Description of an improved Capstan or Windlass. Communicated by Captain THOMAS HAMILTON, of the Royal Navy.

With a Plate.

My intention in the present instance is to demonstrate

the form a capstan should obtain, relative to the friction of the messenger, when weighing anchor.

It is generally known in ships of war, when heaving at the capstan with but little strain or resistance, there is a difficulty to hold on the messenger; and, on the contrary, when heaving with a great strain, it is often found necessary to slack the messenger to let it surge or rise up the whelps of the capstan.

To use mechanical language, the surge or power to prevent the descent of the messenger with three and a half turns round the capstan, is too great for the friction when applied to little comparative weight or strain ; and the surging power is too little for the friction, when applied to a great weight or strain.

The surge of the capstan is the angle from the perpendicular the outline of the whelps make, and in our capstans is about 9 degrees uniform from top to bottom, the outline of the whelps being straight; it follows, the less that angle is, the surging power is proportionally diminished, and conversely increased.

To counteract the surging power, the number of the whelps have been reduced from six to five, forgetting the friction or descending power is increased in the same

*The messenger is the rope fastened to the cable, and passed round the capstan, to weigh the anchor.

ratio, the surge or ascending power is diminished; hence the use of lifters, rollers, &c.

Four powers relative to the friction may be considered as belonging to the form or figure of the capstan; two of which may be called ascending powers, and two descending powers.

1st. Reducing the angle of the whelps, or approaching a cylindrical form, greatest descending power. (See Plate VII. Fig. 1.)

2d. Increasing the friction, by reducing the number of the whelps, second descending power, (see Fig. 2.)

3d. Increasing the angle of the whelps, or deviation from a cylinder, greatest ascending power, (see Fig. 3.). 4th. Adding to the number of whelps, or approaching the circle, second ascending power, (see Fig. 4.)

In this plan it will be perceived that the two descending powers are applied to the upper part, and the two ascending powers to the lower part of the capstan, and may be altered till the just angle of the surge is attained; though I have no doubt the present angle is very near the truth, and was quite sufficient in the trials I was witness to in His Majesty's ship Argo, where twice a very great strain never caused the descent of the messenger an entire turn round the circular part of the capstan.

The following letter, from Commodore Hallowell, an officer fully competent to judge, which the Commissioners of the Navy were so good as to send me, will convince those, who are ignorant of mechanicks, of the advantage to be derived from adopting the proposed form for either a capstan or windlass, and save much expense or vexation, and probable mischief.

N. B. The lifters which are ordered for the use of the navy are, upon an average, not less than 201. expense for each capstan.

REFERENCES

REFERENCES TO PLATE VII.

Fig. 1, greatest descending power.

Fig. 2, second descending power.

T

Fig. 3, greatest ascending power.
Fig. 4, second ascending power.

Fig. 5, A, capstan as usually made, 9.30 angle of the surge. B, as fitted in the Argo. cc, open as usual. d d, filled up with the chocks circular, making the lower part nearly a troncated cone. ff, tangent to the arc gg. gg, arc of a circle to the cord hh and tangent ƒƒ. hh, outline of the whelps usually made, and cord to the arc g g, as altered in his Majesty's ship Argo.

Copy of Commodore HALLOWELL's Letter to the
Commissioners of the Navy.

His Majesty's Ship Argo, in the Downs, Oct. 31, 1802.
Gentlemen,

On the first trial made at Long Reach with our capstan and roller when unmooring, I observed the roller to be of no use, as the messenger never required its assistance; I therefore ordered it to be removed, and, in repeated trials made between Long Reach and the Downs (having anchored six times), I am perfectly satisfied that the roller is useless with such a capstan as is fitted in the Argo, which is nothing more than the old one with the lower part made more obtuse, and filled up circular by the chocks, and the upper part more perpendicular in the sides, and open. The alterations in the common capstan may be made without any expense, farther than the men's time employed in reducing the upper part of the surge, and putting the filling pieces to the lower part, and I am certain will be approved by every person who