Tuning-Up and Driving the Racing Motor Boat [1933]
On more than one occasion I have heard expert skippers of sailing yachts remark that motor boat racing must be deadly dull because it left so little to the skill of the crew. When I try to explain that proper handling and proper tuning-up are fully as important in winning motor boat races as they are in sailing matches, my statements are not believed. Unless one has had some experience with a racing motor boat, the very fact that it is driven by a motor of a certain rated horsepower leads one to the belief that the boat must always have a certain speed regardless of other factors. But everyone who has designed, built or driven a racing boat knows that, from the smallest outboard to the Harmsworth monster, the crew — helmsman and mechanic — is more important in winning races than the boat.
Of course a slow, clumsy boat can never win races even with the best of crews — nor can it do so in sail. Whether in power or in sail, the crew must have something with which to work. But the best boat in the world cannot do much without a good crew. Boat and crew — the two are inseparable.
When the Skipper of YACHTING asked me to tell something about tuning-up and handling racing motor boats, I felt reluctant to do so because I have never driven a boat in any important race and it might seem presumptuous to try to tell about it. But I have had the opportunity of driving every type of speed boat except the Harmsworth class — testing out the boats before they were turned over to the owners — and though my point of view is primarily that of the designer, perhaps some drivers may find a few hints in this article.
When the boat is put into the water the first runs should be more for the purpose of finding out how she handles and how she acts in the wash of other boats than for tests of speed over the mile. Every boat is as individual and has as much personality as a woman. Find out how the boat acts when in a little chop or when crossing a wake, and drive her enough to become familiar with her idiosyncrasies. Drive her enough to ascertain that everything is working properly, that the oil cooler has the proper amount of water going through it, that the pumps are giving the correct amount of water through the jackets, that all the controls — especially the foot throttle — are working freely and without too much lost motion, that the oil pressure is correct and holds up after the motor and the oil are warmed. See that the stuffing box does not overheat; if it does, slack away on it until it runs freely. While you are checking up on the thousand and one little items, such as those mentioned, you will become accustomed to the boat, to the manner in which she responds to throttle, and how she acts in different water conditions. If you are really tuning-up in scientific fashion you should keep a record of the actual weight of the boat, including gas, oil and crew on every run, and should notice how she acts under various conditions of loading.
These preliminary runs may require only a single afternoon or a couple of weeks, depending on how much alteration must be made in order to get the boat working properly and whether or not it is necessary to make changes in the bottom and in the location of weights in order to cure "porpoising," or jumping. When they are finished the serious testing and tuning-up may be started. Before going into detail regarding testing it may be of interest to note how to stop "porpoising." There are many theories about this peculiar action. Throwing them all into the discard, and working only from experience, "porpoising" can be reduced by moving the weights farther forward or by decreasing the angle of the forward planing surface and increasing the angle of the after one. Any one of these remedies, or any combination of them, can be tried out until the desired result is obtained. If a boat goes out of shape she usually sags in the center, thus decreasing the angle of the after plane and increasing it on the forward plane. Nine times out of ten the result is severe jumping from one plane to the other. Such action is hard on the crew and on the heart action of the spectators.
Some experienced drivers hold to the theory that a boat which is "porpoising" is faster than one which runs steadily. They are undoubtedly correct — within limits. It is entirely possible for a boat to be held down on the water by suction on the forward plane and run as steadily as if she were on rails. But such a boat is never fast for her power although she may be easy to handle. Experience has shown that a boat is in her fastest trim when she is just on the point of "porpoising" in smooth water. She is then free and clear of suction and reaches her most efficient lifting point.
After the boat is running decently, and all the major defects have been eliminated, then the real tuning-up can be started. In order to do this intelligently only a few items of equipment are needed, but these must be absolutely accurate. First and foremost is an accurate tachometer. The ordinary stock tachometer may be a couple of hundred revolutions out of the way, just as the speedometer on a motor car is often ten miles off in seventy. Check the tachometer against a standard calibrated one, unless it is already calibrated — as it should be --- when you receive it. A check can be made against the tachometer by using a stop watch and a revolution counter, but this is sometimes difficult as it takes considerable skill and experience to handle the revolution counter and watch and get accurate results, and it is hard to find a convenient rotating part on many motors on which to apply the counter. At any rate, do not consider the revolutions of the tachometer accurate unless the instrument has been checked in some fashion. Failure to observe this caution may lead to an entirely erroneous interpretation of tuning-up results as far as propeller slip is concerned.
