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COMINCH FILE
21 June 1944 CONFIDENTIAL
1. This is a Confidential, Non-Registered Publication, prepared in the Bureau of Ships from notes submitted by Commodore W. A. Sullivan, U.S. Navy, Chief of Navy Salvage. It is issued for information. 2. This publication is distributed by the Commander in Chief, United States Fleet.
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CONFIDENTIAL These notes have been prepared for the guidance of officers concerned with the operation and administration of tugs and related craft. Heretofore insufficient information concerning the characteristics of the various types of tugs has been generally available to such officers to permit intelligent assignment to tasks. As a result there have been many instances in the various theaters of operation where the limited tug boat facilities have not been used with the greatest effectiveness and in some cases serious errors in assignments have been made. In the absence of familiarity with the characteristics of the various towing craft, it appears that officers directing towing operations have been guided by the official designations of vessels or nomenclature, which, in the past has not been sufficiently descriptive for operational purposes. The nomenclature more or less loosely distinguishes between certain seagoing, rescue and harbor tugs. It is not especially indicative of the suitability of individual types, within the nomenclature groups, for the many and varied tasks for which tugs are now employed. The number of tugs presently available are quite insufficient for current needs of a most important Naval and military operational nature. As little improvement in the situation can be expected for sometime and as there will always be temporary shortages of tugs in different areas or localities from time to time it is essential that the maximum effective use be made of available facilities. The efficient selection of tugs for any mission requires an analysis of the task and the best choice of tugs suitable for performing that mission. In analyzing the task preliminary to the selection of tugs and the issuance of necessary orders and instructions, certain points should be considered with a view to avoiding the following if practicable: a. Unnecessary delay in keeping tugs waiting while tows are being prepared or disposed of after the mission has been accomplished. In this connection, if the draft of the towing tug is too great for the depth of water at either terminal, advance arrangements should be made to deliver or to take over the tow before the arrival of the deep sea tug outside. b. The employment of large tugs on work that available smaller and less powerful or less seaworthy tugs can do. An estimate of the required towline pull and horsepower of the towing vessel should be made as a first step preparatory to making an assignment. (See tables in back of pamphlet). c. The employment of small tugs to undertake work beyond their capacity. This also requires a consideration of the towline pull. d. The employment of tugs on tasks for which they have insufficient endurance unless arrangements have been made to provision or to fuel them en route. e. The unnecessary employment in rear areas of tugs designed or especially suited for duty in combat zones. The large Indian Class (ATF67—76 etc.) tugs are well suited for combat towing and for emergency salvage or fire-fighting in combat areas. Therefore, they should not be employed in the rear areas if other tugs suitable for this work are available. f. The employment of tugs in forward combat areas that have insufficient stability, reserve buoyancy or subdivision to enable them to survive even moderate damage or which are insufficiently armed to ward off attacks by enemy planes. g. The routing of tugs with large tows over areas where the depth of water is insufficient for the catenary of the hawser. Arrangements should be provided for shortening the towline where necessary. Tows are frequently lost or involved in difficulties due to the towline fouling submerged objects. - 1 - |
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CONFIDENTIAL h. The unnecessary employment of tugs for standby duty on salvage or rescue operations. Tugs should not be ordered to standby unless there is a definite possibility that their services may be needed and they are capable of rendering the service likely to be required. i. The unnecessary diversion of rescue tugs from areas in which tugs equipped with rescue (salvage or firefighting) facilities may be required. j. The unnecessary employment of tugs for tows that could be undertaken by other craft scheduled to make the same passage or by a ship that may perhaps be more easily made available for the tow than a tug. Information concerning the chief characteristics of tugs and related craft of interest to those concerned with their operation is contained in the following paragraphs together with certain tabulated data at the end. Changes in nomenclature or designation with a view to grouping craft with similar operating characteristics in the same group have been effected in enclosure (A). The following takes into account the new designations as established in enclosure (A). ATF - Ocean Tugs, Fleet This class consists almost entirely of large seagoing tugs of the Navajo Class (ATF 67-76 etc.). They are excellent all purpose, long range, powerful, very seaworthy tugs, particularly well suited for operations with the combat forces. They are excellent for long tows of large vessels including mobile drydocks. They have good firefighting and good salvage (ship rescue, emergency damage control and repair) facilities. For firefighting they can be improved by the addition of portable fire pumps and equipment. They are well armed and can take considerable punishment. ATFs have a maximum draft of about eighteen (18) feet and consequently are not suitable for inshore work in amphibious operations. When used in combat operations, and unless already included in the ship's company, they should carry as additional personnel — one salvage officer, four salvage divers, six general salvage men, one firefighting officer and eight firefighting specialists. The regular allowance of salvage and firefighting gear should also be supplemented as may be considered advisable for the particular operation. ATA - Ocean Tugs, Auxiliary