THE ROYAL ARTILLERY INSTITUTION. 
35 
from the effects of the salt water, the only evidence of wear was in a few 
spots where the plates had been rubbed and worn by mechanical means. 
This vessel shortly after she was built was found to want permanent ballast, 
and it was thought the best way to meet the difficulty would be to build in 
between the ribs for about 15 or 20 ft. on each side of the keel with bricks 
covered with Eoman cement. Several thousand bricks were used for this 
purpose, and remained where they had been laid until the middle of last 
year, when the “ Bipon ” was sent into dock to be lengthened. As these 
bricks had been 16 years without being moved, it was naturally thought 
that the plates under them might require renewing; it was found however 
on examination that the plates thus covered were with the exception of a 
thin coating of rust, as good and as sound as on the day they were made; the 
only plates that had suffered were those not protected by the covering, and 
even these were not harmed by corrosion, but were worn away by the friction 
of the bilge water and pieces of the bricks and cement which were detached 
by the rolling of the ship. 
The great difficulty to contend against in iron ships is their liability to 
foul,—a serious disadvantage where speed is an essential quality. A variety 
of paints and oils have been proposed, but all have failed to prevent the 
collection of barnacles and weeds which always fasten upon a ship if not 
coppered. It was long supposed that copper prevented the accumulation of 
these parasites by means of its poisonous qualities, but it has since been 
proved that its efficacy is due to oxidation, which as it were mechanically 
detaches the barnacles and weeds; copper is however inapplicable to iron 
ships owing to the galvanic action that would take place unless the copper 
were perfectly insulated. Several methods have been proposed to effect 
this; the two most practicable have been recommended for trial, as experiment 
alone can determine their relative values; one of these methods, pro¬ 
posed by Mr John Grantham, is to rivet the ship's plates below water to 
the inside instead of the outside of the timbers , and to fill the intervals 
between them with hard wood; another layer of wood is then bolted 
to this with copper bolts, and the ship coppered in the ordinary manner. 
Objections have been raised on account of the plates of the ship being 
covered with wood, and so preventing any examination of the state of 
the rivets, and it was urged that corrosion might proceed to a dangerous 
extent without being discovered. Mr Grantham meets these objections by 
covering the ship's bottom with a very thick coating of bitumen and tar 
before fixing the first layer of wood, the joints of which are then carefully 
caulked, and the same process repeated after the second layer of plank is 
fixed; by these means he proposes to exclude any dangerous amount of 
moisture, and to make the exterior lining nearly if not perfectly water-tight; 
any moisture which might reach the plates under these circumstances would 
produce slight corrosion, but this would act rather as a preservative to the 
iron than otherwise. 
The wood lining was also objected to from its liability to decay, but as 
the wood would certainly last as long as the copper, this objection can 
hardly be considered valid, as it would take but very little extra expense to 
renew the wood at the same time as the copper. Two vessels were built at 
Liverpool, and coppered on this plan 10 years ago; both appear to have 
been unfortunate, one was abandoned on the sand heads of the Hooghly, 
