Mailport April 15, 1999 Issue

Mailport 04/15/99

Hydraulic Propulsion
To Charles Kanter, whose letter (August 1, 1998) condemning hydraulic drives as a viable propulsion system came to my attention: Your lack of expertise in this subject was obvious by your groundless, irrational attack.

One of your experiences was dated “Circa 1970.” Hydraulics, like almost everything else, have undergone a bit of refinement in the past 30 years. I shall address your points:

Hydraulic motors and components are available in aluminum for aircraft use and hoses and fittings can be stainless steel (non-magnetic).

Hydraulic motors need not be heavy. In a twin cat installation, a single spare motor would serve either port or starboard. A reversible motor would not require any control other than a Morse or Teleflex cable.

I agree this is a potentially noisy system, but by going to higher volume and lower pressure components, this could be minimized. Also the drive motors are aft; the power unit could be placed centrally for weight advantage and could provide a power source for a refrigeration compressor. Like everything else, there have been great improvements in sound insulation.

Not having inspected the systems with which you had problems, I cannot evaluate them, but very high grade components are available. Just because you haven’t seen a quality system doesn’t mean one doesn’t exist.

There is a power loss as there is with any transference of one form of energy to another, but I strongly consider your estimate of 20% loss in the power train to be on the high side. One of the pluses for hydraulics is the virtually unlimited cooling that is available for the fluids through heat exchangers.

Yes, you still have the underwater gear, but the components can be matched to minimize electrolysis and the replacement cost of these standard items is minimal.

Now to your perfect alternative, saildrive. These have also greatly improved since the early Baldwin, OMC-powered units. The alloys are much better, but you still have aluminum, sometimes in the highly corrosive Tropics. You also have a large housing directly in front of the rudders, very likely to cause cavitation above 10-12 knots. Pick up a bit of loose, floating monofilament in the prop and you cut the seal out.

I have no doubt you had a problem with a hydraulic system, but you neglected to mention if the system had ever been checked periodically. Before you left, did you, with your surveyor’s experience, check it over for chafe or wear spots? Was it possibly installed so that the anchor chain rubbed the hose when it was used? Could a valve have been installed for use only when the anchor winch was used?

I am presently converting a 40' Prout to inboard power and hydraulics are a very viable consideration. A pair of saildrives will cost more than $20,000; a 4-108 and all components is well under half that. Installation cost appears to be likewise much lower. Every propulsion system has its advantages and flaws. I strongly suggest you pass basic engineering 101 before your next pontification.

Irwin Victor
East River Boat Yard
North, Virginia

Prop Size
The question you received and replied to in the November 15 issue concerning the proper propeller for a Cal 34 with an Atomic 4 engine was of particular interest since we manufacture a propeller specifically for that engine. You made reference to Dave Gerr’s book, which is excellent and as complete as any, but unfortunately, is a little beyond most sailors’ ability to comprehend. You also point out the importance of experience. In the case of the direct drive Atomic 4, experience is probably the most important ingredient in specifying a prop.

The correct size prop varies with horsepower and inversely with shaft rpm. The more power, the bigger the prop. The higher the shaft rpm, the smaller the prop. Like all engines, the Atomic 4 reaches its maximum horsepower at maximum rpm. Because there is no reduction gear (as there normally is with diesels) the engine rpm and the shaft rpm are the same. Unfortunately, because the motor is pushing an auxiliary sailboat rather than a planing hull, the prop would have to be pretty small, perhaps 8" or 9" in diameter, to get even close to the 3,500 rpm maximum of the Atomic 4. But, a prop that small can only convert about 3 or 4 horsepower of rotational energy into thrust.

As a result, you need to compromise between horsepower available and the ability of the prop to convert that horsepower into push or pull. Experience, and a lot of testing, suggests a 12" prop to be the best compromise (unless the prop is mounted behind a thick deadwood, in which case a 13" does better). This does not vary much on boats between 25 and 35 feet. With a 12" prop, the engine can reach somewhere between 1,700 and 2,000 rpm, which converts to about 14 horsepower. The 12" prop can convert just about all that horsepower into thrust before cavitation begins.

