If you're in the market for a new or recently built sailboat, odds are good that it is equipped with a saildrive system vs. a conventional shaft drive set-up.
Basically a sail drive set-up is much like an outboard engine’s mid and lower section projecting through the boat’s hull. It’s a bit different in the sense that unlike an outboard engine or inboard/outboard (IO) set-up, the engine exhaust is not exiting the boat via the drive leg, but rather through the hull just like with a conventional drive system. However, raw-water intake for engine cooling is drawn up through the saildrive leg, just as with an outboard.
The flexibility of the saildrive configuration on a new hull design is compelling. The fact that the engine and drive system form essentially a single unit eases installation, and by design can keep weight “out of the ends,” which is always desirable with sailboats.
With the saildrive, the weight of a shaft, stuffing box, and propeller are moved forward, almost under the engine. Further, the propeller’s angle of attack is more parallel to the surface of the water, which will enhance efficiency and help to minimize traditional prop-walk characteristics common to conventional drive configurations. There's also a wide variety of folding or feathering propellers available for saildrives -- also desirable for the sailing crowd aboard modern designs with relatively flat underwater surfaces aft of the keel that can accommodate saildrive systems. (One of many examples is the the Hanse 545.)
One thing is clear: boatbuilders are embracing saildrives in a big way. Of the saildrive makers, and there only five that I’m aware of as of this writing, two are preeminent, at least here in North America: Volvo Penta and Yanmar. Beta Marine, Lombardini and Nanni offer saildrives, but their market share is so small that there is not much known about them from a global perspective. When we compare the two majors, things shake out a lot like it does with cars: Some people love Chevies, some like Fords.
But for many sailors, questions regarding saildrives abound. Are they a better choice over conventional drive systems? What about the rampant tales of excessive corrosion? How about a rubber boot in the bottom of the boat to keep the water out? What are the advantages and disadvantages of using a saildrive system? Can you easily retrofit a saildrive to your older boat as part of a repower? Let’s work through answering these questions.
Lower Initial Cost, Quieter
Boat builders can certainly save money on installation by using a saildrive system. With no shaft or strut required, engine installation is as simple as dropping a drive leg through a hole in the bottom of the boat and sealing it up with a rubber bladder.
My experience during on-the-water test comparisons has shown that saildrives run significantly quieter and with less vibration than conventional shaft systems. Less noise and vibration are things that make life on board a much more pleasant experience when motoring. Engine and shaft alignment procedures are no longer a part of the maintenance regimen, also a plus. But what about some of the other maintenance concerns?
Three Major Maintenance Areas of Concern
There are really three major issues that a boat owner needs to think about when it comes to saildrives: the integrity of the watertight seal around the drive leg, ensuring that the seals that keep the oil in and the water out of the gear mechanisms are doing their job, and combating corrosion.
Keeping the Water Out
The matter of the gaiter, or boot, that seals the perimeter of the drive leg to the boat’s hull is one that, if neglected, could cause a boat to sink. In fairness, both Volvo and Yanmar drives employ a double seal with a water alarm system that will notify the boat owner if the outer seal begins leaking. Recommended replacement intervals for this rubber seal range from five to seven years between Yanmar and Volvo Penta, and both manufacturers consider this service a dealer-only procedure. Many boat owners have gone much longer than this before replacing the seals, but one has to wonder if an insurance company would pay a claim for a sunken boat if the service interval had been ignored by the boat owner. Certainly this is a good question to ask an insurance agent before something like this happens. Both Yanmar and Volvo provide an “aqua sensor” that will sense water leakage if this bladder begins to leak, but periodic inspection of this critical rubber seal at least every two years is of the utmost importance. Without question this is one of the most important not-to-be-ignored service items related to the saildrive system. Depending upon how difficult engine access is on a given boat, replacement of the bladder and associated service parts can cost in the neighborhood of $1,000-$1,500.
