New borescope technology


MARIN recently improved the borescope technique sig- nificantly. Now, more detailed observations of propeller and other appendages are possible in normal daylight.


Ivo van der Hout i.v.d.hout@marin.nl


In the past cavitation observation was per- formed using a time-lapse camera looking through a window in the hull above the propeller. Later on, the time-lapse camera was upgraded to a high-speed video, which made it possible to continuously observe cavitation dynamics and the propeller for several minutes. Nowadays, for most observation purposes a borescope is used instead of a window because the installa- tion time and costs are significantly lower. The borescope can be installed when the vessel is in the water by drilling a small 12mm hole through the ship’s hull and by welding a special flange over the hole.


Comparison between the second generation (100Hz) and the third generation (1000Hz) borescope technique.


The challenge with the borescope technique is illumination, as no external lights are used and the diameter is not bigger than a keyhole. Using an image intensifier in combination with the high-speed camera, normal daylight provides just enough light to observe the pro- peller and cavitation. MARIN improved the borescope technique by merging a dedicated image intensifier into a high-performance CMOS high-speed camera, resulting in an in- crease in light intensity by at least factor 20.


Window Purpose


Sampling rate conventional video


Sampling rate High Speed Video


Camera location


Diameter of hole through the hull


Advantage Disadvantage


Fundamental Research 25 Hz


2000 Hz


inside the vessel 200 mm


High quality image High Speed


Installation during docking period


New TowCam technique Another new, more experimental technique is the TowCam. A TowCam is a camera installed underneath the vessel and is towed by its cable. The camera lens faces downstream, making it possible to observe the suction side of the propeller. The wide-angle lens makes the complete propeller visible, including the blade in the 6 o’clock position, which is not possible using other techniques. However, installation through the hull is still difficult and systems to make this easier are under development. Another development is focused on the positioning of the TowCam and manoeuvring in the water. An overview of three different observing techniques is given in the table.


The newly developed borescope high- speed camera and the TowCam open a completely new window on cavitation and flow observations. The equipment is hand- carry and can be installed with the vessel in the water. Therefore, the new technology enables swift deployment and a speedy interpretation of results.


Borescope


Commercial and Research 1st generation (25 Hz)


2nd generation (100Hz) 3rd generation (1000Hz)


inside the vessel 12 mm


Good quality image Easy Installation 360-deg viewing angle


TowCam Research 25 Hz


Future plans


outside the vessel 80 mm


Large viewing angle (only suction side of propeller) Adjustable in position


Installation is difficult Positioning of TowCam under water difficult Low frequency images


14 report


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