Cutless Propeller Shaft Bearings

Lubrication: Water

Material: Naval Brass or Non Metallic with Nitrile Rubber Lining

Placement: Forward Stern Tube, Aft Stern Tube, Strut and Rudder Shaft

Size: from 3/4 to 15 inches shaft diameter (mm sizes available)

Styles: Flanged, Non Flanged, Fully Split

Advantage: Low Cost, No Oil Dumping Hazard

Disadvantage: Costly for the Larger Shaft Diameters

Water lubricated cutless shaft bearings are the tried and tested standard bearing for small pleasure boats with inboard motor up to larger workboats, tugs, ferry boats and offshore supply boats with medium to larger shaft sizes.

These bearings are made with naval brass shell for shaft up to 15 inch diameter.  In addition to naval brass, the smaller non flanged types (up to 6 inch) come in a non metallic material for installation in aluminum boats thus avoiding dissimilar metals issues.  The smaller non flanged sizes (up to 6 inch) also come in metric sizes.

These bearings are made to be press fit into the housing but other installation methods can be used. 

The bearing interior is lined with nitrile rubber and V grooves are machined into the rubber to increase the water flow inside the bearing.

These bearings are for water lubricated stern tube systems that are not in danger of dumping oil into marine waterways.

During retrofit the costly naval brass shell can be relined with new nitrile rubber if time permits.  This option is advantageous only for bearings of larger shaft diameters.  This option is not available if the housing has been damaged or is out of round tolerance.

Clearance and Replacement Guidelines for Cutless Propeller Shaft Bearings

How to Install or Modify a Cutless Propeller Shaft Bearing

Hole Drilling Diagram for Flange on Flanged Cutless Propeller Bearings

Split Roller Propeller Line Shaft Bearings

Lubrication: Grease Packed
Material: Steel, Stainless Steel, Rubber
Placement: Propeller Line Shaft
Size: 1 3/16 to 24 inch (Metric Sizes Available)
Style: Fully Split

Advantage: Long Life

Disadvantage: Higher Cost (Especially for Large Diameter Shaft)

Fully split roller bearings are the standard method for supporting the propeller line shaft inside the vessel for small to mid shaft diameters. 

They are installed to support longer propeller shaft between the gearbox and the stern tube. 

These bearings are grease packed for lubrication. 

Because they are fully split the bearing cartridge can be changed easily when it wears out.  Because they are roller bearings with roller balls inside the bearing cartridge they have extremely long service life. 

In a propeller shaft application an "Expansion" type bearing should be selected to allow for thermal expansion of the shaft and the resulting small shaft length changes with temperature. 

Composite Marine Propeller Bearings 

Lubrication: Water or Grease or Dry

Material:  Woven Fabric, Solid Lubricants, Resin

Placement: Forward Stern Tube, Aft Stern Tube, Strut and Rudder Shaft

Size: Inside and Outside Diameters As Needed

Styles: Non Flanged and / or Fully Split

Advantage: Fast Production Time, Any Size as Needed, Long Life, Dimensionally Stable in Water

Disadvantage: No Flanged Models

The various types of composite marine bearing have become popular with larger shaft applications.  Pacific Marine's bearing is water lubricated in marine applications but can also be grease lubricated or run dry in some non marine applications.

Pacific Marine's composite bearing is dimensionally stable in water and will not swell making machining easier.  

Some composite brands are not dimensionally stable.

The method of production, by wrapping a mandrel, means that production is fast (1 day in an emergency) and any inner or outside diameter is possible.

The bearings are easily machined including the addition of water lubrication grooves for water lubricated stern tube systems.

These bearings are popular with sport fishing boats as the composite material dampens the engine room noise entering the water.

Demountable Rubber Stave Propeller Bearings

Lubrication: Water

Material: Nitrile Rubber

Placement: Forward Stern Tube, Aft Stern Tube and Strut, Rudder Shaft

Size: from 2 1/2 to 35 1/2 Inches Shaft Diameter

Advantage: Low Replacement Cost

Disadvantage: High Initial Cost to Construct the Housing

Demountable stave bearings are water lubricated cutless bearings without the costly outer naval brass shell. 

The housing for the demountable stave is built into the vessels and is part of the vessel structure.  This makes initial cost high but replacement cost low as you are replacing the rubber bearing material only and not replacing the costly brass outer shell. 

This bearing system becomes more economical with larger sizes shaft diameters.

Babbitt Propeller Stern Tube Bearings

Lubrication: Oil

Material: White Metals, Cast Iron, Steel

Placement: Forward Stern Tube and Aft Stern Tube

Size: As Needed but Usually Larger Shaft Diameters

Advantage: If an Oil Lubricated Stern Tube System is Required

Disadvantage: Leaking Hydrocarbon Oil Into Seawater

This is a traditional bearing for larger shaft diameters when stern tube systems were oil lubricated and before composite bearings were developed.

With environmental policy that included large fines for dumping hydrocarbon oil into waterways, these bearings quickly became out of favor.  With the advent of environmentally friendly oils, these bearings may return to more routine use.

Babbitt Propeller Line Shaft Bearings

Lubrication: Oil with Slinger Ring and Optional Water Cooled

Material: White Metals, Cast Iron, Steel

Placement: Propeller Line Shaft Support Between the Gearbox and Stern Tube

Size: As Needed but Usually Larger Shaft Diameters

Advantage: Less Cost Compared to A Spilt Roller Bearing for Large Shaft Sizes

Disadvantage: Shorter Wear Life than a Split Roller Bearing

This type bearing is a common bearing type for large shaft applications due to the cost being much less than a split roller bearing of similar size.   For smaller shaft sizes this bearing is equivalent in cost to a split roller bearing.

This type bearing is oil lubricated with slinger ring and can also have a water cooling system to remove unwanted heat.

This bearing is self aligning and is designed to support long propeller shafts inside the vessel between the gearbox and stern tube. 

Molded Rubber Rudder Bushings

Lubrication: Water

Material: Nitrile Rubber

Placement: Rudder Shaft

Size: 1 1/2 to 9 inch shafts

Advantage: Cost Savings

Disadvantage: None

Nitrile rubber bushings are a rudder shaft bearing material that can withstand the high impact in rudder applications. 

They include water lubrication grooves inside but are otherwise shipped unmachined.   They can be machined upon request.

These bearings are installed with set screws and are not press fit like a cutless bearing.

Romor I, Class III Propeller Stave Bearings

Lubrication: Water

Material: Romor

Placement: Forward or Aft Stern Tube or Strut

Size: Larger Shaft for Military or Coast Guard Application

Advantage: Great Wear and Other Performance Properties, Oversized Bearings Available

Disadvantage: High Replacement Cost, Initial Cost to Construct Bearing Housing

Romor bearings are installed into a housing similar to demountable stave bearings described above.  Romor material has much better performance and wear properties than the nitrile bearing material of a demountable stave. 

Typically Romor is used in Military and Coast Guard applications and has a high cost.

Romor staves can be shipped oversized in thickness during retrofit to avoid replacement of the shaft liner and thus saving cost.

Brass Backed Stave Bearings

Brass backed staves are no longer made and this product is listed for reference only.

These staves were superseded by the advent of Demountable and Romor Staves described above.

Lignum Vitae and Other Hard Wood Bearings

Prior to the development of modern propeller and rudder bearing technology, hard wood bearings, often Lignum Vitae, were used extensively for ships rudder and then propeller shaft upon the advent of engines for ship propulsion.