The second requisite is an accurate course over which to run trials. A statute mile is 5280 feet long — no more and no less. It is hardly sufficient to say that "it is a mile from the 49th Street bridge to the corner of Kelly's dock." Perhaps it is — but more often it isn't. The course should be accurately surveyed and correctly marked with front and back markers. There are a number of accurately laid out courses in the New York district, but they are most unpopular with those who test boats. The course should be in protected water in order to avoid delays caused by rough water. Tide and currents should preferably be directly in the line of the course and not across it.
If the crew is honest with the boat and with themselves, there is no objection to using a course much shorter than a mile provided the actual length of the course is taken when calculating the speed. And a shorter course does expedite the process of tuning-up because it does not take as long to make the runs, and there is less chance of spoiling a run due to some other boat coming on the course and blocking it. A convenient length for testing is 1466⅔ feet; this is long enough to get fairly good comparative results and the speed of the boat can be figured quickly by dividing 1000 by the time over this course in seconds. For example, if it takes 20 seconds to travel the 1466⅔ feet, the speed — found by dividing 1000 by 20 — is 50 miles an hour. But the timing must be accurate when using such a short course and any records over it are of no value except for tuning-up.
The third implement needed in tuning up is a good stop watch. No matter what the tachometer says, the final answer lies with the watch. To check the stop watch is simple and easy. All that is required is to start it against a good clock and check it for half an hour. If this check shows a discrepancy of less than a second for that duration of test the watch is well within the accuracy demanded.
And there is a fourth item which is only too often entirely neglected. That is a note book in which to set down the result of every trial and every test, with your remarks and conclusions. Unless these are noted at the time there is bound to be confusion a little later and the discussion as to when a certain thing happened and under what conditions it occurred will be endless. One of the most interesting things of this sort I have ever seen is the note book of the mechanic on a Gold Cup boat — the Greenwich Folly, which twice won the cup. There, in detail, were set down the results of all the experiments which were made while tuning-up that boat to winning form.
Before going into detail, a word of warning which deserves a paragraph all by itself. When making changes, change but one thing at a time and find out what the effect of that change is before changing another thing in any manner whatsoever. If more than one change is made before trying out the effect of the first one, then the results are apt to be misunderstood and no end of argument will follow. Never change carburetor adjustments when trying to compare wheels. Try to have the same amount of gas and oil aboard when comparing speeds. In other words, always eliminate all variable factors except the one which you are investigating.
Time trials over the course can then be started in earnest. Naturally, times have been taken during the preliminary runs, but at this stage in the process of tuning-up the tests are being made for the purpose of trying out different wheels, fins and perhaps different rudder arrangements. All trials should be made in pairs, taking the two runs in opposite directions, figuring the speeds of each run, and then averaging the speeds to get the true speed. Do not average the time and then calculate the speed — that is incorrect. The error will not be large when dealing with a 60-mile-an-hour boat, but if the boat is a slow cruiser the error may be a large one when the speed is figured from the average of the times.
The slip of the propeller should then be calculated from the speed, the revolutions, and the pitch of the propeller. For the method of figuring the slip, refer to some of the articles which have been published in YACHTING on propellers, as space is too limited to go into this here. If the slip is excessive for the type of boat, try a wheel somewhat larger in diameter and of a little less pitch. And do not be afraid to try another one marked by the manufacturer as having the same diameter and pitch, for experience shows that propellers which are almost identical do have a different action at very high speeds. Sometimes a gain of more than two miles an hour can be obtained simply by using another propeller of the same make, the same diameter and pitch — all due to minor differences in the shape of the cross sections of the blade.
The time trials can be carried on indefinitely. Investigations of the proper temperature of the oil and the cooling water in order to get the most out of the motor are important. Tests for the size of the carburetor jets, the spark advance, and the action of different types of plugs are all matters which should be investigated and the results carefully noted. But eventually a point will be reached where no gains in speed can be obtained.
