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Outboard thrust bearing for sailboat.
I have a Scampi 30 sailboat. The shaft has a thrust bearing behing the
propeller that is made out of some kinda oil impregnated plastic. This is wide open to the outside. I want to replace this friction bearing with a thrust roller bearing. I am thinking that I should get an encapsulated stainless bearing but I cant find such an animal. Can somebody point me in the right direction, or tell me if this is a good idea.. Thank You |
Outboard thrust bearing for sailboat.
To me, this is a bit confusing??
Does your boat have an inboard engine with a propellor shaft?? or are you talking about an Outboard motor or Out drive?? A properly installed marine engine will have the thrust bearing in the reduction/reverse gear. If it is an OB or Out Drive, the thrust bearing is inside the lower unit. I've never heard of a thrust bearing at the propellor. There should only be a water lubricated cutlass bearing. Please provide more information on what you have, engine/rev. gear, etc. and maybe we can figure a solution. Steve s/v Good Intentions |
Outboard thrust bearing for sailboat.
Why do you want to replace it?
Brian W On 8 Mar 2004 18:22:01 -0800, (john m.) wrote: I have a Scampi 30 sailboat. The shaft has a thrust bearing behing the propeller that is made out of some kinda oil impregnated plastic. This is wide open to the outside. I want to replace this friction bearing with a thrust roller bearing. I am thinking that I should get an encapsulated stainless bearing but I cant find such an animal. Can somebody point me in the right direction, or tell me if this is a good idea.. Thank You |
Outboard thrust bearing for sailboat.
John,
The only Scampi I have ever been real close to had a Farrimann diesel hoooked to a Standadyne (I think) hydraulic drive. The actual thrust bearing on that is inside the hydraulic motor. The prop shaft bearing had worn and the owner got another bearing somewhere and since he could not upull the original out without completely disassembling the drive motor, he just pushed it in with the new bearing. Matt Colie john m. wrote: I have a Scampi 30 sailboat. The shaft has a thrust bearing behing the propeller that is made out of some kinda oil impregnated plastic. This is wide open to the outside. I want to replace this friction bearing with a thrust roller bearing. I am thinking that I should get an encapsulated stainless bearing but I cant find such an animal. Can somebody point me in the right direction, or tell me if this is a good idea.. Thank You |
Outboard thrust bearing for sailboat.
"Steve" wrote in message ...
To me, this is a bit confusing?? Does your boat have an inboard engine with a propellor shaft?? or are you talking about an Outboard motor or Out drive?? A properly installed marine engine will have the thrust bearing in the reduction/reverse gear. If it is an OB or Out Drive, the thrust bearing is inside the lower unit. I've never heard of a thrust bearing at the propellor. There should only be a water lubricated cutlass bearing. Please provide more information on what you have, engine/rev. gear, etc. and maybe we can figure a solution. Steve s/v Good Intentions Here is a link that shows a diagram of the boat http://home.worldonline.dk/sejler/scampi/scampi.htm This boat has an hydraulic drive system. The brace that you see in front of the impeller is where the bearing should be ( I think) It looks like a very strong support made out of metal and imbedded in the fiberglass. |
Outboard thrust bearing for sailboat.
john m says:
This boat has an hydraulic drive system. Probably just a hydraulic gearbox, from the looks of things... The brace that you see in front of the impeller is where the bearing should be ( I think) It looks like a very strong support made out of metal and imbedded in the fiberglass. THat would be called the strut, and the bearing in it is just a cutlass bearing, Rubber in a metal tube. It is supposed to be like that, as it's only job is to support the shaft. The actual thrust bearing is inside the boat, usually either just aft of the transmission, or integral to the tranny. Steve |
Outboard thrust bearing for sailboat.
From what I see of your drawing, the fitting your discribe forward of the prop is a standard strut.. I doubt that your strut installation is made to take the full thrust of the propellor.. I agree with Matt. Conventions would have the thrust bearing in the hydrolic pump and only a cutlass bearing in the strut. I suspect someone has tried to 'Improve' the installation.. Or the hydraulic motor has a bad thrust bearing. If in doubt, contact the manufacture of the hydraulic motor and determine if the the motor has a thrust bearing in it.. If so then you need to verify that it is in good condition and leave the one you found out of the installation.. Or there is another possibility, that the original builders hydraulic motor went bad and some one put a conventional/industrial replacement in it's place. In this instance the industrial motor most likely wouldn't have a thrust bearing. Just my speculation, FWIW. Steve s/v Good Intentions |
Outboard thrust bearing for sailboat.
Brian Whatcott wrote in message . ..
Why do you want to replace it? Brian W Less friction. I want all the energy of the 12hp diesel engine to go to the prop. |
Outboard thrust bearing for sailboat.
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Outboard thrust bearing for sailboat.
Thank you guys for the replies.
There is one problem. The propeller shaft has a roller chain coupling that connects it to the hydraulic drive. I think that this type of coupling does not take any axial load too well. The only place left to take the axial load is the strut in front of the impeller. When I look at the plastic washer I can see where the axial load eats away at the plastic thrust washer. That is why I was thinking to replace the plastic thrust washer with something more robust. |
Outboard thrust bearing for sailboat.
