No. 64 - September 1985

A NEW RUDDER FOR THE TANZER 22

Rich Knowles

 

A LITTLE HISTORY

 

After a whole year of listening to a friend extolling the virtues of sailing a Tanzer 22, I finally broke down and bought one in early 1982. He was right. The boat is a fine seaworthy craft in virtually all conditions. The only idiosyncrasy that it seemed to exhibit was a tendency to round up in a fresh breeze. With some practice we eventually learned to control things and stay relatively dry. I also noted that the tiller seemed to take a lot more effort that many other boats to achieve the same effect on the boat's heading. These two items gave rise to much conversation with other Tanzer 22 owners. They all grinned at me and said, "That's the way it is, Rich, you'll learn to love it anyway!"

 

Several months later I was busy learning to love it in the first leg of a windy regatta, when an extra strong, unexpected gust defeated my plans to duck an opponent and, with the tiller pulled to windward and the rudder stalled, I nailed him amidships. As with most incidents of this type, a little more anticipation might have prevented the accident completely. However, after waking up in the middle of the night for the umpteenth time cramming an imaginary tiller into my stomach while my dream­world yacht sailed blithely on to its date with the gelcoat repair man, I came to the conclusion that the rudder had not perhaps done all it could to help me in my moment of need. From then on it came under somewhat closer scrutiny than it normally might have.

 

In May, 1983 I noticed that a number of cracks had developed in the rudder just above and parallel to the water­line. Some extensive grinding, glassing, filling, polishing and painting permitted me to sail through to the end of 1984 before I noticed that some more cracks were appearing above and below the repaired area.

The only satisfaction this gave me was knowing that the work I had previously done was now the strong part. More drastic action was needed before something really embarrassing happened. The mind reeled with thoughts of all the possible consequences of a broken rudder.

 

 

Perhaps this is a good time to note that SARRAQ (Inuktitut for 'sandpiper', for the ornithologically inclined) is a 1971 boat, hull number 48, and, as those who slave over her winches will attest, a true tribute to the skills of her makers. Three years and several hundred pounds of various marine cleaning, polishing and waxing compounds, each more highly touted and expensive than the last, have trans­formed her from the elderly, graying dowager I bought, into her former, youthful sleek self. The rotten rudder had to go.

 

WHAT TO DO?

 

The price quoted for a new factory produced rudder brought all my do-it-yourself instincts out of hiding (it doesn't take much), and I started to do some research. I noted that the Class rules state that the rudder either has to be made by Tanzer or in moulds approved by them. I also noted that the Class permits two rudders; the regular one and the quarter ton rudder.

 

The regular and quarter ton rudders are very different in both size and shape. For those who have not seen the quarter ton unit, take a peek over the stern of a Tanzer 26 and you'll get the idea. Kind of made me wonder if two rudders as different as these can co-exist, why might not yet another design be allowed in class competition? I knew that the quarter ton unit was supposed to be a bit of a bow-wow according to those who had tried it out and, quite naturally, its use would probably be tolerated in the same kindly way as would a three-foot midget in a pick-up game with the Harlem Globetrotters. No big threat. Perhaps some of the shortcomings of both the existing rudders might be corrected with a new design. If a new rudder design turned out to be an improvement, however, would it be viewed with the same benign tolerance as the quarter ton unit?

 

The challenge of designing and constructing a new rudder was so strong, however, that I decided to go ahead and worry about the politics later.

 

An analysis of the stock rudder yielded the following observations.

 

a) The scimitar shape places the center of effort unusually far abaft the pivot point (the pintles), making a somewhat high amount of force on the tiller necessary to turn the boat. Solution: A straight rudder would bring the center of effort forward and thus reduce the force required on the tiller.

 

b) The 1'll" depth is less than might be expected on a boat the size of the Tanzer 22. This will further decrease as the boat heels. Solution: A deeper rudder would extend the limits of control to some degree.

 

DESIGNING THE RUDDER

 

Since I only had some vague ideas about shape, size, and construction methods, some education was desperately needed. I started by taking a walk around the boat show in Montreal and examining all the rudders on the various boats. I also took a stroll through three feet of snow around the boats at my yacht club, Beaconsfield. I then examined all the literature I could find on hull and foil design.

 

It rapidly became obvious that the only common notions that designers of boats seemed to share were some basic ideas that tops should be shapely, bottoms should be roundish, fronts should be pointyish, and if it looks nice it must be fast. Sounds like this girl I used to know . . . Anyway, the more I looked, the more convinced I became that an improved rudder could be built, probably at a reasonable cost.

 

The following became the principal objectives.

a) The underwater shape of the rudder should emulate that being used on popular boats of modern design known to be successful in competition.

b) The construction method had to be within my capabilities and resources.

c) The new rudder should use the existing pintles and tiller and no modifications to the boat should be necessary when installing it.

d) The cost should be reasonable. Certainly it should not exceed the cost of a new stock rudder from the factory.

e) The rudder should exhibit improved performance characteristics over the existing design. i.e. The boat should require less effort to steer and the limits of control should be significantly extended.

 

The design and construction turned out to be less difficult than I had anticipated. The above-water portion was kept virtually identical to the stock rudder. This enabled the interchangeability objective (item "c" above) to be realized. Below the waterline was another story. As the photograph indicates, the leading and trailing edges are perpendicular and parallel. The depth was also increased some four inches. A foil section was adopted that approximated the proportions I found used on most of the latest designs. This decision was supported by a considerable amount of reading on airfoil design and standard foil shapes. A decision was also made to bring the leading edge of the foil as far forward as possible without fouling the boat when the rudder was lifted for removal. This placed the leading edge virtually in line with the pintles. I gave some thought to extending the leading edge even further forward, under the boat, to achieve

some degree of balance, but discarded this notion because; a) installation would be more difficult, b) weeds would be harder to remove, c) some degree of helm was felt to be desirable to retain the feel of the boat (balancing the rudder would remove this "feel") and, d) construction would be more complex.

 

BASIC DIMENSIONS

 

Having made all these preliminary decisions, it was relatively easy to draw up a set of dimensions as follows:

 

ABOVE WATER: Essentially the same as the stock rudder.

BELOW WATER:

Leading and trailing edges perpendicular and parallel.

Leading edge in line with the pint1es.

Depth: 28 inches below water line.

Chord length: 13 inches

Maximum thickness: 2 inches

Position of maximum thickness: 30% of chord length from leading edge

Radius of leading edge: 1/4 inch

Thickness of trailing edge: 3/16 inch

 

CONSTRUCTION

 

A 4 x 8 sheet of 5/8 in. plywood was sliced lengthwise into three 14 inch wide strips. These strips were then glued together to form an 8 ft. x 14 in. x 1-7/8 in. plywood slab. This slab was then cut, massaged, tortured and sanded into a reasonable facsimile of the dimensions noted above. Having won this battle, (at times it was wood: 10; Rich: no score), the whole thing was covered with several layers of fibreglass cloth and epoxy resin. An appropriate paint job then neatly hid all the visible flaws.

 

DID IT WORK?

 

In short, yes. The new unit was ready for the 1985 sailing season in mid-May, and, I must report that, from the beginning, the change in sailing characteristics was quite astonishing. The boat is now responsive to the slightest touch on the helm, the tiller is light and one can sail all day in any kind of weather without experiencing the fatigue that the stock rudder induces.

 

In heavy air, the limits of control are extended quite considerably, thus, I feel, making the boat safer and more predictable in unusual conditions. Finally, although difficult to quantify, the new design does not appear to have any significant effect on speed. It has been tried by a number of Tanzer 22 sailors. To this point the reaction has only been positive.

 

 

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