The Cruising Sailor’s Drivetrain

Key components in a boat's propulsion system can take the edge off extreme sailing.




Andy O’Grady and wife Ulla Norlander have sailed their 42-foot gaff cutter Balaena to the far corners of the planet.

At the end of 1999, I sailed away from New Zealand with my wife, Ulla Norlander, aboard our 42-foot gaff cutter, Balæna. We have spent many of the last six years sailing in high latitudes and remote places. Ocean crossings are a good test for sails and the rig, but sailing in fjords where the wind whistles between high mountains challenges the power train. In places like Chilean Patagonia, many of the best and most sheltered anchorages would be inaccessible without a reliable engine. Also, where winds can reach hurricane force even in a sheltered nook, it is important to ensure that the anchor is dug in well, which we test with full power astern. We have put over 2,000 hours on the engine since leaving home, and much of that was in challenging conditions, so our gear has been well tested.

Here’s our report on some drivetrain modifications we’ve made to boost the performance. While cruising in the vicinity of Cape Horn and South Georgia Island, we used a fixed, three-bladed prop to give us the maximum thrust in reverse. However, on the ocean crossings from South America and to South Africa, we had to put up with a lot of shaft noise, not to mention drag and wear, because our transmission is hydraulic, and we have no shaft lock. In less strenuous cruising grounds, we had used a two-bladed folding Gori-type prop that achieved reasonable performance under power, but brought with it vibration, noise, and expensive wear of bearing surfaces on the prop and the shaft. It also lacked thrust in reverse, something that PS and the Massachusetts Institute of Technology noted in joint tests of similar folding props Practical Sailor, Oct. 1, 1993, Jan. 1, 1995).

I actually observed our prop as it opened to only about 75-percent of full diameter in reverse. Changing props to suit a particular cruising area was fine in warm waters, but with more cold-water cruising ahead, we knew this was not a sensible option. I was thinking about investing in an expensive three-bladed feathering prop.

In Cape Town, I started asking other skippers what props they were using, and twice in the same week I got the response:

“You are from New Zealand, surely you’ve heard of the Kiwi feather prop? It works like a dream, costs much less than the competition, and has plastic blades.”

Both of these skippers had tried other props like the Max Prop and were convinced that the Kiwiprop was superior.


Kiwi Feather Prop


engine components

The blades of the feathering Kiwiprop are made of Zytel, a light, high-strength composite compound. Because the blades are so light and weight is concentrated near the hub, vibration, prop noise, and wear on the shaft bearings and moving prop parts are reduced. This is great for those of us who need our motors, but don’t like to hear them or maintain them. Three strong, stainless steel shafts on the hub act as bearings for the blades. These allow the blades to pivot freely and feather to whatever direction the water flows over them. This permits a very large blade area, which is important for thrust. The hub design locks pitch and the blades when in reverse.

The blades are so light that balancing is not required. Also, there are no matching gears to machine. This makes the prop relatively inexpensive to manufacture. These savings are passed on to the customer in the very reasonable price. The only servicing required is an annual application of grease, which is done without any dismantling. Because there is so little metal, corrosion and consumption of zincs is reduced.

The design allows a high pitch (fixed) in reverse and guarantees good power at relatively low revs (though there is a risk of overloading the motor if the revs are pushed too high). There is also a simple way to adjust forward pitch without dismantling the prop. I can free dive and change pitch. The blades are easily removed and replaced, which allows for the possibility of changing prop diameter and for replacing damaged blades.

From a customer service perspective, we’ve found Kiwiprops to be an impressive company to deal with. Both before and after our purchase, they were prompt and helpful in responding to e-mails. Here is what we have experienced over the last three years:

The instructions and information that came with the prop were excellent, and the installation was simple (I did it by free diving at anchor). I liked the nylon “nut” that required only the handle of a socket wrench to tighten. Instructions were to paint it with bottom paint, which seemed sensible to me, though many prop manufacturers frown upon the idea.

The difference was apparent from the first moment. Power in reverse is very impressive, much more than we had experienced with our folding or fixed-bladed props. And there is never any doubt about whether it will deliver reverse thrust as there can be with a folding prop. When coming into a marina or testing the anchor, the prop always functions perfectly. In forward, the reduction in noise and vibration was immediately apparent. Because the manufacturer claims a substantial increase in static thrust over conventional props, I was expecting to go much faster in forward. So I was a little disappointed that we did not actually gain speed , but I guess that demonstrates that the old prop was well matched.

