Subsea calculator
ROV thruster sizing calculator
Estimate how much thrust a vehicle needs to hold a given speed, and how many thrusters that takes once vectoring angle and a working margin are accounted for.
Estimation tool, not design authority. This calculator gives a first-pass figure from the stated method and the assumptions listed below the result. It does not replace engineering sign-off, and it does not model everything a real build has to account for — see “Assumptions and limits” for what is left out. For a figure you can build against, send us the requirement.
Result
Why it matters
Drag rises with the square of speed.
Thruster count drives frame geometry, battery size, wiring and the buoyancy budget, so it is one of the first decisions on a build and one of the most expensive to revisit. Getting a rough figure early is worth more than getting an exact one late.
The square law is the thing most first builds get wrong. Doubling target speed does not need twice the thrust — it needs roughly four times. A vehicle specified for 1 knot and later asked to work at 2 knots in current is not slightly under-powered; it is short by a factor of four.
How it is calculated
Bluff-body drag and vectoring.
Hydrodynamic drag on a bluff body is F = ½ × ρ × Cd × A × v². Holding a steady speed in still water needs thrust equal to that drag. The margin covers what the equation does not: current, tether drag, marine growth and the fact that a real vehicle is rarely pointed exactly where it is going.
Thrusters mounted at an angle contribute only their forward component, so a 4 kgf unit at 45° gives 2.83 kgf of forward push. That is not waste — a vectored layout buys sway and yaw authority, which matters far more in survey work than top speed — but it has to be in the sum.
This covers horizontal thrust only. Vertical thrusters for heave and depth-holding are additional, and are usually sized against the vehicle's out-of-trim buoyancy rather than against drag.
Related
Other calculators and guides.
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