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SPEEDING UP THE MOTOR BOAT BY LAWRENCE LARUE HE question of speed in a horsepower were much larger and more motor boat is an intricate clumsy than the present-day engines de- one, as there are many veloping over twice that power, and factors to be considered; while, under the same conditions, a and these do not always greater bore and stroke will give an in- give the results that are creased power, it is the actual test of expected. A fleet of boats may be built, the motor on the blocks that really all of exactly the same size, constructed counts. from the same patterns and equipped But a more powerful motor is not an with the same make and size of motor, Aladdin's lamp that may merely be and yet there may be a consistent differ- rubbed with the starting crank to shoot ence of from ten to twenty per cent be- the boat off at a greatly increased speed. tween the speed of the fastest and slow- There are, in fact, certain limits beyond est. It is such results as these, consist- which a boat may not be driven, no ent by virtue of their inconsistency, that matter how great the power installed, puzzle not only the owner, but the de- and this applies to the motor canoe and signer and builder as well; and it is safe converted cat boat as well as to the es- to say that not a single one of the most pecially designed racer. The tendency expert of the latter can accurately deter- to "overpower" is one of the great faults mine what speed a motor boat will make of the average amateur and of many until she is actually launched and tried builders; every design has a certain out under the best of running conditions. speed beyond which any increase in num- If the expected results are not then ber of cylinders or size of motor is an obtained, it may require no small amount actual waste of power. of experimenting before the real diffi- An incident illustrating the futility of culty is found; when it is believed that crowding excess power into a hull that an increase in power will produce the de- is already being driven at the top speed sired speed, it may be discovered that this for which it was designed is found in the will not be nearly so effective as a simple case of one of the well-known racers of change in the pitch of the wheel. It is a few years ago. This particular craft small wonder, then, that both expert and was thirty feet long, and when equipped amateur will be found making frequent with a forty-eight horsepower motor, changes in the details of his boat in could maintain an average of twenty- search of that elusive extra mile-an-hour. four miles an hour—a speed considered The power plant will probably receive remarkable in those days. But her more than its share of praise or censure, owner was not satisfied and decided that according to the performance of the boat, if he could get twenty-four miles with and it is to this that the ordinary owner forty-eight horsepower, he would have will first direct his attention if any in- no trouble in making a world-renowned crease in speed is desired. The greater racer if a one hundred and fifty horse- the speed desired, the more powerful power motor was installed in her. must be the motor installed to drive the He made the change, but instead of boat. But it must be remembered that being able to travel over the water at the by power is meant the actual ability to rate of thirty-five miles an hour, as he do work, and not necessarily the size of expected, he found that his craft could the motor or bore and stroke of the make scarcely a mile an hour more than cylinders. The old-style motors of ten she could with her old motor, and that 751 752 THE OUTING MAGAZINE the greater part of the increased power The power plant of a boat can be only served to drive her into the water, increased or reduced to suit the desires instead of over it. When the motor was of the owner, but once the shape and opened to its full power, the hull almost size of the hull have been decided upon, submerged itself in its own wave, and it changes of this nature are not easily was found that the fastest running was made. Consequently, the "lines" of the obtained when only about one-third of boat become really of foremost impor- the available power of the engine was tance in a consideration of speed. The used. best designed hull for any practical pur- pose is that which is sufficiently large Vagaries of Power and heavy to carry the load intended for This, of course, was an extreme case it, is seaworthy, and yet one that will of ignorance on the part of owner and travel over the water and will make as builder (or re-builder, rather), but re- little wave and disturbance as possible. sults of this nature are liable to be ob- A boat which "pulls the whole river be- tained, to a less extent, when applied to hind her" is either overpowered and is smaller boats of low power and slow being forced through the water at an speed. "Let well enough alone" is a uneconomical speed, or she is poorly de- good maxim to follow, although this signed and her lines offer a greater re- does not mean that better results can- sistance than should be the case. not be obtained often by increasing the Although many boats are designed to power of a motor boat. Many hulls are "draw down" at the stern when under not equipped with an engine sufficiently way, this characteristic should not be large to obtain the speed for which the carried too far, as an undue drag is then craft was designed. formed by the after half of the hull. Even in this case it will require a The once popular canoe model of speed greater amount of additional power than boat gave way to the torpedo stern, and the owner will probably deem necessary, this, in turn, has been replaced by the for the resistance to the passage of a moderately wide hull with the "V-tran- boat through the water may be said, in som" stern, a design well adapted for general, to increase as the square of the almost any purpose, from a small, one- speed, and the power necessary to obtain man "runabout" to a racer or a large a greater speed has been found to vary cruiser. This model raises slightly at as the cube of that speed. This, per- the bow at the higher speeds, but the haps, is a sufficient reason why the under side of