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Old 28-07-2013, 15:06   #1
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Oil Filled Prop Shaft

Anyone familiar with oil filled prop shafts? Thinking of replacing existing one in a 45' ketch.
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Old 28-07-2013, 15:20   #2
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Quote:
Originally Posted by billdriver View Post
Anyone familiar with oil filled prop shafts? Thinking of replacing existing one in a 45' ketch.
On a large ship with a CP prop, sure. But on a small boat?
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Old 28-07-2013, 16:41   #3
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Re: oil filled prop shaft

Malo Yachts installs oil-lubricated propeller shaft seal on their boats. Manufactured by Sleipner. I think you can find similar system from Imtra Marine Products.

I am very satisfied with it on my 37' 2007 Malo.

Marc
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Old 28-07-2013, 16:56   #4
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Re: oil filled prop shaft

I have been mucking about with various prop shaft seal arrangements for a number of years now and have considered an oil filled shaft as the final solution.

I have done the engineering and would use a tapered roller bearing with ordinary lip seals at each end of the shaft. Since the shaft is then fixed fairly rigidly in the tube one then needs a short stub shaft between the prop shaft and the transmission. Since there is not a lot of lateral movement involved I would use a polyflex flexible coupling rather than universals or constant velocity joints on the stub shaft.

The arrangement I am trialing now as a shaft seal uses a number of lip seals held concentric by two roller bearings. I have tried bushes but they tend to wear fairly rapidly and if their is any vibration between shaft and seals the lip seals leak.

There are a number of hitec types of shaft seals available however whilst some folks have good experiences with them there appear to be just as many who have had bad. Over the years I have encountered two fellow yachties who have oil filled, rigidly fixed shafts using roller bearings and both of them claimed to have had many years of reliable, trouble free service.
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Old 29-07-2013, 06:43   #5
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Ahh so this is an oil filled stern tube, presumably with a header tank to keep the tube at a positive pressure to the environment.
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Old 29-07-2013, 06:55   #6
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Re: oil filled prop shaft

Greetings and welcome aboard the CF, billdriver.
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Old 29-07-2013, 07:20   #7
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Re: oil filled prop shaft

Big ships moved over to oil lubricated because they had problems with crevice corrosion and props falling off. Long periods between survey was a unanticipated benefit.
What problems have you had or anticipate that you wish to overcome.?

For discussion, are your seals going to rub on a liner or the shaft? How will you deal with lip wear, will you move the seals. Ships can support the shaft very well because the bearing is very close to prop hub, have you got such a after end shape that enables both support and blade tip clearance, perhaps you use a external bearing support with traditional bearing

Concerning aft end, If you use a lip type seal the spring has to be on inside so its protected by the oil, the pressure here is only marginally above the outside. Maybe a double seal so that any contamination would not effect the bearings (till later).

Think you need traditional bearing in case your roller bearings fail. But then you’d have to rip off the fwd end lip seal to get a traditional gland packing.

Would recommend copying a design that works and don’t go too far till its proven.
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Old 29-07-2013, 07:31   #8
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Re: oil filled prop shaft

Thank you for all the response.
The main objective is to eliminate the stuffing box, cutlass bearing and remove the engine from the critical alignment requirement. From what I've researched the major advantage was the quietness (from being able to soft mount the engine) and smoothness that results form the installation. Also near zero maintenance.
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Old 29-07-2013, 07:43   #9
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Re: oil filled prop shaft

Not that familiar with what you mean by Soft mount, but the thrust up the shaft has to be restrained by something real firm and a solid piece of ships structure, normally this is done at the Gearbox.
A stern tube shaft properly lubricated would run beautifully alignment would be more crucial, if you did adopt CV joints (as suggested above) and the like less so, but you have to be certain such a CV joint could take the thrust.
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Old 29-07-2013, 08:06   #10
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Re: oil filled prop shaft

Billdriver,

Here is how Malo Yachts are built: The shaft enter the boat thru the cutlass and an oil-lubricated shaft seal. There is a small reservoir mounted near the front of the engine to maintain positive oil pressure.
Right after the shaft seal is a sturdy small bulkhead glassed to the hull where a thrust bearing is bolted on. Here the thrust of the impeller ends.

Between the thrust bearing and the transmission is mounted an Aquadrive, consisting of two CV joint and short shaft.

Maintenance free and very quiet operation of the engine.

Hope this help,

Marc
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Old 29-07-2013, 17:18   #11
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Re: Oil Filled Prop Shaft

Header Tank.

The oil filled tube needs to be vented so that excessive pressure does not build up in the tube as the oil gets heated and I think that if you want to be certain of maintaining a seal under the constantly cycling pressure regime experienced by the seal due to the constantly changing pressure head of the vessel in a seaway you need to ensure positive pressure on the seals lip. I would have an elevated oil reservoir.

On Thrust Transmission.

The reason for using a tapered roller bearing at either end of the shaft is to transmit the thrust to the hull via the stern tube. In my case this is feasible because I have a steel boat. If I was going to implement the scheme on say a fibreglass or timber vessel I would ensure that the tube/hull arrangement was sufficient to allow this.

Potential Noise and Vibration Problems.

One of the reasons I am persisting with the lip seal shaft gland rather than going to an oil filled shaft is the probability of transmitting prop and shaft vibration into the hull and the consequent increase in noise and vibration. Cutless bearings do a good job of absorbing the noise generating vibrations generated by the prop and shaft. A double tube with an elastomer in the anulus between the tubes would solve this potential problem.

I am using grease lubrication on the bearing/lip seal stuffing box I am presently trialing.

With the relatively little use, in comparison to power vessels, that the stern gland and cutless bearing experience on a sailing vessel I am hoping that the present arrangement will give me many years of problem and leak free use.
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Old 29-07-2013, 17:54   #12
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Re: Oil Filled Prop Shaft

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Old 29-07-2013, 20:00   #13
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Re: Oil Filled Prop Shaft

AFAIK the prop "shaft" is the driveshaft, the metal rod that the prop is screwed onto. In larger ships, this is a tube not a rod, but in any case, I've never heard of the shaft itself being oil filled.

You guys really aren't talking about an oil-filled PROPSHAFT are you? You're talking about enclosing it in an oil-filled tube with bearings, right?
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Old 30-07-2013, 00:16   #14
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Re: Oil Filled Prop Shaft

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Originally Posted by hellosailor View Post
AFAIK the prop "shaft" is the driveshaft, the metal rod that the prop is screwed onto. In larger ships, this is a tube not a rod, but in any case, I've never heard of the shaft itself being oil filled.

You guys really aren't talking about an oil-filled PROPSHAFT are you? You're talking about enclosing it in an oil-filled tube with bearings, right?
Roger, the stern tube not the prop shaft is poil filled.
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Old 30-07-2013, 05:16   #15
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Re: Oil Filled Prop Shaft

Maybe this will clear up any confusion:

Seatorque Control Systems, LLC
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