Range is the spec that separates a chase boat from a tender. A tender is built to do a 25 nautical mile beach run twice a day. A chase boat is built to keep pace with a mothership across an ocean leg, run a fishing tournament 80 nautical miles offshore, or reposition coastally between charters without bunkering. This page covers what range you actually need, what current production hulls deliver, and how to specify range without overspending on tankage you will never use.
For sizing context see chase boat sizes. For the specification process around range see chase boat specifications.
What "range" means in practice
Three numbers matter, and only one of them is the brochure figure.
- Manufacturer range. The optimistic number on the spec sheet. Calculated at flat-water cruise speed, full tanks, light load, no current. Treat it as the ceiling.
- Working range. What you actually get with passengers, gear, and a 70 per cent fuel reserve at landfall. Roughly 60 to 70 per cent of brochure.
- Reserve range. What is left in the tanks if the day plan goes wrong. Industry practice is to plan landfall with 30 per cent fuel onboard.
If a builder quotes 700 nautical miles at 30 knots, the working range you should plan against is around 450 nautical miles. The reserve at the end gives you weather, current, or a deviation to a different port without anxiety.
Typical range by size band
Numbers below come from current builder spec sheets and our own delivery data. They assume modern common-rail diesels, twin or triple sterndrive or shaft drive, and full tanks at departure.
| Length | Fuel capacity | Cruise speed | Brochure range | Working range |
|---|---|---|---|---|
| 9 to 11 m | 600 to 1,000 L | 30 to 35 kn | 200 to 350 nm | 130 to 230 nm |
| 12 to 14 m | 1,200 to 1,800 L | 32 to 38 kn | 350 to 500 nm | 230 to 330 nm |
| 15 to 17 m | 2,500 to 3,500 L | 30 to 35 kn | 450 to 700 nm | 300 to 470 nm |
| 18 to 21 m | 4,000 to 6,000 L | 28 to 35 kn | 600 to 850 nm | 400 to 570 nm |
Two reference points from the current market: the Windy SLR60 (18 m) carries 4,620 litres for a boat-tested 850 nm range at 25 knots. The Vandal 60 Chase (19.7 m) is rated for 700 nm at 30 knots. Both numbers sit at the optimistic end of the band above.
How fuel burn scales with speed
Diesel-powered chase boats burn roughly:
- 80 to 130 litres per hour at displacement speed (8 to 10 knots)
- 200 to 320 litres per hour at cruise (28 to 35 knots)
- 400 to 600 litres per hour at top speed (45 to 55 knots)
The speed/range curve is brutal in the top third. A boat that delivers 500 nautical miles at 30 knots may give you only 180 at 50. If your day plan needs both speed and range, plan the run at cruise and reserve the top end for short bursts.
Range planning by use case
Different programmes demand different range envelopes. Here is what we see in practice.
Day boat from a stationary mothership
The mothership is at anchor in Porto Cervo or Saint-Tropez. The chase boat day-trips to lunch in another bay 30 nautical miles away and back. Total daily run: 80 to 120 nautical miles. A compact 9 to 11 metre hull covers this comfortably.
Sport-fishing tournament
80 to 120 nautical miles offshore, full day fishing, return at dusk. Total daily run: 200 to 280 nautical miles. You need a 12 metre minimum, and most owners specify 15 metres for the comfort margin. See sport-fishing chase boats.
Coastal repositioning
The mothership moves from Mallorca to Corsica overnight at 12 knots. The chase boat covers the same 320 nautical mile run during the day at 30 knots. This needs working range above 350 nautical miles, which puts you in the 14 metre and up band.
Mothership consort across an ocean leg
Atlantic crossing or trans-Pacific. The chase boat is towed or carried, not run independently. Range is irrelevant on the leg itself, but matters on arrival. Plan for the working range of the destination programme.
Expedition support
Greenland, Norway, Antarctica peninsula. Long coastal runs between protected anchorages, fuel scarce, weather windows narrow. Working range of 400 nautical miles minimum. Expedition hulls usually add a fuel bladder option for an extra 30 per cent. See expedition chase boats.
Tank planning
Two installation choices affect real range.
- Single keel tank versus split tanks. Split tanks let you trim, but the cross-feed plumbing costs you 4 to 6 per cent of usable volume.
- Aluminium versus polyethylene. Aluminium tanks last longer and survive grounding events better, but reduce volume by 5 to 8 per cent for the same envelope.
If you are specifying a new build, push the builder for a fuel volume number, not just a range claim. A 1,800 litre stated capacity that delivers 1,650 litres usable after baffles and pickup geometry is common. The remaining 150 litres is unrecoverable in normal trim.
Range and the towing question
If the chase boat is towed behind the mothership on long passages, range under its own power matters less. The mothership becomes the fuel platform. The constraint shifts to towing speed and bridle loads. We cover the trade-offs at chase boat towing.
If the chase boat is carried on a shadow vessel, range matters only on day operations. Most expedition programmes are built around this configuration: shadow vessel for the deep run, chase boat for the daily envelope.
Common specification mistakes
Three we see repeatedly.
- Specifying maximum tankage on a hull that will only ever do 60 nautical mile day runs. The extra fuel weight slows the boat by 1 to 2 knots and costs cabin volume.
- Underspecifying tankage on a hull intended for sport-fishing or expedition use. Owners discover at season two that they cannot complete the day plan without a refuel stop.
- Trusting brochure range without a working-range calculation. The 30 per cent landfall reserve is non-negotiable in offshore work.
For the wider context on chase-boat specification, return to chase boat specifications and the chase boats pillar.