118 



IlVnROnVNANflCS IN SHIP DESIGN 



Sec. 45.19 



n fourth from tlii.s causf; ami iH-rasionally it is 

 increaiicd more." I'nfortimatoly, Hankiiie (Iws 

 not say what rosistaiuo is involvoil, whether 

 frietioii or total. W. V. Diiraiul, in liis 1903 hook 

 entitled "Re-sistanee and Propulsion of Ships," 

 pages 55 and 56, tabulates increases in total 

 rcsistanec due to fouling on V. S. Naval vessels of 

 the ISDO's as varying from 20 to 200 per cent at 

 speetis of 7 to 11 kt. The.se are understandable in 

 view of the r2-in barnacles reported to have 

 grown on an old ironelad which spent most of its 

 time at anchor [SBSR, 24 Feb 1938, p. 229]. 

 The reader who ma.v question these data has 

 only to look at the photographs in the book 

 "Marine Fouling and Its Prevention," prepared 

 by the Woods Hole Oceanographic Institution 

 and publi.shed by the l'. S. Naval Institute in 

 1952. 



The deposits which form on the surface of any 

 ship or ship element, immersed in any type of 

 water, are divided roughly into two classes: 



(1) Gelatinous coatings and soft slimes containing 

 no visible solid matter and representing a rela- 

 tively thin deposit of apjiroxiniately uniform 

 thickness. These are often a factor in the take-off 

 characteristics of seaplanes and Hying bouts. 



(2) Rough coatings, semi-rigid or rigid, composed 

 of grasses or other marine vegetation, shells, 

 barnacles, and the more-or-less rough and firm 

 growths of all visible types of marine life. 



Fouling of the first class usually begins immedi- 

 ately upon immersion, following launching and 

 undocking. It develops its own friction drag from 

 that hour, increasing slowly but progressively 

 until its effect is overtaken bj' fouling of the second 

 class. A ship resting in w-arm, quiet water usually 

 acquires a slime coating rather rapidlj', whereas 

 one moving continually or resting in cold water 

 may never have more than a thin coating form 

 on it. 



Although not to be classed as fouling, in the 

 strict .sense, there is mentioned here a deteriora- 

 tion of the bottom paint which occurs at unex- 

 pected places and times. The causes of this action 

 .seem t(j be related to the causes of particular 

 kinds of fouling in certain areas at specified times. 

 The deterioration ajjpi^ar.s to vary by j'ears in the 

 .Maine locality, in somewhat the same way that 

 extra-warm Hummers or unusuallj' .severe winters 

 are fni'oimtere(l. The action is often extremely 

 rapi<l, especially when a vefwel is at amhor. In 

 one 8hort week of immersion a new c-oat of I ml I mi i 



paint may lake on the a|)|)earance of ha\ing been 

 made up of a mixture of paint and sand. 



.Mso mentioned here is the deterioration of hot- 

 plastic paint coatings due to unfavorable weather 

 conditions, improper application methoils, and 

 similar factors. This deterioration sometimes 

 occurs before the ship is waterborne at the end 

 of the docking period. Runs, supcrpo.sed layers, 

 folds, "icicles," and peeling of the plastic coating 

 involve roughnesses of the magnitude of those 

 encountered in fouling. 



Fouling of the second class is accelerated in 

 warm, salt water, especially with slow relative 

 motion of the ship and water. It is augmented by 

 seasonal and other conditions, not too well known, 

 conducive to the rapid growth of marine life, both 

 vegetable and animal. Growth is slower in cold 

 water; much slower when the ship is in almost 

 continual motion. It is practically nonexistent in 

 fresh water, giving trouble onlj' in exceptional 

 cases and then usually along the watcrline. 



Fouling of both classes maj' be arrested by the 

 on.set of unfavorable conditions for the growing 

 organisms, such as moving a ship from .salt water 

 to fresh water. It can not be expected, however, 

 that this will le.s.sen the added friction resistance 

 or that it will eliminate the fouling drag altogether. 

 The firmly fixed barnacle shells on a ship entering 

 the Panama Canal from a long sea voyage will 

 not drop off just liecause the ship anchors for a 

 few days in the fresh water of Gatun Lake, long 

 enough to kill the barnacles themselves. 



The effect of hard, rough fouhng is to create a 

 friction drag of the tantjua type, defined in Sec. 

 5.21 on page 108 of Volume I, varying as the 

 square of the speed. For a ship of medium or 

 large size, this involves a constant AfV allowance 

 above the ATTC 1947 mcanline, or above any 

 other modern flat, smooth-plate, turbulent-flow 

 friction line. Whether fouling roughness is a 

 negligible factor at /?„ values of 2, 3, or 4 milHon, 

 as smaller si^es of roughness appear to be, espe- 

 cially at .slow speeds, is not yet known. What 

 applies to the latter should, however, also apply 

 to the former. 



Numerous rules have been devel()|)c(l from 

 time to time to predict the effect of fouling on the 

 resistance, j)ower, and speed of ships. For any 

 one kind of anti-fouling coating these an? based 

 generally upon tlu- time which has elapswl from 

 llic application of the last anti-fouling coating, 

 iipiiii IIk- average speed of the shi|) iluring ccrt^iin 

 |ii'ii(Hls, ami npon the kind and llie IciiipiTMliirc of 