the stern is flattened so power in a certain hull may be doubled that the submerged portion is pushed with an attendant increase in speed of over the surface of the water, rather than but one or two miles. through it. On the other hand, even though the This is the principle applied to the increased power necessary seems out of hydroplane, except that the under side of all proportion to the results obtained, this model is shaped in a series of steps this is not necessarily all lost. Take, slanting from stern to bow so that, as for instance, the case of a heavy, thirty- the speed increases, these successive steps, foot pleasure boat, constructed more for or planes, will rise out of the water and service and comfort than for speed. A the hull will finally be riding on a single twelve horsepower motor may drive this surface that will glide, or slide, with craft at eight miles an hour, and yet much less attendant resistance than double this power would scarcely serve would be the case were the entire hull to shove the heavy boat through the forced through the water. Other vari- water a mile an hour faster. But while ations may be applied to the design of the this added power would not exhibit its hydroplane, but all are developed on the presence by a noticeable increase in the theory that a hull that skims over the speed of the boat, other craft could water meets with less resistance than be taken in tow with no apparent re- does one that must move aside a great duction in the original eight or nine-mile amount of water in order to push its way speed of the tug boat. through. SPEEDING UP THE MOTOR BOAT 753 Although some of the highest speeds shape of the after section does not pre- attained by a motor boat have been made vent this undesirable dragging and con- in a hydroplane, this is not yet adapted sequent reduction in speed. for an all-round pleasure, speed, or work This trouble can be easily remedied, boat as is the ordinary hull, and conse- however, by simply attaching a piece of quently such a design does not attract sheet iron to the stern at the waterline the interest of the average boatman. so that it will act as a plane when the There is no reason why the generally ac- after portion of the hull tends to drag cepted type of hull should not remain down. This piece of sheet iron should the standard for any motor boat, except be cut the same shape as the stern deck racing freaks, for years to come. so that no portion of it will project too If a hull does not seem capable of far beyond the hull and be damaged by attaining the speed expected of it, the a wharf or rock, and it should be well impulse of many a builder seems to be supported by struts riveted to the iron to "cut her in two and add five or six at one end and screwed into the plank- feet to her length." Although this will ing at the other. be a time-consuming operation, it will be effective to a certain extent, for the speed When the Stern Draws Down of a boat increases with its waterline length. On the other hand, the greater The value of such an attachment has the beam of a boat, the slower will be been demonstrated many times, but in its maximum speed. no instance of my personal knowledge The observation of these two rules more strikingly than in the case of an will result in the conclusion that a hull old twenty-five foot cat boat equipped that is "stubby and square" will never with a twelve horsepower motor. When succeed in landing a racing trophy if first installed, this motor seemed to be it is competing with a long, slim craft. too powerful for the craft, the stern But craft of "toothpick" proportions are dragged down, and eight miles an hour unstable and unseaworthy and can be of was the highest speed that could be ob- no possible interest to the man looking tained. A sheet iron plane was at- for a practical boat that will combine tached in the manner described above, utility and speed in the proper degree. and by forcing the hull to travel on the For pleasure craft of from twenty to lines for which it was designed, the speed, forty feet in length, a beam of from with the same power plant, was in- one-fifth to one-sixth this measurement creased to eleven miles an hour. is a good proportion which will admit Changing the location of the motor of both stability and medium speed. will sometimes have the effect of obtain- An increased speed may sometimes be ing a slight increase in the speed of a obtained from a motor boat by making boat, particularly if the stern is found changes other than those in size of engine to draw down too much. A speedy or design of hull, and these are the re- boat will never be found with the motor finements that help make the average located in the extreme stern, and the pleasure boat of to-day from two to five majority of racing boats have their miles faster than its sister of a few years power plant placed in a compartment ago. It has already been pointed out well forward. Consequently, by mov- that the bow of a boat should not rise ing a heavy motor from the stern to the from the water more than a certain bow, the position at which the boat amount when it is under way, and that travels will be changed on account of the V-shaped transom was designed to the shifted weight, and in many in- keep the proper length of the hull un- stances the speed will be noticeably in- der water. But the tendency of all creased. hulls when traveling at normal speed When an owner has made all changes or above is for the stern to settle an imaginable in his boat in the endeavor to undue amount, and in the case of old obtain more speed; when he has enlarged style boats with the fan-tail stern and the power plant; when he has refined the such craft as the converted cat boat the lines of the hull until it seems to run 754 THE OUTING MAGAZINE with scarcely a ripple; when he has There are four things to be considered, tuned up his engine; when he has then, in connection with a propeller, as smoothed and scraped the planking and follows: Size, or diameter of the wheel; given it its coat of friction-reducing shape of the blades; pitch; and number paint, there always remain the possible of blades. The first and third of these surprises to be found by putting on a considerations are regulated by the nor- new propeller. This