Documentation and information

Surveyors and ship’s officers should discuss documentation details and location and state of all compartments. The instruction pages of the stability information and calibration tables should be studied and a check made of the tank capacities with the capacity plan. It should be remembered that the port and starboard tanks might not be the same and consequently have separate calibration tables. The base for measurement of vertical heights, the reference point for longitudinal measurements, the units and the sign conventions used in the tables must all be verified. The units used in the correction table should also be carefully noted because there is sometimes a mixture of units and sign conventions contained within the same documentation. The whole survey should be conducted using the units of the ship and the final result changed to a suitable unit, if necessary. When feet and inches are the standard unit, convert to feet and decimals of a foot for the convenience of a calculator. The full sounding depths of tanks, the summer draught and freeboard and the record of recent tank soundings should be noted. If a bunker survey is not to be carried out, the chief engineers bunker figures (fuel oil, diesel oil and lubrication oil) are required, also the daily port consumption quantities. Should any bunker or stores be delivered during the stay then the delivery notes must be sighted for the additional quantities to be included in the final survey. The draught survey is only interested in changes in the bunkers on board, that is consumption and deliveries.

The position of the anchors should be checked, should any alternation be proposed during the stay then the weight of the anchors and cables should be determined.

The ship’s staff and surveyors should work together throughout.

Take accurate overboard water samples and draughts

Density

Using a sample bucket take samples from half draught depths from at least two position on the offshore

And the onshore side, avoiding the discharges, stagnant water between ship and jetty and outfall areas. Take samples of about one litter and do not mix the samples. Rinse out the bucket and the sample jar with the first sample of water. Take the density readings promptly, protecting the sample jar from the wind and direct sunlight. Hold the hydrometer vertically by the top of the stem and gently lower into the sample until it floats freely. Take the hydrometer reading where the overall level liquid surface meets the graduated stem, not the top of the meniscus. Avoid parallax by filling to near the top of the sample jar and placing the eye in line with the liquid level. The bottom of the sample jar should have 25 mm clearance below the base of the hydrometer and have a minimum internal diameter of 50mm. If densities obtained show no major variation then calculate the average value, however if there are suspicious variations in the readings then additional samples should be taken and this factor included in the report. Measure the apparent density with a Zeal glass draught survey hydrometer and be aware of any tidal changes, which may affect the sample density.

Draughts

The draughts and density should be obtained at nearly the same time if possible. Draughts and densities taken at slack water are the most accurate but may not be practicable. All the draughts should be read with great care and every effort made to read directly from ship’s side using a boat, ladder or other available means. The figures should be written down as they are obtained to avoid mistakes of memory. If required, the midships draughts can be obtained by measuring the freeboard from the waterline to the top of the deckline, when a correction must be applied. A tape with a float plate at the zero mark can be very usefully employed to achieve this measurement.

4. Calculate the ship’s underwater volume and displacement

a) Correct the observed draughts to the centerline, i.e. the mean of the port and starboard draughts.

b) Correct the centerline draughts to their value at the correct position of the perpendiculars.

c) Allow for hog or sag and obtain the correct draught amidships.

d) Enter the hydrostatic tables with this corrected draught to obtain the uncorrected displacement.

e) Correct this value of displacement for:

First trim correction

Second trim correction

List (if necessary)

Density

Date: 2016-01-03; view: 766