7_Attachment 26 - NSWCCD-23-TM-2011-05 Boat Mechanical Practices.pdf

Naval Surface Warfare Center

Carderock Division

Bethesda, MD 20084-5000

NSWCCD-23-TM-2011/05 November 2011

Ship Systems Integration and Design Department

Technical Memorandum

U.S NAVY CRAFT MECHANICAL PRACTICES

by

Combatant Craft Division (232)

DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited

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N a v y C ra ft

M e c h a n ic a l P ra c ti c e s

U.S. NAVY CRAFT MECHANICAL PRACTICES

NSWCCD-23-TM-2011/05

Post-Release Revisions

Revision Reviewer/ Approver

Date Change Description

Page, Section

REPORT DOCUMENTATION PAGE

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OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person should be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN

YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE

11-18-2011

2. REPORT TYPE

Final

3. DATES COVERED (From - To)

Dec 2009 to Nov 2011

4. TITLE AND SUBTITLE

US Navy Craft Mechanical Practices

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Combatant Craft Division (Code 232)

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NAVSEA Carderock Surface Warfare Center Division

Combatant Craft Division

2600 Tarawa Court, Suite 303

Virginia Beach, Virginia 23459-9235

8. PERFORMING ORGANIZATION REPORT

NUMBER

NSWCCD-23-TM-2011/05

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Attn: PEO SHIPS, PMS 325G

Commander

Naval Sea Systems Command

1333 Isaac Hull Avenue, SE Building 197

Washington Navy Yard, DC 20376

10. SPONSOR/MONITOR’S ACRONYM(S)

PMS325G

11. SPONSOR/MONITOR’S REPORT

12. DISTRIBUTION / AVAILABILITY STATEMENT

Approved for public release; distribution unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

This document provides guidance to assist boat builders, designers and engineers in the design, integration, installation, inspection, and acceptance of mechanical systems for U.S. Navy craft. It conveys typical government preferences and expectations as an educational tool for builders and system integrators offering boats and craft on the General Services Administration

(GSA) Federal Supply Schedule (FSS).

15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF:

17. LIMITATION

OF ABSTRACT

18. NUMBER

OF PAGES

19a. NAME OF RESPONSIBLE PERSON

Scott Petersen a

R E P O R T

U n c l a s s i

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified

See 12.

19b. TELEPHONE NUMBER

757-462-3107

Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 ii

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Contents

Figures..............................................................................................................................................v

Administrative Information ........................................................................................................... vi

Acknowledgements ........................................................................................................................ vi

Summary

Background

Introduction

Objective

Scope

General Guidance for Design and Construction

Equipment Specifications

Installation of Equipment & General Access

Workmanship

Corrosion

Noise and Vibration

Noise

Control of Noise and Vibration

Welding Machinery and Piping

Threaded Fasteners

Bolted Connection Design

Fastener Materials and Features

Self-tapping Screws

Reliability and Maintenance

Safety

Machinery Foundations

General Guidance for Propulsion Design and Installation

Diesel Propulsion Engines

Marine Transmissions iv

Outdrives, Waterjets, and Outboard Motors

Raw Water Cooling Systems

Engine Exhaust Systems

Fuel Systems

Fuel Tanks

General Guidance for Auxiliary System Design and Installation

Piping and Piping Systems

Fluid Velocity Limits

Pump Suction Lines

Equipment Isolation

System Isolation

Remote Valve Operation

Relief Valves

Piping and Hose Supports

Piping Arrangement and Installation

Materials

Hoses and Tubing

Hose Connection Design and Installation

Hose Support and Protection

Piping Systems Labeling

Heating Ventilation and Air Conditioning

System Design

Insulation

Machinery Space Ventilation

Fresh Air Ventilation

Arrangements

Seawater Systems

Inlets 30

Drainage

Overboard Discharge

Air, Gas, and Miscellaneous Fluid Systems

Hydraulic Equipment

Potable and Fresh Water v

Waste Water Systems

Firefighting Equipment

Fast Lubrication Oil Change System (FLOCS)

Bilge Drainage System

Lubrication of Equipment

Fuels and Lubricants

Steering System

Auxiliary Machinery

Handling and Stowage

Winch System Design

Abbreviations and Acronyms

References

Distribution

Figures

Page

Figure 1. Dry Exhaust Lagged to Prevent Personnel Hazard Figure 2. Example of Shaft Guard

Figure 3. Insufficient Flexibility in Cable for Mount Excursion Figure 4. Proper Bolted Connection with Two Washers and Nylon Locknut

Figure 5. Properly Designed Resilient Engine Mount System Figure 6. Mechanical Tie Bar Figure 7. Wet Exhaust with Flexible Joint Double Clamped Figure 8. Properly Supported Hoses Figure 9. Insulation Liner in a Pipe Bracket

