Running out of fuel on the water is a preventable disaster. Fuel planning separates experienced powerboaters from those who panic every trip. It’s simple math, but it requires honest assessment of your boat’s consumption and conservative planning.
Calculate Your Boat’s Fuel Consumption
Every powerboat has a consumption rate (gallons per hour at cruise speed) and a different rate at wide-open throttle (WOT). You need both numbers.
Finding Consumption at Cruise
Cruise speed for a powerboat is typically 60–75% throttle, producing a comfortable speed without excessive fuel burn. At this setting, your boat consumes fuel at a predictable rate.
To find your consumption:
- Start with a full tank (fill until fuel is at the fill line)
- Run at your normal cruising throttle for a known distance or time
- Return to a dock and refuel
- Divide gallons used by hours run
Example: You cruise for 3 hours and use 18 gallons. Your consumption is 6 gallons per hour (GPH) at cruise.
Write this number down. It’s the foundation of all fuel planning.
WOT Consumption
Wide-open throttle burns fuel at a much higher rate. Most powerboats use 1.5–2.5 times their cruise consumption at WOT. If you cruise at 6 GPH, you might use 12–15 GPH at WOT.
You rarely run WOT except in emergencies, but know this number for planning worst-case scenarios.
Speed and Consumption Trade-Off
A simple principle: higher speed burns more fuel, not linearly but dramatically. Reduce speed by 10% and you might reduce fuel burn by 20–30%. This matters for long-distance cruising.
Example: A 35-foot powerboat cruising at 10 knots at 6 GPH has a range of about 100 nautical miles on a 60-gallon tank. Reduce to 8 knots (slightly lower throttle) and consumption might drop to 4.5 GPH, extending range to 133 nautical miles—33% more distance on the same fuel.
The Rule of Thirds
The rule of thirds is the fundamental principle of fuel planning:
- One-third of fuel for outbound journey
- One-third of fuel for return journey
- One-third reserve (for headwinds, detours, emergencies)
This rule builds in safety. If you burn through your outbound and return thirds and encounter a headwind or missed a waypoint, you have a buffer.
Applying the Rule
If your boat’s tank is 60 gallons and cruise consumption is 6 GPH:
- Outbound third: 20 gallons (3.3 hours at cruise = ~18 nautical miles at 5.5 knots)
- Return third: 20 gallons (3.3 hours)
- Reserve third: 20 gallons
Total safe cruising range: ~36 nautical miles from your starting point. Anything beyond that requires refueling.
Many boaters violate this rule and rely on finding fuel at a destination or running on reserve. That’s gambling. Fuel docks break, aren’t in the expected location, or run out in summer. Don’t count on them.
Range Calculations with Current and Wind
Theoretical range (based on fuel consumption) must account for real-world conditions: tidal current and wind.
Tidal Current
Puget Sound currents can be 1–3 knots depending on tide and location. A 1-knot adverse current reduces your effective speed and increases fuel consumption over a set distance.
Example: You plan a 20-nautical-mile trip. Against a 1-knot current:
- Your boat’s speed through water: 5 knots
- Effective speed over ground: 4 knots
- Time to complete: 5 hours instead of 4
- Fuel burned: 30 gallons (6 GPH × 5 hours) instead of 24
- Extra fuel consumed: 6 gallons
Check tide and current tables before departing. Plan to run with the current when possible. If you must run against current, burn extra fuel in your planning.
Wind
Wind affects larger boats less than small ones, but it matters. A 10-knot headwind increases fuel consumption 10–15% in many hulls. A strong tailwind reduces consumption slightly.
Windy days reduce range. Plan accordingly, especially in the Strait of Juan de Fuca, Deception Pass, or other areas known for wind funneling.
Real-World Example
You plan to run 30 nautical miles from Seattle to Bremerton.
- Tank: 60 gallons
- Cruise consumption: 6 GPH
- Theoretical range on full tank: 50 nm (good)
- But: current runs 1.5 knots against you (ebb tide)
- And: 10-knot headwind (morning Strait effect)
Real consumption: 8 GPH (higher throttle needed to push against current and wind) Real time: 4 hours Real fuel burned: 32 gallons
You arrive with 28 gallons remaining. Rule of thirds: safe trip. If conditions worsen, you have a buffer.
Always plan the worst case (adverse current, headwind) not the best case (favorable conditions).
Finding Fuel Docks in the Pacific Northwest
Knowing where fuel is available prevents desperation.
Major Marinas with Fuel
- Seattle (Ballard Locks area): Ballard Oil, numerous moorages
- Shilshole Bay Marina: Full fuel facilities, busy in summer
- Bremerton: Brownsville Marina, Sinclair Inlet marinas
- Olympia: Port of Olympia, several private marinas
- Tacoma: Point Defiance, Hylebos Waterway marinas
- Port Townsend: Port of Port Townsend, multiple vendors
- Port Angeles: Ports O’Call Marina, City Dock
Puget Sound also has fuel availability in smaller towns (Gig Harbor, Westport, Bellingham), but summer demand is high. Don’t assume fuel will be available; call ahead.
