Boat Trip Fuel Planner

Decide what a boat trip will cost in fuel, how long it will take, and how far you can go — with reserve margin and speed scenarios.

Reviewed by neutrino.au·Last updated: August 2026·Editorial policy

Boat Trip Fuel Planner

Plan fuel, cost, time and safe range for a real boat trip. Enter known burn rate when you have it — HP estimate is labelled as approximate only.

Burn & vessel

Fuel burn (L/h)

Best source: engine display, flow meter, or logged trips

Trip plan

Cruising speed (knots)

Compare at speed (knots)

Optional second scenario (burn scales with speed^2.5)

Trip distance (nautical miles)

Return trip (double distance)

Fuel price (per L)

Tank capacity (L)

Used for safe range and reserve margin

Enter cruising speed and a burn rate (or HP estimate) to see trip fuel, cost and range.

How this calculation works▾

Primary path: fuel burn × travel time. Travel time is distance ÷ speed (nautical miles ÷ knots). Cost is fuel × marina price. Safe range uses 85% of tank capacity as usable fuel. Remaining fuel and reserve margin show whether the trip dips into reserve.

HP-derived burn is an optional rule of thumb (~0.05 gal/h per HP at full throttle, adjusted for throttle and hull). Prefer logged burn rates from your vessel when available.

Sources

USCG / recreational boating — fuel planning & one-third rule (practice guidance) — Planning heuristic, not a legal requirement for all vessels
Manufacturer engine/hull data for vessel-specific burn rates — Prefer over HP rule of thumb

Marine range figures are estimated planning ranges only. Always apply the one-third fuel rule and verify with manufacturer data and local conditions.

How Marine Fuel Consumption Works

Unlike car fuel economy, which is relatively predictable at highway speeds, boat fuel consumption varies dramatically based on hull design, engine configuration, throttle position, and sea conditions. Understanding these variables is essential for safe trip planning — running out of fuel on water is far more dangerous than on land.

The most important principle in marine fuel planning is the one-third rule: allocate one-third of your fuel for the outbound leg, one-third for the return, and keep one-third as an emergency reserve. This calculator applies a conservative 85% factor to range estimates, reflecting this safety margin.

Hull Type and Its Effect on Fuel Burn

Planing Hulls

Planing hulls (speedboats, bowriders, centre consoles) ride on top of the water at speed, which is efficient at high speeds but inefficient at low speeds when the hull is pushing through water. Fuel consumption rises steeply as you accelerate through the “hump” — the point where the boat transitions from displacement to planing mode — but then levels off at cruise. Most recreational planing hull boats consume 5–15 gallons per hour at cruise.

Displacement Hulls

Displacement hulls (trawlers, full-keel sailboats, lobster-style cruisers) push through water rather than riding on top of it. Speed is limited by hull length (hull speed = 1.34 × √(waterline length in feet) in knots), but fuel efficiency is excellent. A 40-foot trawler might cruise at 8 knots on 3–4 gallons per hour, achieving 2 nautical miles per gallon — comparable to some planing hulls going twice as fast.

Pontoon Boats

Pontoon boats have unique hydrodynamics — their parallel tube hull design creates significant drag at higher speeds. Smaller pontoons (20–22 ft with 115–150 HP) typically burn 5–8 gallons per hour. Tritoon configurations with larger engines (250+ HP) can burn 15–20 gallons per hour at full throttle. Pontoons are typically most fuel-efficient at 15–20 mph cruise.

The HP-Based Fuel Consumption Formula

Marine engineers use a simplified rule of thumb: 0.5 gallons per hour per 10 horsepower at full throttle for typical 4-stroke petrol outboards. This calculator implements this as 0.05 gal/hr per HP, adjusted for throttle position using a cubic throttle-to-load relationship (since fuel consumption does not scale linearly with throttle) and a hull efficiency factor.

For exact fuel consumption data, consult your engine manufacturer's fuel consumption curves, which are included in most owner's manuals and are published for popular engines like Yamaha, Mercury, Honda, and Evinrude/BRP. These curves show actual gal/hr at various RPM settings, which you can cross-reference with your tachometer.