Figure 10. Pipe Insulating Material Figure 11. Cadmium Plated Steel Hose Fitting---Not Preferred

Figure 12. Stainless Steel Hose and Fitting - Preferred Figure 13. Example of Double Hose Clamps Figure 14. Valve Label – Improper Installation Figure 15. Typical Fire Extinguishing System Installation Figure 16. FLOCS System Manifold for Shore Storage of Transfer Pump vi

Administrative Information

The guidance described in this report was assembled by the Systems Design and

Integration Branch (Code 232) of the Combatant Craft Division of the Naval Surface Warfare

Center, Carderock Division (NSWCCD). The work was funded by PEO SHIPS, PMS 325G under funding document N0002409WX31038 during fiscal year 2010-2011.

Acknowledgements

The Systems Design and Integration Branch, Code 232, would like to thank Mr. J.M.

Coughlin, Program Manager at the US Navy Small Boats Program Office (PEO Ships, PMS

325G) for sponsoring the development of this guide, and Mr. Denis Bushey, PMS 325G for his overall management and guidance. The authors also thank Ed Hulick, Brandon Bagwell, Greg

Gaston, Scott Petersen, Allan Demmelmaier, Brian Mishoe, Tom Harrell, Mike Nierman, Gary

Jernigan, D. “Smokey” Glover, Jason Marshall, and Mack Whitford for their technical contributions. Their input was crucial to addressing specific lessons-learned from numerous craft acquisition programs. Michael Riley, The Columbia Group served as technical editor.

vii

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Summary

The mechanical system design and installation practices described in this guide are provided as information for builders offering craft for U.S. Navy service on the General Services

Administration (GSA) Federal Supply Schedule (FSS). They represent a combination of proven commercial practices and lessons learned during previous craft programs. The overall purpose of the guide is to:

• Achieve craft performance requirements

• Increase reliability and ruggedness

• Decrease maintenance over the lifecycle of the craft

• Standardize across the larger fleet

• Simplify mechanical system operation and troubleshooting

• Increase survivability of the craft

The information presented in this guide is not contractually binding, and does not supersede any contract requirement. It reflects accepted practices and Government preference unless otherwise specified in the contract. Consult the contract Technical Point of Contact

(TPOC) for clarification or resolution if any aspect of this guide conflicts technically with a contract requirement.

Background

Introduction

There are numerous references that provide excellent information related to the design, arrangement, installation, and outfitting of propulsion and auxiliary machinery systems for craft.

As an example, Navy craft contract documents often cite equipment selection and installation “in accordance with” The American Boat and Yacht Council’s (ABYC) Standards and Technical

Information Reports for Small Craft, reference 1. Other references are cited throughout this guide that govern regulatory safety and environmental protection topics, including United States

Code of Federal Regulations (CFR), Title 33: Navigation and Navigable Waters, (reference 2), CFR Title 46: Shipping (reference 3), and the International Standards Organization. This guide builds on these source documents by adding additional best practices and lessons learned from numerous Navy craft programs. It is anticipated that later revisions of the guide will be published as new information becomes available.

This guide summarizes technical information and includes “TIPS” that highlight lessons learned and cautions for avoiding common issues.

TIP: Successful acquisition and delivery of a new craft relies on collaborative teams of knowledgeable individuals. Ask the TPOC immediately if there are questions related to craft requirements, applicable standards, or acceptance criteria.

Objective

This document provides guidance to assist boat builders, designers and engineers in the design, integration, installation, inspection, and acceptance of mechanical systems for U.S. Navy craft. It conveys typical government preferences and expectations as an educational tool for builders and system integrators offering boats and craft on the General Services Administration

(GSA) Federal Supply Schedule (FSS). Information for military and civilian government engineers and naval architects on the development of mechanical system requirements is also presented. The primary objectives of the guide are to (1) provide baseline knowledge that facilitates effective communications between builders, equipment providers, system integrators, and government representatives, (2) highlight the critical importance of original equipment manufacturer installation specifications, and (3) provide guidance for requirements generation, and design review and acceptance processes so that government engineers (in-training) understand the responsibilities of a government Technical Point of Contact (TPOC). This guide is not a substitute for, nor should it preclude, sound engineering practices. It is to be used only as a guide.

Scope

This guide is applicable to a broad range of topics related to propulsion and auxiliary systems installed in US Navy small boats and craft, including engines, couplings, motors, pumps, generators, piping, hoses, fittings, fasteners, mounts, fresh air and cooling, exhaust, fire-fighting equipment, access, and fluid systems. It presents a collection of lessons learned and best practices for consistent applications across various platforms. The information is not contractually binding, and does not supersede contract requirements. This guide provides a useful tool set, but it should not preclude the use of other good engineering practices or processes that may also deliver effective mechanical systems for craft.

