SOME CALCULATIONS OF SHIP TRIM 
AT HIGH SPEEDS 
By T. H. HAVELOCK 
(Presented to the International Congress of Applied Mechanics, at 
Paris, 1946. The Proceedings of this Congress have never been 
published) 
SUMMARY 
Although much work has been done on the theory of wave resistance, that 
is on the horizontal resultant of the pressure system round a ship, there do 
not seem to have been any calculations of the resultant moment of the pres- 
sures about the transverse axis. 
The present note records some work on this problem and a comparison of 
the results with measured trim in experimental models. Assuming the 
usual approximate theory of the pressure system, the effective part of the 
pressure for a symmetrical model is put into a suitable form and an expres- 
sion is obtained for the moment for a certain series of models, used at 
Teddington, for which experimental results are available. Numerical cal- 
culations have been made for three models of this series over a consider- 
able range of speed and curves are given Showing the comparison between 
calculated and measured trim. The agreement is reasonably good, especially 
at the higher speeds, and in general the order of agreement is much the same 
as between calculated and measured wave resistance. 
1. The pressure changes established by the forward motion of a 
ship may be considered in two parts: (i) those associated with the 
so-called local disturbance, (ii) those due to the wave motion trailing 
aft from the ship. In the usual approximate theory of wave resistance, 
neglecting viscosity, the pressures from (i) give no resultant hori- 
zontal force on the ship as a whole and we only need to calculate the 
resultant of these from (ii). If we wished to examine the sinkage of 
the ship, we should require the vertical resultant of the total pres- 
sure system and such calculations would be too laborious in general; 
though we may estimate the effect at low speeds by ignoring the sur- 
face disturbance of the water [1]. On the other hand, if we limit con- 
sideration to a model which is symmetrical fore and aft, the moment 
of the pressure system about the transverse axis will only involve 
the pressures from the wave system (ii). As this calculation does 
not seem to have been carried out hitherto, it was thought of interest 
to see how the results so obtained compare with the measured trim of 
experimental models. 
520 
