If you usually cruise around 25 to 28 knots and can use a boat around 30 feet, the single diesel Targa 27.2 and single outboard Axopar 29 XC are useful starting points. Their builders publish figures near 0.42 and 0.44 U.S. gallons per nautical mile, respectively. The figures are close, and differences in test conditions and speed reporting make them a poor basis for choosing between the two boats. Ask for a run on the exact engine package at the speed and load you use.
Published fuel burn by boat and engine package
ABG selected enclosed boats with identifiable engine configurations and published cruise figures. Compare boats that fit the same job and look at the speed column before comparing fuel. The last column converts the builder figure to a common unit and rounds to two decimal places.
| Boat and source | Engines | Cruise speed | Published L/nm | Calculated U.S. gal/nm |
|---|---|---|---|---|
| Targa 27.2 | 1 × 380 hp D6 diesel | 27 knots | 1.6 | 0.42 |
| Axopar 29 XC Cross Cabin | 1 × 350 hp outboard | 24–34 knot economy band | 1.65 | 0.44 |
| Targa 30.1 | 1 × 440 hp D6 diesel | 27 knots | Approx. 1.8 | 0.48 |
| Targa 32 | 2 × 320 hp D4 diesels | 27 knots | Approx. 2.2 | 0.58 |
| Axopar 37 XC Cross Cabin | 2 × 300 hp Mercury outboards | 28 knots | 2.3 | 0.61 |
The builder pages give a single figure or an economy band. They do not provide enough detail about crew, tank loads, water conditions and equipment to rank these boats in a controlled comparison. Axopar’s 29 XC figure describes a speed band, with no separate observation at 27 knots on that page. Model names also differ from overall length. Check cabin and deck layouts before treating the listed boats as substitutes.
Calculate fuel per nautical mile and per trip
- Gallons per nautical mile = total U.S. gallons per hour ÷ speed in knots.
- Nautical miles per U.S. gallon = speed in knots ÷ total U.S. gallons per hour.
- U.S. gallons per nautical mile from a metric figure = liters per nautical mile ÷ 3.7854.
- Cruise fuel cost = gallons per nautical mile × nautical miles at that speed × price per U.S. gallon.
A knot is one nautical mile per hour. If a report uses statute miles per hour, divide by about 1.1508 to get knots. Use the combined burn from all engines. A boat running 24 knots and burning 6 gallons per hour on each of two engines uses 12 gallons per hour total, or 0.50 gal/nm. On a hypothetical 60-nautical-mile cruise leg, that is 30 gallons. At an illustrative $5 per gallon, the cruise fuel would cost $150.
For an ownership budget, add fuel for harbor transit, warmup and other parts of the trip separately. A boat that covers 60 nautical miles at 24 knots and spends another 30 minutes at harbor speed has two fuel calculations. Use measured hourly fuel burn for the harbor portion. Use the local pump price for each fuel type when comparing a diesel package and a gasoline package. The cruise example omits idling, generator use, detours and reserves.
What one boat’s test shows at different speeds
Yamaha’s February 2018 Parker 2820 XLD Sport Cabin performance bulletin (PDF) provides several speed and fuel-flow points for twin 300 hp outboards. The test boat weighed 8,672 lb as tested, including three people and 58 U.S. gallons of fuel. The converted values below use Yamaha’s published mph and total gph.
| Engine rpm | Published mph | Calculated knots | Published U.S. gal/hr | Calculated U.S. gal/nm |
|---|---|---|---|---|
| 2,000 | 11.2 | 9.7 | 7.7 | 0.79 |
| 3,000 | 25.4 | 22.1 | 12.9 | 0.58 |
| 3,500 | 31.6 | 27.5 | 16.4 | 0.60 |
| 4,000 | 37.8 | 32.8 | 24.6 | 0.75 |
In this one test, moving from about 22 to 27.5 knots added 3.5 gallons per hour but only about 0.01 gallon per nautical mile before rounding. Going from 27.5 to about 33 knots added about 0.15 gallon per nautical mile. The 9.7-knot point also used more fuel per mile than the 22.1-knot point. Ask for readings across the speeds you will actually use. A single cruise number misses these changes.
How to compare two engine options on the same hull
Targa lists diesel and twin outboard packages for the 27.2 and 32, but the published consumption figures above describe specific diesel builds. For a same-hull comparison, ask for matching cruise tables for each engine option. You can also ask the Nimbus Commuter 11 dealer to compare the builder’s twin Mercury outboards and twin Volvo Penta D4 DPI diesels at the same speed. Nimbus publishes range figures for the two propulsion types, but the range statement does not show the speed, load or usable fuel behind those figures. Request those inputs before converting advertised range to an operating budget.
Ask for comparable hull versions, loaded weights and speeds rather than matching rpm. Record how options change weight and usable cockpit space. Then compare the fuel budget with the quote for each package, local service and expected maintenance. The outboard vs. diesel buyer guide covers those ownership tradeoffs in more detail.
What to record on a sea trial
- Set the baseline. Use the same practical load of people, fuel, water and equipment where possible. Write down hull year, engine model and count, propellers, bottom condition and any heavy options.
- Pick three speeds you use. Include a low-speed leg and two typical cruise speeds where conditions and the captain permit. Let speed and fuel flow settle. Record actual speed, total fuel flow, rpm and trim. Distinguish GPS speed over ground from speed through water.
- Note what the water is doing. Write down wind, chop and current. If conditions allow, ask the captain for equal-distance runs in opposite directions at comparable settings and divide total fuel used by total nautical miles traveled. Treat the result as a comparison for that day.
- Keep unknowns on the sheet. Mark a reading missing if you cannot confirm the display unit, combined fuel flow or load. Recheck on a comparable day if the reported difference is small or the conditions diverge.
Bring the sea trial worksheet for the rest of the evaluation. If you are still deciding which layouts belong on the shortlist, start with what makes a boat a pilothouse and the pilothouse buyer guide.