General Guidance for Design and Construction

Many Navy contracts for small boats or craft require, as a minimum, general compliance with the ABYC Standards and Technical Information reports for Small Craft (ref 1). Specific contracts may also provide additional requirements. The contents herein are provided to offer additional guidance that may lead to improved design, fabrication, and testing techniques and a higher quality product delivered to the government. Another good reference document for historical US Navy practices is the 1993 version of the Standard Specification for US Navy

Craft, reference 4.

Equipment Specifications

The most important factor that leads to achieving successful mechanical system integration is to ensure that mechanical system components are installed in the craft in accordance with the original equipment manufacturers’ (OEM) specifications. OEM design and installation documents are directly related to the engineering criteria used to design the equipment and therefore are necessary for the safe and effective operation of the equipment. Machinery system parameters such as operating temperatures, internal pressures, motor output, propulsion system thrust, noise and vibration, excursion envelops, and system safety switches or alarms, just to name a few, can be adversely affected if improperly installed. This can lead to loss of performance, unsafe conditions, or costly maintenance and repair before warranty expiration.

When the boat builder performs the installation of any major component or system (engine, transmission, water jet, propulsion unit, generator, HVAC, etc.), the boat builder should get a certificate from an authorized OEM representative stating that the design, installation and integration of the equipment was accomplished in a manner that is in compliance with the OEM instructions and does not void or violate any OEM warranties. Any deviation from OEM installation guidance must be approved by the OEM and documented by a letter of approval from the OEM on OEM letterhead (not the distributor) and the builder’s technical point of contact.

TIP: It is typically required that builders obtain certifications from engine, propulsor, generator, and other major systems (e.g., HVAC) OEM’s that equipment has been integrated and installed to their specifications and all the requirements of the contract. Failure to share all requirements of the installation with the OEM defeats the purpose of the OEM certificate. Ensure the OEM is fully aware of the requirements, including environmental conditions, support system parameters, and overall system performance requirements.

TIP: Boat builders should follow all specifications and guidance provided by the equipment OEM for selection and installation of machinery system components.

This can prevent costly rework prior to craft delivery, and avoid boat builder warranty liability for improperly installed equipment. Technical evidence should be included in the design folder documenting compliance with OEM instructions when possible.

Installation of Equipment & General Access

Systems, equipments, and components should be installed to facilitate accessibility for operating efficiency and for inspection, adjustment, maintenance and repair. Permanent fittings and structure should be kept clear of routes required for the removal and servicing of machinery and equipment, and space behind equipment installations should be provided to allow sufficient access for repair, preservation, and maintenance. This includes the location of pipes, ducts, wire-ways, and other permanent fittings behind equipment that allows access. Nooks, cracks, and openings where water, dirt, dust, or foreign material can accumulate should be avoided.

Foundations and brackets for equipment should be configured to provide access for cleaning, painting, preservation, and maintenance, and to prevent accumulation of water, dirt, and foreign material.

Protection of personnel against operating hazards should be provided to the extent practicable. For example, in spaces normally not manned, high temperature surfaces above 200 degrees Fahrenheit (per reference 1) should be labeled and insulated or shrouded as shown in

Figure 1. In spaces that are normally (or occasionally) manned, the insulation protection should be applied to surfaces above 120 degrees Fahrenheit in areas where personnel could come in contact with a hot surface. These types of protection are especially important where a person might be likely to inadvertently grab a potentially dangerous item. In some circumstances, such as very small craft or machinery spaces that are not accessible, the installation of protective insulation may not be practical.

Mechanical systems should be routed and secured to not impede passage or present a source of danger to personnel. Similarly, mechanical systems should be arranged to prevent them from being used as steps or handholds. When potentially hazardous installations cannot be avoided, guards or protective padding should be provided. In particular, rotating equipment such as shafting, couplings, gears, flexible shafts, and similar items should have adequate guards installed for protection of personnel. Protective guards should be removable without dismantling the machinery surrounded. Guards should be as light as possible without jeopardizing required protection and strength. In some locations it will be necessary to add additional strength so the guard may be used as a step or hand hold. Figure 2 shows an example of a shaft guard that is also a step. Delicate items such as small tubing, pull cables, sight glasses, gauges, etc. should be provided with protection where they might be a grab hazard.

Protective guards should also be installed as barriers to prevent personnel from inadvertently contacting energized and exposed electrical circuits, components, and terminals. Electrical equipment should be protected against the hazard of personnel brushing against or being thrown against the equipment, particularly under heavy sea conditions, and inadvertently causing damage to exposed components or resulting in maladjustment of exposed functional controls such as push buttons, knobs, and switches. Protection can also be provided by equipment arrangement or design or by installation of enclosures, screens, or guard rails.

Access to mechanical systems for operation, maintenance, inspection, and repair is vital.

