The Blue View - Replacing a Cutlass Bearing

When we hauled Nine of Cups in December, as soon as the power wash was done and all the sea life was removed from her bottom, I took a walk around looking for problems. For the most part, everything looked good – no blisters, the anti-fouling looked depleted but good, no play in, or issues with the rudder. We hadn't run aground since the last haulout, so there wasn't any damage below the waterline. There were several expected maintenance issues, but the only surprise was that the cutlass bearing needed replacing. The cutlass bearing supports the propeller shaft as it exits the hull, and the actual name is a stave bearing. Originally, they were made of the hardwood, lignum vitae, which is resistant to rot, is very hard and doesn't swell when wet. We know of at least one sailboat that replaced their worn cutlass bearing with a locally fabricated hardwood version when the modern equivalent wasn't available, and it worked just fine.

The name 'Cutless' is actually a tradename owned by Duramax Marine for their molded rubber stave bearing. This then evolved to cutlass bearing and became the generic name. I think if I walked into a marine chandlery and asked for a stave bearing, I'd get some puzzled looks – but everyone knows what a cutlass bearing is. For a boat the size of Cups, the bearing consists of a bronze tube with a grooved nitrile, rubber-like lining.

Since it was eight years since we last replaced it, I was half expecting that it might be time again. To determine whether it needed replacing, I took hold of the end of the prop shaft and wiggled it up and down and from side to side. There should be virtually no movement with a good bearing. I was seeing considerable play in the shaft, so I knew it was time for a new bearing.

The first step in removing the cutlass bearing is to remove the propeller. It is pressed into place with a large nut and cotter pin. These come off easily, but the prop itself is always reluctant to come free. I remember the first time I tried getting ours off – I spent most of a day prying, heating, tapping and pulling on it before renting a prop puller tool. All boatyards have such a tool, usually homemade, that makes the job quite easy. Here at Power Boats in Trinidad, I couldn't rent just the tool – I had to hire the guys along with it. The cost was higher, but they had the prop off in just a few minutes.

Next, the prop shaft has to be removed. On Cups, this entails disconnecting the hydraulic piston connected to the rudder, removing the anode on the rudder, then removing the shaft coupler and shaft seal. I also had to remove the pulley for the prop shaft generator. Once these were all loosened and pulled off, the shaft slid right out. I used a scouring pad to clean and polish the shaft.

Removing the cutlass bearing itself is next. It is held in place with two set screws and, in theory, once these are removed, the end of the cutlass bearing can be gripped with a pair of vice-grips or pipe wrench and the bearing can be pulled out. If only it were true. We were in Tahiti the last time we replaced it, and I spent two days trying to extract it. I tried all sorts of schemes and finally resorted to cutting it in half, patiently sawing through it with a hacksaw blade. This time I hired the same guys that had the prop puller. They cut through the old bearing in just a few minutes, using a SawzAll fitted with a 10” blade. In order to pull the bearing out, however, they had to perform some surgery to the end of the shaft tube as well.

The new bearing was slid into the tube, and I gave it a few taps with a piece of wood and hammer to ensure it was seated. The set screws were screwed into place, and with help from Marcie, the prop shaft was slid back in. It was a tight fit in the new bearing, and lubricating it with a little dishwashing soap and water helped. The rest of the process was the reverse of the removal process.

The final step was to repair the fiberglass that was cut when the old bearing was being removed. I mixed up a batch of West System epoxy, thickened with 403 filler to about the consistency of peanut butter, and built up and faired the damaged edge. Once it cures, I will sand it, then give it a couple of coats of anti-fouling.

Hopefully, it will be another decade before we have to replace it again.

The Blue View - Alternative Antennas

In the last Blue View, I talked about a long line antenna, which is what most cruising boats use for transmitting, either on the marine bands or on the HAM frequencies. As I mentioned, probably 95% of the cruising sailboats we see use a long line type antenna for their HF radios, but there are a couple of other alternatives.