As for the drive leg seals that keep the seawater out and the gear oil in, periodic checks of the transmission oil level and looking for any discoloration (milky white color) will indicate if problems exist. (See Saildrives: How to Check/Change the Oil.) It is recommended that the gear oil level be checked before each use, so any problems should show up rather quickly. Unfortunately, repairs needed here are going to require hauling the boat for seal replacement. Again, it is recommended that trained service personnel take on this task. Basically the task of resealing a drive leg is not much different than seal replacement on an outboard engine leg, and should not have a repair frequency any worse than with an outboard engine or IO drive, meaning service intervals measured in the 5- to 10-year range depending upon how many hours of use you put on in a given year.
Changing the transmission oil is recommended at 100- to 250-hour intervals depending on the specific drive, and both Yanmar and Volvo provide methods for accomplishing this task without hauling the boat out of the water.
Corrosion Concerns and Solutions
Corrosion is perhaps the most frequent issue associated with modern saildrive units. There are a few different causes for premature or excessive corrosion on these units, and if certain guidelines are followed, problems can be eliminated.
The number-one thing to remember about these drives is that the anodes on the units are engineered to provide corrosion protection for the drive only! Manufacturers recommend anode replacement every 100 hours, but it is of absolute importance to remember that this recommendation is based on some important assumptions that only the boat owner can maintain control over.
The first step in ensuring that your drive’s anode(s) provide good service is to make sure that any of the factory original paint on the drive leg that gets scraped off gets touched up. Also, you need to be certain that the anode material is appropriate for the water your boat stays in most of the time. The standard zinc anodes won’t do the job in fresh water and may even fail in brackish water. For brackish water use aluminum alloy anodes, and in fresh water magnesium alloy anodes are the best choice. Anodes should be replaced when they are 50-percent depleted.
Volvo electrically isolates their drives from their engines to minimize the chance of any electrolytic, more commonly known as “stray current” corrosion, occurring. Yanmar does not, and so one of the potential issues here occurs whenever your boat is plugged into shore power. Without electrical isolation, any boat plugged into shore power is connected electrically to all of its dock mates via the green grounding wire in their shore power system. This connection creates a galvanic cell and means that your boat’s anodes may actually end up protecting one or more of your dock buddies. This is a sure-fire way to deplete your saildrive’s anodes too quickly. The next bit of metal in the galvanic food chain once your drive anodes are depleted is the drive case itself. A galvanic isolator installed in the shore power system will prevent this from happening.
Also, keep in mind that accessory bronze folding propellers, which are popular especially with racing sailors, can add a rather substantial mass of extra metal to your drive and make for extra hard work for the anode(s). This very addition will require that anode consumption be monitored carefully until you establish a known service interval with your drive’s anodes.
Bottom Line on Saildrives
So, which is better, the saildrive or a more conventional set-up with a shaft, stuffing box, and propeller? This is a really tough question to answer. From a user's perspective, better weight placement, improved motoring performance, and reduced noise and vibration make the saildrive the clear winner. From a maintenance perspective, I think the conventional set-up will always win out. Neglecting prescribed maintenance procedures and intervals with saildrives is going to cost you big. The conventional drive configurations are much more forgiving in this regard.
Update: March 2017
Since this article was originally published a lot more saildrives have hit the water, and without a doubt most mid-sized cruising sailboats being produced today are taking the saildrive route. And more time has passed with older units in service. So we thought it might be a good time to get an update on the “state of the saildrive.”
What have we learned? What problems may have surfaced, and how are the manufacturers dealing with the issues?
One of the best ways to get a feel for what’s going on is to hit the online forums and follow the moaning and groaning — sometimes it really does indicate real problems among boat owners. These online boating communities, although often fraught with bad advice and “alternate truth” (to use a contemporary description), can at least identify trends. If you get to three or four different sites, consistently hear the same complaints, and make sure that it’s not just two or three boaters with the same name griping on all the forums, then it’s reasonable to think that the complaints might have some validity. Another telling clue is to look for manufacturer service bulletins. Both the forums and posted service bulletins help tell this story.
As for consensus on whether saildrives are better than conventional drives, it really seems to be based on builder opinion. Catalina Yachts still refuses to use saildrives, even though it would help them to reduce build cost. I’ve spoken to Gerry Douglas at Catalina about this topic several times and he is adamant that the added maintenance and risk for catastrophic failure if proper maintenance is not performed is something he intends to keep protecting his customers from. In the multihull sector, Antares Yachts offers this up in their “Facts for the serious liveaboard” literature: Item #4, Never Install Saildrives.