Operating handles for valves on critical systems, such as seacocks, fuel supply valves, or emergency bilge pump suction should be located to be accessible and operable quickly, easily, and safely while underway without tools. Where operating handles are not able to be accessed, reach rods should be installed to make the item operable from a more suitable location. Service items such as filters, strainers, cartridges, fluid fills, etc. should be accessible without having to remove other components or without causing personnel to crawl over, under or rest against machinery and mechanical systems to service them. Adequate maintenance envelopes should be maintained for all service items. Where major machinery may not be adequately accessed due to size, weight, and space constraints, machinery mounts should be readily accessible for unbolting from the craft, and adequate machinery removal access should be provided.

Figure 1. Dry Exhaust Lagged to Prevent Personnel Hazard

Figure 2. Example of Shaft Guard

For exterior equipment, connecting piping and wiring should be run to allow only minimum exposure to weather. Bulkhead and deck penetrations should be as close as practicable to the equipment being served, preferably by direct connection through the adjacent deck or bulkhead.

Wiring and piping to equipment mounted on spars should be contained within the spar structure to the maximum extent possible.

Workmanship

Quality of work throughout the craft should be first class, reflecting the best marine practices.

Structure should be fair and free from objectionable buckles or uneven sight edges.

All joints should be neatly and accurately made. Faying surfaces should be free from gaps, hollows or warping. Shims or filling compounds should not be used to correct improper fit.

All sharp edges exposed to personnel should be dressed, ground or rounded to avoid injury to personnel.

Metal parts should be completely fabricated before installation on the craft. Internal corners should be filleted and external corners should be rounded.

All exterior aluminum surfaces, except where painting is specified, should receive a non-directional silica sandblast to achieve a uniform, clean, matte finish. This finish should remove all heat treatment films, surface corrosion and oxidation by-products, weld spatter, paint and ink identification marks, and foreign matter from the aluminum.

Piping, wiring leads and vent ducts should penetrate the bulkhead as close to the top of the bulkhead as practicable unless otherwise specified.

All mechanical system installations, including their foundations and attachments, must be constructed to withstand all operational loads while the craft is operated at full speed in a seaway. Operational loads include all loads associated with fully loaded and functioning equipment subject to dynamic loads such as wave induced slamming loads, vibrations, and other loads induced by equipment operation. If additional guidance is required consult with the TPOC.

Corrosion

All items used in the construction of craft should be fabricated of non-corroding materials or should be suitably protected against corrosion for service in a marine environment. Ferrous metals other than stainless steel should not be used except where specifically required by the contracts.

Where practicable, ferrous metals other than stainless steel should be galvanized or coated with wire-sprayed aluminum; the protective coating should be applied after fabrication. Alternatively, ferrous metal items may be replaced with stainless steel items, or items of other non-corroding materials, subject to the approval of the TPOC.

Dissimilar metals, with the exception of stainless steel fasteners, should not be joined directly unless specifically allowed. Galvanic corrosion should be prevented by insulating dissimilar metals from each other with suitable gaskets, washers, sleeves, bushings and hose of insulating material. Insulating materials should be non-porous, with mechanical properties suitable for the application. In order to exclude moisture from the joint, faying surfaces between mechanically fastened metal components (and between metals and laminates), except machinery foundation shims, should be protected by the use of bedding compound or structural adhesive, as applicable.

TIP: It is considered good practice to avoid the use of bare carbon steel or zinc coated alloys for any craft mechanical system subassembly parts.

Noise and Vibration

Typical sources of craft noise and vibration include the propulsion engines, propeller/impeller pressure pulses on the hull, hull slap, auxiliary systems, and masts and antennas. The craft and all craft components should be free from excessive vibration. Vibration is excessive when it: contributes to undue annoyance, discomfort, distraction (physical or audible) or accelerated fatigue of personnel; interferes, or threatens to interfere with the proper operation of any craft component; or shortens life expectancy of any craft component. Any unsatisfactory conditions resulting from the excitation of a resonant frequency by any equipment should be corrected by local stiffening of structure, installation of suitable mountings, modification of components, or other effective means. Means to prevent excessive vibration during normal craft operating conditions should be incorporated in the construction of the craft.

Means should be provided to prevent rattling of removable plates, ladders, gratings, and similar items.

Noise

Noise level standards in reference 5 were adopted by the Navy to establish exposure limits for potentially hazardous noise levels. References 6 and 7 provide additional background regarding noise limits. Noise requirements should state not only the desired noise level and frequency of interest (e.g., A weighted) but also the expected exposure duration and operating conditions. A common requirement is to limit noise levels at operating stations to 84 dB(A) or less at maximum speed (typically loudest condition, for durations up to 8 hours). Exceeding this level or duration results in permanent hearing loss. Careful attention must be given to expected duration of exposure and operating conditions when specifying noise levels. Where signature reduction is required, reference 6 provides aural non-detectability limits for far-field noise reduction. Other specified noise levels may be considered depending upon the size, type, mission profile, and design of the craft.

