Keels & Appendixes

by Nils Lucander, designer

Nils Lucander, based in Tacoma, Wash., has designed boats for more than 40 years. The views and claims presented in the following article are those of Mr. Lucander, and do not necessarily reflect the views of the Maritime Reporter & Engineering News staff, but are merely a vehicle to present a viewpoint and foster discussion.

During the latter part of World War II, John L. Hacker, the famous powerboat designer in Detroit, invented what he called the Fairline Strut (see Fig. 2) which looked like a fish's anal fin. Its function was to eliminate detrimental rotational turbulence caused by the propeller shaft, (see Fig. 3) This turbulence is approximately four times larger than the shaft diameter, and runs from where the shaft emerges to the propeller and beyond. Mr. Hacker's invention reduced this to just .5-in., and in the process, according to Navy tests, improved propeller efficiencies from 16 to 22 percent.

After the war, Mr. Hacker designed the Fairline Strut into his unlimited racing boatsMy Sweetie and Miss Pepsi, increasing the vessel's speeds while preventing skidding. Several of his powerboat designs were also fitted with these, most notably the 72-ft. (21.9-m) Mercury V, adding to its performance.

I worked with Mr. Hacker from 1952 to 1960, when he died at age 84. During the following years I designed derivations, Fairline Fins used to retrofit open shaft installations, followed by Log Knocker Fins extending below propeller depths, (see Fig. 1) In 1975 I received a request for the design of a 78-ft. (23.8-m) fishing trawler, a boat which was to have twin aft engines, short level shafts and full protection for propellers and rudders.

After considering several options, the center keel was eliminated and two husky ones were added, one on each side halfway out to the waterline from the centerline of the boat. In length, they ran from near midships to stern posts and were so large the engines fit partly into them.

The bottom of the keels and forward center hull were in line so the boat could be beached, hauled, stored and transported without need for cradles or supports, like an aircraft landing gear. It became known as the "3-Point" concept.

The first pleasure boat was a 52-ft. (15.8-m) trawler yacht in 1979. In 1994 the owner, a charter boat captain in Panama City, Fla., praised the smooth reduced roll even in heavy weather.

In 1981 I designed an 80.5-ft. (24.5-m) commercial tug for the Cheramie Brothers in Louisiana, built by St. Charles Steel Works Inc. and featured in several national publications after launching in 1982. A year later, St. Charles launched an 85.5-ft. tug, operated by N.J. Bourgeois, Jr. as part owner, part skipper. In 1985, it was caught by the 120-mph Hurricane Elena, and when asked afterwards what happened during the storm, he said: "I don't know, I was off over watch and slept through it all." Both the Cheramies and Bourgeois stated these "3-Point" tugs simply would not roll. In addition, due to the undisturbed flow of water to propellers, they were able to handle tow jobs equal to other tugs with up to 50 percent more power. At last report, the first tug was being operated by American Marine in Houston; the second by Foss Maritime in Port Angeles, Wash.

In the 1980s I designed several aluminum fishing boats fitted with skinny aft keels housing only the shaft logs and shafts.

To attain shallow draft, the keels were in part tucked in under the bottom and the new concept called "3-Point Gullwing" designs. Four of these are presently fishing in the Bering Sea and are noted for stability and performance.

Most open shaft installations have propeller slips ranging from 30 to 35 percent; up to 75 percent for poor installations. My fin and aft keel designs have ranged from 18 to 25 percent.

The Cummins service manager in Anchorage said: "So far, we are seeing on that Gullwing hull design that the engines are consuming 30 to 40 percent less fuel than what the engines are rated at. This is 10 engines in five boats. There is something about the hull design that allows those engines to get better fuel economy than what they're dyno tested at." In one of its newsletters, Cummins Engine Co.

claimed a 30 to 40 percent fuel savings by the 80.5-ft. tug fitted with a pair of its 980-hp engines.

Both the Cheramies and Bourgeois support this claim coming from users, not this writer.

Being conservative when it comes to performance claims, I question the high fuel savings, but even if just half, they are substantial, proven again for more than 35 years.

What has not been discussed is how diesel engines work. When a propeller blade enters turbulent water caused by rotating shafts or other obstructions, pressure on it is reduced without reaction by the en- If you order now, you will receive the 1 9 9 4 MARITIME DIRECTORY at a special rate of only $132. That's 20% off the cover price!

gine. Then, as the blade re-enters solid water, the blade load increases suddenly, sending a signal through the power train, demanding more fuel.

This will not happen when there exists none or so little turbulent COMPANY ADDRESS STATE COUNTRY SIGNATURE Make alt checks payable to Maritime Reporter and mail to:.

118 East 25th Street. New York, NY 10010 water that the blade load remains constant.

What must be emphasized is that any appendix or keel added under water must be properly shaped to fit hydrodynamic natural laws, not man-made assumptions, theories and beliefs.

Personally, I began my fuel saving work in the late 1950s when challenged to design a small 40-ft.

(12-m) tug yacht to run at one penny a mile and get triple design fee, or just half if I did not succeed. At the time, diesel fuel sold for five cents a gallon.

Fitted with one 30-hp engine, the Great Lakes yacht ran at 7.53 statute miles burning 1.5 gallons at a cost of 7.5 cents, which translated to .996 penny per mile. I received my triple fee and my designs have ever since been part of saving fuel.

After this, I began to work on reducing wave making since — in theory — it represents about 75 percent of overall resistance.

When a boat moves through the water, displacing it, the direction of least resistance is up to the surface, producing waves. I have called this the "Pump Effect." The long-since abandoned British Codfish Head - Mackerel Tail hull forms with blunt bows pumped the water up quickly to form the lifting transverse bow wave.

The taper towards the stern caused the midships trough and stern wave. While this hull shape has been discarded, many naval architectural theories, rules, numbers and formulas on hull speed — like the square root of the WL x 1.34 — are based on the performances of these abandoned and inefficient boats, retained in textbooks and technical papers.

Any hydraulic engineer can confirm that the faster water is pumped up, the more power is used, wasted.

To delay this "Pump Effect," I made bow sections finer, eliminating the transverse bow wave.

I then moved the largest sections of hull aft of midships and with the emergence of twin aft keels on full displacement boats, the upward motion of water was delayed even more, in most cases eliminating both the trough and stern wave up to socalled hull speed, sometimes even when running faster.

The 80.5-ft. tug shows a midships wave at 13 knots or 10 percent over formula speed.

A midships trough forces propellers to suck scarce water, adding to the trough depth, but a midships wave increases water availability and this is another reason why all the "3-Point" boats are so efficient.

It is also clear the addition of aft keels adds to course holding, reduces roll and chances of broaching.

All of this makes these boats excellent work platforms, liked by the crew which in turn increases their efficiency and, with big fuel savings, adds to overall profitability.

While more than two dozen "3- Point" boats were designed in the 1980s and before, more than a dozen have been done in the 1990s to date.

They include a 100-ft. (30-m) longliner for Tahiti and two smaller fishing vessels, five trawler yachts sizes 34 to 63 ft. (10 to 19 m), and, surprisingly, four husky cruising sailboats.

A purpose-designed 100-ft. (30- m) dive boat is currently under construction in British Columbia using old growth Douglas Fir, epoxy encased strip planking. Just begun is the design of a 78-ft. (24-m) "3-Point" trawler yacht, and the interest in these is growing.

Other stories from September 1994 issue


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