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Old 29-05-2009, 11:33   #1
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Lost Thrust! Lost Prop?

Greetings!

I just successfully installed a replacement rudder on my new-to-me Contessa 26. (Thanks to the incredible help of the kind people on this forum ). Upon departing the haul-out dock to head to my slip, under power, I gave the throttle some goose to gain steerage way in reverse. This was working well, until all of a sudden the motor spun free, like as if the prop resistance had stopped, and then, when I turned the tiller, my fancy new rudder was jammed on a portward heading.

I won't get into all the details of my rescue by jet-ski, or my failed attempt to anchor using the electric windlass, but Larry and Lin Pardey's "simplification of systems" has been occupying my thoughts for my new ship.

I will be returning to her on Monday, June 1, and will be bringing my mask and snorkel.

Any ideas what I might find and what might have happened? Are props simply friction fit to the shaft? !

Any comments on the workings of these contraptions would be great!

all the best,

Mike
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Old 29-05-2009, 13:20   #2
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all the reply's disappeared!

lakdfhakldhf
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Old 29-05-2009, 14:02   #3
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Mike,
It's very improbable that the propeller went off the shaft, because it is normally held securely by a locking cone. IMHO, the shaft went free from the coupling on the engine gearbox. It can happen if the coupling is'nt tight enough. It happened to me last summer (not on my own boat), when I had to run astern while turning in a constricted harbor. This would also cause the shaft and propeller to jam your rudder.

To restore things, you just have to disconnect the coupling from the gearbox, then reattach it first to the shaft and second to the gearbox.

Consider that you were lucky: a friend of mine had this happen when he was sailing a twin-rudder boat. He completely lost the shaft and propeller (they went between the rudders), so the boat flooded through a 1"-diameter hole well below the waterline. It took him and his crew some time bailing with buckets before he found the cause and plugged the flooding.

Alain
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Old 29-05-2009, 15:24   #4
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This boating thing can be such fun. These are the kind of things that keep me somewhat humble.....lolololol......i2f
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Old 29-05-2009, 20:57   #5
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OK.... it sounds like it might have been as mentioned.... the shaft coming out, rather than the prop flinging itself off. Unfortunately, I am now again 4+ hours from the boat and will have to wait until Monday. I had someone mention that I might want to check the stuffing box a.s.a.p. Hahaha.... I hope Monday is soon enough. !!

I would hope that the stuffing box should have enough shaft left in it to keep it sealed.... if that makes sense. I have the auto-bilge pump on as well, so assuming (love THAT word) it works, the boat shouldn't be hanging from her spring-lines when I get back. Cheechako, I started a new thread for this problem, that is probably why all the previous responses disappeared.

Thanks to you all for helping me out. Hopefully one day I can return the favour as a wisened old salt!! Hahaha...
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Old 03-06-2009, 12:20   #6
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Prop shaft coupling separated

Hi Guys!

OK... I am back at the ship, and upon inspection discovered that the shaft had not come out of the coupling. Instead, the coupling had separated from a rubber bushing. I have been told I can get another bushing, with plates attached. It appears to have been bound together with some sort of glue on the inboard end, and the outboard end has parted from the bushing.

While I understand this arrangement is good because of the rubber bushing, and it's inherent tolerances, I think that the method of attaching it seems Mickey Mouse, right from the factory (back in the day).

My concern is with it coming apart again. It could damage or jam the rudder etc.

I have attached a couple of pics. Any comments on whether I should go with the new part, or a repair would be appreciated.

Thanks,

All the best,

Mike
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Old 03-06-2009, 12:24   #7
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Wow, not seen that one before, I was going to suggest you just eliminate th bushing and align your engine properly, but that's a long piece of rubber! Maybe someone recognizes the unit, may be you can have something made....
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Old 03-06-2009, 12:25   #8
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Also, put a zinc on your shaft just forward of the stuffing box, it will k eep the shaft from going back into the rudder if you ever have the problem again.
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Old 03-06-2009, 13:19   #9
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Mike,
I had no idea that this kind of mounting existed. However, from the designer's point of view, it makes perfect sense: vibrations are certainly reduced by the rubber block.

