of the East-Indian Archipelago, as regards sounding and dredging, and to the working of such 

 instruments as have only lately come into use or of which little is known as yet. 



The working of the appliances for the paying out, dredging and hauling in of the bottom 

 nets is sufficiently explained in the description of the Plates I, II and III. Experience bas taught 

 us that for the successful working of the nets it is not safe to trust to the ordinary ship's fittings 

 and gear, unless they have proved by practical trial beforehand that they are suitable for the 

 purpose intended. For instance we decided to dispense with a specially constructed steamwindlass 

 with stoppers on account of the very limited space on deck. Had we however foreseen the 

 trouble caused afterwards by the use of the existing capstan and stoppers this objection would 

 scarcely have been taken into consideration. 



For one thing it was a most difficult matter to regulate the speed of the dredge-rope, 

 when paving out ; and when hauling in the speed was not as quick as we had expected. Sometimes 

 it ran out much faster than anticipated, at other times, with very cleep soundings, the strain 

 put upon the capstan threatened to be too much for it. The ropes, winches, electromotor, and 

 other instruments gave every satisfaction, and in many cases we succeeded in overcoming the 

 difficulties just mentioned. 



The difficulties due to the peculiar conditions of the East-Indian Archipelago as compared 

 with those experienced in the open ocean, are the following. In the Archipelago the bottom 

 of the sea presents as much variety in levels as the dry land, and this explains how it 

 is that the depth at which the net reaches the bottom, sometimes varies so much from 

 the depth indicated by the sounding line. It is therefore of the utmost importance that the 

 net should reach the bottom as near as possible to the place where the sounding was made. 

 Before bes'innino- to dredsje we had carefullv to note the effect of currents and winds upon 

 the motion of the ship, and after the sounding had been taken we steamed away from the 

 point to a distance of a few miles. The net was then let down while the ship slowly steered 

 back to the sounding place. The choice of the starting point naturally depended upon wind 

 and current and upon the approximate speed of the ship during the letting out of the rope, 

 and the length of time it would require to reach the bottom. 



In the Archipelago the constancy of the currents cannot in the least be relied upon, 

 because it is dependent upon tidal currents of which very little is known, and which sometimes 

 are very strong. Changes in the current, taking place after the rope is let down or while the 

 dredging is in operation, often have a most undesirable influence. For apart from the possibility 

 of the net reaching the bottom at a different depth than had been calculated upon, it may 

 happen that the course fixed upon is no longer favorable to the free play of the rope. The 

 speed of the ship also may become considerably faster or slower than arranged for, according 

 to the variation of the current. These circumstances may cause the net to tear, or to be kept 

 floating; they may also spoil the dredging, not sufficiënt area of ground being covered. It will 

 therefore be seen how important it is that the position and the actual course and speed of the 

 ship over the ground should be controlled as accurately as possible. In many cases we did so 

 successfully by use of the sextant, by constantly verifying the modifications in the angles of 

 suitably chosen points while the net was being paid out or drawn in. 





SIBOGA-EXPEDITIE II. 



