Paul Waring writes about Corisande— 1955 vintage Huckins meets modern Volvo Propulsion
When our client first came at us with the need for our help on getting this project off the ground, we were working with him on a 44 ft planing power yacht design of very light weight and minimal accommodation. This is a high performance hull with very traditional flare blended with modern vision, and capable of 44+ knots with only 520 hp! A project that was getting all of us very excited to pursue.
Well, one day as he was making rounds about Rockport, ME, he stumbled into a 45 ft dream. In storage at the Yachting Solutions facility, was this 1955 Huckins classic, sitting idly and on the market for immediate sale to interested company. Our man was the guy; he simply couldn’t pass on such a honey. Corisande is an interesting boat, with a certain pedigree, and it is a yacht that has been well-maintained through the years.
The beautiful 1955 45 ft Loa Huckins-- Corisande
We heard the news shortly after, and we somberly shelved the new design project that occupied my desk to pursue our client’s interest and desire to employ pod drive technology in the repower specification for this craft. Pod drives offer a great deal of flexibility in performance and maneuvering, never mind the conceptual simplicity in the installation of the system. We can eliminate the standard shafts, bearings, struts, propellers in the drive train and, further, we can eliminate the separate steering system as all of this gear is now integrated within these tightly designed pod drive packages.
There are two major manufacturers producing pod drives for the pleasure boating industry, at the moment. First, Volvo offers five different configurations built up from their proprietary propulsion packages in horsepower starting with the 260 hp D4 and ranging up to the 435 hp D6. The range offered in hp is expected to increase in the very near future. Second, is ZF Inc., the well known leading reverse gear manufacturer. Pods have become a competitive sector of their business, as they have forged partnership with Mercury and their Zeus Pod Drive System. ZF now builds pods for use outside of the Zeus program, offering equipment suitable in two ranges—up to 450 hp and a larger version capable of working up to 1200 hp. The enticing part of ZF’s program is the fact that a client can consider a range of power options in hp and engine manufacturers. Where Volvo will only sell you their proprietary package of machinery—the pod technology that they have designed and proven coupled to their well known line-up of motors.
The Huckins had twin Cummins 2504BTA motors installed driving 1 ½” diameter Aquamet shafts that turn 21” x 21” propellers. As indicated by speed trials taken during survey, the yacht would not exceed 19.5 knots maximum speed under this configuration. Now, these are older engines and very likely tired, possibly delivering less hp than optimum. But any basic speed predicting calculations that I have done suggest that she was operating well within normal speed ranges due to the 500 hp of two Cummins engines thrusting her through the water. Now, considering the desire to update to new technology and benefit from what that notion has to offer, enter the pod drive. Because of the very nature of the design, the horizontal thrust lines, the forward facing counter-rotating dual propellers, we have a much more efficient system right out of the box. Actually, I should point out that one major difference between ZF and Volvo is that ZF has chosen not to face their props forward while they still employ the dual counter-rotating prop idea. So, when one compares these concepts to the conventional shafted system where thrust angles are in the area of a 15 to 20 degree angle measured from the yacht’s horizontal axis, mix that with shafts and struts in the way of a prop traveling thru clear water, we realize a reduced maximum effectiveness of the propeller delivering energy to the water.
Pod systems also offer great maneuvering both at speed and in tight quarters as they rotate on a vertical axis much like a rudder, in fact they replace the rudder via their ability to turn 360 degrees to vector thrust in any direction. When you start to think about the ability of the pods to work independently at low boat speeds, they will actually drive the boat directly sideways by a signal from a joystick, making docking simple for the most novice helmsman—just twitch the joystick in the direction you want to go, and there you head. This all comes at a price of course, wiring harnesses replace steering cables and black boxes replace complex pulleys and gears. The end sum of it all is a system that proposes great efficiencies in delivering power to the water and an ultimate boat handling experience………..to be cont’d….
(This is part one of a multi part series….Please stay tuned more to come on performance prediction and storyline about the progress of the refit.)