Noise measurements are typically taken during the pre-delivery trials of Navy craft. If further measurements and testing are required, they may be performed by the Navy after delivery of the craft, or in some contracts, the boat builder may be responsible for conducting noise and vibration testing. Reference 6 provides additional guidance on testing requirements and is available upon request from NSWC CD Detachment Norfolk.

Vibration

Vibration is considered excessive when it interferes, or threatens to interfere, with the proper operation of any craft component, or threatens to decrease the reliability or life expectancy of any craft component. Generally, prominent resonances found in equipment or structure will be considered unsatisfactory when they are within the range of vibration generated by the main propulsion system. This is to prevent early failures from fatigue loading.

TIP: If required, it is highly recommended that the frequency content measurement of noise and vibration be accomplished by a third party specializing in the measurement and identification of noise and vibration sources. Standard A-weighed onboard noise levels can be conducted by most people with modest training.

Control of Noise and Vibration

Noise reduction can be accomplished by isolating the noise source, by covering the source with sound absorptive materials, or by insulating the compartment when an unmanned space.

Insulation for sound should be accomplished in conjunction with thermal insulation in cases where adjacent space has habitability requirements. Examples of isolation include the use of flexible mounts on engines supported by solid foundations and the use of a layer of damping material between vibrating components and support structure. Typical approaches to covering the source of the noise includes routing engine exhaust underwater, installing engine exhaust silencers, installing bulkheads or partitions, and by installing sound absorption treatment.

Vibration isolation mounts should be used for the specified application or for machinery and equipment which fail to meet noise or vibration requirements. Focal point (inclined) mounting employing mounts with special properties should be utilized where required to achieve optimum noise control. The selection of mountings and design of the mounting arrangement should be such that the natural frequencies of the installed unit are not adversely excited by any forcing frequency of the mounted equipment or other machinery. Snubbers should be used to limit the excursion of mounted equipment due to craft motion in a seaway. All resiliently mounted equipment should have flexible connections. Sufficient clearance should be provided to prevent the unit from striking structure, adjacent fixed or resiliently mounted units, or other fixed objects during maximum deflections of the unit.

Resilient mounts should be used to reduce engine noise and reduce the effects of engine vibrations. When selected properly they are very effective in reducing potentially harmful effects on the hull structure, surrounding equipment, and personnel health and comfort. If not properly selected, noise limits can be exceeded, damage to system components can occur, and recurring maintenance and repair costs will grow if problems are not resolved. To avoid these issues most machinery original equipment manufacturers (OEMs) or their suppliers will provide resilient mount information which, if followed, will maintain the warranty on their equipment. Suppliers of resilient mounts can also provide important assistance in selecting mount designs, but maintaining the integrity of OEM warranties is paramount. Particular attention should be paid to electrical and piping system flexibility across equipment to the full extent of the machinery excursion. Hoses and cables often need extra length to accommodate such movement. Figure 3 shows an example of insufficient cable flexibility to allow full mount excursions.

Additional restraints may be needed to prevent such systems from becoming pinched over time due to the repeated movement. Equipment should be located to avoid interferences at the resilient mount stops.

OEMs should be made aware of the magnitude of impact accelerations that can be expected in high performance craft applications. These accelerations can exceed the capacity of poorly designed mounting schemes and cause damage to the craft and equipment.

Figure 3. Insufficient Flexibility in Cable for Mount Excursion

Other factors affecting mount selection for the marine environment include: (1) the ability of mount material to resist corrosion in the marine environment, (2) material breakdown due to exposure to engine compartment chemicals (e.g. fuels, coolants or lubricants), (3) the inherent ruggedness to withstand repeated wave impacts, and (4) the use of snubbers to limit engine motions (referred to as excursion envelopes).

TIP: During the installation phase it is important that evenly distributed loads across all mounts be maintained, and system alignment procedures must not result in one or more mounts that are “bottomed out” to achieve alignment. Additionally, resilient mounts must not be pre-loaded in a transverse or longitudinal direction to accommodate machinery misalignment.

TIP: Experience has demonstrated that the use of resilient noise mounts or shock mounts must be considered early in the arrangements and equipment integration process, especially for engines, generators, and air conditioning units. Improper selection or installation of mounts can result in mount bottoming that can cause failure due to shock loads or repeated impacts with adjacent equipment or structure, or damaged fuel or hydraulic hoses due to crimping. Excursion distances provided by mount manufactures should be considered to determine suitability of candidate mounts.

TIP: While it is considered good practice to cover metallic elements of mounts with a marine grade paint to resist corrosion in the marine environment, the resilient elements should not be painted.

Reference 7 and 8 provides additional information on the control of noise and vibration.

