How Much Fuel Does a Long Pacific Northwest Crossing Actually Take?

The one leg where "I'll just top off when I get there" doesn't work

Most Pacific Northwest cruising has a fuel dock within easy reach of wherever you're headed next. But push north past the San Juans and the Gulf Islands, toward Desolation Sound, the Broughtons, or further, and you'll eventually hit a leg with nothing in between. No marina, no fuel dock, sometimes no cell signal, until you're on the other side.

That's not a reason to avoid those trips. Boaters run legs like this safely every season. It's a reason to know your real fuel range before you leave the dock, instead of estimating it once you're already underway.

Sailors have an out that powerboats don't

We came across a great account of a sailboat's run from Anacortes up to Haida Gwaii, about 500 miles over two weeks. The boat motorsailed most of it, and when the wind dropped or the forecast turned, the crew had an option we don't have on a powerboat: slow down, wait, or let the sails carry some of the load while the engine idled.

A powerboat's range lives entirely in the tank. There's no light-wind version of the trip where you use less fuel and get there anyway. That's exactly why the math is worth doing properly, and it's genuinely simple once you know what to look for.

Four numbers, specific to your boat

Skip the rule of thumb from a different boat, a different speed, or a different day. What actually tells you your range on a given leg is four numbers, and they need to be your boat's:

  • Your real cruise-speed burn rate, in gallons per hour, not your top-speed burn rate.
  • Your tank capacity.
  • Your planned cruise speed for that specific leg (current, load, and sea state all move this around).
  • Your reserve, the fuel you commit to never touching. Twenty percent is a common starting point, a long remote leg deserves more, not less.

A real worked example

The example boat built into the Pacific Northwest Fuel Mate calculator, the M/V BROOKLYNN, is a 2000 Trojan 440 Express with twin Cummins diesels: a 450-gallon tank, an 18-knot cruise speed, and a 36 gallon-per-hour burn at that speed. Run the roughly 140-nautical-mile open crossing from Port Hardy toward Haida Gwaii, and the math looks like this:

  • 140 nautical miles at 18 knots is about 7.8 hours underway.
  • 7.8 hours at 36 gallons per hour burns about 280 gallons, leaving 170 in the tank by the gauge.
  • A 20% reserve on a 450-gallon tank locks away 90 of those 170 gallons as fuel you don't touch.

That leaves 80 real gallons of margin beyond the reserve line, on a leg that used 82% of a full tank with nothing to refuel at partway through. Not a reason to second-guess the trip. It's exactly the number you want to know before you're out there, not after.

This is exactly what the calculator does for you

Save your boat's real numbers once, tank capacity, cruise speed, burn rate, your own comfortable reserve, and every leg you plan after that runs the same math, for your boat, with a clear safe, caution, or unsafe read before you ever leave the dock.

Create your free account and plan your next crossing! Save your boat, run the numbers on your longest leg, and know your real range before you go.

Get started at pnwfuelmate.com

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