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Saving fuel…

Most marine diesel engines have a sweet spot. Combine this with the hulls sweet spot and you’ll get the most out of every litre of diesel you burn.

On Waiata, like most 450s the difference between motoring at 2200 RPM and at 1800RPM is about half the fuel bill. More over the difference between two engines at 1800RPM and one at the same revs is half the fuel consumption and about 1kt slower.

We find with one engine at 1800RPM we can hold 4.8-5kts most days and consume only 5ltr an hour or a litre per Nm!!!!

With two engines we will be doing about 5.5-6kts but burning 10litres an hour or about 1.7 Litres per Nm.

At 2200RPM we gain about another kt (with both engines) and more than double the fuel consumption.. much more actually.

So we passage plan based on 4.5kts, running one engine and planning on burning the Nm in diesel or less because as soon as we can motor-sail (or sail of course) we drop that considerably again.

Oh, BTW we always do better than 4.5kts average… especially if we get wind because we can easily manage 6kts average with a decent blow…. without burning any diesel at all!!! The best we have managed so far on a single passage was a 10kt average, but that was particularly unusual and involved calm seas and constant 30kt winds on the beam.

What’s your sweet spot and is it worth planning your passages on your official cruising speed?

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