For reasons which were set forth at the commencement of the chapter on scientific oarsmanship, the very best oar may fail to see his own faults. For this reason, in dealing with the methods for detecting and curing faults, it seems more to the point to write as addressing the tutor rather than the pupil. The latter will improve faster under any adequate verbal instruction than by perusing pages of bookwork upon the science of oarsmanship. A coach may often know much more than he can himself perform; he may be with his own muscles but a mediocre exponent of his art, and yet be towards the top of the tree as regards knowledge and power of instruction. A coach, like his pupils, often becomes too 'mechanical'; he sees some salient fault in his crew, he sets himself to eradicate it, and meanwhile it is possible that he may overlook some other great fault which is gradually developing itself among one or more of the men. And yet if he were asked to coach some other crew for the day, in which crew this same fault existed, he would be almost certain to note it, and to set to work to cure it. For this reason, although it does not do to have too many mentors at work from day to day upon one crew, nevertheless the best of coaches may often gain a hint by taking some one else into his counsels for an hour or two, and by comparing notes. We have said that it is not absolutely necessary that a good coach should always be in his own person a finished oarsman; but if he is all the better, and for one very important reason. More than half the faults which oarsmen contract are to be traced in the first instance to some irregularity in the machinery with which they are working. That irregularity may be of two sorts, direct or indirect--direct when the boat, oar, rowlock, or stretcher is improperly constructed, so that an oarsman cannot work fairly and squarely; indirect when some other oarsman is perpetrating some fault which puts others out of gear. If a coach is a good oarsman on his own account (by 'good' we mean scientific rather than merely powerful), he can and should test and try or inspect the seat and oar of each man whom he coaches, especially if he finds a man painstaking and yet unable to cure some special fault. Boatbuilders are very careless in laying out work. A rowlock may be too high or too low; it may rake one way or other, and so spoil the plane of the oar in the water. An oar may be hog-backed (or sprung), or too long in loom, or too short; the straps of a stretcher may be fixed too high, so as to grip only the tip of a great-toe, and the place for the feet may not be straight to the seat, or a rowlock may be too narrow, and so may jam the oar when forward.