The Navy has recently begun using water bags accomplishing periodic weight tests of boat davits. A result of a teaming effort between NAVSEA, NAVSEA Philadelphia-SSES and FTSCLANT, this innovation will save the Navy over $3 million per year compared to traditional methods. In the past, tests using concrete block or steel weights required
a pier side or barge crane plus four-six individuals, cost as much as $20 thousand and required up to eight hours.
Using water bags is simple. A flexible container is filled with water, acting as the test weight. Water supplied from the ship fire main fills the bag to the required weight. (Remember "A pint's a pound the world around"?) A wireless load cell shackle connected between the bag master link and the davit hook provides an accurate reading as the bag fills. Adding or draining water adjusts the weight.
Once the operation is complete, the container is drained and packaged for storage. Since it can be packed up at the relatively small size of 175 - 300 lbs, the process requires no crane supporting or positioning the bags on the davit. Only about three workers are needed over a three-hour job.
Cost savings constitute the greatest advantage. The Navy spends
between $3.6 and $5.2 million per year for weight tests. Estimated annual costs will decrease approximately $560K per test by eliminating the need for a crane plus reduced labor and time, producing savings of over $3 million.
Safety is enhanced, as physical handling of large weights is no longer necessary.
Scheduling flexibility increases for the testing activity and the TYCOM, ship's force and FTSC. Without the need to schedule a crane, tests can be accomplished with very little advanced notice. Greater flexibility generates additional savings that defy accurate calculation.
Funding obtained from NAVSEA's Engineering for Reduced Maintenance Program enabled the teaming effort between NAVSEA, NSWCCD-SSES and FTSCLANT. The first step called for identifying a manufacturer whose product was safe, functional and reliable. Water Weights Inc.
was quickly identified.
The second step entailed resolving physical size constraints for the bags because of unique test requirements associated with boat davits. Unlike many other hull and deck machinery systems, boat davits must inhaul the test weights to the fullest inboard point, ensuring the davit winch and structural members are subjected to loading experienced during actual conditions. This brings the weights within the shell of the ship, requiring shapes small enough to avoid deck obstructions. Water Weights Inc. was able to modify "off the shelf" bags to fit.
The final step was development of operational and maintenance procedures for incorporation into manuals and a training video. It shows the principle of operation as well as the test. The footage was taken and the operational and maintenance procedures "proofed in" during actual tests on USS GEORGE WASHINGTON (CVN 73), USS BARRY (DDG 52), and USS MOUNT WHITNEY (LCC 20). - (By Tom Warring, Public Affairs Officer, Naval Station Warfare Center, Carderock Division)