Paul Waring continues to write about the Corisande refit project at Yachting Solutions— 1955 vintage Huckins meets modern Volvo Propulsion
Two packages were considered and we worked on them together, and parallel to each other, until we had enough data from each representative to base a sound decision. On the ZF side of the equation, our client was very interested in looking at a pair of Steyr Motors, 300 hp engines, each configured with 7 kw integrated flywheel generators. This is now one of Steyr’s breakthrough technologies that can offer new ideas in the designers’ approach to the arrangement and management of a given machinery installation. On the Volvo IPS side of the drill, we were quickly settled by our initial speed calculations to work up a performance analysis using an IPS 350 package. This is the lowest hp offering in Volvo’s range, a D4 motor of 260 hp.
At the outset, this project posed a few challenges and hurdles for these companies to examine. As the technology is still very new, the idea of getting these systems into new boats has been the focus and intent by each company. While first discussing the viability of the system working with this old Huckins, I was faced with some resistance, hesitation at the very least, and it took a bit of sweet talk and convincing to get people to engage this idea. For one thing, recognize that the refit opportunities are incredible. For another, this is a unique boat and a natural candidate for the system while considering its size, speed and usage purposes. I made this pitch and others to both Volvo and ZF, and over several conversations was able to convince them all that this was a good idea, an exciting idea and a high enough profile that they would not want to miss an opportunity like this. We began the performance prediction analysis process.
Both corporations have carefully developed software that works with 3d CAD models to calculate speed and trim predictions. The investment in time and production of this software is substantial and this is closely guarded with only a few people working directly with the programs. My duty from the outset was to build a 3 dimensional CAD replica of the yacht and then carefully determine the boats’ center of gravity. This was an effort that took a couple of weeks worth of design and analysis effort. To determine the weight and center of weight of the vessel, I first weighed the boat with commercial truck scales provided to us by the Maine State Police. These scales are designed to be easily placed under the tires of a tractor trailer rig and are accurate within 20 lbs for every 1000 lbs. One scale was placed under each end of the boat and a hydraulic trailer was used to lower and raise the boat on and off the scales. The readings were carefully measured and averaged, the scales were carefully measured to be referenced along the hull in a drawing and the center of gravity and total weigh was determined with this data. Long story short, I then went into a spread sheet and laid out calculations to back out original equipment and structure and then add in the new equipment and structure to determine the “new” center of gravity and weight. This information was then furnished to Volvo and ZF to be entered into their software along with the 3d model and many other crucial data points for the program to crunch the numbers and determine speed and trim results based on the vessels’ hp and weight.
The predictions were interesting and the results vary between each company. In the end, ZF was not able to stand behind the idea of using the Steyr diesels due to the particular torque characteristics in the lower end scale of rpm on the performance/ power curves for the motor. These pods require an engine that is better suited towards working with a jet drive, where torque numbers are very important at lower rpm and need to meet a certain performance threshold. So, ZF concluded that if the torque were to meet the standard, the system would drive the boat at 25 knots top speed and at a comfortable 4 degrees running trim angle, but they said there would be some gamble on the performance in maneuvering at low rpm and this would be experimental due to their doubts about the lower end torque numbers.
Volvo was more solid in their predictions and the engineer ended up running several scenarios to accommodate weight errors and varying tankage conditions. Interestingly enough, the boat is predicted to run at 28.9 knots in light to medium load condition running at 3-4 degrees trim. In heavy condition, they predict top speed of 27.5 knots. This represents around a 27-28% increase in speed with nearly the same horsepower as the more conventional shafted installation! Remarkable on both counts for ZF and Volvo. ZF loses out on this argument, not able to guarantee a solid package with Steyr, and their performance numbers just aren’t as pretty as Volvo’s.
To be continued……
(This is part two of a multi part series….Please stay tuned more to come about the progress of the refit.)
Where did you find the Volvo IPS models? I’ve been looking for those like crazy…