NSMB 8 kPa

BSRA 10 kPa

KRISO Conventional Stern : 8 kPa Naval Ship : 4 kPa

Review of Hull Pressure Measurement

The conventional method, which is to install the pres- sure transducer on the inside of hull with a hole on hull surface for measuring the fluctuation pressure of actual vessel, is relatively safe work and possible to install at the accurate measurement position because it is possible to work after confirming the position of the construction drawing。

In comparison with previous method, the new method has features of installing the pressure transducer on the surface of hull from the exterior of ship, which requires more scrupulous attention due to installing the pressure transducer after choosing the basis position on the 3-D space and has dangerous factors of the safety accidents due to work at high place。 Table 2 shows the compari- son between new method and conventional method。论文网

Table 2:  Characteristics of Pressure Transducers

Magnetic Sensor Pressure Transducer Cost(US $) 1,250 1,700

Maker 1 ( HHI ) Some

Installation Difficult Easy

Re-application Impossible Possible Work place No limit Limit (Dock)

         Hole None Required         

Fig。 3:  Major Position of Pressure Sensor

Allowable Pressure Limit

For the allowable limit of propeller fluctuating pressure, no international standard is now established however some institutions provide the guidelines of pressure limits in Table 1。

Table 1:  Allowable Pressure Limits

Institution Allowable Pressure Limit DNV 8 kPa

HSVA Merchant Ship : 4~8 kPa

Naval Ship : 2。5 ~ 4 kPa

LR Transom Stern : 6 kPa Conventional Aftbody Form : 8 kPa

The pressure measurement during sea trial of actual ship has to take care of the change of the environmental condition because it is changeable in accordance with a route of ship, weather and sea state etc。 For detecting the accurate propeller rpm, it is strongly recommended to directly measure rpm by tachometer installed on engine shaft。

Magnetic Sensor

The conventional method for fluctuating pressure meas- urement induced by propeller was recently applied on the trouble shooting of ships built by Hanjin Heavy Industry Co。 Ltd and Samsung Heavy Industry Co。 Ltd in Korea。 For improvement of conventional method, HMRI (Hyundai Maritime Research Institute) designs magnetic sensor which does not damage to hull surface and apply it to fluctuating pressure measurement of the actual ship。

The magnetic sensor is feasible to be installed anywhere because it is attached to hull surface and does not influ- ence the strength of hull surface owing to being de- tached naturally by the outside fluid force after  definite

time。 Moreover, it can be quickly used to examine the cause of problem originated from fluctuating pressure after ship’s delivery。

The magnetic sensors were attached to hull surface and the line connection with the measurement system for data acquisition is required。 Fig。 4 showed the magnetic sensor installation for the LNG carrier at the  dockyard of HHI。