At first, I had a little trouble with the prop not feathering completely and slowly freewheeling when we were sailing. A quick look in the instructions told me how to deal with this, and I removed the blades and took a thin layer off the base of the blades with fine sandpaper. Since I did that, the propeller feathers so well that there is never any auto-rotation.

Recently, I dismantled the propeller, and after three years and many thousands of miles sailing, there was no appreciable wear. I was initially worried about the strength of the plastic blades, but upon inspection, I found only a little bend on one tip. This was all there was to show that the prop had twice been stopped by fouled lines and had several collisions with Greenland’s ice.

This is an excellent piece of gear and so simple, I confidently recommend it to all sailors. Prices in the U.S. run about $1,250, including shipping. The main website ( is packed with useful information and even has a library of details of installations with type of motor, gear reduction, and boat. (There are also links to U.S. suppliers’ websites).

Manecraft shaft seal

Manecraft Deep Sea shaft seal

Stern gland packing was always a nightmare on my old boat. Replacing packing sounds so simple in theory, and nowadays the materials used give excellent performance for most people. However, correctly installing packing down in a dark, narrow space in the bilge with my legs in the air and elbows crushed against the hull is not my strong point, and I never succeeded in getting a decent seal. So it was a great relief when the suppliers ofBalæna prop shaft recommended that I install a new type of drip- and maintenance-free stern seal: the Deep Sea Seals Manecraft water-lubricated stern seal, made in the United Kingdom by a subsidiary of the Finnish marine power company Wartsila.

This is a very robust piece of gear consisting of two parts: a stationary seat and a rotating seal. Both are molded from heavy neoprene. Bonded into the seat is a bronze ring against which runs a ring of bearing material that is bonded into the rotating part. The seat is clamped to the stern tube with two stainless hose clamps, and the seal is similarly clamped to the shaft after being pushed up against the seat with sufficient pressure to prevent water entering. As the shaft spins, the bearing ring also spins against the bronze plate, and the seal is maintained. The bearing is lubricated by water that is supplied by a small tube from the cooling system. The latest model of the seal also includes an emergency clamp in the seat that could be used in the event of failure. Fitting instructions are detailed, and the unit comes with a custom gauge that is used to confirm correct positioning of the seal on the shaft.

Not a drop of water comes into the boat. Once set up, the seal needs no further attention other than occasional visual inspection. Since launching Balæna, we have had 18 years of experience during which time, the boat has been out of the water for only six months. There is no wear on the shaft and little wear on the seal itself.

Age, not engine hours, is the limiting factor in life span, the main risk being that with age, the material will lose its elasticity and not function so well. The manufacturers do not give a specific recommendation here, but say that if the shaft has to be removed for some reason after a number of years, that would be a good time to replace the seal. We have followed this advice and replaced the seal after approximately seven years, which means that we have just fitted our third unit. The first one is still onboard as a spare and appears to have plenty of elasticity remaining and no sign of deterioration or splitting of the material.

We have had two problems, both of which were my fault. The first was shortly after launching when we had a small leak and traced this to the seal slipping forward on the shaft because I had not tightened the clamps sufficiently. Others must have had the same problem as the latest instructions specifically mention that there will be visible distortion of the neck of the seal with tightening and that this is completely normal. They also recommend installing a hose clamp on the shaft just forward of the seal as a form of insurance against slipping.

The second problem was with something in the bilge falling onto the rotating seal and causing wear. Luckily, the material is very thick, so no water leaked in, and the elasticity of the seal was not affected. But this highlights the importance of providing the seal with some sort of guard, as recommended.

In Chile, a cruising boat with a more common type of drip-free seal had a catastrophic leak, and the skipper called for help. It took four of us with pumps and rags wrapped around the shaft to control the leak. Luckily, the skipper had a spare, and we managed to replace the whole unit with the boat in the water. It was a frightening and worrying experience. The unit was constructed in the form of a bellows with a ring seal at one end. The relatively thin material of the bellows had hardened and split, even though it was less than two years old. I was very relieved that our seal was considerably thicker, more elastic, and apparently, made of much better material.

Perhaps the most common seal today uses a thin lip mounted on a heavy flexible rubber tube. These seem to perform well. However, they will eventually cause wear of the rubbing surface on the shaft and will need to be moved to another position or worse, require shaft replacement. They are also dependent upon the surface of the shaft being absolutely unblemished: An accidental knock with a tool at installation time could roughen the surface and spoil the performance. I have to admit that Balæna’s shaft has a few nicks and scratches so would not accept this type of seal.