A 6" pitch also tests out to be the best for forward thrust in most applications. However, the Atomic 4 direct drive has a 1.3:1 reduction gear in reverse, that further complicates prop selection. Because the prop moves slower for a given engine rpm, you need either more diameter or more pitch in reverse. Again, you have to compromise, this time between forward and reverse performance.

The consensus prop is a 12" x 7", which is what we are offering. By improving the blade shape in profile and cross section, the CDI prop is more efficient. Normal props on sailboats operate at about 50% efficiency so you can see there is a lot of room for improvement.

Charles E. Angle
Beverly, Massachusetts

Mr. Highfield
I thoroughly enjoyed your article on Highfield levers, but I was a little surprised that you had so much trouble tracing their origins. In his 1930 book, Sailing, Seamanship and Yacht Construction, Uffa Fox writes, “The Rear-Commodore of the Royal Thames (Yacht Club) has invented many useful things for sailing vessels…but the backstay lever, which J. S. Highfield has thought out and tried with great success on board his 15-meter Dorina is simple and effective...”

In his book, Racing, Cruising and Design, Uffa wrote, “Four years ago, in my first book, Highfield’s runner lever was one of the gadgets described. Since then it has been adapted to forestays as well as runners and backstays…” He goes on to describe some later modifications and adaptations of Highfield’s lever by Rod Stephens, Russel Harmer and John Illingworth.

How large was Dorina, the original test bed for Highfield’s running backstay levers? My library has no reference for her, but the old 15-meters were roughly equivalent in size to the later M-class yachts, which measured some 80-90 feet overall, 52-58 feet on the waterline, and carried about 2,800 sq. ft. of sail. The size of the M-class yachts fell roughly between the larger J-class, which contested for the America’s Cup in the 1930’s, and the later 12-Meter class contestants.

Chris Chadbourne
Arlington, Virginia

Thanks to the many readers who supplied us with similar information regarding Mr. J.S. Highfield. Many referred us to the Oxford Companion to Ships and the Sea, edited by Peter Kemp, the Overlook Illustrated Dictionary of Nautical Terms by Graham Blackburn, Rigs and Rigging of Yachts by D. Phillips-Birt, published by Adlard Coles Ltd.We’re feeling a little stupid for not having searched harder, owning as we do the Oxford book.

Where Credit Is Due...
To Harken: “Recently, I called the Harken Customer Service to replace a badly bent shackle swivel bracket on my traveler car. They indicated they no longer made this size swivel bracket or the 10-year-old car that it was fitted to, but if I would send the traveler car and the two brackets back to them they would see if they could ‘custom fit a shackle bracket.’ This sounded like it could get a little expensive but I sent off the parts. A couple of weeks later I received a package from Harken that contained a new, larger traveler car with two new swivel brackets. The packing slip said ‘warrantee replacement—no charge.’ When I looked up the catalogue value of this hardware it was well over $200. The next time I have a hardware choice to make, guess which company has a significant edge?”

Bruce Lawton
Richmond, Virginia

To Westerbeke: “Last summer I called them to help me solve an irritating tendency of their 27-hp. diesel engine to stall out. The woman who answered the phone said, ‘Everyone’s out to lunch, but let me try one number.’ The man who answered listened to me describe that I’d already tried changing the fuel filters, cleaning the fuel tank and polishing the fuel. Then he suggested that I might need a new fuel pump. I said, ‘Would you be able to give me a discount price even though the engine had been installed four years earlier by a previous owner?’ He sent me a new fuel pump by overnight delivery—free of charge. I found out later from my mechanic, who deals with Westerbeke, that I’d talked with the president of the company!”

Gene Lepley
Midlothian, Virginia

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