19 June 2001
PR-2: Repair of Drydock Caisson Seal by Replacement
Problem: Caisson wood or "rubber" seal is deteriorated or damaged and leaks.
Procedure: Move the caisson into the drydock and secure. Remove the existing
wood or synthetic "rubber" seal assembly (see Figures 9-1 and 9-2.) Unless the
old seal is "rubber" and the existing studs are still serviceable and in the correct
configuration, remove the old mounting studs. Clean any wood or "rubber"
remnants or any other obstruction on the caisson seal mounting surface. Repair
surface flaws and irregularities in the caisson seal substructure to within an
allowable tolerance as follows.
Caisson seal mounting surface roughness profile should not deviate
from the nominal profile by more than 2.5 mm (98 mils.)
Caisson seal mounting surface waviness profile should not deviate
from its nominal profile by more than 0.3 mm (12 mils) over a waviness
spacing of 30 cm (12 inches.)
Caisson seal mounting surface should be parallel to within at least 10
mm (393 mils) over the length of a span section (2.75 meters (9 feet)).
Install new mounting studs onto the caisson seal sub-structure if required. The
stud material should be a MONEL alloy with the weld filler material and weld
process conforming to the correct specifications for welding MONEL to carbon
steel. A wood template duplicating the seal configuration hole pattern must be
made for each type of seal configuration. These templates are used to properly
position the new studs. Starting with the corner section, position and align the
wood templates around the caisson. Mark the stud locations on the caisson using
a center punch.
Mount a new isoprene "rubber" seal onto the caisson seal sub-structure. Use
MONEL washers and nuts to mount the seal assemblies. Use the following
procedure starting with the corner section. Be careful not to damage the
Position the lifting fixture at the top end of the seal and lower the fixture
retaining bar over the seal.
Lift the seal out of the crate and position the bottom end of the seal
over the corresponding mounting studs. The bottom of the seal should
make contact with the caisson first.
Apply a coating of rubber adhesive to mitered joints before mating.
Install at least two nuts and washers onto the studs at the bottom to
hold the seal in place while the lifting fixture is removed.