With half a dozen tidal gates on a passage from the Solent round Lands End, we managed to get through four of them in 24 hours last week. The westerlies that usually slow a cruise to Devon and Cornwall gave way to light winds from between north and east, with calm seas.
Two of us were standing ready to sail to Plymouth as soon as we had the right weather forecast, so we would be better positioned for rounding Lands End on our way to Wales and Ireland next month.
We went to Cowes on Monday afternoon, left at 5am on Tuesday and were in Plymouth Sound about the same time on Wednesday.
We logged about 130 miles, mostly doing two hours on and two hours off, because there was not much sail handling to do – we motorsailed for all but two hours. We had to plug contrary tides twice, of course, but that’s a lot easier to plan when you aren’t beating at the same time against a contrary wind.
A friend who will join us for the next leg found us a friendly berth at his club at Saltash on the Tamar, and that’s where Spring Fever is at the moment.
How much fuel do you burn?
We all know that fuel consumption per hour rises dramatically with rising engine revs. But that doesn’t give a true efficiency rating because with higher revs and speed you go further per hour, of course. What really matters is consumption per mile, which is harder to measure. There is an excellent article on this subject in the summer issue of Cruising, the Cruising Association’s magazine.
Our nearly new Beta 30 is proving helpfully economical measured per hour: purring along at only 1500 -1800 revs, fuel consumption was less than 1.5 litres an hour on the way to Plymouth. We were getting a knot or two from the sails so we averaged just over 5 knots. If we had pushed the boat at engine cruising speed of 6.5 knots we’d probably have doubled or trebled the consumption per hour.
The good news is that Cruising’s research report shows very clearly that consumption per mile also rises with engine revs, though not as fast as consumption per hour. Our 1500 to 1800 rpm looks close to the optimum engine speed. Consumption per mile rises steadily as the engine revs up beyond that. The tests were on a 50HP Beta, so are not directly comparable, but it seems unlikely our Beta 30 would be very different.
There is also some useful related data in the article on the effect of headwinds and waves on consumption per mile at different revs, which is of course to drive it up further. But other than at very low revs, the data shows that the relation between rising revs and fuel consumption per mile is maintained.