BLADE ON WHICH 
FORCES ARE MEASURED 
AHEAD (+v) 
PROPELLER 
CENTERLINE 
COORDINATE SYSTEM FOR RIGHT HAND PROPELLER 
(PROPELLERS 4710 and 4402) 
THE COORDINATE SYSTEM 
ROTATES WITH THE PROPELLER 
F,,2 BLADE ON WHICH 
FORCES ARE MEASURED 
PROPELLER 
CENTERLINE 
COORDINATE SYSTEM FOR LEFT HAND PROPELLER 
(PROPELLER 4661) 
Fig. 1 — Components of Blade Loading 
water characteristics of the pro- 
peller, 
Ao A linearized lightly-loaded 
unsteady lifting surface theory 
developed by Tsakonas, et al (6,7) 
at Davidson Laboratory, 
3. A moderately-loaded unsteady 
lifting surface theory developed by 
Kerwin and Lee (8) at MIT, 
ay A refinement by Kerwin (9) to the 
method of Kerwin and Lee which 
considers the inclination of the 
propeller slipstream for opera- 
tion in inclined flow. 
BACKGROUND 
In previous work unsteady loads 
(see Figure 1) were measured on a single 
blade of model propellers operating 
behind model hulls with open-shaft 
transom sterns (1,2,3,4). It was found 
that for these vessels the unsteady 
blade loads were produced primarily by 
the tangential component of the wake 
velocity; see Figure 2. For the steady 
ahead conditions, the experimentally 
obtained unsteady loads were correlated 
with unsteady loads deduced from strains 
Measured on the respective full scale 
propeller blades and with predictions 
based on unsteady lifting surface theory 
developed by Tsakonas, et al (6,7), and 
the quasi-steady method of McCarthy (5). 
For each of these propeller-hull 
combinations, the circumferential 
variation of loading determined from the 
model experiments agreed fairly well 
with full-scale data, but was substan- 
tially larger than the predictions by 
the two theoretical methods. 
In an attempt to isolate the 
reasons for the large discrepancy 
between these experimental and 
theoretical results, the following 
experimental work on model propellers 
was undertaken: 
V, Positive Downstream 
(Looking Upstream) 
Fig. 2 — Sign Convention for Ship Wake 
Velocity Components 
