For the average trawler or scalloper, putting a nozzle around the propeller has been standard operating procedure for decades. According to Jan Hass, propeller designer at Schaffran Propeller in Lübeck, Germany, it makes sense. “The nozzle itself, working with the propeller, will produce thrust at lower speeds,” says Hass. It provides an advantage in terms of bollard pull when you are towing something, for example.”
But Hass notes that a nozzle will certainly slow a vessel down at higher speeds. Schaffran Propeller’s skewed propellers offer a compromise in terms of fixed propellers. “You have to find the right propeller for your engine and gear and match that with what you are going to be doing. But you have to look at your primary purpose: Do you need speed or towing power?”
When New Bedford scallop fleet owner Dan Eilertsen opted for a Schaffran USA skewed propeller for his new boat, the Vigilance, he broke from the norm. It was the second boat he had fitted with a skewed propeller, and as with the first, he gained efficiency at higher speeds while retaining sufficient towing power.
“Yes, towing at low speeds, you could still have enough power,” says Hass. “The designer would have to make those calculations. The point of the skewed propeller is basically if you have something in front of the propeller, like the keel. The water behind the keel is moving slower.” As Hass describes it, they skew the propeller so that the outer edge and the rest of the propeller that is in faster water all grab the water at the same time as the smaller radius part behind the keel. “The more even inflow reduces vibration,” says Hass.
read more at nationalfisherman.com.
