| Tweet |
Custom Search
|
|
|
||
 TB 55-1900-232-10
stability generally is considered inadequate. Equally important is frequent checking for a change in the tow's roll period.
Even if overall criteria are satisfactory, investigate promptly any significant increase in period, since this suggests
flooding and/or additional free surface.
For small craft and barges which do not have a Damage Control Book, follow a few general guidelines when attempting
to improve stability:
a Completely fill any slack tanks
b. Lower and secure or off-load high weights
c Secure any large hanging weights and add ballast.
Completely filling tanks or adding ballast will decrease freeboard as well as improve stability. For commissioned ships in
the U.S. Navy, the Damage Control Book contains specific measures appropriate to the ship which can be employed to
improve the stability. The book also contains stability characteristics for various loading conditions which meet the
Navy's stability criteria
3-2.7.5 Structural Reinforcing.
CAUTION
Many barges and barge-like vessels tend to be more susceptible to damage and deterioration than conventional
ship-type vessels. They should therefore be inspected for hull strength prior to towing.
To avoid special dry-docking before towing, barges, cranes and other service craft should be thoroughly examined during
routine maintenance. Plate thickness and weld inspections should be made during regularly-scheduled dry-docking, or
by ultrasonic inspection in water, and repairs made then In emergencies, such as salvage and rescue towing, structural
reinforcement and load distribution may be accomplished with additional structure or shoring. See Figure 3-4 for typical
timber framing practice. Protection against slamming damage may be effected by pressing up the bow section of the hull
with water. This action may require counter-flooding or shifting of cargo.
Inspection may reveal damage or deterioration of the frames, bottom or weld seams. Particularly when this occurs in the
forward one-fifth of the vessel's length, the vessel should be dry-docked or ultrasonically tested, and necessary repairs
made. Bottom plate thickness must meet minimum values for safe towing. See Table 3-1 While in dry-dock, check
bottom, side, decks and inner bottom. All defective welds and plating should be repaired or replaced.
3-2.7.6 Rudder.
CAUTION
Do not use temporary lashings or other makeshift measures to lock the rudder of a towed ship. Lock the rudder
amidships for towing.
The tow's rudder should be locked, generally amidships. A drifting rudder will cause the tow to behave erratically.
During preparation of the tow, an examination of the steering gear on the tow will permit the selection of the best method
to secure the rudder. Several general methods are shown in Figure 3-5. Using any method, care and proper engineering
should be accomplished to ensure the securing device(s) and supporting structure are strong enough to withstand the
forces generated by the rudder. It should be kept in mind that the forces on the rudder, even at low speeds through the
water, may be very large due to wave impact and other sea action. These loads will be transmitted through the steering
gear and will have to be absorbed by the ship's structure as imparted by the securing device.
3-8
|
||
|
||
