Boating

Propellers, trim, fuel, anchoring, trailering and hull numbers. 12 calculators for powerboats. The sail side lives under Sailing.

Prop slip is the diagnostic most owners never run, and it is the fastest way to tell whether a propeller is right for a boat. Slip is the gap between the theoretical distance a prop should travel per revolution and what the boat actually does. Typical planing hulls sit somewhere around 10 to 15%. Much higher and the prop is over-pitched, slipping rather than gripping, and the engine will not reach its rated RPM. Much lower often means under-pitched, with the engine over-revving and short of top end. Both cost fuel, and both feel like “the boat is a bit slow” rather than like a specific fault.

Anchor chain and rode works to scope including tidal range and bow roller height, not depth sounder reading. The usual guidance of 7:1 for rope and 4:1 for all chain assumes settled conditions, and the page shows what happens as wind builds.

Fuel range takes a reserve rather than quoting tank capacity as range. The old third-out, third-back, third-in-reserve rule exists because sea conditions on the way home are rarely the ones you had on the way out.