Posted by Steve Dashew (October 22, 2011)
Todd Rickard is just back from a quick trip to New Zealand to check on the engine room layout now that a get home system is being added to the FPB 64s. Those of you who have been aboard one of the FPB 64s knows the engine room is a work of art. Circa, our clients, and ourselves are concerned that the hit on engine room access and aesthetics be minimized with this extra diesel. As you can see from the lead photo the 100 HP Yanmar is very compact. In the context of an empty engine room it looks positively diminutive. The Yanmar goes where the Kabola boiler once stood, while the Kabola moves overhead. Access on the outboard (port) side of the little diesel isn’t overly generous, but is still better than the main engines on most yachts, and everything is accessible. The Yanmar will be soft mounted, and connected to a remotely mounted v-drive with a CV axle. The remote ZF gearbox gives us a flatter shaft angle for better efficiency while keeping the engine out of the way. The plywood box above the Yanmar represents where the Kabola heater will now reside. This set up looks like it will not materially impact the engine room. But there are some hits on propulsion efficiency, drag from the skeg and disturbed water flow to the main propeller being chief amongst them. We’ve previously discussed the full skeg which protects the get home prop. Here are a couple of shots of the finished shape. There are two types of drag with this skeg. The first is from the cross sectional area of the skeg. The forward section is fatter than ideal for drag so there is room for the transmission to drop down and improve shaft angle. Then there is wetted surface drag. Between form and wetted surface drag we are easily going to cost ourselves three to four percent in efficiency. The other issue is interference with the water flow to the main prop. The get home skeg is well outside the swept main prop area, so we are hopeful the negative here is on the order of a percent or less. There will also be an impact on maneuverability with the second skeg. The FPB 64s handle so well now, without their bow thrusters, that we can afford to give up a bit of close quarters handling. Bottom line, we are talking a three to five percent increase in fuel burn for the insurance of the get home system. Worth it? Only our clients can answer that.