The new HS4 4-blade propeller was launched in early 2017 and is designed for Yamaha outboard engines over 200 hp. With the addition of Yamaha’s Shift Dampener System, it is much quieter and offers smoother operation at low rpm.
The HS4 propeller has a diameter of 15 inches and is available in 21", 22" and 23" pitches in both right- and left-hand rotation.
Our Saltwater Series II 3-blade test propeller is also equipped with SDS, has a diameter of 15 ¼" and is available in 18" and 19" pitches.
Having the 4-blade HS4 15" x 21" and the 3-blade SS II 15 ¼" x 19" we wanted to try them on the Yamaha F 300hp which was mounted on AirHull 25 Cabin.
Observing the above table we see that the HS4:
- got the rib on plane at the same rpm despite its longer pitch and its smaller diameter
- offered longer time to plane due to its longer pitch
- was faster at the whole rpm range, but achieved slightly lower top speed
- offered the same fuel economy at 3500 rpm, while over 4000 rpm we recorded quiet more fuel consumptions than SS II
- didn’t show low slip values due to its longer pitch
- gave 400 rpm less at WOT.
Comparing the behaviour of the two props, HS4:
- provided impressive stern lift, raising the AirHull’s stern higher, due to its larger blade area
- offered particularly smoother ride while we had the ability to run closer to the water surface
- improved handling and had added grip and greater stability at high trim angles and sharp turns.
We can definitely say that HS4 15" x 21" is unsuitable for the particular set-up and the specific loads because it is far from the maximum engine rpm limit of 6000 rpm.
Unfortunately, HS4 is currently not available in shorter pitches. It is certain that an HS4 15" x 19" would fit perfectly with the specific boat-engine-load combination and would offer shorter time to plane, keep the rib on plane at even lower rpm and provide outstanding acceleration.
We can also conclude that, taking into account the extra blade and the slightly smaller diameter of HS4, when switching from a Saltwater Series II 3-blade propeller with dimensions 15 ¼" x 19" to a HS4 4-blade propeller 15" x 19" - when it will be available - then we should expect a reduction by about 100 to 150 engine’s rpm.