Some Notes on Outboard Motors
Authors: Rainbow H. S. 
Published: June 2010

The mention of an outboard motor may conjure up for many people an image of a small, noisy, two-stroke engine driving a propeller attached to the end of a long shaft, a particularly noticeable feature being the rather primitive starting means. However, the modern, American style outboard motor, which may have a power rating of up to 100 hp, is a relatively complex, highly developed, means of propulsion. In its present form it is capable of giving a consistent and reliable performance under arduous conditions of operation and exposure.

The outboard motor has not been used so extensively in Europe and in other areas as in the U.S.A. In consequence, the complexity of the product and the problems associated with its manufacture and operation have not been so well understood. It may not be widely known, for example, that the outboard motor, like the refrigerator, motor car and many other products, cannot be produced as a technically and economically competitive article unless it is fully tooled for volume production, with a considerable home and overseas market to support it. It has to satisfy standards of size, shape, weight, finish and cost that make this essential. Against this background very high standards of performance and reliability are demanded which, in terms of specific size, weight and power, must be at least equal to the standards for light aircraft piston engines. To achieve these results a very considerable and sustained engineering effort on design, development and proving, on a world-wide operational basis, is necessary.

Outboard motors are expected to run for long periods under extremes of exposure and climatic and corrosive conditions. The mostly unforeseen and not obvious differences in the behaviour of components and accessories arising from this have led to a very common and widespread under-estimation of the complexity of the problems involved. Materials, components and equipment that will function satisfactorily under chainsaw, lawnmower, motor cycle and automotive conditions are prone to many problems when operated in the damp, humid and corrosive environment normally associated with the operation of an outboard motor.

In the U.S.A. the output of outboard motors represents an annual cash turnover in the region of 160 million dollars. In consequence the industry has been able to support the production of specialized accessories and equipment developed to function satisfactorily under the most adverse operating conditions. By contrast, it has been the tendency in Europe to follow and be influenced by automotive experience and practice, particularly in the choice of materials and design of accessories. Because the actual operating conditions differ so considerably this approach has hindered development and has not produced satisfactory and serviceable answers to many of the problems involved.

Experience has shown that to compete technically and commercially with the volume-produced, highly developed American counterpart the outboard motor must be a sophisticated machine, both in its component features and in its operation and must be produced in large volume by line production techniques.

The author's main object has been to outline some of the more interesting features and to record information on many of the less obvious problems experienced, against the background of the unusual, and sometimes conflicting, operational requirements.