ON A MODEL OF THE U. S. AIRCRAFT CARRIER LANGLEY. 91 
The curves that Mr. McEntee has shown throw a little light on that subject, and a 
good deal of the loss in sea speed can be traced to the rolling of the ship when half loaded. 
Mr. SmitH:—In connection with Captain Gleason’s remarks, it would seem to 
me desirable to express the propulsive efficiency under rolling conditions as the 
ratio to the propulsive efficiency under the ideal or model tank conditions, and thereby 
take into account not only the increase in resistance but also the decrease in the pro- 
pulsive efficiency proper. Ifsome curve or table could be arrived at whereby the designer 
could approximate the actual seagoing horse-power of a ship, it would be very useful, 
because, in designing and powering a ship, the speed that we desire is the seagoing speed. 
It is not the speed on the trial trip always, but usually it is the continuous seagoing speed 
under average conditions. 
This topic has an important bearing on that subject, and I may say, in addition, 
of course, the fouling of the bottom has a big effect on the power of the ship, and in ordi- 
nary merchant ships which are dry-docked periodically (about every six months), it 
would be good practice to approximate the increased resistance at a time when the 
ship has been out of dock about three months, so as to get about an average seagoing 
power for the ship, and in addition to make any allowance for the increase in resistance 
and decrease in propulsive efficiency, due to the normal rolling and sea conditions that 
might be expected. If Commander McEntee can throw any further light on that phase, 
it will be interesting. 
Mr. EtmMer A. SpeRRy, Member:—A year ago, when I read a paper on this sub- 
ject, we had made calculations as to what, in all probability, the rolling losses were, 
but they were so large that we hardly dared trust them. We had them checked over by 
two outside people, who arrived at almost our figures. When I read the paper I only 
used one-quarter of these values, not daring to assign what apparently the values were. 
I determined, however, that we would actually find out what these rolling losses 
were, and Commander McEntee has shed a great deal of light on the problem through 
his model work. I think the shipping interests are indebted to him profoundly for aiding 
in clearing up this matter. 
By way of reference to these losses, we have known for some years that a marked 
difference exists between the actual power demanded by the ships the year through 
and the model results, as referred to by Professor Sadler. We have also known that 
the model results, under the same efficient officer, attained at the tank where he had 
carefully calibrated motors in the model itself, were almost absolutely coordinate with 
results on the range in fair or favorable weather; a fraction of 1 per cent marked the 
total difference, if I remember correctly. 
These data were secured in calm weather—of course the tank is very calm—and 
yet we have known for the last twelve years that there is a very large discrepancy 
between these, including the tank results, and the actual operating results over long 
periods on the high seas. Mr. Gibbs, of the International Merchant Marine, has also 
made some interesting observations on this very point. 
Now, of course, with Commander McEntee’s model—it is really quite a large model; 
I suppose it would support say 12 people, being 23 feet long—with this model we have no 
possibility of yawing, as it is towed down the course lashed both forward and astern. 
Of course there was no “‘helm”’ used. 