Welding Machinery and Piping

Successful welding of machinery and piping requires preparation, expertise, and quality control. There are many government and industry welding documents that provide instruction and guidance for control of welding aboard ships that is applicable to small boats and craft. Good welding starts with proper joint design, joint preparation, filler material selection, base material identification and weld sizing. Further, it is essential that vendors have a qualified welding staff that includes weld inspection and a quality assurance process. In general, the welds for machinery and piping should be as strong as the base material they are connecting, but there are limitations and exceptions that should be clarified with a government design representative as part of the design planning process. Specifications detailing the level and methods of weld control may be identified in the contract requirements, but invoked or not, there are several good references for weld guidance. Reference 9 is a primary reference for aluminum welding, and reference 10 is a primary reference for steel welding.

Threaded Fasteners

Bolted Connection Design

When possible, equipment should be secured to structure using a through bolt and nut connection. Male threads on threaded fasteners, after being installed and tightened, should protrude at least one thread beyond the top of the nut or plastic locking element, but no more than three threads. Excessive protrusion should be avoided when the fastener is accessible because excess length can constitute a hazard, particularly where necessary clearances, accessibility, or safety are affected. Washers should be used to distribute bolt force and protect surfaces from abrasion from torquing nuts, not for the sole purpose of lessening thread protrusion. Where it is necessary to reduce thread protrusion, excess length should be removed without damaging the threads and the bolt dressed to remove rough edges. Threads should be dressed prior to application of self-locking nuts to prevent damage to the self-locking inserts.

Where nuts or bolt ends may constitute a hazard or where appearance is a consideration, prevailing torque elastic self locking acorn nuts should be used. Figure 4 shows a proper bolted connection.

Figure 4. Proper Bolted Connection with Two Washers and Nylon Locknut

Fastener Materials and Features

All threaded fasteners should be stainless steel, UNS S31600. All nuts should be the prevailing torque elastic self locking type (e.g. Nylock). One stainless steel flat washer should be used under each bolt and machine screw head, except countersunk types, and under each nut.

Where washers bear directly on laminate or other soft material, wide series washers should be used where space allows. Use of material other than stainless steel due to geometry constraints, specific strength requirements, or OEM equipment integration constraints must be approved in advance by the TPOC.

TIP: Unless otherwise specified, avoid the use of mechanical thread-locking devices and methods such as lock washers (either spring, tooth or tab type) and avoid peening, wiring, pinning, or thread upset after assembly.

Self-tapping Screws

When the back-side of a panel is inaccessible, use of threaded inserts for both fiber reinforced plastic and metal panels is the preferred securing method, particularly if the panel must be removed for regular access or maintenance. Self tapping screws should be used only where the opposite side is inaccessible and threaded inserts are impractical or where, for appearance, it is desirable to use self tapping screws for non structural applications in sandwich laminates. Self-tapping screws should not be used in aluminum.

For all other applications, through bolts or machine screws should be used. Screws should be sized to support design loads and should be no less than ¼ - 20UNC. Length should be sufficient to carry one full diameter of the screw through the entire thickness of the material to which it is fastened, including opposite face of sandwich laminates. Pilot holes should be sized appropriate for the screw size. Screws should be dipped in catalyzed resin at the time of installation (if installed in a laminate), except where the screw is encapsulated with resin or resin impregnated fabric during a succeeding step in the lamination of the craft.

Reliability and Maintenance

All installed equipment should conform to the OEM design and installation recommendations for sustained reliability, performance, and warranty coverage. Ancillary components of equipment and fittings should be high quality marine grade components, and when necessary, properly protected from the environment with a marine grade paint or coating

(taking care to avoid covering any OEM markings or instructions). Products should be selected in accordance with OEM intended service. Maintenance practices for equipment should be demonstrated to ensure feasibility and access, and required maintenance actions should be evaluated for ease and required frequency.

Failure modes should be considered when designing and installing systems. An example is an isolation valve for a sight glass. If the glass fails, the system can still be operated with the valves shut. Otherwise, the entire system will be inoperable, potentially affecting the mission.

Repairability should be considered throughout the design and fabrication processes.

Systems should be selected and installed to ensure that special tools are not required, and that components are easily accessible while underway.

TIP: To avoid early repair issues ensure that grease fittings are properly installed in drive shafts, and install shaft couplings with rotation markers in the proper direction of shaft rotation.

Safety

The objective of system safety is to optimize the safety of the craft within the constraints of operational effectiveness, time, and cost. Safety is defined in this context as freedom from those conditions that can cause death, injury, occupational illness, or damage to or loss of equipment or property.

System safety design requirements include, but are not limited to the following:

(1) Eliminate identified hazards or reduce the associated risk through design.

