Skipasyn is working on a project named 6516TP. The project is a twin propulsion version of the original 6516 project for a 65m stern trawler.  One of the problems with the larger designs is achieveing high enough efficiency due to excessive loads on the propellers, because of the draft there is a limit to how big the propeller can be, so a pracitcal maximum size is somewhere between 5m and 6m for a 65m vessel. A 5m diameter propeller is not enough for a trawler with an engine of more than 4000kW. A 4000kW main engine driving a 5m propeller at optimal revolutions can hardly deliver more than 20kg of pull per kW, wheras a 2000kW engine turning the same propeller delivers 30kg of pull per kW, there is a clear efficiency penalty with the larger engine. To achive an 80-tonne bollard pull with a single 5m propeller, 4800kW is required. But with two propellers, 3800kW will produce the same towing power.  The design has two keels or skegs, one for each of the propulsion units, streamlined to route optimum water flow to each propeller. The real advantage of this approach is that this provides an increase in bollard pull of 3 0% for the same horsepower compared to the conventional single-screw.  The project was presented at the Icelandic Fisheries exhibiton in Smarinn 23.-25.sept 2011. |