Cutlass Bearing Lubrication

[Idon84]

Got a question about lubricating the cutlass bearing. I noticed some manufactures of stuffing boxes add a nipple for water lubrication while others do not. The stuffing box I bought for my install is NOT the type with the nipple for water lubrication.

My question is, how important is it to get water into the stern tube from inside the boat (near the stuffing box) vs water from the outside seaping in the log? How would this be done? Just cut a hole into the FG log that I bough and install a fitting that "T's" into the salt water intake for the engine. What kind of fitting/size etc.? Is it even necessary? My old system had a grease nipple attached to the stuffing box to a calking gun in the engine room that used standard wheel bearing lubrication from the auto parts store. Wierd...

Thanks!

[mitiempo]

I don't think I would worry about inside water flow for lubrication. Many boats have none and there are no issues. There is one caution though. The zinc, if installed between the cutlass and the prop should allow enough room for water to reach the cutlass easily. I think there should be a space equal to 1 1/2 times the shaft diameter between the cutlass and the prop. Some apertures don't have this much room.

The grease remote greaser solution is very common on UK built boats but rare over here. I have owned 2 UK built boats and both had this. The subject also comes up regularly on their forums but not very often here.

[Chris Campbell]

The two boats I've owned with inboards (and therefore cutless bearings) had a hole drilled from the outside of the keel into the shaft log, angled forward, to encourage water to enter the shaft log and cool the cutless bearing. I have no idea how effective they were/are - the holes are about the size of a pencil around, and are probably pretty quick to fill with little creatures and bottom paint - but they are there on both boats.

In case my description is of where the holes are is poor - imagine that you are the water flowing around the keel, and are about to come to the back of the keel and flow through the propeller. If you're right next to the keel you will come to a little hole through which you can swim, continuing going back toward the stern but into the shaft log and then out through the cutless and over the prop.

That should make it clearer and hopefully only slightly silly.

[Idon84]

Thanks for the responses. I guess I'm going to have to do some investigation on some sister ships to see how they are set up. From what I saw of a local sister ship, it did not have any additional means of cooling the bearing besides just sitting in the water so we'll see.

Thanks again,

[Figment]

Just how hot do we imagine these constantly-immersed-in-seawater surfaces ever get?

[Duncan]

Just how hot do we imagine these constantly-immersed-in-seawater surfaces ever get?

Surprisingly hot, I'd say! This is based on the shakedown cruise of a friend, where water wasn't getting into the dripless shaft seal. We ended up pouring cupfuls of water over it to cool things off.

[mitiempo]

The lubrication of a thin layer of water is not great. When the shaft is spinning at 1000 or 1500 rpm it needs all it can get.

This link may help. Some of these stern tubes are designed to direct water flow into the cutlass.
http://www.teignbridge.co.uk/stern_tubes_bronze.html

[Quetzalsailor]

As noted above, stern tubes with cutless bearings have intake holes which you need to clean when the boat's pulled. The bearing itself has passageways in the rubber surface that collects and distributes water. Dripless seals used to be sold, in the smaller sizes, with no provision, beyond 'burping' at launch, for ensuring that the seal itself has water behind it for cooling. New and larger dripless seals have the water injection off the engine raw water pump.

I used to be an enthusiast of dripless seals until I read the fine print (later, naturally) that says that the bellows has to be replaced every 5 years or so. That's about when you'd have to repack an ordinary shaftseal, and either operation would be inconvenient in the extreme on Quetzal.

A friend of mine on the O'Day 34 on the next mooring found out, after about 8 years, why he should have replaced the bellows after 5.

[mitiempo]

I agree. A conventional stuffing box is predictable, a few drips when the engine is running or an increasing number of drips. A dripless is either perfect or a bit of a disaster.