Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
were out of the water during the constant-speed portion of the runs.
height. The screws were tightened and the shim removed. alignment
This set up made for easy and accurate of the hull
section. Weight typical run and a typical underwater photograph.
Turbulence stimulation is not applied to planing hull models because of the large variations in wetted length, and because at planing speeds the Reynolds numbers are high enough to achieve turbulent flow. The model beam is approximately 2 times the ITTC recommended minimum size for planing hull tests.
Figure 6: Body Plan of Model
Table 1: Principal Characteristics Table of Principal Characteristics LOA 2032 mm LPP 1969 mm Chine Beam
Depth 180 Deadrise
15
Step Location LCG
Displacement 43.1
445 mm mm
degree
508 mm fwd transom 838 mm fwd transom kg
The model was built to allow easy reconfiguration of the hull while the model was attached to the towing rig. The connectors between the hull segments could be loosened and the bow and aft sections slid up or down to allow variation in step height.
3.3 TEST PROGRAM AND PROCEDURES
The test matrix included 5 step configurations (0%, 1.42%, 2.85%, 4.29% and 5.71% of beam, corresponding to even ¼ inch increments in the model), one longitudinal center of gravity at 1.88 beams forward of
the transom, at a single displacement, ∆ 0.49.
Step heights of 1-2% are common on recreational planing hulls. Thus, exploring 1.4% - 5.7% covers the range typically found on recreational craft and extends it to larger step heights than are ordinarily seen. Tests did not include higher step heights than 5.7% because of problems with dynamic stability, discussed later.
The loading condition tested and the length-to-beam ratio
of this model ( for special ope 4.57) correspond to typical values
Temporary
shims were placed on top of the section bulkhead and sandwiched between a piece of aluminium angle attached to the contiguous bulkhead to set the step
rations craft in the 25 meter size range that
are currently in operation. The choice of one displacement and one LCG limits somewhat the general applicability of these results but was necessary due to time and cost contraints. The purpose of these tests was to clearly illustrate the effect of aft steps on a single generic hull. Air resistance of the hull was included in the total measured resistance.
posts were
located forward and aft of the pivot to secure ballasting weights.
Figure 8 shows a photograph of a
Figure 7: Profile View of Test Setup (dimensions in mm) ©2014: The Royal Institution of Naval Architects B-91
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