378P_Sonar Dome Report
- jr_crowder
378P Dry Dock(s) Sonar Dome Report
July 27 to November 12, 2018
Keppel shipyard - Subic Bay
Preparation for removal of the sonar dome
All tools, supplies, and plates were collected in the downhole lab in preparation for removal.
A roughly 35" x 51" inside dimension support structure was fabricated to hold up the soar dome inverted for maintenance. The structure is 21" high to accommodate the neck of the sonar dome with the lifting plate installed.
Sonar Dome Removal in dry dock
The sonar dome was removed while the vessel was dry in the Keppel Subic dry dock on August 6th, inverted, and landed on the Bridge Deck.
Prior to removal, plywood covers were banded to the dome to cover the transducers and protect them during removal.
Disconnected the signal cables from the top side through the hatch in the forward thyrig room.
Pad eyes were welded to the hull and chain falls were used to lower the sonar dome onto a wheeled skid fabricated by the shipyard. The dome was wheeled out to the starboard side for crane access. The dome was inverted by the large shipyard crane, straps, and chain falls down in the dock prior to lifting.
The hull blanking plate was installed using new threaded studs. The studs where protected from sandblasting (see below).
Maintenance
The following maintenance was performed.
Hull and dome mounting flanges buffed and cleaned. Measured for flatness (see below).
All transducer faces cleaned of growth on the outside.
Threaded lifting eyes were installed in the 4 corners of the 3.5 kHz array mounting plate for removal.3.5 kHz array The array was removed from dome, inverted, and landed on the deck on wood blocks.. Threaded lifting eyes were installed in the 4 corners for removal.
The two small transducers were removed by hand and inverted in place for cleaning.and cleaned.
The interior of the dome was scraped, scrubbed, and washed.
The accessible metal surfaces inside where chipped, buffed, primed, and painted.
The mounting flanges of all of the transducers were chipped, buffed, primed and painted.
Additional ½" rubber sheeting was adhered to the interior ceiling of the dome.
Sonar Dome mounting flanges
The mounting flanges of the dome and hull were roughly measured for flatness after removal. The flange on the hull has some minor deflection. The flange on the sonar dome has an obvious mushroom shape.
The sonar dome was removed from the ship and taken to a warehouse in the shipyard and a request made to weld the four lifting eyes on and mill the flange.
sonar dome modification
Four new lifting eyes were fabricated at IODP and threaded into the four lifting points. The shipyard welded them in place.
Projects in shipyard
The 4 new lifting eye bolts were welded in place. Welding test was performed by the shipyard to satisfaction. Primer was painted over the welding spot
The leveling of the neck surface and re-machine of the O-ring groove was conducted by a machine shop in Manila. Zenon was instructed to supervise the machine work. Sonar dome was transported from shipyard to the machine shop on August 23. It remained in the machine shop for all repairs. It was transported back to the shipyard on August 27th.
The machine shop secured the dome in a 90 degree angle and leveled the top surface of the neck.
They deepened and added a dove tail, pointing outward, in the O-ring groove. All specification is in a separate report, filed together with all Sonar Dome document.
Sonar dome was installed back under the ship on August 27th with a new set of nuts, bolts, and washers, under the supervision of IODP staff. A new o-ring was installed with silicone grease. Note: although the question arise that all the designated o-rings are slightly bigger than the groove. Although we made it fit, we are not sure if they are the right size.
Performed a 5 psi pressure/leak test from inside the ship and passed with no issue.
Transducers, both 3.5 and 12 Khz, were tested after ship went wet, and functioning.
The entire sonar dome was painted with ship hull, except the lifting eye bolts. The eye bolts were not initially painted but did get painted as of Sept. 3, 2018.
In Machine shop in Manila, and after leveling.
Stock O-ring is bigger than the diameter of the groove
Inner O-ring was the one removed from the groove, no record of where it comes from and part number. The outer O-ring is the new one installed
Installation
Sept 3, 2018
After shipyard painting
Hong kong dry dock
The sonar dome managed to survive another dry dock but not without needing a little attention. During the storm evacuation of Subic Bay something must have gotten caught around the neck of the dome and scraped the paint off down to bare metal in one sectionbeen caught around the neck of the dome, scraped the paint off down to bare metal in one section, and removed the top two layers of anti-fouling paint on the back. The anti-fouling paint also came off the pins, nuts, and bolts likely due to the incorrect primer being used or no primer used at all.
Sections of the dome were prepped and dried before applying the primer that goes with the red anti-fouling paint. Then the red anti-fouling paint was applied. Now let's hope it sticks!