In issue 15 of this journal, published in 1924, the various compasses were described in detail according to their design, possible uses and their particular suitability as yacht compasses. The quest for ever greater refinement of technical aids means that instruments across a wide range of applications are subject to constant changes and, where possible, improvements; the specific requirements placed on individual instruments contribute significantly to this.
The shortcomings inherent in magnetic compasses – which, despite all the improvements and attempts to adapt them to the requirements of modern shipping, still persist and are rooted in the nature of magnetic force – led, a number of years ago, to the development of the electrically powered gyrocompass, which subsequently found its way onto larger merchant ships and has proved to be a reliable navigational aid. However, such a gyrocompass system is a very complex and costly piece of equipment and, for these and other reasons, is not suitable for smaller vessels.
However, in order to provide even smaller vessels, particularly yachts, with a more reliable navigational aid than has previously been possible, attempts have been made to adapt both the magneto-fluid compass and the magnetic compass in general to meet the latest requirements. Building on the experience gained with aircraft compasses, attempts have been made to make the compass’s magnetic system virtually oscillation-free – ‘aperiodic’ – in contrast to the earlier requirement for a long period of oscillation, i.e. to dampen the oscillations even more effectively than before.
Earlier fluid compasses were fitted with a heavy magnetic system possessing a high magnetic moment, which was mounted on a float that, due to the buoyancy provided by the liquid in the filling, was very light and thus prevented excessive friction between the tiller and the magnet. The damping of oscillations achieved in the compass filling with floats of this type was quite good compared with dry compasses; however, it still took between 50 and 70 seconds for the rose system to settle back to rest after a deviation, meaning that the compass could only be read accurately again after this time had elapsed.
Askania-Werke AG, a Bamberg-based company in Berlin-Friedenau, has now, following around half a year of extensive trials and testing in the construction of magnetic systems for fluid compasses, made a fundamental change and launched a new yacht compass which no longer exhibits the aforementioned shortcomings. In these innovative yacht compasses, the magnetic system consists of a series of lightweight yet very powerful short magnets, which are rigidly connected to one another and to the compass rose. The arrangement of the magnets achieves very high damping of the compass rose’s oscillations, so that, for example, the rose of the 115 mm compass comes to rest after just 14 seconds and two simple oscillations, whilst the same compass with the older magnetic system required 51 seconds and six simple oscillations to return to its resting position under the same conditions.
Another significant advantage of the new magnetic system lies in the considerable increase in magnetic moment relative to its weight; consequently, such a compass possesses a significantly greater directing moment than an earlier instrument of the same type and size. The resulting increase in magnetic moment, combined with the increased damping of oscillations, means that such an ‘aperiodic’ compass offers great resistance to all forces seeking to displace it from its resting position, without, however, being any less sensitive to changes in course. The compass of this new design therefore exhibits great ‘stability’ and is consequently particularly well-suited as a steering compass on yachts and smaller vessels, which operate under harsh and turbulent conditions at sea.
Figures 3 and 4 show the individual test results, both in numerical form and as graphs, for the fluid compasses with rose diameters of 85 and 115 mm; the same results are also given for the older models of these compasses. The graphs and figures clearly demonstrate the considerable superiority of the new magnetic system over the old one, so that further explanation on this point is probably unnecessary.
The new magnet system for the fluid compass with an 85 mm rose diameter is so lightweight that the use of a float has become entirely unnecessary. Externally, the compass has not undergone any changes compared with previous models, so the external dimensions etc. remain unchanged. The magnetic system for the 115-mm compass is connected to a small float in order to minimise friction between the tiller and the cap. This new system, too, is so lightweight that it weighs less than a quarter of the old one when suspended in the air.
Two standardised rose designs have been selected for these new yacht compasses, namely a plain line compass rose with ¼-line graduations and corresponding labels, and a ‘double-degree compass rose’, which features 2°-to-2° graduations with special markings and numbering on the tens-degree line. The latter compass rose is numbered continuously from 0 to 360. In addition to this degree scale on the outer rim, this compass rose also features an inner degree scale to facilitate any necessary rapid orientation.
The fitting of a two-degree rose is likely to allow for more precise steering than the older rose with ¼-degree graduations, particularly as the rose is now considerably more stable, enabling the individual graduations to be clearly distinguished even at a moderate distance from the compass. When taking bearings, the 2-degree scale is also considered entirely sufficient for reading the compass rose, as it is possible to estimate the reading to within 1 degree without any difficulty.
The new 115 mm compass is designed to have the compass rose illuminated electrically, by fitting the relevant equipment into the compass’s base weight. Lamps of 6 or 12 volts may be used, depending on the type of lighting system available on board. The light from this lamp passes through a window fitted in the spring base into the interior of the compass housing and illuminates the rose from below, so that no light reflections occur which might distract the helmsman’s eye. This type of lighting is particularly preferable for a bearing compass, as the cap or cover of the compass housing is removed when taking bearings, and the compass would therefore be unlit if the lighting were still fitted only within the cover.
The previous type of illumination has been retained for the 85-mm compass; this is not a cause for concern with this instrument, as compasses of this size are not manufactured as bearing compasses and are not used for that purpose.
As the purchase price of these new compasses is the same as that of the older models, it is to be expected that the various advantages of the new model will win it many admirers.