ATAs are new tugs designed for major towing operations at sea. This category includes all new seagoing tugs except ATFs and ATRs. Many new War Shipping Administration tugs manned by civilians have the same general characteristics as ATAs. They have a large radius of action and considerable endurance. ATAs are not supplied with appreciable firefighting or salvage facilities, although they do at least have the minimum amount which should be expected on any seagoing tug. They have a maximum draft of about 14 — 15 feet. They are well suited for use in reserve areas just outside combat zones where they will be in a position to relieve any ATF that may be engaged in towing a disabled vessel to a repair base or in performing any other similar task, thereby permitting the Fleet tug to return to the zone of combat. They should be used for major towing operations not in combat areas. Their armament is somewhat less than ATF's and they have about one half of the ATF horsepower. ATR - Ocean Going Tugs, Rescue ATRs are new wooden tugs originally designed to render emergency assistance to vessels disabled on the high seas in enemy submarine infested coastal waters of the United States. They are extremely well fitted for firefighting and have moderate salvage facilities. ATRs have excellent seagoing qualities and good towing power -2- |
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CONFIDENTIAL but are sharply limited in endurance and radius of action. These vessels are excellent for towing operations of a large magnitude but of a limited distance. ATRs are well suited to supplement the services of ATFs in combat areas, where cruising endurance is not an important factor and particularly where fire may be one of the great potential hazards. When a sufficient number of these tugs are available, one should be assigned to each major base for standby duty. ATO - Ocean Going Tugs, Old This class includes a miscellaneous assortment of seagoing tugs not meeting the requirements of the ATF, ATA or ATR groups. They are largely World War I type tugs or ex—Mine Sweepers (Bird Class). Some are deficient in stability, reserve buoyancy and freeboard or have been fitted with blisters or ballast as a partial remedy. Others have sufficient stability but insufficient freeboard and radius of action. In general they have widely varying characteristics but due to their age and general condition, limitations, etc., should normally be used to fill demands in rear areas where repair facilities are readily available and duty will not be too rigorous. In general they have no appreciable firefighting or salvage facilities. YTB - Harbor Tugs, Big Harbor tugs with more than 800 h.p. YTM - Harbor Tugs, Medium Harbor tugs with 400 - 800 h.p. YTL - Harbor Tugs, Little Harbor tugs with less than 400 h.p. The facilities of the existing harbor tugs vary widely. Some individual tugs are fitted with good firefighting pumps and other facilities-and some are not. Some of these tugs have been very successfully employed for rescue (towing) along beaches in amphibious operations. Their main and almost exclusive purpose is towing. Their assignment and use should be based chiefly on their size, power and endurance. Salvage Vessels and Submarine Rescue Vessels: Most of the vessels in these classifications are capable of towing to a greater or a lesser degree. However, they were designed and constructed for certain other specific purposes and were fitted with some limited towing arrangements for work incidental to their primary function. These ships are extremely valuable and their number is limited. They will be even more difficult to replace than tugs if lost. Their services for towing operations not incidental to salvage or submarine rescue should, therefore, only be employed in emergencies or where it is considered availability for their designed purpose will not be jeopardized or required. There are four classes of salvage vessels in the Naval service as follows: ARS - Seagoing Ship Salvage Vessels (l) One class, (ARS1, 2, 3, 11, 12, 30, 31, 32) consists of converted ex-Bird Class Minesweepers and other suitable craft acquired from Various sources. These vessels have satisfactory characteristics and have been fitted out for ship salvage work to be accomplished by civilian crews in the coastal waters of North America and the Caribbean Sea. They have been fitted out for definite specialized ship salvage purposes encountered in coastal salvage work and are not especially suitable for towing nor are they suitable for employment as Naval manned salvage -3- |
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CONFIDENTIAL vessels, due to lack of accommodations. With one exception, the USS BRANT (ARS32), they are civilian manned and are operated by Merritt—Chapman & Scott Corporation under the direction of the Supervisor of Salvage, USN. In the case of the BRANT, or any similar vessel which may be manned by a Navy personnel, the number of salvage men carried aboard and available for salvage operations is too small for any ordinary operation due to the fact that the number of men required to man these ships according to Navy operating standards takes up most of the available accommodation space. When one of these vessels, Navy manned, is used for a salvage operation it is necessary to temporarily place on board an additional number of salvage personnel and to provide sleeping accommodations on deck or wherever any space can be found. (2) Salvage Base Ships (small coaster cargo type recommended) are used for transporting salvage gear and personnel to and from occupied harbors and bases incident to harbor clearance and miscellaneous salvage operations. They are not suitable for use in the actual conduct of salvage work but are chiefly an auxiliary to the salvage vessels or salvage forces. (3) Newly constructed large Steel Salvage Vessels (AES 5-9 inclusive, 19-27 inclusive, 33, 34 and 38—49 inclusive). These vessels were designed primarily to be operated by Navy crews and to be used for offshore salvage work in distant waters. They carry a salvage crew of two officers and twenty—one men in addition to the regular ship's operating crew. Their chief characteristics are: length - 213'; beam — 39'; draft — 13'; full load displacement — 1630 tons; cruising radius — 5,000 miles; speed — 15 knots; shaft h. p. — 3,000; propulsion plant — twin diesel electric. These