Mr Bald on a Steam Passage-Boat for the AUoa Ferry. 
wiiigs. They will therefore be confined to thjit space, by three 
tier of chains, which hook and unhook at pleasure; and a simi^ 
lar set of chains are stretched in the line of the wings along the 
side of the platforms, as represented in the drawing. 
With regard to the power of the steam-engine, it must bfe 
kept in view, that the run of the tide at this Ferry, in particular 
the ebb at the South Pier, is uncommonly rapid ; and this, 
when aided by the strong prevailing south-west wind in the di- 
rect line of the Pier, evidently requires considerable power to 
propel so large a boat with her loading. 0n the other hand, 
the boat being flat-bottomed, without a keel, and drawing only 
9. feet water, the resistance of the water is very little, compared 
with other steam-boats. 
Mr Napier is of opinion, that an engine of twelve horses 
power will be quite sufficient; but, in order to remove every 
dubiety about making the passage in all weathers, an engine of 
sixteen or eighteen horses power may be adopted. 
Mr Napier proposed that t!?e engine should be constructed 
with the engine-beam working over the cylinder ; but, in order 
* to throw the centre of gravity as near the bottom of the boat as 
possible, I think it would be preferable to have two beams placed 
near the bottom of the condensing cistern, after the manner of 
those in the Morning Star Steam-boat of Alloa, 
With regard to the expence of a boat with an engine of 
twelve horses power, Mr Napier estimates that it will cost 
L. 1200 ; and for every additional horse'^s power from L. 40 to 
L. 50 more. 
From the construction of the boat, it is probable, that, when 
a heavy loaded cart is resting upon the wings, either in going in 
or out of the boat, ^he may heel considerably with the weight ; 
and, \vhen the carts, with their loadings, are in. their position, 
the boat may not float upon a horizontal floor. To obviate this, 
I propose that an iron railway be laid across the boat, upon 
each poop next the platform ; upon which railw^ay, t^vo w4ieei- 
ed carriages, or trucks, may be placed, wnth about a ton of iron 
m each. These can, with the greatest case, be moved from side 
to side, to produce an equipoise, and firmly secured at any par- 
ticular point. 