One alternative is a whip antenna. This is a 23' fiberglass antenna that is mounted to a rail, usually near the stern of a sailboat. The rail is typically used as the counterpoise. The whip antenna is more often used on power boats, but we have seen a number of sailboats using them as well. The drawbacks: they are expensive (although no more so than buying and installing a couple of backstay insulators); the mounting method must be robust as a 23' pole aboard a sailboat that is rolling in a seaway will put a lot of stress on the mounting point; the transmission range is typically less than that of a properly installed long line antenna – some estimates I've seen indicate as much as 30% less.

Another alternative is a dipole antenna. A dipole antenna may be the most widely used antenna for shore-based systems. The most common version is made up of two identical length conductors placed end-to-end. The radio signal connection is made at the junction of the two wires. The dipole antenna is only resonant within a small frequency range (example: 14.0Mhz-14.5Mhz), and is tuned by adjusting the length of the two conductors. If it is operated at the tuned transmission frequency, no antenna tuner is needed – the dipole can be connected directly to the radio. We commonly transmit in the 14Mhz range, so the dipole I built was tuned for this range. I found, however, that if I connected it through my antenna tuner, it transmits reasonably well throughout the 10Mhz to 18Mhz range – maybe not quite as well as the long line, but not bad. On the other hand, within its resonant frequency band, it is superior to our long line antenna.

I built a rather simple version. I used coax cable from the antenna tuner to the junction of the two dipole conductors. As an insulator, I used a one foot section of 1x2 wood, and soldered the connections between the coax and the dipole conductors. Each of the conductors were secured with cable ties, and the entire insulator was wrapped in rigger's tape to protect it from the elements. I used a spare halyard to hoist one end of the antenna and secured the other end to the stern rail. The coax wire was led from the insulator to a cable tie on the backstay, then to our antenna tuner.

The length of the two dipole conductors should be 1/2 wavelength in total which, if you're not a radio geek, is determined by the formula: length in feet = 468/frequency in megahertz. So if you want to transmit at 14.2Mhz, the theoretical length of the conductors should be 468/14.2 = 32.96 feet, and each conductor should be half of this, or 16.48 feet. Note that this is the theoretical length. The optimal length will vary from the theoretical based on a host of variables – the type and length of feed line, other rigging, masts, angle of the dipole, etc.

To tune the antenna length, I used my radio's built in Standing Wave Ratio (SWR) meter. I was at anchor, but if I was at a marina, I would have moved Nine of Cups to an anchorage or mooring to avoid any interference from other boats or structures. I started by making the length of the dipole conductors slightly longer than the theoretical lengths, hoisted it into position and checked the SWR. The SWR will be lowest at the resonant frequency of the dipole, and to start, the center of the resonant frequency was lower than the desired frequency of 14.2Mhz. I lowered the antenna and trimmed off an inch from each conductor, then repeated the process until the the resonant frequency was centered around 14.2Mhz.

The purists out there will know this wasn't the optimal method of building a dipole. I should have used a balun between the coax feed line and the dipole conductors, or alternatively used a twin lead feed line instead of coax. There are also ways to build a multi-frequency dipole that will transmit at three frequency ranges. This was my first attempt, however, and I wanted to keep it simple. As it turns out, I was quite happy with its performance and didn't modify it.

If I didn't have a SWR meter, I would have made the lengths of the conductors the theoretical lengths and used an antenna tuner between the dipole and the radio. This is the configuration I use anyway, since I often use the dipole at other than the resonant frequency.

So what do we actually use? Most often we rely on our old long line antenna, and the dipole is our backup. Since it doesn't require a ground plane, I also dig it out when we are on the hard where the performance of the long line drops dramatically.

Well – to paraphrase my dear old dad – I've taught you everything I know about HF radios and antennas and you still don't know nuthin'.

Next week I'll move on to a totally new subject – stay tuned.

The Blue View - HF Radio Ground Systems

In the last Blue View, I talked about a typical marine HF radio setup, consisting of the radio, an automatic antenna tuner and a long line antenna. As I mentioned, the wire of the antenna is only half of the antenna. To transmit any distance, a good ground plane or counterpoise is also needed. On a land based antenna, the earth is sometimes used as the ground plane, but often a network of wires is run radially out from the base of the antenna, and this type of ground system is called a counterpoise. On a boat, the seawater acts as a great ground plane as long as there is a good connection between the antenna ground and the water.

