There are numerous propeller variables in displacement yacht design. Given the restrictions of draft, and the massive drag to be overcome with most ocean crossing yachts, props are forced into a predictable pattern.
However, the efficiency of the FPB, and the low cruise power needs, allow a variety of options.
In our case we are using a three bladed wheel with relatively small blade area. This allows high aspect ratio blades which are very efficient. However, with fewer blades you have a tendency toward vibration and prop noise. This is not a problem for the FPB (she is proving to be almost silent and there is no vibration) because of the following factors:
- Extra propeller tip clearance from the hull.
- 2.5″/62mm prop shaft (way oversized).
- Extra heavy hull plating (12mm.15/32″)
- Careful engineering of bearings and alignment.
- Low power requirements at cruise.