John,
The reason the plastic "thrust washer" looks eaten away is that it is not intended to be a thrust washer. Neither it or the strut are intended or designed to take thrust loads. Your best bet is to take it to a yard that knows their stuff, and see what they recommend. That or a marine engine specialist. They will be able to recommend any of a number of aftermarket thrust bearing setups that can be installed, if somewhat painfully.... Steve |
Outboard thrust bearing for sailboat.
what happens in reverse?
"john m." wrote in message m... Thank you guys for the replies. There is one problem. The propeller shaft has a roller chain coupling that connects it to the hydraulic drive. I think that this type of coupling does not take any axial load too well. The only place left to take the axial load is the strut in front of the impeller. When I look at the plastic washer I can see where the axial load eats away at the plastic thrust washer. That is why I was thinking to replace the plastic thrust washer with something more robust. |
Outboard thrust bearing for sailboat.
barry lawson says:
what happens in reverse? Heehee..... I hadn't even thought about that. Good question. ;-) |
Outboard thrust bearing for sailboat.
Opps! Been there done that!
Once had the shaft spin out of the coupling while in reverse.. It even cleared the packing box but jammed against the rudder.. Took on some water until I could warp myself back into the dock and drive a plug into the packing box.. Later had a diver push the shaft back in, knocking the plug out. Since then I have always had a through bolt or pin in additions to the set scews. -- My opinion and experience. FWIW Steve s/v Good Intentions |
Outboard thrust bearing for sailboat.
"barry lawson" wrote in message . au...
what happens in reverse? "john m." wrote in message m... Thank you guys for the replies. There is one problem. The propeller shaft has a roller chain coupling that connects it to the hydraulic drive. I think that this type of coupling does not take any axial load too well. The only place left to take the axial load is the strut in front of the impeller. When I look at the plastic washer I can see where the axial load eats away at the plastic thrust washer. That is why I was thinking to replace the plastic thrust washer with something more robust. I have a folding prop, so in reverse its very slow. It also makes a funny noise when the shaft pulls on the roller chain coupling, but so far I never had a problem with it. |
Outboard thrust bearing for sailboat.
This whole installation sounds 'Rub Goldberg' and I can't imagine any
professional builder or boat yard doing such an installation where there is no proper thrust bearing. As I stated earlier in this thread, I suspect someone, in the past, has replaced the OEM hydraulic drive motor with this chain drive system. I find no fault with the chain drive if there is no way to get a hydraulic motor down into the space. It's hard to say without seeing the installation.. However, to salvage this installation, I would recommend putting a thrust bearing on the forward (inboard) end of the shaft and the bearing should be mounted to some substantial member in the bilge. This would have to be glassed in and should be able to absorb both the forward and reverse thrust of the shaft. Even though the engine is only 15hp the thrust is not to be taken lightly (literally). If it move the boat, then there is a mechanical force against the hull or in this case, the strut, IMHO. Steve s/v Good Intentions |
Outboard thrust bearing for sailboat.
John,
Yes, I was contracted to repair the strut bedding when the boat got run with a damaged blade. That boat did not have the couple you describe between the hydralic motor and the prop shaft. There was also no conventional stuffing box. The prop shaft is enclosed in the stern tube from the after end of the strut into the hydralic motor. The motor is actually attached tot he stern tube and is supported by both that and a torque brace. After we got all of the other stuff fixed, the boat still would not make more than 4 knots and the engine was not loading. It back like a mad man. So the owner got another set of blades for the other rotation and shifted the pump to astern for ahead and now makes hull speed just fine. When I talked to him last he was trying to find someone that knew how to overhaul the pump and motor. When I see him next, I will ask him. A chain coupling in a drive shaft is rare and not a proper application. There is no way to put an axial load bearing (thrust) inside the stern tube, so it must be in the hydraulic motor. That is part of why the plastic washer is both installed and torn up. I suspect the washer is required to keep the coupling halves from wearing on each other. It is, however, not costing you horsepower. Bearings going bad can cause vibration and failures, but if they eat horsepower they burn up real fast. I suspect that if you are short on boat speed as you seem to say farther down the thread, you have hydraulic drive problems just like the Scampi I know had (may still). I would see about getting both the pump and motor looked at before you invest much effort in other paths. Good Luck Matt Colie - See Prior Sig john m. wrote: "Steve" wrote in message ... To me, this is a bit confusing?? Does your boat have an inboard engine with a propellor shaft?? or are you talking about an Outboard motor or Out drive?? A properly installed marine engine will have the thrust bearing in the reduction/reverse gear. If it is an OB or Out Drive, the thrust bearing is inside the lower unit. I've never heard of a thrust bearing at the propellor. There should only be a water lubricated cutlass bearing. Please provide more information on what you have, engine/rev. gear, etc. and maybe we can figure a solution. Steve s/v Good Intentions Here is a link that shows a diagram of the boat http://home.worldonline.dk/sejler/scampi/scampi.htm This boat has an hydraulic drive system. The brace that you see in front of the impeller is where the bearing should be ( I think) It looks like a very strong support made out of metal and imbedded in the fiberglass. |
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