Related Expert Tools
More precision tools in the everyday-life niche.
0-60 Calculator
The 0-60 Calculator estimates the time a vehicle takes to accelerate from 0 to 60 mph (0 to 96.6 km/h) using horsepower, vehicle weight, and drivetrain type. It applies the power-to-weight ratio formula alongside real-world drivetrain loss coefficients to produce an estimate close to track-tested results. Use it to compare acceleration potential between vehicles or evaluate the effect of weight reduction and engine upgrades.
Boost Horsepower Calculator
The Boost Horsepower Calculator estimates how much horsepower a turbocharger or supercharger adds at a given boost pressure, starting from your engine's naturally aspirated baseline. It applies an adjustable efficiency factor to account for intercooling, heat, and tuning quality rather than assuming a perfect, lossless gain. Use it to sanity-check a boost target before committing to a turbo, injector, or fuel system upgrade.
BSFC Calculator
The BSFC Calculator solves for brake specific fuel consumption, fuel flow rate, or horsepower from the other two values, and separately sizes fuel injectors from a target horsepower, BSFC, cylinder count, and maximum duty cycle. It converts the result between lb/hr and cc/min automatically. Use it to size injectors correctly before a power upgrade rather than guessing at the next size up.
Boat Speed Calculator Logic
Speed = Distance / Time; Hull speed (knots) = 1.34 x sqrt(Waterline Length in feet)What Is the Boat Speed Calculator?
The Boat Speed Calculator has two related but different jobs. Its first mode works out your actual average speed in knots, mph, or km/h from a distance travelled and the time it took, the same basic speed calculation used across boating, sailing, and navigation. Its second mode estimates the theoretical top speed of a displacement-hull boat using the classic hull speed formula, a figure sailors and trawler owners use to understand why their boat tops out where it does regardless of engine power.
Recreational boaters, sailors, and anyone planning a passage use the speed-from-distance mode to check average pace against a plan. Boat owners and prospective buyers use the hull speed mode to understand a displacement hull's practical performance ceiling before assuming more horsepower will fix a speed problem it cannot fix.
Hull Speed: Why Displacement Boats Have a Practical Speed Limit
As a displacement-hull boat, most sailboats, trawlers, and traditional motor cruisers, speeds up, the bow wave it generates stretches longer. Once that wave's length matches the boat's waterline length, the boat sits in the trough between its own bow and stern waves, and adding more power mostly builds a bigger wave rather than more speed. The hull speed formula, speed in knots equals 1.34 times the square root of waterline length in feet, describes this practical ceiling. A 25-foot waterline boat tops out near 6.7 knots regardless of whether it has a 20 or 200 horsepower engine.
The constant 1.34 comes from the physics of deep-water wave propagation, not an arbitrary rule of thumb: it is the speed at which a wave with a length equal to the boat's waterline naturally travels. This is why hull speed scales with the square root of length rather than length directly, and why a slightly longer waterline can matter more for top speed than a much larger engine.
Efficient Cruising Speed vs Hull Speed
Pushing a displacement hull toward its hull speed costs fuel at a steeply rising rate for a shrinking speed gain, since most of the extra power beyond a certain point goes into wave-making rather than forward motion. Most experienced cruisers run at 70 to 80 percent of theoretical hull speed as the practical sweet spot for fuel efficiency, only pushing closer to hull speed when time genuinely matters more than fuel burn.
| Waterline Length | Hull Speed | Efficient Cruise (70–80%) |
|---|---|---|
| 20 ft | 6.0 kn | 4.2–4.8 kn |
| 25 ft | 6.7 kn | 4.7–5.4 kn |
| 35 ft | 7.9 kn | 5.6–6.3 kn |
| 45 ft | 9.0 kn | 6.3–7.2 kn |
When Hull Speed Doesn't Apply
Planing hulls, the design used by most fast powerboats, work on a completely different physical principle: above a certain speed, they rise up and skim across the water surface rather than pushing through it, escaping the wave-trapping effect that limits displacement hulls entirely. The hull speed formula does not predict or limit a planing hull's top speed in any meaningful way. Semi-displacement and slender multihull designs also often exceed classic hull speed, though usually at a steep fuel cost, since they are only partially escaping the wave-making limitation rather than fully planing above it.
Accuracy and Limitations
The speed-from-distance mode is exact arithmetic for the values entered; its accuracy depends entirely on how precisely distance and time were measured, and it reflects average speed over that interval, not instantaneous speed at any single moment. The hull speed mode is a well-established approximation, not a guaranteed physical ceiling: actual achievable speed depends on hull shape, displacement, power available, sea state, and loading, and some efficient, slender hulls exceed the formula's prediction by a meaningful margin.
Neither mode accounts for current, wind, or sea state, all of which can meaningfully change a boat's speed over ground versus speed through water on a real passage. For distance-time calculations from GPS tracks, always confirm whether the recorded distance is over ground or through water before treating the result as a true boat-speed figure.