Page 14: of Maritime Reporter Magazine (January 15, 1980)

Read this page in Pdf, Flash or Html5 edition of January 15, 1980 Maritime Reporter Magazine

Reduced Towing Costs

Subject Of Study On

Towing Surge Pendants

The following is a condensation of a technical study prepared by the engineering and research de- partments of Samson Ocean Sys- tems, Inc., Shirley, Mass. The re- port analyzes and compares the performance characteristics of the traditional towing surge pendant utilizing heavy chain with those of a nylon rope pendant.

A surge pendant is an energy storage device typically located between the towing bridle and the towing hawser. They are used with wire towing hawsers where desirable to reduce the scope and catenary depth of the hawser without reducing the overall en- ergy storage of the hawser sys- tem. Traditionally, a surge chain has been used consisting of one or two shots of very heavy chain.

The chain catenary provides the necessary energy storage with the penalty of increased weight and towing resistance and greatly increased catenary depth at low speeds. It is desirable to replace the surge chain with a pendant of nylon rope. This offers the re- quired energy storage because of nylon's elasticity without the weight of the chain.

The performance of a tow in a seaway requires the continuous transfer of energy between the vessels involved. Any difference in speed between the tug and tow (during start-up or under wave impact) means the tug must ac- celerate the tow or be slowed down by it. If the energy neces- sary to accomplish acceleration or deceleration must be transmit- ted instantaneously, as it would through a rigid link, it would re- sult in enormous loads on the deck fittings. It is, therefore, es- sential for a towing hawser sys- tem to store energy from one ves- sel and transfer it gradually to the other without excessive loads.

Nylon rope offers this energy storage capacity with less length than wire or chain catenaries with the resulting advantages of improved control, reduced weight, little or no catenary, and reduced towing resistance. Improved con- trol results from the reduced length or scope of the hawser which provides a greater angle of the hawser at the tow, or turn- ing moment, for the same side- ways motion of the tug.

The energy storage character- istic is required primarily by deep ocean tows. Harbor tows usually call for precise control of the tow' and therefore less elongation.

Tows which have utilized surge pendants include U.S. Navy op- erations between San Diego, Long

Reach and Hawaii, and the RAR- 347 tow. The RAR-347 is a 51,- 000-ton pipelay barge which was towed, on 21-inch 2-in-l nylon, from the Netherlands to the Gulf' of Mexico by Dr. Jack, a 7,500-hp oceangoing tug.

The use of a surge pendant with a wire rope hawser offers the advantages of utilizing exist- ing towing equipment and locat- ing the synthetic rope outboard of both the tug and tow, thus minimizing abrasion. The basic procedure is to connect one end of the pendant to the bridle on the tow and the other end to the tow wire. When entering or leav- ing harbor, the tow wire is paid out just enough to clear the tug bulwark. This puts the tow on a short scope for better control.

Once at sea, the tow wire can be paid out until the tug and tow are in step (i.e., riding up and down the waves together). If the selection procedure outlined in the complete Samson study has been used, there is no need to pay out wire for a catenary. The surge pendant has all the energy storage capacity required by the tow. This allows the tow hawser to be kept near or even above the water surface, and thus reduces the resistance of the tow. The reduced resistance can result in either higher speeds or reduced fuel consumption.

The study concludes the prin-

Crude Oil Washing problems come in many shapes and sizes.

So do BUTTERWORTH tank cleaning machines.

The Right System

Reduces

Turn-around Time...

Increases Profits.

Because tank washing problems can be simple or complex there is no one machine that is right for every tank or task

But with this wide range of equipment

Butterworth Systems can help you select precisely the right machine or combinations of machines for your vessel, so you get the optimum cleaning system at minimum cost.

With the IMCO deadline approaching, there couldn't be a better time to let Butterworth

Systems solve your tank cleaning problems.

The Industry Leader

Yesterday, Today and Tomorrow

For over fifty years

Butterworth Systems has been the world leader in tank cleaning equipment

Our complete line of tank washing machines offer thoroughly proven performance and the highest reliability Each

BUTTERWORTH* tank cleaning machine has its own unique cleaning capabilities and advantages which can provide a tailor-made system for your specific crude oil washing needs 1.

The LAVOMATIC*

SA Machine. For

Fastest Cleaning of

Large Tanks.

The deck mounted

LAVOMATIC" SA tank cleaning machine has a capacity of 90-150 tons per hour and a Selective

Arc feature for single or multi-stage crude oil washing. It is the only tank cleaning machine in the world which has a patented programed speed feature which concentrates cleaning effectiveness wherever sludge buildup is normally heavy. The

LAVOMATIC" SA unit automatically slows down when washing critical areas and then speeds up over less critical areas. This speed programming feature can result in up to 60% reduced cleaning time

The LAVOMATIC" SA aduantage: the fastest economical cleaning of even the largest tanks plus a long history of superb performance and reliability.

I I 2Introducing • the

BUTTERWORTH•

P~ 60 Machine.

Making Multi-stage

Crude Oil Washing

More Economical.

The latest addition to the

Butterworth

Systems family of tank cleaning machines, the

P-60 is a single nozzle, deck mounted machine functionally similar to the

LAVOMATIC® SA machine. The capacity of the

P-60 ranges from 90 to 150 tons per hour. It features a permanently mounted control box/power source, preset speed and full-flow turbine.

Three preset selectable arcs are available to the tanker crew for a full wash, side wash or bottom wash. The bottom wash setting features a closer wash pattern to provide the greater cleaning power required there.

The P-60 aduantage: provides multi- stage washing and proven

Butterworth

Systems reliability while reducing initial cost. 52 ZIDELL Maritime Reporter/Engineering News

Maritime Reporter

First published in 1881 Maritime Reporter is the world's largest audited circulation publication serving the global maritime industry.