After 18 years of service, I am very pleased with my choice of the Manecraft seal and consider it money very well spent. Prices vary according to stern tube and shaft diameter, but a a 1-inch-diameter shaft will cost approximately $225-$275.


K&N Air Filter


In San Diego, Calif., I was looking in an auto parts store for an electrical part when something caught my eye: a reusable engine air filter. The advertising seemed to be directed to youngsters with hot rods, but I did not let this put me off and looked closer. At about $40, the K&N Filtercharger seemed to be the answer to my dreams.

K&N Air Filter

Our 1.5-liter BMC diesel (a near twin to the old Westerbeke 30) already had cartridge filters, but I always had problems finding the correct replacement cartridge in different parts of the world as we cruised.

The K&N filter comes in many different shapes and sizes. I chose one that attached to the engine air intake via a short hose and would fit into the engine compartment very neatly without needing a special housing. However, there is a big selection to fit conventional filter housings. The filter consists of a special cotton barrier held in place by robust metal elements and fitted to heavy rubber end pieces. The secret of its function is a specially formulated oil that is tacky and traps dust in the cotton.

Cleaning is simple with the kit that K&N supplies. Excess dust is brushed off, the unit is sprayed with a special cleaner and, after soaking, flushed with water. Once it is dry again, the unit is saturated with the supplied oil and refitted.

I had my filter for six years and 2,000 engine hours and was very happy with it. I decided to clean it before photographing it for this article and discovered a disadvantage: it blows away easily. I found the filters here in Norway at a workshop that was assembling heavy generators for the offshore oil industry quite reassuring. Unfortunately, they were too large, and so our cruising friends in Arkansas had to find us a new one and send it to us.

PRM150 Transmission

My old mechanical transmission had several expensive failures, and the clutch was very heavy to operate, requiring a special cable and a large lever that always seemed to catch hold of any sheet or halyard that came its way. When the engine was out for a rebuild, I decided it was time to change to a new hydraulic transmission and chose the UK-made PRM150, which is distributed worldwide and is available on many marine engines. The manufacturer lists several U.S. distributors on its website, one of them, Transmission Marine Inc. (, 954/467-1540), in Fort Lauderdale, Fla., gave us a base quote of $1,500 for a PRM 150.

PRM 150 Transmission

The transmission is a high quality piece of gear and functions smoothly, quietly, and reliably. It has had no mechanical problems, and after 2,000 hours, there are no signs of wear. An attractive feature is that it operates equally well in forward and reverse. This means that there is no need to match the direction of prop rotation to engine rotation, so you don’t need to replace the prop at the same time as the transmission. Another advantage is the “get you home function,” which allows a manual bypass of the clutch in the event of a failure. However, we thankfully have not needed to use that particular feature.

The parts are steel and aluminum. It is supplied mostly unpainted, which is not a good thing for equipment in a marine environment, so I painted it at installation.

It was not all smooth sailing. Even though I had a professional marine engineer fit the transmission, I still hadquestions that were not answered by the supplied handbook. I bought the workshop manual, but even that was a little vague on some details.

We have had a problem with oil leaks. It is very hard to determine where oil is leaking from, because if any gets onto the output shaft it gets sprayed all over the place. I felt that it was coming from the rear plate and changed the gasket. Unfortunately, that did not help, and we had to put up with leaking approximately a pint of oil for every 100 hours running. Thinking that the oil pressure could be too high, I tried fitting the expensive but crude oil meter the manufacturer supplies as an option. This is a mechanical meter fitted directly to the transmission. With the motor running, vibration makes the needle almost impossible to read. Then one day, we had a complete loss of power and I found that the gauge had broken and allowed all the oil to spray out.

After several years, I had the opportunity to remove the engine and dismantle the transmission. I had decided that maybe the drive shaft oil seal was the cause of our persistent leaking. Unlike many transmissions, the oil seal is not reached by a simple locating plate on the rear of the transmission but involves completely dismantling the transmission and the use of special tools only available from PRM. This at least gave me the opportunity to see that all the mechanical parts were in perfect condition and replace all the oil seals. But, once again, there was no difference with the leak.

I contacted a PRM representative who told me that there was a new gasket available that should solve my problem, and they sent me two free of charge. That fixed the problem, and I expect that newer models would not have the same trouble as mine.

This is a nice transmission, but the oil leaks have spoiled an otherwise perfect track record.