“Antares doesn’t cut corners by installing saildrives. A shaft drive propulsion system is far superior.” They go on with a short list of disadvantages of saildrives. The bottom line here is that those who oppose saildrives are quite adamant about it, but none of that is stopping the clear majority of builders from using them. If you want a new sailboat, either mono- or multihull, it’s probably going to have one or more saildrives installed.
So, let’s get as look at some of the specific issues related to saildrives as we’ve gathered more field experience over the years.
The Bladder Issue
One of the biggest questions surrounding the saildrive is the rubber bladder that surrounds the perimeter of the unit, maintaining watertight integrity with the hull. Despite initial fears, these seem to have held up well. Yanmar for example, recommends replacement every five years, Volvo Penta recommends replacement every seven years. Anecdotal evidence in online forums suggests that many have gone over a decade in service with no leaks.
Prices for replacement bladders vary on location, and seem to range from $2,500 to $4,000 — which probably explains why folks are holding off until it appears absolutely necessary. The units are a double-seal configuration and come equipped with water sensors that screw into the drive base and provide early warning if water intrudes from the outside past the outer seal.
Several tips regarding these sensors are worth noting. One of the forum contributors complained of a false alarm. After much to-do, it was apparently learned that condensation in the space between the inner and outer bladder is all it took to trigger the alarm, and that in fact there was no actual leak. Another reader talked about testing the sensor periodically by unscrewing it and dropping it into a cup of water to make sure it triggered the alarm system. Seems like a simple enough annual check to me.
Boat Resale Value
Although it won’t be much of a consideration with newer boats, boats built with early saildrive technology vs. conventional shaft technology can show a lower resale prices compared with same-model boats built with conventional inboards and propeller shafts. Compare asking prices on online owners’ forums as well as on sales sites like YachtWorld.com and boats.com.
One of the major concerns with aluminum saildrive assemblies is corrosion, and there is certainly a significant amount of documented evidence to validate fears about it. To address that issue, Yanmar back in 2010 issued a service advisory, number MSA2010-007 (PFD file), that does an excellent job of explaining how to prevent saildrive corrosion and also how to check to see if any issues exist. Every boat owner with a Yanmar drive, or any other saildrive for that matter, should print out a copy of this document and follow its guidance.
Issues related to shifting have been reported for both the Yanmar and Volvo Penta products. Volvo’s recommendation for drive gear lubricating oil changed back in 2010. The original recommendation was for the use of ATF (automatic transmission fluid) only. The updated recommendation for all saildrives manufactured after September 2010 is to use SAE 15W-40 engine oil. Also, Volvo gives instructions for how to set the gear shift when sailing with the engine off: “When sailing, set the control lever to reverse if a folding propeller is fitted. If a fixed propeller is fitted the control lever should be set in neutral or reverse.” (The bulletin points out that locking the shift in reverse causes more drag but less noise.)
As for Yanmar, they have had problems with the cone clutches slipping on their SD 50 models. My online searches did not come up with any revelations or advice from Yanmar on this matter but there is plenty of scuttlebutt from the forum crowd. One do-it-yourselfer claims to have repaired his unit with about a $200 investment in parts. Another paid $4,000 to have a shop take care of the problem. I did find one Yanmar bulletin (PDF file) that discussed what was needed to upgrade from the SD 40-50 series of drives to their new SD-60 series. Based on the number of hits this query gets online I think the best advice for anyone in the used-boat market is to confirm what drive model is installed in the boat they may be considering and adjust purchase offers accordingly. Even though the unit may be functioning normally at the time of your inspection, trouble could be right around the next corner with this saildrive model.
I see no turning back when it comes to the continued proliferation of saildrives on new boats. As is true when purchasing any complex system, you have to consider that maintenance and parts replacements are real issues and a part of the big picture. The important point to remember here is that these units are not very forgiving. Ignoring the recommended maintenance will cost you big time.
(An earlier version of this article was published in May, 2012.)