Fuel Planning for Overnight and Offshore Passages

For passages beyond day-trip range, fuel planning becomes critical. Key considerations:

Headwinds and current: Fighting a 15-knot headwind or 2-knot adverse current can increase fuel consumption by 20–40%. Plan for worst-case conditions.
Load: A heavily loaded boat — full water tanks, guests, dive gear — requires more power and burns more fuel. Add 10–15% for heavy loads.
Sea state: Rough conditions (2–4 foot chop) significantly increase fuel consumption as the engine works harder to maintain speed.
Jerrycan reserves: For offshore passages, many experienced cruisers carry additional fuel in portable jerrycans — typically 20–40 gallons of reserve beyond the main tank.
Fuel availability: Research fuel dock availability at your destination and along your route. Remote anchorages and small island marinas may not have fuel or may charge significant premiums.

Marine Fuel Types and Prices

Most recreational powerboats use regular unleaded petrol (87–89 octane) from marine fuel docks. Many newer four-stroke outboards and all diesel inboards require E0 (ethanol-free) fuel, which is available at most marine fuel docks and priced 10–30 cents per gallon above regular pump prices. Ethanol can damage rubber fuel components and absorb water, creating phase separation in tanks — always verify your engine's ethanol compatibility.

Diesel inboards (common on larger cruisers and sailboats) typically consume diesel at significantly lower rates than petrol outboards of equivalent power. Diesel also has higher energy density, providing more power per litre. However, diesel marina prices vary widely — budget $4.50–$6.00/gallon in most US coastal areas, and $1.80–$2.50/litre in Australia.

Worked example

A 6.5 m centre console runs from Pittwater out to Broken Bay and back — 40 nautical miles each way at a 24-knot cruise. The owner knows the engine burns about 55 litres an hour at that setting, and wants to know whether the 400-litre tank covers it with a proper reserve.

Inputs

Distance each way: 40 NM (return trip on)
Cruise speed: 24 knots
Known burn rate: 55 L/h
Tank capacity: 400 L
Marina fuel price: $2.45/L

1Total distance40 NM × 2 = 80 NM
2Time under way80 NM ÷ 24 kn = 3 h 20 m
3Fuel required3.33 h × 55 L/h = 183 L
4Trip cost183 L × $2.45 = $449
5Safe range(400 L × 0.85) ÷ 55 L/h × 24 kn = 148 NM

183 litres, $449, three hours twenty minutes under way, on a safe range of 148 NM.

The trip fits, but read the one-third figure rather than the range figure: a third of usable fuel is 113 litres, which is about 49 NM outbound. A 40 NM leg sits inside that with 9 NM of margin — enough for a headwind on the way home, not enough to add a detour without refuelling.

Frequently Asked Questions

How much fuel does a boat use per hour?

Fuel consumption depends heavily on engine size, hull type, throttle level, and load. A general rule of thumb is 0.5 gallons per hour per 10 horsepower at full throttle. A 150 HP outboard at 75% throttle burns approximately 5–7 gallons per hour. Displacement hull boats (trawlers, sailboats with engine assist) are significantly more efficient — typically 1–3 gallons per hour for the same distance covered. Always consult your owner's manual for manufacturer specifications.

What is the one-third rule for boat fuel?

The one-third rule is a fundamental marine safety guideline: use the first third of your fuel to travel out, the second third to return, and keep the final third as a reserve for unexpected conditions, headwinds, detours, or emergencies. This means your usable range is approximately two-thirds of what a full tank would theoretically provide. The calculator applies an 85% safety factor to range estimates, which aligns with conservative one-third rule application.

How do I convert boat fuel consumption to miles per gallon?

Divide your speed in knots (nautical miles per hour) by your fuel burn rate in gallons per hour. For example, at 25 knots burning 10 gallons per hour, your fuel economy is 2.5 nautical miles per gallon. Note that boat fuel economy is dramatically lower than cars — 2–5 NM/gal is typical for planing hulls, while displacement hulls may achieve 5–10+ NM/gal at lower speeds. Speed is the biggest factor: doubling speed roughly quadruples fuel consumption for planing hulls.

How much does it cost to fill up a boat?

Fuel costs depend on tank size and current marine diesel or petrol prices. A typical recreational powerboat has a 60–120 gallon tank. At $4.50/gallon for marine fuel, that is $270–$540 to fill from empty. Larger sportfishing boats with 300+ gallon tanks can cost $1,350+ per fill. Many marinas charge a premium over pump prices — factor in 10–20 cents/gallon for marina convenience pricing when budgeting trips.

Boat Trip Fuel Planner