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24 A. TUNÇER, G.T. TAYYAR and Y. ÜNSAN

By calculating the maximum shear stress (τmax), minimum thickness of the blade can be decided.
Note that it is important to remember the distribution of force on the interceptor blade is not
linear, but polynomial. Refer to Figure 4.1.

Figure 4.1 Pressure distribution [16]

4.3 Case/Housing

A housing to be designated to contain and protect the selected interceptor blade, appropriate
bearings, required fastening elements and allows the actuator to work properly. Important items
to consider during the design progress are as follows;

 Rigidity
 Ease of assembly
 Sufficient shear and tensile stress values for bolts or other fasteners
 Secure and long-lasting fastening
 Water-tightness towards inside of the vessel
 Working conditions to be considered as immersed in sea water or exposed to sea

water splash
 Having no sharp corners exposed
 No obstacles to block the actuating movement
 Protection against corrosion and fouling
 Low bearing friction coefficient with the selected blade material

4.4 Reference Design

Sample vessel with below specifications was considered for the reference design [13] in this
study:

 L= 10.5 m
 B= 3.3 m
 ∆= 4500 kg
 ν= 45 knots
 2x385 hp Sterndrive Bravo II engines

Allowed space for the interceptor is given in Figure 4.2 (considering 50 mm margins from both
sides of the vessel)

GiDB|DERGi Sayı 7, 2016