Parallelism of the Side Runners

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Parallelism of the Side Runners

Igor & Georgi Bolchakov

Monotype-XV is an ice-yacht of very conservative construction. Small proportion between sailís leech and foot and some other technical restrictions eliminate the ability of further rapid growth of speed on racing courses. The lap time can be shortened mainly by tacking more windward when sailing upwind and leeward when sailing downwind.

Actually, the racing characteristic of an ice-yacht is the difference between sailís drawing and runners blades resistance (we donít take into consideration the aerodynamic resistance because itís practically the same among Monotypes). Letís leave the problem of sailís drawing improvements for sailmakers and discuss the ways of the runnerís sliding improvement.

Smooth sliding is possible just when there is a parallelism between the side runners blades. Every deviation from the parallelism transform the sliding into ice-shaving. Moreover, the parallelism has to remain in all racing circumstances; when the runner plank is bended by ballast and sail up to the ice in hard wind conditions and when itís almost free of uploading while wind is light, with the huge side forces while tacking upwind and free inertial sliding downwind. Even on the bumpy ice the runners must remain parallel.

Actually, this objective is unreachable. The problem itself of measuring the parallelism in real conditions is impossible without electronic equipment, which has not been used in ice-yacht racing yet. We have to imitate the expected forces on immovable ice-boat in order to meet any consequence in parallelism. Many years of experience in this item suggest some ways of solving the problem. So, the front edges of blades are likely to be set 1 - 1,5 mm wider than aft edges. It might help to compensate bending of the runner-plankís ends forward under the pressure of shrouds and side twist of the runner.

But on Monotype R-5 we used to set runners strictly parallel. For this we put the main and spare runner-planks together with chocks outside and tied them up with a rope in order to get an enforcement of nearly 120 - 130 kg ( see figure 1). This is compatible with a loading of 250 kg in the middle of the plank, i.e. approximately the same forces that appear when wind speed is 4 - 5 m/sec which consist of 60 % of the ice-yachtís weight, 60 per cent of the crew weight and 100 per cent of the ballast, i.e.

126 + 94 + 30 = 250 kg

We have left aside the wind forces. The most important here is inertial sliding.

With the help of two runner-planks one can comfortably measure the parallelism of all runner sets. Moreover, the planks now will be really changeable if on the one we adjust the parallelism with the runner plates, and the other one with a rotation of chocks. Measurements are made with the help of steel measuring line in two points fixed equally distant from the centre of the bolt (see figure 2). The blades must be not only parallel but perpendicular to the line of the measurement line as well. In a whole, to reach the parallelism one needs to have hardened "reliable" steel chocks. And the runnersí reinforcements must provide their inability to twist.

We used to make no measurements of the parallelism on a prepared Monotype, especially during the competitions. Even a small concern in this part of the ice-yacht tuning might eliminate psychologically the capacity to perform high sports results.

One can minimise the influence of the parallelism on speed of the ice-yacht by increasing the curve of blades or by smoothing the sharpness of the edges... but this is an item for the article about runners sharpening.

 

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This page was last updated on 08-dec-2016.