II. THEIR USE.
In order to understand the true action in a slide, it will be well to recall the action of fixed-seat rowing. On the fixed seat the swing of the body does the main work, being supported by the legs, which are rigid and bent.
On a slide the legs extend gradually, while at the same time they support the body. On a fixed seat the body moves as the radius of a circle that is stationary; on a slide the body moves as the radius of a circle which is itself in motion. Suppose a threepenny-piece and a half-crown placed alongside of each other, concentrically, with a common pivot. Let the threepenny-piece roll for a certain distance on the edge of a card. Then any point in the circumference of the half-crown will move through a curve called a ‘trochoid.’ This is practically the sort of curve described by the head or shoulders of an oarsman who rows upon a sliding seat.
The actual gain of rowing power by means of this mechanism is considerable. The exact extent of it is not easy to arrive at, there being various factors to be taken into consideration.
In the first place, the length of reach, or of the ‘stroke,’ is considerably increased. Mr. Brickwood in 1873 conducted some scientific experiments on dry land upon this subject, in conjunction with the editor of the ‘Field’ and Mr. F. Gulston. The result of these measurements was to demonstrate (in the person of Mr. F. Gulston) a gain of about 18 inches in length of stroke upon a 9-inch slide.
In 1881 some casual experiments of a similar sort were conducted on a lawn at Marlow by the Oxford crew then training there. The writer was present, and, so far as he remembers, the results practically confirmed the estimate of Mr. Brickwood above recorded, allowance being made for the fact that the gentleman by means of whose body the ideal stroke was measured at Marlow was longer-bodied and longer in the leg than Mr. Gulston.
As a second advantage, the sliding seat decidedly relieves the abdominal muscles and respiratory organs during the recovery. In dealing with scientific racing we have previously remarked that the point wherein a tiring oarsman first gives way is in his recovery, because of the relative weakness of the muscles which conduct that portion of the action of the stroke. It therefore is obvious that any contrivance which can enable a man to recover with less exertion to himself will enable him to do more work in the stroke over the whole course, and still more so if the very contrivance which aids recovery also gives extra power to the stroke.
On the other hand, there are two drawbacks to the slide. One of these is, that when sliding full forward the legs are more bent than would be the case on a fixed seat. The body cannot reach quite so far forward over the toes on a full slide as it can on a properly regulated fixed seat. This slightly detracts from the work of the body at the beginning of the stroke.
Again, when a slide is used to best advantage, the greatest mechanical benefit occurs just when the body arrives at the perpendicular, and when the legs are beginning to do the greater portion of their extension. This causes the greater force of the stroke to be applied behind the rowlock, in contradiction of all old theories of fixed-seat oarsmanship.