(2) Ensure that details of equipment installation minimize exposure of personnel and equipment to hazards such as sharp edges, points, moving parts, high temperatures, noise, vibration, acceleration, toxicity, high voltage, and electro-magnetic radiation.

(3) Ensure that details of design and construction minimize the consequences of human error in the operation and support of the craft.

(4) Ensure that warning, caution and instruction markings are provided as necessary to identify hazards and reduce the associated risk.

(5) Minimize the severity of personnel injury or damage to equipment in the event of a mishap.

Machinery Foundations

Foundations throughout the craft should be constructed to withstand the loads imparted by the equipment they support while the craft is operated at full speed under all conditions.

Foundations should provide restraint in all directions. The rigidity of foundations and supporting structure should be sufficient to prevent misalignment, deflection, or vibration which would interfere with the operation of the equipment. Scantlings should be adequate to provide the necessary strength and rigidity for maintaining positive and accurate alignment where necessary for satisfactory operation of the equipment.

Foundations should be as light as possible commensurate with the requirements of the equipment. To minimize weight, structural members should be used as parts of foundations; the structure should be reinforced as necessary. Foundations should be constructed so as not to contain pockets which can retain liquids. Drain openings should be provided as necessary.

Foundations should be arranged to provide sufficient clearance for servicing and disassembling equipment. Consideration must be given to the flexibility of equipment foundations. Though equipment is “hard mounted”, the flexibility of piping and other connections to the equipment must be considered. Piping and other connections must have sufficient flexibility to account for relative movement of equipment and hull.

General Guidance for Propulsion Design and Installation

Diesel Propulsion Engines

Diesel engine and transmission selection may be specified in the contract or accomplished by the vendor. In all instances, the engine OEM is to provide a certification letter that the engine installation was selected, designed and installed to meet the intended requirements within the manufacturer’s guidelines. Specifically, the engine should be capable of providing the desired horsepower, at the government defined duty cycle, in the identified environmental envelope for the identified service life of craft. If the service life of the engine is shorter, then the length of service is to be identified. If the engine cannot provide the desired power through the defined operational temperature range, a curve or engine de-rating formula should be provided to identify actual power available. If use of any military fuels (such as JP-5 or JP-8) causes a decrease in service life, this should be stated in the certificate. If meeting these requirements places any abnormal or increased sizing on the raw water, fuel, combustion air delivery, lube oil, electric, or other ancillary systems, it also should be stated in the certification letter. In all instances the certification is for a post-installation engine. Duty cycle restrictions, if any, for the engine should be clearly posted on the console stating the amount of time the engine can be run at maximum power and the reduction from maximum power required for continuous operations.

Similarly, for the transmission, clutch, or other power transmission equipment, certification letters should be provided stating the equipment provided can deliver the intended service life for the range of engine power and environmental conditions expected.

The most important factor that leads to successful installation and operation of diesel engines on craft is to ensure that the selection and installation is in accordance with the OEM specifications. It is incumbent upon the boat builder to provide craft that are certified by the

OEM of all major propulsion components (engine, transmission, clutch, etc.) to be within operational design specifications of equipment provided for the entire range of environmental and operational envelopes of a particular boat or craft. This certification should provide full

OEM warranty regardless of the distributor service area. This includes the mechanical installation and all required ancillary support services (combustion air, cooling, power, fuel, etc.). It is very common for engines to be purchased from a distributor in one region of the country and be serviced in several other regions of the country. When modifications to OEM configurations are necessary, it is preferred that the OEM establishes part numbers for these configurations, so that any distributor can obtain the necessary parts. Unique configurations that require components specific to the original selling vendor / distributor should be avoided.

The foundation of the engine bed should be designed to support the propulsion weight and have sufficient height to minimize the need for shims or bedding material. The flatness (or trueness) of the engine bed should conform to the engine OEM requirements.

Figure 5. Properly Designed Resilient Engine Mount System

TIP: Engine beds should be fabricated using a jig to represent the engine mount locations relative to shafting locations. The locating tolerance should allow for adjustment (e.g., shimming).

Engine beds and other equipment foundations should be manufactured and assembled with precision to achieve OEM recommendations and to provide a permanent connection to craft structure. Fixed equipment mount interfaces should be permanently aligned using supporting structure with shims, liners, or manufacturer provided systems such as threaded adjusters to optimize equipment performance and life. Alignments should be checked after initial trials and anytime equipment is removed. Builders should seek TPOC approval when "Chockfast" or other methods are planned to be used in lieu of approved permanent alignment techniques. These are typically considered corrective or temporary, and may not be approved as the intended permanent installation.

Preference is for diesel inboard engines to be equipped with a duplex (where practical) fuel water separator/filter with filtration capability and of appropriate size to be in compliance with engine manufacturer’s recommendations. The duplex filter is desired to allow service while underway without impacting vessel performance. These filters are typically 30 micron and onboard engine filters are 2-10 micron depending on OEM.