Again, another word of warning. Of late years there has arisen a group which worships the tachometer. They prefer to see an extra hundred "revs on the tach" than to cut a second off the time over the mile. In the final analysis it is the stop watch which is the court of last resort and the tachometer readings are only incidental. Speed over the course is what you must get regardless of what the tachometer reads.
With an experienced driver at the wheel, the boat has been tried out on turns long before now. But the testing of the boat on the turns of the course should be undertaken in earnest. Boats differ greatly in their turning ability. And with different boats the best method of getting around the turns must be suited to the boat rather than any hard and fixed rule followed. But, in general, if a very short turn is to be made — a hair-pin turn — it is usually best to drive full speed right up to the point of the turn, take the foot off the throttle, swing the boat sharply into the turn and, as she swings, feed her gas just as fast as she will take it. After a few trials even a green driver can get the feel of this and can get around in good shape.
When the turns are easier — such as the turn on the Detroit Gold Cup course near the Belle Isle bridge — the throttle can be held wide open all the way around without any trouble. But if this is attempted on a hair-pin turn, the boat is sure to hop sideways and give the crew a ride. As the driver gains experience with his boat the speeds can be raised to the point where these side hops are in evidence, but not dangerous. Almost every boat does it more or less, so she should not be condemned for it.
Some of the motor builders do not seem to appreciate the magnitude of centrifugal force when the boat is on a turn. Unless the carburetors are so designed and placed on the motor that gas will feed when on a turn, centrifugal force will throw the gas away from the nozzles and the motor may back-fire, or refuse to pick up on the turn. Cases have occurred in which the boat has actually stopped. The float bowl should be so set that centrifugal force does not change the level of the fuel at the nozzles. Races are won or lost in the pick-up on the turns.
Practice in timing the start must be carried on with every boat after she is put in racing trim. Here, just as in the working out of the boat over the straight measured course, the stop watch is all-important. The driver selects some known point on the actual course over which he is to race and finds exactly how many seconds it will take to hit the line after he has gained full speed. By all means, try to go over the line at full speed as closely after the gun as possible. More races are won or lost right on the line than anywhere else on the course. Provided boats are of about the same speed, the boat first over the line will surely win unless it breaks down or drops in speed. A competent driver should be able to hit the starting line within two seconds of the starting gun and, if expert, he can cut this to a fraction of a second. Check the stop watch with the chronometer used by the committee and rely on your own time instead of following some competitor.
During the races the mechanic, in addition to his other duties, should watch the other boats and should signal their position to the driver by means of some prearranged code. The driver should not take his eyes off the course ahead of him during the race. A small piece of driftwood, which might easily be avoided if he is alert and watching where he is heading, can easily lose a race for which months of preparation have been made. If other boats are ahead, a capsize might be a fatal mishap if he is not looking ahead every instant.
In case two boats are ahead and are almost side by side, avoid steering a course between them. Select one or the other and follow in that wake. There is no place where the danger is as great as in the space between two leading boats where the wakes meet and form a ridge of water. That ridge is the cause of most of the upsets during a race. If the two leading boats are doing tricks and are working in league with each other, they can increase or lessen the distance between them and, as that distance, changes, the spot where the two wakes meet rushes ahead at terrific speed as the distance between the boats decreases, and drops back as they draw farther apart. These changes are so rapid that no helmsman, be he ever so skilful, can retain control of his boat if he tries to ride the ridge between the wakes of the two boats ahead of him. Pick out one boat and stay in her wake until there is a chance to break through somehow.
Another caution — this article seems to be full of cautions which are so evident that mentioning them is almost needless. Do not run the boat to death before the race. Even in the outboard class, as well as in the larger classes, you may see a driver who goes out and runs what is practically the whole race before the start and then breaks down after covering half the actual race. When the boat is running as she should, save her in every way possible. Racing motors have a limited life, and unnecessary practice at full speed may decrease this life so that the break-up comes before the actual race is finished.
(Reprinted from Yachting, August 1933)