Got my first ride yesterday from Towboat US. Boat would not go under power - I thought maybe I had snagged a crab pot or something while I was anchored yesterday afternoon. Luckily, I was right across from the marina and got back to the dock quickly.
Turns out the key on the propeller shaft at the transmission had worked its way out. Everything was working (engine and transmission spinning) but the shaft and the transmission were not engaged! Fixed it at the dock and went back out last night.
Has anyone else had an issue with that?
Bob Gehrman
NS30U #396 “Quickbeam”
Baltimore, Maryland
Same thing happened to me last season. Another key was installed and red locktite was used as well. Coupler was replaced at end of season.
Brian Chipman
Nonsuch 30U
Mawingo
Mahone Bay NS
Yup, the same thing happened to us. Even though the shaft rotated in the housing the set screws held the shaft in place for years. Once I noticed it I put the key back in and put a hose clamp around the end of the shaft to hold the key in position. The set screws did score the end of the shaft. This proved to be an issue when I wanted to install a dripless shaft seal. The prop shaft had to be pushed back to do the install which meant that the cast coupling had to be removed.
The set screw damage to the prop prevented the coupling from being pulled off. Using a puller I managed to break the coupling. The yard then damaged the shaft when trying to press the remainder of the coupling off thus forcing us to buy a new prop shaft and coupling.
Ron
Ron & Diane Schryver
“Alpha Waves” 1987 NS30U #393
Georgian Bay Midland ON
Sympathies to all. Is this a problem just with the V-drive installations, or have people with the straight connection had it happen also?
In the spirit of another thread, the picture you posted, Bob, looks like another one that’d be good to have on the INA website. Where’d you find it?
Small reminder to members: your INA membership no longer gets you a discount on the base cost of BOAT/US membership, but it does get you a 10% discount on whatever towing service you sign up for with them.
– Bob
Robert Neches
INA Co-President
Solar Wind, Nonsuch 26C #143 (for now – in process of buying a 26U and putting Solar Wind on the market)
Do you not have a small set screw in the coupling above the key to secure it in the keyway?
My coupling has that set screw and two bigger set screws that penetrate drilled holes in the shaft deep enough to prevent any turning if the key did ever get out.
I just looked at my “V” drive coupling/shaft. Something is wrong with the fit if that key comes out. 1. The shaft should have dimples in it where the set bolts touch it. 2. The bolts should be a little pointed to fit in the dimples. 3. The bolts should have safety wire correctly wound on them to prevent working loose.
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
The coupling has 2 bolts that provide pressure on the shaft, but neither one is located on the keyway.
When I unbolted the shaft coupling, it was interesting how long the keyway groove is. I presume it could slip inside the coupling at some point as well except that it is limited by the mate of the coupling. However, I’m still mystified how it slipped out towards the front of the boat. To prevent this from ever happening again, I added a hose clamp to the end that prevents the key from slipping forward.
Bob Gehrman
NS30U #396 “Quickbeam”
Baltimore, Maryland
That should stop it from slipping out. I am, however, still puzzled as to why. The only thing I can think of is a mis-match between the slot and the key.
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
I’ve had two more instances of the shaft slipping in the coupling. The ring clamp prevents the key from falling out. Good prevention method.
However, the bigger issue of why the dang thing is slipping in the first place.
Problem 1) I tried measuring the ‘dimples’ from the end of the shaft to align them with the bolts, but obviously miscalculated and they were not aligned on the dimples as I thought. The best way to align the dimples and the bolts is to take the bolts all the way out and visually look through the threads to make sure they are centered.
Problem 2) The end of the bolts were dead flat, and the dimples weren’t much dimpled. On our way back from a trip when it had slipped, I took the bolts out and one of them had the end threads needing some attention to the threads. The marina I was at gave me a new bolt that seemed made for the same purpose (square head, hole through the head). It was fabricated with a pointy end which made sense to me to fit into a dimple. Therefore, when I got home I put the bolts on a grinder to make them similarly pointy. I then used my countersink bit on the shaft to make the dimples more dimply. Kind of a nip-tuck update to my 34 year old. Fits much better.
Problem 3) I noticed when I got back that the new bolt was loosened on the shaft. I hadn’t put the wire through the heads. However I’m skeptical that a wire through the heads is going to do much to keep them from moving. I added a nut on the bolts to act as a lock once everything was tightened up and in place to prevent the bolts from backing out. Then, added the wire through the heads as a last ditch effort to keep this from happening again.
I’ll keep you posted if this solves the issue.
Bob Gehrman
NS30U #396 “Quickbeam “
Baltimore, Maryland
When we got the Beta 20 engine install in our 26, the yard mentioned that the inboard end of the prop shaft had worn undersize and thus the coupling was loose on the shaft.
The end result was a new prop shaft machined. It was less $$ than I had expected. (somewhere around $400.00 Canadian, if I remember correctly)
A properly safety wired bolt will not loosen. The wire should wrap at least 1/4 the way around the bolt in a clockwise direction then the two parts of the wire are twisted together until they reach the second bolt, again wrapped around that bolt to pull in a clockwise direction, twisted once again to secure and then trimmed neatly and tucked away.
For the shaft key to fail it is likely
1.the key was the wrong size
2. or the shaft bolts were not sufficiently dimpled into the shaft causing rotation and wear on the key
And / or the bolts were not properly seized with wire.
Paint some nail polish on the shaft / coupling / bolt interface at a couple of places ant movement will show.
Hi, I am not a machinist but I think some youtube videos by Keith Fenner are worth a look. He has a number of very good videos but on this topic look at ‘a Pair of Shafts’ especially about the 8 minute section. Also see his video on facing a coupling and another on lapping a prop and shaft. I take from his videos that it is the fit of shaft and coupling not the key or the set screws that keep a shaft from slipping.
After about 40 or so hours with no issues, the prop shaft slipped yet again. Since it was headed to a working boat yard to pull the mast it was good timing (if there is such a thing). Again, the shaft had pushed into the engine compartment. The points on the 2 bolts holding into the dimples had been flattened/ground flat. We got to the yard and had the boat pulled today to see what’s going on below the waterline. See photo.
Is something missing between the prop and the strut? I can’t imagine that just the dimples on the shaft are supposed to keep the shaft in place laterally.
Bob Gehrman
NS30U #396 “Quickbeam”
Baltimore, Maryland
The proper fitting of the coupling to the shaft, the key (secured by a small grub screw), and the two large square head grub screws in their sufficiently deep dimples should be all you need to keep the shaft in place but it never hurts to have a safety. I have one of these even with my shaft seal which has its own locking collar.
