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Old 25-11-2012, 11:14   #31
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Re: Cutless bearing, flex coupling and PSS packing gland

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Originally Posted by NoTies View Post
Please tell me they meant to say bronze nut, not brass.
Sorry! I meant Bronze! You are quite right about getting the best information from a marine engineer. I am sailing as first assistant engineer now and will upgrade to chief unlimited in March when I complete my next 90 day rotation on a heavy lift ship with a huge flexible coupling about 6 feet in diameter! I know that every ship that I have worked on has had more than one bearing on the shaft and I understand what you are saying about shaft whip and I have decided to eliminate the flex coupling on my boat but I will look into another type of rigid coupling that has a sacrificial part that will break if there is something that hits the propeller. In this case I would care a spare part so that I could get underway again after replacing the part. I may in the end go for a direct coupling from the shaft to the gear box. I guess I didn't think things out very well when I blindly followed Beta Marine's opinion about that Centaflex coupling. The main reason that I took that coupling was because I needed to fit my shaft on a Beta instead of a Volvo gear box and this seemed to be a quick and easy solution to solve this problem. I think that if there were two bearings on each end, which must be rare in a sailboat, that I would still go for the Centaflex coupling. I will also contact Beta Marine and try to educate them a bit better about the shaft whip that I did experience on my my boat. It was Beta Marine that was pushing the idea of the Centaflex coupling as an option on their new engine and gearbox installation. However it may be a good idea to get that rigid coupling that will break if I hit something hard enough to protect the gear box from damage just like a shear pin on an outboard motor. What is your opinion on that?
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Old 25-11-2012, 11:23   #32
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Re: Cutless bearing, flex coupling and PSS packing gland

I am always leery of sweeping generaliztions in the marine world, what may be true in one arena is not always true elsewhere. I own a vessel over 40' at this time with rubber footed mounts, and due to the nature of the fishery, it has to run smooth, the less vibration the better the catching. Vibration sources can come from several different sources, unbalanced or damage propellers, bent or improperly supported shafts, excessively worn cutlass bearings, shaft flanges that are unbalanced or the flange face has a dish in it, bad tail shaft or tail shaft bearings, or flange face dish on the transmission, or something out of whack in the engine itself, including excessive wear in the engine mounts, any one of these issues can cause excessive wear in all of the bearings along the power transmission process and or excessive wear points where the shaft comes in contact with the cutlass bearings, the shaft itself can become worn due to contact with the cutlass bearings, I have also come across on rare occaisions the vessel itself can be bent or warped and the vibration gets transmitted to the hull of the vessel.
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Old 09-01-2013, 21:34   #33
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Re: Cutless bearing, flex coupling and PSS packing gland

Our work also suggests that soft (rubber) bearings can contribute to shaft vinration and noise. We've replaced a few vessels rubber shaft bearings with the new Maritex Aquarius (this is a hard phenolic bearing/surface) Noise levels drop wear rates drop significantly in some cases. This is on commercial vessels mainly and yachts from 12 - 60m. It makes sense as the rubber in an old fashioned shaft bearing will give under pressure so as the shaft tries to flex clearances in the bearing will change and the water film/support will change at different positions around the shaft. Some Naval architects/engineers still think the rubber in bearings helps damp vibration, but I haven't heard a good explanation of how.

There are a few old school ideas in marine engineering that don't stand up to interogation.
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Old 08-04-2013, 02:32   #34
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Re: Cutless bearing, flex coupling and PSS packing gland

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Originally Posted by 4HMainer View Post
Our work also suggests that soft (rubber) bearings can contribute to shaft vinration and noise. We've replaced a few vessels rubber shaft bearings with the new Maritex Aquarius (this is a hard phenolic bearing/surface) Noise levels drop wear rates drop significantly in some cases. This is on commercial vessels mainly and yachts from 12 - 60m. It makes sense as the rubber in an old fashioned shaft bearing will give under pressure so as the shaft tries to flex clearances in the bearing will change and the water film/support will change at different positions around the shaft. Some Naval architects/engineers still think the rubber in bearings helps damp vibration, but I haven't heard a good explanation of how.

There are a few old school ideas in marine engineering that don't stand up to interogation.
I have decided to go with a solid coupling on my new shaft instead of the Centaflex coupling. However, I am still looking for a solution to the cutless bearing and I think I will go with the Maritex Aquarius type. Can you give me a source to buy this material. I am in Fort Lauderdale now until April 22 when I will fly to Phuket to complete the job. I think the best would be to get the material locally or have it shipped to me hear and then carry it in a suit case for the flight to Phuket. Any help would be greatly appreciated. Also, I am looking for good source for buying the PYI dripless stuffing box for the 1 1/4" shaft. I was going to buy with Port Supply but they shut down my account so I need to find it elsewhere. Maybe Defender?
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Old 08-04-2013, 12:21   #35
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Re: Cutless bearing, flex coupling and PSS packing gland

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Originally Posted by thaisail View Post
I have decided to go with a solid coupling on my new shaft instead of the Centaflex coupling. However, I am still looking for a solution to the cutless bearing and I think I will go with the Maritex Aquarius type. Can you give me a source to buy this material. I am in Fort Lauderdale now until April 22 when I will fly to Phuket to complete the job. I think the best would be to get the material locally or have it shipped to me hear and then carry it in a suit case for the flight to Phuket. Any help would be greatly appreciated. Also, I am looking for good source for buying the PYI dripless stuffing box for the 1 1/4" shaft. I was going to buy with Port Supply but they shut down my account so I need to find it elsewhere. Maybe Defender?
You may want to read this. >>>> Rudder bearings.....material?
And he's supplied a link to the mfgr.

The PSS can be purchased direct from PYI.>>> PSS Small Shaft Seals | PSS Shaft Seal Or call them and they can give you a local vendor.
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