propulsors
Froya, one of three Norled
ferries that have been refitted with MJP waterjets
Waterjet refits highlight GRP benefits
The use of waterjets with GRP inlets has generated significant cost and M&R savings compared with the technology they replaced for two vessel operators
by Clive Woodbridge
TWO recent waterjet refit projects enabled Swedish company Marine Jet Power (MJP) Waterjets to provide a direct comparison with other brands, highlighting in particular the maintenance and fuel saving capabilities of its technology. In one case, the operator of a 10-year-old vessel decided to change to MJP’s DRB jets due to significant service and corrosion issues on its existing waterjets. The vessel was originally equipped with axial flow jets but
MJP replaced these, installing mixed-flow jets with intakes completely made of GRP. The rest of the equipment, including the engine, remained unchanged. According to MJP, using GRP for the intakes provides a smooth and efficient shape and eliminates any corrosion issues. The MJP DRB waterjets are otherwise completely made of stainless steel and have a high level of inherent strength, allowing the company to offer a five- year warranty, which it claims is unique in the marine market. Sea trials following the refit showed “stunning” results, said
MJP, with vessel speed increasing from 38 to 43 knots due to the to the change of waterjets. According to Hans Andersson, executive vice president for global sales and marketing, “the vessel with its original waterjets never achieved more than 38 knots, even when the ship was new. The overall efficiency has also increased from 57 per cent to 67 per cent meaning that the
52 I Passenger Ship Technology I 2nd Quarter 2013
vessel can obtain an 18 per cent lower fuel consumption. In addition the engines can operate at lower load, giving less wear and longer service life.”
The operator is said to be very satisfied with both the installation and functioning of the new system. As a result, more vessels in the company’s fleet are set to be refitted with MJP systems in future. In the second case, MJP was able to assist a Norwegian newbuilding yard, Oma Baatbygeri, which had three brand-new ferries that could not be delivered to their owner as performance levels fell short of specification. After a period of evaluation it was decided to switch the existing waterjets on one of the vessels to MJP DRB mixed flow jets, also with GRP intakes. “Interestingly enough,” Mr Anderson said, “when comparing the two jet systems on paper, they both claimed to deliver the same thrust. In reality, however, the MJP jets consumed 8.5 per cent less power at the same operating speed, according to measurements carried out under the supervision of DNV.” In addition, noise levels in the aft part of the passenger compartment were measured after the refit. This also demonstrated the advantages of the MJP technology, with a 50 per cent reduction compared with the existing waterjets. Based on successful sea trials with the first vessel, the
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