30 APPENDIX. 



not being carried sufficiently above the load water line : thus placing the inference beyond a 

 doubt ; the activity of employment by no means interfering with the chemical action induced. 

 The wheels and sides of those vessels employed in the Channel only do not exhibit the 

 above effects to such an extent as those employed in the Mediterranean and Tropics. 



Since the accumulation of matters on the ship's side abreast the wheels must be submitted to, 

 I suggest that protectors, on Sir H. Davy's principle, be applied to all steam vessels in this 

 particular place, in order to prevent the wheels operating as such. 



Thus it is probable that the influence of the sea water only will have to be encountered with. 

 I have found coal tar, heated by a shot plunged in to drive off the naphtha, when applied to 

 such parts as were chafed, or otherwise left unprotected, to be a very good varnish for paddle 

 wheels; the wheels being examined, and covered in such places on the arrival from every 

 voyage : by this treatment, a paddle wheel may resist the action of the sea water for several 

 years. 



Wood floats, as usually applied, directly on the arms, are constantly becoming more com- 

 pressed thereon ; so that in a short time they are cut partly through, and of course are much 

 weakened in these places : this is not all ; the portion of the arms impressed are eaten away 

 by the moisture retained by the wood, long before any other part of the arm is decayed. 

 From these causes, the bolts, which secure the floats to the arms, are constantly getting loose 

 at sea, and are frequently lost before an opportunity is afforded to secure them ; the boards in 

 consequence become slack on the arms, to the imminent risk of other parts of the wheels : 

 to remedy this, iron plates not less than three or four inches broad, and three-eighths to half 

 an inch thick, may be advantageously applied above and beneath the boards, across the entire 

 breadth, in order to compress the board between the two. When the plates are defective, they 

 may be thrown aside, and new ones substituted, the arms remaining perfect, and the bolts less 

 liable to be lost : indeed in the Mediterranean packet service from Falmouth to Corfu, 

 bolts are required to be replaced or secured at the end of each trip of six or seven days, 

 in the common paddle wheels. 



Boards, if possible, should never be carried out beyond the inner edge of the segments, or 

 extreme ring of the wheel ; for no protecting coat can be applied within the slot made in the 

 board ; and, of course, the board being always moist on both sides of the segments, they are 

 eaten through in a very short time, while apparently in very good condition. Segments thus 

 decayed often give way at one end, being whirled about the other in a flail-like manner, 

 cutting the beams which carry the wheels, very destructively. In a sea-way this can rarely 

 be remedied, and they must consequently be permitted, in such case, to come in collision till 

 completely broken adrift. 



