When vessels don’t perform, or an owner wishes to improve performance, one of the easiest ways to drastically change the vessel’s overall performance is by changing the propeller. But how do you do that without messing things up?
Though we are an engine manufacturer, we sell many engines complete with the customer’s desired propulsion as a package. In these instances, we usually ask our partners or the propulsion makers to make calculations.
Critical to performance is the proper calculations. Any major propeller maker can make calculations for their props. It is a balance between hull, engine, and propeller. For propellers, you can always contact our partner, France Helices, though any manufacturer that makes quality can design you a good prop.
In order to make calculations, a minimum of information is required: Vessel specs (LOA, LWL, Beam, Disp, etc.), Engine specs, and at minimum, a GA drawing of the hull since these have different efficiencies (or, items like foils or spray rails can alter performance).
There are several important factors that impact a propeller design:
2. Pitch (how the blades are “twisted”)
3. Skew (the degree of transverse offset of the blade from the hub)
4. Rake (The degree of angle of the blade from 90 degrees perpendicular to the center of the hub)
5. Camber (sometimes referred to as the “cup”)
6. Blade Thickness (Thicker blades result in less vibration, but can give greater cavitation).
If the propeller is not designed correctly, or is installed with incorrect parameters, then cavitation, which causes prop damage, engine strain, and gearbox strain among other things, is sure to result.
This is why you should always input bona-fide data into any calculations: Especially the correct displacement, which is the most common error made in calculations.
Should you not have a propeller manufacturer make calculations, there are several tools online: