Oil changes at sea get pretty close to a universal response from boaters I know. Everyone says loudly “DON’T DO IT.” The risk of something going wrong when hundreds, if not a thousand miles, from shore is simply too high. And, with oil change intervals ranging between 250 and 375 hours, there typically is no need to change the oil at sea. Why take an even small risk of an issue when 250 hours is 1,625 nautical miles and a perfect reasonable 375 hours would take you out to 2,400 nautical miles. The majority conclude it’s simply not worth it.
I generally agree, and in the 6+ years we have operated Dirona, we have never changed the main engine oil at sea. What’s makes the question interesting here is we are now going 3,650 nautical miles. Dirona‘s range with all fuel it can carry is not far beyond this point. It’s a long, long way. In fact so far, that we need to slow down to 6 kts and perhaps even 5.5 kts. At 5.5 kts, that’s is 663 hours at sea — just about a month. So, even though we just changed the oil a week ago in St. Helena at the start of the trip, in 3 more weeks it will be past double the engine manufacturer’s oil change interval. When I was in high school I worked at an oil change shop and got to see the negative impact of people forgetting to change their oil. Many time I’ve drained oil that was so thick with impurities that it came out in globs. Very ugly.
I’m sure our engine would be fine not having the oil changed. It’s a big, tough tractor engine. But we are averaging more than a thousand miles a year and operate at fairly high power levels when coastal cruising. We tend to drive it hard and, with the rate the hours are mounting, we need it to last a very high number of hours. When we bought the boat, my goal was to make 12,000 hours without the engine cylinder head needing to come off and out past 15,000 hours without engine overhaul. At the time, that seemed like an impossibly high number of hours. It’s like talking to a 16-year-old about living past 30. It’s just doesn’t feel like an issue but, as that age looms near, it starts to feel “young” and lasting longer starts to look like a priority. Same thing with our engine. At over 7,000 engine hours, longevity is starting to feel like a very real issue and my 15,000-hour goal no longer feels like a far away target. I lean towards doing the oil change at sea, even understanding the downside risk.
Let’s look at the risk. Generally, as with most life safety issues in modern society, the risk of a fault is actually fairly low, but the downside impact of a fault can be very high. Our John Deere has started before the first turn of the engine every time I’ve pressed the start button for 7,173 hours. It’s very reliable. But, if it doesn’t start after the oil change made 1,800 miles from the destination, then we have a pretty big problem.
We carry a lot of spares, so we can manage many of the unlikely fault scenarios without substantial impact. Amongst the most likely is a starter failure, and we do carry a spare. Unfortunately, I recently came across a mention in the Deere manual that Deere special tool #KJD10213 is needed to change the starter. We work hard to be fully prepared for any reasonable issue but I guess I missed that one. What are the odds there will be a boat in the area willing to lend me a Deere Part #KJD10213? :-).
Another concern is simply doing anything different. One thing I’ve learned from being around big engineering projects over the years is faults are very densely packed around the unusual. For example, power failures that bring down servers in data centers are very rare with the high degrees of redundancy usually employed. But, when there is a fault, it’s amazing how many servers don’t power back up after it. When something different happens, “near” faults become real faults. There is some risk to doing anything different.
A further concern is that it’s been 2.5 years, since Dirona has had bottom paint, Prop Speed treatment, and the wing engine Gori folding prop greased in New Zealand. It’s all looking fine, but there is a chance, if we shut down the main engine and use the wing, that the wing engine prop will not deploy correctly from the folded position. This isn’t particularly likely but the reverse is very possible. The prop may not be able to refold when we return to the main engine which would add drag and slightly reduce fuel economy. And spinning the prop without the engine running is hard on the wing transmission if the ZF15 doesn’t have the oil pump on the output shaft (I’ve not checked on this).
Changing the 200°F oil in an active sea way brings some risk as well. I generally like doing the oil changes hot—actually I don’t like it but the engine does—so it’s not all that different from usual. But, the oil would be somewhat hotter and the boat will be moving around more in open ocean. Another more minor issue is the heat in the engine room. We currently are running around 110°F and it may be warmer as we near the equator. Generally, the engine room runs about 30°F over ambient temperature. 110°F is taxing but not dangerous and I have a large fan I can use for safety reasons if major work is needed in the ER while the engine is operating at sea. This one probably is more of a comfort issue than a real risk.
The last time we had this debate on Dirona we needed to cover 3,023 nautical miles with the same fuel load, so we were able to run faster. The conclusion at the time was not to change the oil which still seems like the right decision for those circumstances. But, on this run, I lean towards shutting down the main engine just before the equator and doing an oil change even though there are some low probability, but potentially high, downside risks.