OF SHIPS WITH CONDITION OF WETTED SURFACE. 



Table II. 



41 



*At 6 knots. 



fThis lo«f coefficient of resistance is combined with a high velocity exponent and probably would become greater 

 at speeds lower than those at which experiments were made. 



DISCUSSION. 



The President : — Gentlemen, you have heard this paper on "The Variation in Fric- 

 tional Resistance of Ships with Condition of Wetted Surface," by Naval Constructor William 

 McEntee. Is there any discussion of the paper? 



Sir Archibald Denny, Member (Communicated) : — That fouling of the nature and 

 extent dealt with in this paper has a most prejudicial effect is not surprising, but we have 

 found here that fouling which does not exhibit any visible growth is also prejudicial. After 

 launching, the vessels lie in brackish water in our fitting-out basin, and it is our practice, 

 as often as possible, to run a preliminary trial before docking, and a complete set of pro- 

 gressive trials after docking, when we frequently get an increase in speed of half or even of 

 three-quarters of a knot. 



Examining the bottom in dock we find no apparent fouling; indeed the surface seems 

 exceedingly smooth and even slippery. By repeated comparisons before and after docking 

 we have got a figure for the effect of this fouling, namely, that for each day a vessel lies in 

 our dock the skin friction resistance increases at the rate of nearly )^ per cent per day, 

 and this we have found to be true for periods as long as three months. It would be interest- 

 ing if similar experiments could be made in other districts, as, although we have no definite 

 evidence of it, we have reason to believe that the kind of fouling that takes place in Glasgow 

 harbor disappears when the vessel reaches salt water. The Glasgow harbor is only 16 miles 

 up the river Clyde from here, but our yard is on the river Leven — a tributary to the Clyde, 

 and it may be that the water of the river Leven causes a different kind of growth. 



Naval Constructor McEntee (Communicated) : — The statement of Sir Archibald 

 Denny with regard to the experience of his firm in the increase of frictional resistance of 



