Earlier in the spring, I had the pleasure of motoring through the magnificent Finnish Archipelago sea with absolutely no wind and very flat water. As I also had a freshly cleaned bottom, it was a great time to retest the motor cruising speeds of our Hanse 388!
Our Hanse (model year 2019) has the standard Yanmar 29 hp engine (3YM30AE) and uses the SD25 saildrive. We have the upgraded propeller, which means a two-bladed Gori folding propeller instead of the two-bladed fixed one.
If you want “one bigger”— and there might be good reasons for that!—, you can upgrade to a 39 hp Yanmar with the model code 3JE5E. Over here in the Baltic sea, we don’t have crazy tidal currents to overcome, and with the 388 being such a great sailing boat (using the crossover, you need just a bit of wind to get it going), we’ve been quite happy with the smaller standard engine.
As I mentioned, there was no wind and the water was very still (see the video above).
My very simple testing methodology: I adjusted the engine throttle to a specific rpm reading, then waiting for a while until the boat reached its speed equilibrium, and then recorded the maximum sustained speed (SOG).
Here are the readings:
At 1500 rpm, SOG 4.0 knots
At 2000 rpm, SOG 5.1 knots.
At 2200 rpm, SOG 5.5 knots.
At (just a tad under) 2500 rpm, SOG 6.1 knots.
At (almost) 3000 rpm, 7.0 knots.
Everything put together in Excel blow. It looks quite linear! (And the figures closely match the ones recorded at the hand-over in Greifswald.)
Adding estimated fuel consumption (from the Yanmar data sheet), it looks like this:
With a roughly linear speed correlation and an obviously exponential fuel correlation, the most economical motoring— getting the most miles out of the diesel— seems to go as slow as possible. (Note, however, that Yanmar recommends running the engine periodically at full throttle to clean out carbon deposits and give the engine a long and happy life!)
With the Hanse 388’s 160-liter fuel tank, here’s how a full tank of diesel would (theoretically!) translate into nautical miles.
So, motoring along doing 4 knots (my test conditions) at a comfortable 1500 rpm would yield a total range of 586 (!) nautical miles. Then, jumping to the other extreme at 3000 rpm. This would increase the speed, but reduce the potential distance surprisingly much, leaving only 185 miles in a full fuel tank!
In real life, I’m a bit unsure of how accurate these numbers are. I do, however, vividly remember what happened during the last leg of our delivery trip, from Visby to Turku. Following Yanmar’s new engine break-in instructions, we were motoring with high rpms (between 2800 – WOT) for the whole trip, and we did run out of fuel much before reaching the 200-mile mark.
During our everyday cruising, we’re usually motoring only when there isn’t enough wind to sail. So, when the sailing speed drops below about 2-3 knots (depending on the mood and how badly we want to “get there”), we’ll turn on the engine (but keep the mainsail up!). Generally, we then end up in the 1800 – 2100 rpm range with about 4.5 – 5.5 knots of boatspeed.
And it’s very comfortable, I might add!
Being outside, the engine is purring softly, smoothly, and silently (again, see the video above). Inside, it is considerably louder, but the children have had few to no problems sleeping in the aft cabins while we’ve been motoring.
It’s not magical, of course, but rather practical. The magic starts with the off button.