Since your propeller is 2-bladed, it generates strong variations in thrust and torque. When the blades are vertical and blanked by the rudder post, they receive a slower inflow of water, resulting in increased thrust and torque. The positive side is that when sailing, you can hide the blades in the hull opening, to reduce drag. You just need a mark on the shaft.

There seems to be some rust on the rubber part. IMHO, this would mean that the parting of the glue wasn't sudden, resulting from your goosing the throttle astern, but it was rather progressive, caused by ageing. Then, I would try to clean all parts and glue them back into place. Knowing the engine power and shaft rpm, with the propeller diameter and blade area, it is possible to estimate the average torque and pull that the glue has to withstand, and to check with the manufacturer that it is strong enough.

If you don't trust a glued-rubber solution any more, I think that your boat still needs some elasticity between the gearbox and the propeller. Then, you will need something including springs.

The zinc on the shaft just forward of the stuffing box is a good precaution, even if your rudder is good at catching runaway propellers.

Alain
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Old 03-06-2009, 16:33   #10
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Have you talked to your local propeller shop?

I'd suggest checking the alignment of the engine/gearbox to the propeller shaft, doing some careful measurements and taking the results to your local propeller shop.

If you can pull off the the two steel coupling plates and the rubber bushing and take them along as well so much the better.

I could make some suggestions about what to do with two flexible couplings and a machined coupling plate but I don't know what I'm talking about.

Really needs an experienced marine engineer.
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Old 03-06-2009, 20:52   #11
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Had this coupling on a 1976 CAL 2-29 with a Faryman Diesel. Yep, and once it went bang and split like a bag of rubber bands. Not like yours where the plate separated. Found out the screws had worked loose and the twist caused it to rupture. When I replaced it we then checked the screws once ever couple of months.

Got the part from Chris Oliver at Port Annapolis Marina (can't remember the name of his biz but he's a good diesel guy and handles Yanmar and others). It's called a "rubber shaft coupling" go figure No one else even knew what I was talking about.
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Old 03-06-2009, 21:56   #12
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Great comments!

Thanks Guys,

I spoke to a Faryman Mechanic\ Prop shop in Victoria BC and he wants me to send him (by fax) a template of the fitting. He thinks he may have a spare two or three available.

Interesting comment about placing a zinc on the shaft to prevent it from taking off again.
Is there any danger of off-balancing the shaft by doing this?

I used a piece of copper wire to jury the two flanges together to move to my new slip and by the time I arrived it had broken it.
(It was a VERY temp fix by the way... not intending to use copper to hold things together.)

All the best,

Mike
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Old 04-06-2009, 12:14   #13
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Mike,
A zinc on the shaft inside the hull cannot create more imbalance that it would in the water. Since it will not corrode, no imbalance will appear later.

The sailing association for which I am an instructor puts zincs on the propeller shafts of twin-rudder yachts (because nothing else would prevent the shaft from going away, passing between the rudders).

Alain
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Old 04-06-2009, 17:26   #14
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Zinc on shaft..

Hahaha.... thanks Alain, and everyone. I am new to salt water and have seen the hull zincs and it did not occur to me that there might be one specially designed to fit the prop shaft.

I will get a zinc and install it inboard, as the idea of having the prop and shaft damaging or jamming my rudder is not appealing.

Thanks for the input.

Another question: Any ideas on whether I might use regular West Systems epoxy to re-attach the steel plate on the flange to the rubber?

Once again, thanks for the help and guidance!

All the best,

Mike
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Old 04-06-2009, 19:46   #15
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I didn't see a zinc on your prop either. You should check that out. Not much room between the prop and the cutlass bearing so you would have to put it on the nut side of the propeller.
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