620 



NATURE 



{April 



889 



can in any way explain the great difference in her condition. 

 After several years' close observation, however, certain factors 

 begin to make themselves apparent. Ships at sea from March to 

 August show a worse average than those afloat from 4^ugust to 

 March ; one also begins to realize that the amount of fouling 

 increases enormously if the ship has been long at anchor— ships 

 which have been lying at the mouths of rivers, although quite 

 clean in the brackish water, foul much more rapidly on going to 

 sea than the vessels which have been cruisin?, or even at anchor 

 for the same time in salt water ; and finally, certain ports and 

 certain seas seem to exercise a deleterious effect, both as regards 

 corrosion and fouling, which is not to be found elsewhere. 



Turning back to the naval history of the past, we find that 

 fouling is no new trouble born with the advent of our present 

 iron monsters ; but that it has been the one trouble that the com- 

 bined engineering and scientific skill of many centuries has been 

 unable to overcome. 



With our wooden ships, metallic copper sheathing, if it were 

 of the best kind, answered the purpose fairly well ; but then the 

 copper wasted so fast the inferior kinds and alloys were substituted 

 to prevent the rapid loss, and, with the slowing down of the de- 

 struction of the copper, at once the trouble of fouling returned. 



When iron ships began to replace the wooden ones, as was 

 only natural, attempts were made to utilize the metal which had 

 before given relief ;, but it was quickly found that the effect of 

 the galvanic action set up by the copper was fatal to the iron 

 plates of the ship, and attempts were then made to sheathe the 

 ship with copper plates in such a way that they should be insulated 

 from the iron of the. vessel, a condition almost impossible to attain 

 and attended with great risk, should any accidental injury to the 

 insulation take place. ^ Early in the history of iron shipbuilding 

 the idea was started of using coatings of paint, so prepared as to 

 fulfil the same functions as the copperplates had done ; but from 

 1840, when the first paint of this kind was patented, down to the 

 present day, when there are upwards of thirty-two different com- 

 positions in the market, very little progress has been made in 

 their manufacture, and the best of their compounds cannot be 

 relied upon for keeping a ship's bottom even fairly free from 

 fouling for periods extending beyond nine months, and I am 

 personally convinced that the reason of this is to be found in the 

 fact that a start was originally made in the wrong direction. 



The idea which originally led to the present class of anti-fouling 

 compositions was that the copper salts formed by the action of the 

 sea water on the metallic sheathing owed a considerable portion of 

 their value as anti-foulers to the poisonous action they exerted 

 upon marine animal and vegetable growths ; but, when an observer 

 comes to study the natural history of these lower forms of animal 

 life and vegetation, it is gradually forced upon one that it is only 

 in the early stages of their growth — the germ period — that metallic 

 poisons can affect them. Seaweeds do not take in the constit- 

 uents they require for their growth by means of their roots, as is, 

 to a certain extent, the case with ordinary plants, but absorb them 

 by means of their pores from the water itself, the root only 

 serving to attach them to the solid they choose for their resting- 

 place ; it is also well known that when once a marine plant which 

 has passed the first stages of existence is dislodged or torn from 

 its support, it cannot reattach itself to anything else, whilst most 

 of the mineral poisons have little or no effect upon their life and 

 growth. 



In the same way we find that, with the animal life found on a 

 ship's bottom, the under side is used to cling on with only, and 

 not as an extractor of nourishment, and that, therefore, after the 

 seeds and germs have once obtained a foothold on the side of 

 the vessel, no amount of poison which can be put into a com- 

 position will have any effect upon them. Metallic poisons 

 undoubtedly do exert an influence upon the germs in their earliest 

 stages ; but after that they are perfectly useless as anti-foulers, 

 and only imperil the plates of the vessel. 



The germs of both kinds of growth are of necessity more 

 abundant in the surface water near shore than in deep water, 

 and therefore the period when the ship is in port is the time 

 when the germs are most likely to make good their attachment, 

 after which their further development is, unless other methods 

 of getting rid of them are employed, merely a matter of time. 



