revolutions, but with a little coarser pitch and a little more slip.

There is something to be said for large screws with a small proportion of
blade area to disk. For instance, two bladed screws have frequently given
better results than four bladed screws of smaller diameter, neglecting, of
course, the question of vibrations. Twin screws, however, should, as a
rule, be made as small as possible in diameter without loss of efficiency.
The advantages of small twin screws are the shorter shaft tubes and stern
brackets, deeper immersion, and less exposure as compared with large
screws. The exposure of the screws is usually considered an objection, but,
perhaps, too much has been made of it, for those well qualified to speak on
the subject consider that careful handling of the ship would, in most
cases, prevent damage to the screws, and that where the exposure is
unusually great, effectual protection by portable protectors presents no
insuperable difficulty.

HIGH SPEED TWIN SCREWS.
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|Ship A.|Ship B.|Ship C.|Ship D.|Ship E.|Ship F.
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Length, ft. | 325 | 315 | 300 | 300 | 220 | 250
Breadth, ft. | 68 | 61 | 56 | 46 | 34 | 32½
| | | | | |
Draught on trial, | 26 ft | 24 ft | | 15 ft | 12 ft | 13 ft
forward. | 2 in | 6 in | .... | 6 in | 10 in | 1 in
| | | | | |
Draught on trial, | 27 ft | 25 ft | | 19 ft | 15 ft | 14 ft
aft. | 3 in | 6 in | .... | 9 in | 2 in | 7 in
Displacement, | | | | | |
tons. | 9,690 | 7,645 | 5,000 | 3,584 | 1,560 | 1,544