12 EKMAN. ON DEAD-WATER. [norw. pol. exp. 



"When passing the mole-head, the engine still worked at full-speed; and I only stop- 

 ped it when the ship was a little way (100 or 150 m.) from the buoy to which we 

 should make fast. It was remarkable how quickly the ship lost her speed, and if my me- 

 mory does not deceive me, I was obliged to start the engine again in order to reach 

 the buoy. 



"Finally I will not omit remarking, that the description given above has been written 

 several years after the occurence, but according to my best recollection of the facts cited." 



No. 3. Mr. G. A. Larsen of Fredrikstad has during many years' experi- 

 ence of towing, struggled with the dead-water on the river Glommen and the 

 fjord off it, and he has most kindly, by letters and word of mouth, com- 

 municated to the author the result of his practical experience in these waters. 

 His communications are very inslructive, based as they are on long experience 

 of an extensive district where dead-water seems to be more common and 

 stronger, than in any other place. The different statements have been ar- 

 ranged below in a consecutive account, and this has been revised by Mr. 

 Larsen himself. 



"As is seen on the maps (PI. Ill), the river Glommen branches at Fredrikstad into 

 two outlets — the East Arm and the West Arm — girding Krager Island. Most of the 

 water flows out the straight way through the East Arm, but a considerable quantity flows 

 through the channel north of Krager Island and further on to the West Arm. In both 

 outlets, especially in the East Arm, the current is sometimes very strong, but they are 

 both navigable, as is also the main river all the way up to the Sarp Bapids. 



"On these waters and the surrounding parts of the Kristiania Fjord I have towed 

 ships and lighters with a tug of 200 H. P., and drawing nearly 3 m. The ships and 

 lighters in tow generally have a draught of 3 or 6 m., and on them the dead-water has 

 principally taken effect. The tug-boat may also take dead-water but — on account of her 

 smaller size — very slightly and to no hindrance. The following statements principally 

 concern the effect of dead-water on towed vessels. 



"Dead-water only occurs where there is a layer of fresh or brackish water above 

 the salt water. Its effect depends on the thickness offthe fresh-water layer. If this 

 be great, it is hard to advance; but if it be only small so that the screw throws dark 

 sea-water up to the surface, we never fear dead-water, it has then very little influence ex- 

 cept on very small vessels. At flood-tide, dead-water is always stronger than at ebb. A 

 sharp and fast-sailing ship is always at a much greater disadvantage in brackish water, 

 than a bluff one of bad design. 



"The strength of dead-water in different places changes with the season. In winter, 

 when there is little water in the Glommen 1 , the worst district for dead-water is on the 

 river beyond Fredrikstad, and there it reaches right up to the Sarp Rapids. In winter 

 there is also dead-water in the Fredrikshald Fjord. In spring, as the water rises, the 

 dead-water moves farther off, and in summer it does not exist beyond Vaterland on the 



From the data given in "Hydrologiske meddelelser for Kougeriget Norge, Vandstands- 

 observationer, B. 1", Kristiania 1900, 1 have calculated the average quantity of water 

 carried by the Glommen during the different months. The mean averages for the dif- 

 ferent months during the years 1881 — 1893 are in cubic metres per second: Jan. 180, 

 Febr. 165, March 162, April 265, May 1055, June 1525, July 1045, Aug. 900, Sept. 805, 

 Oct. 740, Nov. 500, and Dec. 260. I am much indebted for these data to Kanaldirector 

 G. SiETBEN, who was kind enough to bring them under my notice. 



