PTL Holland America Line
In September 2000 we were awarded a contract to design a 12 m Power Tender and Lifeboat (PTL) for ships of the Holland America Line (HAL) being built by Fincantieri in Italy.
The contract to build some 30 of these PTL’s had been signed with Mulder & Rijke, a well-known builder of life boats, tenders and the like, in the Netherlands. Mulder & Rijke had themselves looked at the design of this PTL – and even carried out some simple model tests – but was unable to develop a design satisfying the stringent speed requirement of 12 knots, with 120 passengers on board. We were called in specifically to develop the concept and to carry out a large model test programme to evaluate the resistance, propulsion and manoeuvring properties of the design.
The design called for a maximum mass in the life boat “mode”, with 150 passengers on board, of 22.5 tonne. In that condition a speed of 6 knots was required. In the tender mode, with 120 passengers on board, a speed of 12 knots was required. In this condition the maximum displacement was to be 20.25 tonne. In addition, stringent requirements were set on the location of LCG. This LCG location and the set maximum values of the all-up mass were associated with what the davits on board of the HAL vessel could cope with.
After a study of possible alternatives we quickly found that only a catamaran-type of hull form could possibly satisfy the speed and displacement requirements within the length and beam restrictions set (11 m and 4.7 m respectively). A possible catamaran concept was designed and then modified to include a small V-type hull in-between the outer hulls to avoid slamming of the flat deck which was only a little above the waterline.
Meetings with all parties involved resulted in approval to embark on the model testing programme with this concept, after having also designed the propulsion system (two propellers in nozzles set in tunnels in each of the outer hulls) and an acceptable prediction of the required power.
The first series of model tests were carried out in January 2001. The results thereof were good. The additional resistance of the small middle hull, added to avoid slamming of the deck, was only small.
Wake field measurements, paint-smear tests, self-propulsion tests and manoeuvring tests were carried out in February and March 2001. The results thereof led to some small modifications to the design. Finally, a drop test was carried out with the model to measure the forces and accelerations experienced when the PTL is dropped into the water from a height of 3 m. It was decided to install Yanmar engines with a maximum power rating of 172 kW each.
The model tests were carried out by the Wolfson Unit in the Westlands tank on the Isle of Wight (resistance and propulsion) and in the BMT tank (now called Qinetiq) at Haslar (manoeuvring and drop test). The detail design work for the PTL was carried out by De Jager & Simhony in Schiedam.