Everything that moves on a boat wears out over time and will eventually need to be repaired or replaced. Here’s the story of old and persistently replaced rudder bearing bushings until a suitable solution was found.
One of the issues that occupied me for some time on board my Swede 55 was the rudder, specifically the guide of the rudder shaft in the boat. The rudder should rotate smoothly and without play under the boat, making steering enjoyable. Like most modern boats, the Swede 55 has a pre-balanced blade that hangs below the stern without a skeg. Yacht designers call this a full-balance or spade rudder. Since the rudder shaft – in the Swede 55 it’s a 70 mm stainless-steel tube – is guided by two bearings over a relatively short distance, these guides are subject to considerable loads when sailing at high speeds on a spinnaker course.
It’s only natural that the bushings eventually wear out. The guides, which fit tightly on the rudder shaft, create elongated holes in which the rudder rattles with every turn or wave passing the boat. While this can be ignored for a while, the rattling is annoying below deck.
When the Rudder Bearing Rattles
The rattling bothers because the rudder shaft runs through the aft cabin, where I like to retreat while underway. And when anchored, the noise from every wave bothers.
Adjusting this can’t be a big deal, I thought a while ago. You remove the rudder during the crane appointment for winter storage, look at the worn-out bushings, measure the diameter of the rudder shaft, and also measure the space in the boat to accommodate the new bushings. These are tubular bushings with a kind of flange or collar that holds them in place.
A drawing, material called POM (details below) a turning workshop, or my helpful sailing friend Ulli with a lathe in his basement at home: it can’t all be that difficult, I thought. As in other areas of life, there’s unfortunately a difference between theory and practice.
The bushings can’t be as tight as a mechanical engineer usually makes them: because a hull with forestay and runner loads warps. And the bushing material absorbs water and the rudder shaft then becomes stiff or jams completely in the bushings. The devil is in the details here. I once sailed a season with a bushing that was too tight on the shaft and therefore rotating in the trunk. It wasn’t nice, but I could use the boat.
The Fisksätra yard took it easy back then, specifying 72 millimeters for a 70 mm rudder shaft. Two millimeters of play never jams but rattles. The Swedes had installed a grease nipple on the rudder trunk, to fill the cavity with grease. When the boat was stored on land, the grease washed down the rudder blade. An unnecessary mess, since rudder bearings are made of self-lubricating plastic and require no additional lubrication.
Tenth-of-a-millimeter increments of the rudder bearing bushing
The idea apparently was: A little more play won’t lead to complaints. After repeatedly removing and installing the rudder during the annual fall and spring crane service and several pairs of bushings, I finally gave up a few years ago. At the top, the bushing inner width remained at 70.30 mm. At the bottom, 70.1 mm, 70.3 mm, and 70.4 mm were too narrow, and 70.75 mm was too wide. The 70.5 mm inner width of the lower rudder bearing bushing was the limit for me at this time. I had numerous bushings made for the top and bottom, installed, and removed them again.
Gamle Swede hoisted in fall – Photo Swedesail
I didn’t understand why the rudder still rattled, but I understood: when you’re at your wit’s end, you have to let go. “Do you want to take the rudder out again” was the usual mockery.
For the past few years, I’ve accepted that the rudder rattles with every course correction and every wave. Finally, I removed it again in the fall of 2013.
How to replace the bushings yourself
How do you get the bushings? If you have a standard production boat, ask the yard or dealer; otherwise, ask a local boat builder/service shop in winter storage. For an exotic boat like a Swede 55 or a long-out-of-production model, there’s no way around sourcing the materials yourself and having them custom-made.
If you plan to remove your boat’s rudder for an upcoming bushing change, osmosis check, drying, or other repair, first obtain all available documentation from the yard, designer, or class association. A drawing of the rudder with the shaft and its internal components, information on the profile, drawings, and details of the installed rudder bearings will help.
Secondly, check whether the rudder can be removed and installed while the boat is stored in its cradle on the hard. If the rudder, including the rudder shaft, fits vertically under the stern, you don’t have to worry about a crane appointment. If not, have the boat lifted a little higher during the crane appointment. It is a matter f minutes if you are well-prepared.
Thirdly, give yourself the time the job needs. Remove the rudder in the fall and start right away. Then you’ll have time until spring.
It’s best to measure the rudder shaft and the rudder tube to accommodate the bushings using a digital caliper. Then compare the dimensions with the drawing provided by the yard or designer. Obviously, the actual dimensions are more interesting than the assumed or outdated ones.
I would not convert the rudder bearing to technically superior spherical roller bearings. If the existing plain bearing has worked for a long time, stick with it and only replace the wear part, material which costs around €50.
To ensure that the new bushing can be inserted into the tube, it is tapered with a so-called chamfer, a beveled edge. Based on the inner and outer diameters, buy a rod or tube (as a supply for several attempts and bushings) of the new material to have the bushings made from.
Common Material for Rudder Bearing Bushings
In the past, propeller shafts and rudder bearings on large ships were sealed with waxy pockwood, which swells slightly in water. The dark, heavy Central American “Guaiacum officinale” is also known as French wood.
Seawater-resistant bronze, also known as marine bronze, is the classic material for rudder bearing bushings. CG-Cu Sn 12 is a hard alloy. There are harder, but twice as expensive, seawater-resistant bronze alloys. The bushing diameters must be precisely matched to the conditions of the casing and shaft; otherwise they will quickly wear out.
Polyoxymethylene or polyacetal, or POM for short, is a mostly white to ivory-colored material used as an engineering plastic for bearing and sliding purposes in mechanical engineering. On board, the running surfaces of sliding hatches, lifting keel guides, and rudder bearings are usually made from it. It is typically known under the brand name Delrin. The plastic is self-lubricating and maintenance-free. The material is available from any plastics wholesaler (online) for a few euros per kilo under the names homopolymer or POM. It is not expensive and sufficient for normal use. Depending on the wall thickness of the bushing, a few tenths of a millimeter of play should be allowed for due to the swelling effect resulting from the approximately one percent water absorption, unlike marine bronze. The bushing should slide over the rudder shaft by hand with some resistance. If the bushing slides down the shaft on its own, the diameter is too large. Due to a lack of swelling effect, the upper, permanently dry bushing may be a bit narrower.
Thordon is the brand name of a polymer mixture consisting of rubber and plastic. The rubber component ensures the desired elasticity, while the plastic provides the desired wear and impact resistance. As an elastomer, Thordon has the property of not remaining deformed after being subjected to stress. It returns to its original shape. This property makes it an ideal plain bearing material. Expensive, available online, it’s the Mercedes among plain bearing materials. If you’re particularly careful and want long-lasting peace of mind, try working with Delrin to find the right dimensions and then have it finally made out of Thordon.
I would not glue the bushings into the casing. Because some day the worn out ones will have to be removed.
Thanks to: Hans-Ulrich Eichler (for advice and assistance on the lathe), Markus Hamma, Nadella (Thordon info), T&W Metals Hamburg (bronze info), Johannes Waimer Sr. (Speedwave Jettingen, later Dubai), and Friedrich Winterhalter (Beck & Söhne yard).
