Page 359 - Ship Construction.DJ Eyres 6Ed

Ch31-H8070.fm Page 348 Wednesday, October 18, 2006 7:06 AM
348 Ship Construction
The product of the maximum stress thus calculated and the factor 4.25
should not exceed the minimum ultimate strength of the material. The
deflection is limited to 0.0028 times the span under these loads.
For portable beams of mild steel the assumed loads above are adopted,
and the product of the maximum stress thus calculated and the factor 5
should not exceed the minimum ultimate strength of the material. Deflec-
tions are not to exceed 0.0022 times the span under these loads.
--- ใช้เพื่อการศึกษาเท่านั้น---
Mild steel pontoon covers used in place of portable beams are to have
their strength calculated with the assumed loads above. The product of the
maximum stress so calculated and the factor 5 should not exceed the mini-
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
mum ultimate strength of the material, and the deflection is limited to 0.0022
times the span. Mild steel plating forming the tops of the covers should
have a thickness which is not less than 1 per cent of the stiffener spacing or
6 mm if that is greater. Covers of other material should be of equivalent
strength. Carriers and sockets are to be of substantial construction and
where rolling beams are fitted it should be ensured that beams remain in
position when the hatchway is closed.
Cleats are set to fit the taper of wedges. They are at least 65 mm wide,
spaced not more than 600 mm centre to centre; and not more than 150 mm
from the hatch covers. Battens and wedges should be efficient and in good
ึ
condition. Wedges should be of tough wood or equivalent material, with
a taper of not more than 1 in 6, and should be not less than 13 mm thick
at the toes.
At least two tarpaulins in good condition should be provided for each
hatchway, and should be of approved material, strength, and waterproof.
Steel bars or equivalent are to be provided to secure each section of the
hatchway covers after the tarpaulins are battened down, and covers of more
than 1.5 m in length should be secured by at least two such securing appli-
ances.

(4) Hatchways closed by Weathertight Steel Covers Coaming heights are as
for those hatchways with portable beam covers. This height may be reduced
or omitted altogether on condition that the Administration is satisfied that
the safety of the ship is not thereby impaired. Mild steel covers should have
their strength calculated assuming the loads given previously. The product
of the maximum stress thus calculated and the factor of 4.25 should not
exceed the minimum ultimate strength of the material, and deflections are
limited to not more than 0.0028 times the span under these loads. Mild
steel plating forming the tops of the covers should not be less in thickness
than 1 per cent of the spacing of stiffeners or 6 mm if that is greater. The
strength and stiffness of covers made of other materials is to be of equiva-
lent strength.
Means of securing weathertightness should be to the satisfaction of the
Administration, the tightness being maintained in any sea condition.