On the basis of two-dimensional quasi-steady theory, the increase unsteady 
loading should be approximately proportional to the increase in tangential 
velocity.* 
The unsteady loading is important from consideration of fatigue of 
the propeller blades and hub mechanism. Since a ship may operate for an 
extended period in a seaway, the effect of the ship motions, such as 
dynamic hull pitching, on unsteady blade loads is significant. The differ- 
ence between the peak load and the time-average load per revolution is a 
measure of the unsteady loading. With this difference as a measure of the 
unsteady loading, the quasi-steady simulation indicates that for hull 
pitch angles b-Voy up to 1.85 degrees, the unsteady loading for Mo which 
is the largest moment component, increased by 8 percent above its corres- 
ponding value for v=Voye By contrast, the dynamic simulation showed the 
unsteady loading for the Mt component increased by 50 percent above its 
corresponding value for Vow without hull pitching. This indicates that 
the quasi-steady simulation is completely inadequate for estimating the 
effect of the seaway on unsteady loading. This also shows that the effect 
of the ship motions can dramatically increase the unsteady loading on the 
blades. Therefore, the effect of the ship motions due to operation in a 
seaway should be considered in any analysis of blade loading and in any 
fatigue analysis of the propeller blades or hub mechanism. 
The results presented here for hull pitching generally agree with 
the same type of results presented in Reference 2 for a model of the FF- 
1088, which is a single screw transom stern configuration. For ae which 
is the largest measured moment component in both cases, the comparative 
results, presented as a fraction of the time-average value without hull 
pitching, are as follows: 
“Chis simple analysis provides an upper bound to the dynamic pitching 
load, since the hull boundary above the propeller would tend to reduce 
the dynamic pitching induced upward tangential velocity relative to the 
propeller. 
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