On examining the conditions under which a vessel is placed 

 when coated with a composition which relies for its anti-fouling 

 powers on metallic poisons only, we at once see the reasons 

 which must make such a coating of little or no avail. In the 

 composition we have drastic mineral poisons, probably salts of 



' Some copper sheathed vessels still exist, and its revival has been lately 

 warmly advocated in America. 



copper, mercury, or arsenic, which have been worked into a 

 paint by admixture with varnishes of varying composition, and 

 each particle of poison is protected from the action of the sea 

 water by being entirely coated by this vehicle : that this must be 

 so is evident, or the composition would not have sufficient co- 

 hesive power to stick on the ship. As a rule, care is taken to 

 select fairly good varnishes, which will resist the action of sea 

 water for, perhaps, two or three months, before they get suffi- \ 

 ciently disintegrated to allow the sea water to dissolve any of the 

 poison ; whilst, even with the accidental or intentional use of 

 inferior varnishes, three or four weeks will pass before any solu- 

 tion can take place, and any poison be liberated to attack the 

 germs. A ship is dry docked, cleaned, and, her anti-fouling 

 composition having been put on, she goes probably into the basin 

 to take in cargo. Here she is at rest, and, with no skin friction 

 or other disturbing causes to prevent it, a slimy deposit of dirt 

 from the water takes place, and this, as a rule, is rich in the 

 ova and germs of all kinds of growth, whilst the poisons in her 

 coating are locked up in their restraining varnish, and are 

 rendered inactive at the only period during which they could be 

 of any use. After a more or less protracted period, the ship 

 puts to sea, and, the perishing of the varnish being aided by the 

 friction of the water, the poisonous salts begin to dissolve or 

 wash out of the composition ; but the germs have already got a 

 foothold, and with a vessel sweeping at a rate of, say 10 to 12 

 knots through the water, the amount of poison which can come 

 in contact with their breathing and absorbing organs is evidently 

 so infinitesimally minite that it would be impossible to imagine 

 it having any effect whatever upon their growth. If the poison 

 is soluble, it is at once washed away as it dissolves ; if it is in- 

 soluble, then it is also washed away, but there is just a chance 

 that a grain or two may become entangled in the organs of some 

 of the forms of life, and cause them discomfort. As the surface 

 varnish perishes, the impact of the water during the rapid 

 passage of the vessel through the water quickly dissolves out or 

 washes out the poisonous salts, and leaves a perished and 

 porous, but still cohesive, coating of resinous matter, which forms 

 an admirable lodgment for anything which can cling to it ; and 

 by the time the vessel lays-to in foreign waters, teeming with 

 every kind of life, the poison which would now again have been 

 of some use is probably all washed away, and a fresh crop of 

 germs are acquired, to be developed on the homeward voyage, 

 and a " bad ship " is reported by the person who looks after her 

 docking. It is evident that a poison, even if it had the power 

 of killing animal and vegetable life in all stages, could only act 

 with the vessel at rest, unless it were of so actively corrosive a 

 nature as to burn off the roots and attachments of the life rooted 

 to it, and if it did this, what, may I ask, would become of the 

 protective composition and the plates of the vessel? And I 

 think it is also evident that any poison so used must be under 

 conditions in which it is very unlikely to be in a position to act 

 when it might do good. 



The lamentable failure of composition after composition of 

 this kind has gradually reduced them in number to some ten or 

 twelve at the present time, and in most cases it is low price alone 

 which keeps them in the market. 



The practical proof, given by experience, that poisons alone 

 are unable to secure a clean bottom, soon led many inquirers to 

 the conviction that it was the exfoliation in the case of copper 

 which had acted in giving fairly good results, and in many com- 

 positions the attempt has been made to provide a coating which 

 shall slowly wash off, and, by losing its original surface, shall at 

 the same time clear away germs and partly developed growths, 

 and so expose a continually renewed surface, in this way keeping 

 the bottom of the vessel free from life. There is no doubt that, 

 when this is successfully done, a most valuable composition will 

 result, but the practical difficulties which beset this class of anti- 

 foulers must not be overlooked. In order to secure success, the 

 composition must waste at a fairly uniform rate, when the ship 

 is at rest, and also when she is rushing through the water ; and 

 this is the more important in the case of Service vessels, as in 

 many cases they spend a large percentage of their existence at 

 anchor, or in the basins of our big dockyards. If a composition 

 is made to waste so rapidly that it will keep a vessel clean for 

 months in a basin, then you have a good composition for that 

 purpose ; but send the vessel to sea, and under conditions where 

 you have a higher temperature, and the enormous friction caused 

 by her passage through the water exerting its influence upon the 

 composition, and you will find that the coating, which did its 

 work well for six months at rest in the basin, will, in the course 

 of one month under these altered conditions, be all washed 



