The mechanic asked, “Did you check the prop?”

“No,” I said into the satellite phone, “why would I do that?”

“We’ve had some instances where the prop fell off those saildrive units.”

A quick dive revealed that the mechanic knew what he was talking about. I had no prop and I was stuck in a small, remote cove on the west coast of Vancouver Island. It took seven days to rectify the situation.

Over the past two decades, most mid-sized boats have come equipped with saildrive units as opposed to drive shafts. As a result, many people in the market for a good old boat today and in the years to come will consider a boat with a saildrive. And saildrives offer some advantages over conventional drive shafts. They are quieter and vibrate less. They are more efficient and produce less prop walk because their thrust is relatively horizontal. In fact, some naval architects, such as Bob Perry, really like saildrives.

But before any sailor takes the leap aboard a boat with a saildrive connected to the auxiliary, they should know what they’re getting into, perhaps to reduce the need for high blood pressure medication later.

Loose Props

I had no idea that the prop could just fall off. I assumed the saildrive prop shaft used a cotter pin to secure the nut that holds the prop on, like I’ve seen on every conventional drive shaft set-up. But, like many saildrives, mine does not have a failsafe mechanism to keep the prop attached. The prop is designed to be held on by Loctite, a properly and precisely torqued spinner nut, and a bolt that reverse threads into the nose of the spinner nut. This is probably sufficient, until the time a prop is removed and reattached without the use of Loctite or a torque wrench and knowledge of the specs.

And why would someone remove a prop? Most saildrives require a collar-shaped sacrificial anode that sits behind the prop. This anode can be either a one-piece or split anode. If the anode is one-piece, the prop must be removed to replace the anode. The obvious problem is that simply replacing a zinc can introduce the potential for an incorrectly attached prop. In my mind, this is a good reason to use a split anode.


The body of a saildrive is made of aluminum. As one of the least noble metals, it can corrode quickly without proper protection. I have a diver check the zinc anode and housing every three months. When the diver checks the housing, he also checks for nicks in the paint. A small nick in the paint can cause deterioration of the housing. Any nicks should be repaired immediately to preserve the saildrive.

Minding the Fluids

Changing the fluid on some saildrive units can be expensive. For example, on my unit the boat has to be hauled to drain the fluid. I could put a thin tube down the unit to pump out the fluid, but removing the tube intact is problematic. In the likely event that the tube is ripped apart, the entire unit must be removed and taken apart — a much more expensive proposition than a quick haul out to drain the fluid.

Beware the Cone Clutch

In one way, I am lucky that I have to haul the boat to drain and replace the fluid. Many older Yanmar saildrives allow owners to extract the fluid with the boat in the water (I have a Volvo saildrive). However, these older units have cone clutches. The cone clutches require adjustment and other maintenance every 250 hours. For most of us, adjusting and maintaining is not a DIY job. This means it’s expensive, probably around $250 to $500. In addition, the cone clutches require replacement every 2,000 hours. Replacement costs $1500 and up. If you’re getting the idea that saildrives add to maintenance costs, you are on target.

A Big Hole in the Boat

Saildrives require a big hole in the hull to work. The hole is sealed by a boot to keep the water out. The hole is large enough that a catastrophic failure of the boot would cause your boat to sink rather rapidly. As a result, two boots are installed to reduce the probability of catastrophic failure. In addition, a sensor is installed to warn of water ingress due to boot failure. These boot seals have a limited lifetime. Manufacturers recommend that the boots be replaced every five to seven years at the modest cost of $2,000 to $4,000. This also is not considered a DIY job.

The sensor also should be checked periodically. It’s not difficult to check. It’s one of the few jobs on a saildrive that the average DIYer can do.

The saildrive has other seals to keep water out of the gear drive. The gear oil should be checked regularly for both level and color. If the color turns milky white, that means water intrusion caused the gear oil to emulsify, a result of seal failure. The life of these seals is about the same as the life of the boots. As a result, you might as well replace these seals at the same time the boots are replaced. At this point you may think that the saildrive is an ATM machine for the boat yard.

Apparently, some boat owners are extending recommended boot maintenance beyond the five- or seven-year time period. I don’t think extending the maintenance period is a good idea but it’s understandable given the expense. I suspect that plenty of forewarning will be given before a leak will become critical, so long as you sail in an area with lots of boatyards. However, if you plan to go offshore, you should replace the seals before setting out. There aren’t a lot of boatyards mid-ocean.

Why are saildrives dominant in mid-sized cruising boats? The reason is because they are cheaper for a builder to install. I have no idea whether any savings are passed on to the buyer or whether the boat builder pockets the savings. However, I do know that additional maintenance costs are passed on to the buyer.

You shouldn’t eliminate a sailboat from consideration because it has a saildrive. Instead, you should go into it with open eyes, so you won’t be surprised by the maintenance requirements. And by-the-way, you might want to carry a spare prop.

Carl Hunt is a retired economist living in Colorado. He has sailed and cruised his boats from British Columbia to Mexico. He chartered or cruised on other people’s boats (OPBs) throughout the eastern United States from Maine to Florida and the Gulf of Mexico, the Caribbean, the Mediterranean, the Atlantic Ocean and other parts of the world.