is not a compli- mal speed at which the motor will oper- cated or difficult operation, and yet some- ate at its highest efficiency, always re- times it may be the most productive of membering that a wheel with too much results of any change imaginable. pitch will work against itself and absorb The propeller, of course, does the act- power from the motor without delivering ual work of driving the boat through the a corresponding increase in the speed of water and any fault in its design or un- the boat. suitability for that particular hull or motor will result in an absolute waste of power. It also acts as the regulator Getting the Right "Pitch" of the number of revolutions at which The problem of "too much pitch" will the motor will run when "opened wide," be better understood if it is remembered and as there is a certain normal speed at that "infinite pitch" would be repre- which any engine will operate at the sented by a wheel the blades of which highest efficiency, the size and pitch of were set at right angles to the plane of the propeller play an important part in revolution, or parallel to the axis. The obtaining the best results from the power revolution of such a wheel would absorb plant. power with no resultant motion in either The propeller blades are really the forward or reverse direction. Three- development of a screw, and the pitch bladed propellers are used on the major- would correspond to the coarseness of the ity of motor boats, so this is a problem threads. The pitch of a propeller, how- that need not give the owner much con- ever, is measured in inches, and is con- cern. sidered as the distance a point on the For motors under three horsepower, blade would travel in a line parallel to however, it is advisable to use a wheel the shaft during one complete revolution having but two blades, as any greater of the wheel. In other words, the pitch number would necessitate the construc- is the distance that the propeller itself tion of so small a propeller that efficient would travel during one revolution, in results could not be obtained without re- a line extending along its axis, if the ducing the pitch to a very small degree. movement were made in a medium in It is in the shape of the blades, then, which there is no "give," or slip. that the greatest latitude of selection will The greater the pitch of a propeller, be found, and here is ample opportunity then, the greater will be the resistance for the trial of all manner of wheels. offered to its turning; but, within certain Whether the blade should be long limits, if this increased resistance is over- and tapering, thin at the hub and thick come, the boat will be shoved a greater at the end, or of uniform width through- distance through the water at each revo- out the greater part of its length, is lution. Consequently, "easy" pitch and largely a matter of opinion; a certain high revolutions would produce the same shaped propeller that will give excellent result as "heavy" pitch and slower speed results with one boat would be utterly of rotation—always within certain unsuited to a craft of different propor- limits. The longer and wider the blade tions and character, even though the of a propeller, the greater will be the re- proper size of wheel should be selected. sistance to its revolution. The in- But, provided a well-designed wheel can creased blade surface, however, will be obtained, of approximately the proper exert a greater thrust upon the hull with pitch and of such a diameter that the each revolution, and consequently a motor will be held to its normal revolu- large wheel is "faster," for the same tions, the owner need not worry as to number of turns, than a small one. what results could be obtained with a SPEEDING UP THE MOTOR BOAT 755 different propeller, for, except in the case the trial should always be made in a of racing boats, it is not probable that comparatively large body of water, for any change would make a difference of the full efficiency cannot be obtained in more than five per cent in the speed of shallow or narrow streams on account of the craft. the drag of the following waves on the Every propeller should be so placed bottom or shores of the waterway. that its entire periphery will at all times Even the fastest racer would not be able revolve well below the surface of the to travel more than ten or twelve miles water. This is necessary in order that an hour through a narrow canal, and at the propeller may have a solid body of this speed it would "pull the whole river water against which to exert its push. behind it." Unless this distance is at least six inches, Owing to the greater buoyancy of in wheels of sixteen inches in diameter, salt water, the speed of a boat in this and over, a vigorous whirlpool, or eddy, medium is generally considered to be will be formed that will reduce the effi- greater than that on inland lakes and ciency of the blades as they revolve past rivers. This is true to a certain extent, this point of disturbance. but the difference is usually over-esti- Another reason for placing the pro- mated, for it has been found by tests peller rather well below the surface of that the respective speeds are as 5.66 is the water will be seen on a rough day to 5.5—an almost negligible proportion when, if the wheel is not properly lo- except in exceedingly fast racers. cated, it will be uncovered with every The foregoing discussion regarding wave and so reduce the resistance on the speed in motor boats is not intended to motor that the latter will be allowed to make any owner dissatisfied with the race at each forward lunge of the boat. present performance of his craft, for This tendency will be overcome if the that would be to sow the seeds of dis- wheel is placed several feet forward of content. But there are many boats in the extreme stern of the hull, but as high use that, with a little refinement or a speed or efficiency will not be obtained change in equipment, will travel faster in this position as would be the case were with the same expenditure of power, and the propeller located as far aft as pos- if these details are attended to, a more sible. efficient, as well as a more economical When a boat is tested out for speed, craft will be the result.
"Speeding up the Motor Boat"