If the boat is steel, all that needs to be done is to connect the antenna ground to the hull. I'm not sure whether the hull would be classified a counterpoise or a good ground connection. More likely, it is some of both.

On plastic or wooden boats, making a ground connection or counterpoise is slightly more complicated. One method is to attach a large ground plate to the outside of the hull under the water line. It is held in place with large bolts through the hull, then the antenna ground is connected to it using a wide copper strap.

A variation of this is to use a copper strap to connect the ground to one or more bronze thru-hulls. This method is most effective if the thru- hull is located close to the antenna ground, ideally 3-4 feet, but a maximum of 10-15 feet, and the conductor to make the connection is a wide – 3” or more – copper strap. Gordon West, arguably the foremost expert on marine radios, is a proponent of this system.

Another method is to construct a counterpoise by running as many copper straps as possible from the antenna ground, and connecting metal tanks, lead keels and other various metal objects together. Steel lifelines, stanchions and even the mast can be included. This can be a very effective counterpoise, but it is difficult to add all that copper. In addition, since copper and seawater don't go together well, the copper should be protected from corrosion, especially anywhere that the copper strap might come in contact with seawater – like the bilge for example. Some installers encapsulate the copper straps in epoxy and bond it to the hull. We also saw one boat that had a blister problem, and was having the gel coat stripped. Before the new epoxy barrier coat was applied, they bonded a copper mesh to the hull. Unfortunately, we didn't keep in touch with the owners, so we don't know how well the counterpoise worked nor whether there were any long term bonding problems.

A third method is a commercial product, the KISS_SSB, that uses a number of wires of various lengths bundled together and connected to the antenna. The wires are all contained in a flexible tube about the size of a garden hose. The manufacturer claims that the various lengths of wire are finely tuned to make sure the radio transmits well on all the marine and HAM frequencies between 2Mhz and 28 Mhz. It is somewhat costly ~$150, but very easy to install. A heavy wire is used to connect the wires to the antenna ground, and then the bundle of wires can be routed under the cabin sole or in a lazarette locker. The manufacturer's website has lots of endorsements, and those of our friends who have installed them claim their transmission ability has improved. Other knowledgeable experts (whose opinions I respect, BTW) insist that the device can't possibly work as claimed. There are several forums devoted to the topic, resulting in a number of heated discussions between the proponents and the detractors. The only performance testing I've seen was done by John (KA4WJA) on the s/v Annie Laurie. He used a spectrum analyzer to measure the the return loss/VSWR/resonance of a transmitter equipped with the KISS-SSB counterpoise as the transmitter was swept throughout the frequency range of 1.5Mhz to 28.5Mhz. His conclusion was that it would probably work great on three or four frequencies and have a marginal performance throughout the rest of the range. His opinion: “If you just grab some wire out of a dumpster, cut it into a few random lengths (between 12' and 35'), attach a ring terminal to the end of the group of wires...you HAVE made an antenna counterpoise for FREE that works as well as (or better than) the KISS....and if you need to buy some wire, it'll cost you < $5.... “.

So, there is the opinion of several experts as well as John's test results saying it can't and doesn't perform as claimed by the manufacturer versus the actual real world, albeit subjective, experience of a number of actual users claiming it is great. I love it!

Meanwhile, what did we do? Sixteen years ago, when we first started cruising, I read everything I could and decided to use the second method. I bought 100 feet of 3” copper strap and connected all my fuel and water tanks together, as well as a few thru-hulls, and attached it all to the antenna ground. This has worked reasonably well for us over the years, but some segments of the copper have started to deteriorate. Nine of Cups is currently on the hard in Trinidad, and one of the items on my to-do list is to replace the thru-hull for the port cockpit drain. As long as I will be scrunched head down into the lower reaches of the engine compartment, I plan to run a copper strap directly from the antenna tuner to this thru-hull and see whether there is any improvement in our transmission range.

I'll keep you posted. Meanwhile, stay tuned for the next blog when I'll talk about alternative antennas.