How much power the boat needs: hull resistance, propellers, shafts and gearboxes, shallow water, and how predictions compare with sea trials.
What belongs here
- Resistance estimates: Holtrop, van Oortmerssen, Savitsky, Michell, Hollenbach, and when each one applies
- Model tests, CFD, and measured speed–power curves
- Propeller selection: diameter, pitch, blade count, B-series and Gawn
- The power chain from hull to motor: efficiencies, gearboxes, shaft losses
- Shallow and narrow waterways: speed loss, squat, the limiting speed
- Appendages, air drag, sea margin
- Sea-trial results. Sharing measured speed and power is one of the most useful things you can post.
What goes elsewhere
- Motors, inverters and batteries → Energy
- Motions in waves → Seakeeping & Motions
Know the limits of the estimates. The empirical methods give bare-hull, calm-water resistance from statistical fits. Each is valid only within its range, and the calculator flags when your hull falls outside it. In shallow water near the critical speed (depth Froude number around 1), nothing is estimated. Check important powering decisions against a model test, CFD, or trials on a similar boat.
When asking a question, include: length, beam, draft, displacement, hull type, speed range, water depth (if shallow), and which method you used.