vessels are capable of undertaking offshore salvage operations of considerable magnitude, although for some difficult types of work, two or more vessels may be required. They carry a considerable quantity of valuable salvage gear and should not be unnecessarily hazarded. In combat operations the salvage vessels should be stationed in areas just outside the combat zone and kept available for any major salvage operation that develops. At present, these vessels are fitted with towing machines, the drums of which should be locked in position before being subjected to the strain of a tow*. The rescue facilities of the fleet tugs (ATF), will usually be sufficient for any salvage work required of the type which can be undertaken under combat conditions. (4) Newly constructed smaller Wooden Salvage Vessels (AES 13—17 inclusive, 28, 29, 35, and 36). The chief characteristics of these vessels are as follows: length - 183'; beam - 36'; draft - 12'; full load displacement - 1275'; cruising radius — 3,000 miles; speed — 12 knots; shaft h.p. — 1200; propulsion plant — twin diesel electric. In general, subject to the limitations of the wooden hull, smaller cruising radius and speed, the remarks concerning the Steel Salvage Vessels under sub—paragraph (3) above, also apply to the Wooden Salvage Vessels. Due to these limitations, the wooden vessels should be assigned to areas where the radius of action required will not be too great, and on account of the wooden hulls extended duty in tropical waters is not advisable unless the bottoms are suitably sheathed. The Steel Salvage Vessels are of course more rugged than the wooden. ASR - Submarine Rescue Vessels Submarine Rescue Vessels, as such, are neither equipped nor manned for ship salvage. They are designed and equipped primarily for the purpose of rescuing the crews from sunken disabled submarines in waters up to a maximum depth of about three-hundred feet. Equipped for this purpose, they are accordingly suitable for conducting diving operations in relatively deep water whereas salvage vessels (ARS) are equipped for normal diving operations in shallow water (up to sixty feet). Ship salvage operations, expecially during wartime, are seldom practicable or necessary in waters of greater depth. In view of the special function, rescue of NOTE: ARS 21-27, 38-49 will be equipped with 60,000# towing engine. -4- |
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CONFIDENTIAL personnel, for which Submarine Rescue Vessels are provided they should not, except in rare cases, be assigned to ship salvage (including salvage of submarines). As a rule all ship salvage tasks should be assigned to the Ship Salvage Forces, or to salvage vessels operating in the area. If it develops that a particular salvage operation involves the need for the facilities of a Submarine Rescue Vessel, consideration should then be given to the justification for diverting such a craft for that purpose. Otherwise, the Submarine Rescue Vessels may be subjected to unnecessary hazards in connection with tasks for which they are not particularly well fitted. Towline Pull Though dependent on the characteristics of the propeller, speed and other factors, line pull developed by a towing vessel can be estimated to be roughly equivalent to one ton of towline pull per hundred shaft horsepower. This empirical formula is based on many actual tests, and has long been in use by experienced tow boat operators. It will be noted from the straight line curve, Plate II, that speeds, under ideal sea and weather conditions corresponding to a line pull of one ton per hundred s.h.p., are between about six (6) and eight (8) knots for a s.h.p. of less than 2600. Since towing deals with large masses in motion, large forces, incident to changes in inertia, may be set up momentarily clausing wide variations in the towline pull and breakage of towlines which otherwise might be considered amply strong. Towlines should have a factor of safety of 4 - 6, on the basis of the above empirical rule. Elasticity, either inherent in the materials from which the towline is manufactured or in the weight and length of the line (catenary) should be provided to dampen instantaneous changes in forces. Elasticity in the towing arrangements is a vital consideration in connection with the strength of the towline. Manila towlines, having greater stretch than steel before developing full strength can be shorter and, in new manila, can have less ultimate strength than steel wire rope for the same tow. Towing speed, or for that matter, ability to tow at all, is dependent on sea and weather conditions and nature of the vessels involved as much as it is on the s.h.p. of the towing vessel. Forces set up by the weather may easily be of an order equal to or greater than those set up by the towboat. These factors must be considered on the basis of experience and judgment. Often a heavy ship, well loaded down, may be more easily towed and at a faster rate than the same ship in a light condition. The loaded ship having less area exposed to the wind and a greater "rudder" or "center-board" effect due to deeper draft is usually more easily managed in a wind and seaway than the light ship. Bearing the above in mind the data contained Plates I, II and III should be of value in connection with the selection of suitable vessels for conducting towing or related missions. For estimating required towline pull from Plate I, the displacement of a ship to be towed can be obtained from the displacement curve. If this is not available, a sufficiently close approximation can be obtained from the following formula:
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Op-23-S-jk NAVY DEPARTMENT 13 April 1944 RESTRICTED
1. In order to identify the general classes of tugs now in commission, in service or building, the following designations are recommended, effective 15 May 1944.
2. The following present approved classification is recommended for cancellation, effective 15 May 1944.
3. If the above recommendations are approved, the changes in classifications are as follows, effective 15 May 1944.
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CONFIDENTIAL
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13 April 1944 First Endorsement
FRANK KNOX
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SOURCE:
Transcribed by RESEARCHER @ LARGE. Formatting & Comments Copyright R@L.
