
welding temperature stick to check the temperature as I heated it. The
machine shop can tell you what the correct coupling temp will be. I
think 650F was about it. I kept the shaft in a bucket of dry ice to
shrink it and with two people guiding it in, it slipped into place.
Everyone needs leather gloves for the heat and cold. Keeping the key
in place was a pain during the process. It had to be put on just
before we pushed the shaft home. Some with a fire extinguisher is
needed to stand by as you heat the shaft. Soldering protection mats
can be placed around the work space as well.
There are couplings that bolt together but that is another matter that
I have no experience with.
One must always remember to drill a “dimple” in the shaft and the set screw should be “pointy” and safety wired in. I’ve never had them fail when done properly.
Joe Valinoti
S/V IL Gatto NS30U #221 (1984)
Sea Harbour Yacht Club
Oriental, NC
When I converted to electric propulsion four years ago I installed a Stafford Coupling. It is clam shell type and has been propelling the boat just fine for four years now. No set screws needed either just torqued the screws to the recommended setting. Don’t know if it will work in your engine configuration but, you can see it installed in my Nonsuch here: http://biankablog.blogspot.com/2009/03/going-electric-part-13-motor-on.html
> From: M. Davidson mikekath@sympatico.ca > Subject: Propeller shaft & Coupling > To: INA-Nonsuch-Discussion-Group@googlegroups.com > Date: Tuesday, September 20, 2011, 2:03 AM > > Mike Davidson NS 30 Ultra # 222 > Toronto > > I have had an experience that I want to share with the group . After motoring approx. 30 hours over a period of about two weeks , in Aug. from Toronto to Belleville and back , without incident, there was no wind to even motor sail by , at 6 knots ,or more at times. I noticed a lot of black soot around the bottom of the transmission area that I could not account for. to make a long story short the key joining the coupling and the prop shaft was so beaten up I found it in two pieces . What was keeping the prop shaft from slipping out the back were the two set screws in the coupling , which appear to have not been set into the shaft but only compressed against it . The only reason it didn’t go out the back is because I was going forward all the time and only in reverse briefly a few times . I am astounded that the only mechanism keeping the prop in place were these set screws.The end of the prop shaft has been badly chewed up by the loose key and the set screws , which accounts for the black soot . I am thinking the shaft is going to have to be replaced along with the coupling . This time , I am going to have a bolt hole drilled through both the shaft and coupling and install a bolt and dimples set into the shaft for the set screws to fit into . I tried a temporary fix by installing a zinc anode on the shaft between the transmission and the stuffing box but it vibrated loose . My seasons over , but consider my self lucky , there could have been some wind where I would have put up the sails and turned the engine off and zip the shaft could have slipped out the back. So maybe it would be a good idea to check your propeller shafts . Any advice would be appreciated , like where do I get a new shaft and coupling ? > > Regards .Mike Davidson