San Juan Islands Fuel
- Friday Harbor: Port of Friday Harbor (fuel at multiple locations), fuel dock on town dock
- Roche Harbor: Resort marina fuel service
- Anacortes: Anacortes Marina, cap’t Whidbey’s Marina
San Juan fuel is expensive (often 20–30 cents more per gallon than Seattle) and can run out in high summer. Plan to fuel up before leaving Anacortes or Friday Harbor, not on the islands.
Canadian Waters Fuel
- Sidney, BC: Fuel available at the dock area
- Ganges, BC (Salt Spring): Limited; call ahead
- Victoria: Excellent fuel infrastructure along the Inner Harbour
Fuel in Canada is more expensive than the U.S. and is sold in liters (1 gallon = 3.785 liters). Expect to pay 30–50% more per gallon in Canadian dollars.
Fuel Dock Etiquette and Safety
Arriving at Fuel
Call ahead and report your arrival time. Ask about fuel dock procedures (where to tie, what to do). When you arrive, shut down the engine, inform the attendant of your tank size, and be ready to hand-fuel if the dock isn’t staffed.
Procedures
- Tie off properly to a piling or dock, not to other boats
- Ensure fuel caps and hatches are clear and accessible
- Have payment ready (cash or card)
- Ask for the pump to be supervised (fires at fuel docks are rare but serious)
- Turn off engines and electronics during fueling
- Don’t use cell phones at the fuel dock (rare risk, but real)
Payment
Fuel docks accept credit cards and cash. Call ahead if you’re unsure. Some small docks are cash-only, and no ATM is nearby. Carry cash.
Fuel Quality and Ethanol
Modern fuel contains ethanol (E10 = 10% ethanol). Marine engines tolerate ethanol, but long-term storage problems occur.
Ethanol Issues
Ethanol absorbs water from the air. In a boat’s fuel tank, this water accumulates and corrodes fuel system components. For boats sitting over winter or used infrequently, ethanol fuel causes problems.
Solutions
- Use fuel stabilizer (Sta-Bil, Biobor) in every tank of fuel
- Fill your tank completely before winter storage (minimizes water absorption)
- Use a fuel polishing system before the season starts if your boat sat all winter
- Change fuel filters regularly
- Store fuel in airtight containers, not open cans
Ethanol in marine fuel is legal and standard. Stabilizer costs $10 a bottle and prevents thousands in damage. Always treat fuel when storing your boat.
Diesel vs. Gasoline
Most larger powerboats use diesel; smaller sport boats use gasoline.
Diesel Advantages
- Better fuel economy (30–40% less fuel than comparable gasoline engine)
- Higher torque for pushing loads
- Longer engine life if maintained
- Cheaper fuel per gallon (usually 10–20% less than gas)
- Safer to store (less flammable, won’t evaporate)
Diesel Disadvantages
- Higher initial cost
- Dirtier to handle
- “Diesel gelling” in very cold water (antifreeze additive needed)
- More maintenance required
Gasoline Advantages
- Lower initial engine cost
- Simpler maintenance
- Available everywhere
- Lighter engine weight
Gasoline Disadvantages
- Poor fuel economy (burns more fuel)
- Fuel evaporates quickly, requires stabilizer
- Less torque for the displacement
- More flammable
For long-distance cruising in the PNW, diesel wins. For day trips and lake use, gasoline is adequate. Most boaters upgrading to longer cruises transition to diesel for the improved range.
Emergency Procedures
If you run low on fuel far from a dock, you have limited options.
- Check your consumption rate: Calculate how many hours you have left and how far that takes you
- Reduce speed: Dropping throttle to 50% might reduce consumption by 40%
- Monitor reserves carefully: Don’t let the tank drop to empty; sediment and water settle at the bottom
- Call for assistance early: Coast Guard can assist with fuel transfer in emergencies; don’t wait until you’re dead in the water
- Know emergency fuel sources: Some fishing boats or larger vessels might transfer fuel in a pinch, but this isn’t reliable
The goal is never reaching this situation. Conservative fuel planning prevents it entirely.
Final Principle
Fuel planning is about respect for conditions and humility about your boat. The boaters who run out of fuel tell themselves, “We’ll make it,” or “Fuel will be available.” The boaters who arrive safely tell themselves, “Let’s plan for the worst and enjoy the surplus when it doesn’t happen.”
Conservative fuel planning means shorter trips, more fueling stops, and less anxiety. It also means you actually enjoy cruising instead of white-knuckling toward shore hoping you make it. That’s the point.