Marine Transmissions

Marine transmissions are typically used to: 1) match engine RPM output to propulsor

RPM input via reduction ratios, 2) provide a reversing capability for direction on propeller driven craft, or 3) to help free from fouling or debris on waterjet driven craft. If selected within

OEM guidelines and provided with the engine by the distributor, these have historically been trouble free. Attention should be given to engine mount locations when a transmission is installed. Also ensure that the fast lube oil change (FLOC) system (if installed) includes the transmission oil.

Outdrives, Waterjets, and Outboard Motors

Original equipment manufacturers (OEM) of drive systems typically provide installation specifications for their equipment, such as gearing ratios, gimbal housing location (transom height and angle), propeller designs, and alignment tolerances and procedures. While the installation procedures are typically well documented, the typical cause of excessive vibration for new construction craft or overhauled in-service craft is misalignment between the engine and the drive system, including outdrives and water jets. It is therefore good practice, when installing and aligning drive unit splines and mating gimbal bearing assemblies with engine shafting, to request an OEM factory-authorized representative to be onsite to witness and certify

(in writing if possible) the installation. Water jets should include inlet grates, inspection ports for clearing fouling, a properly sized impeller and a spare belt with a means to install it that minimizes shafting disassembly. Propeller shaft sizing and installation procedures should be (as a minimum) in accordance with ABYC section P6.

TIP: It is highly recommended that builders work closely with OEM’s when planning and implementing propulsion drive system alignment operations. An OEM representative on-site during the alignment can help prevent later performance issues.

The twin installation of outdrive propulsion units or multiple outboard motors should, wherever practical, have a mechanical tie-bar affixed between the units to maintain vessel steerage and vessel control in the event that one outdrive unit should fail. Figure 6 shows an example of a tie-bar installation. A means of emergency steering should also be provided should the control system completely fail where practical. Primary steering should be by use of a manual hydraulic helm pump rather than power steering pumps when possible to simplify maintenance.

Figure 6. Mechanical Tie Bar

Many outboard engine manufacturers require that engines be run for a period of time, typically 10 hours, with a prescribed sequence of increasing and decreasing speeds. Builders are typically required to ensure that these break-in periods are performed before pre-delivery inspections and testing (PDIT).

Raw Water Cooling Systems

Ensure that engine cooling system subcomponents such as pipes, hoses, and overboard discharge fittings are properly sized to allow sufficient cooling water flow rate. Improperly sized components or external fouling that restricts water flow can cause engine damage due to excessive temperatures. Particular attention should be paid to seawater system flow restriction, Craft used in shipboard and some expeditionary applications should be equipped with a run-dry capability to permit starting of the engines prior to the craft being lowered into the water.

Often a normally closed three-way valve will be used in the seawater suction line to the engine driven raw water pump to permit the pump to be used as an emergency de-watering pump. The suction end of the valve is connected to a foot strainer in the machinery space. When the valve is opened suction is diverted from the sea chest to the foot strainer in the bilge.

For maintenance purposes, a fresh water flushing connection is oftentimes provided to permit a garden hose to supply water into the seawater suction. This allows engines to be run on fresh water while the craft is on the trailer for maintenance purposes or preparation for long term storage.

Engine Exhaust Systems

A complete and separate exhaust system should be installed for each engine. The exhaust system should be gas-tight throughout its passage through the interior of the craft. The system should be constructed and installed so that it is accessible for inspection and repair throughout its length. Wherever personnel or combustible material may come in contact with hot surfaces, effective protection should be provided by installing water jackets, insulation, or guards. When insulation is used HardCoat

TM

is preferred to blanketing.

Wet exhausts should avoid flexible components located below the waterline. For wet exhaust systems, the exhaust piping should slope downward to provide complete drainage from the water injection point to the hull terminus under all normal load conditions. The system should be designed and installed to prevent cooling water or sea water from reaching the engine through the exhaust system. The preferred location is through the transom with flappers. Routing should preclude engine flooding during backing operations. Components of the exhaust system which are not self-draining and in which freezing of the trapped water might damage the component or prevent satisfactory operation of the engine, should be provided with readily accessible drain cocks. Water muffler systems should be installed in accordance with OEM installation instructions and comply with engine backpressure requirements during all operations.

Figure 7. Wet Exhaust with Flexible Joint Double Clamped

The exhaust system should be adequately supported to provide proper alignment, to prevent undue stress on components, and to prevent vibration. There should be no load applied to the engine outlet connections.

Material selection for wet and dry exhaust systems must be capable of providing required strength, heat resistance, and corrosion resistance for system fluids. Example materials include, stainless steel UNS 31603 and glass reinforced plastic (GRP) in accordance with ABYC recommendations.

Fuel Systems

A complete fuel system should be installed as necessary to serve the engines. The system should provide for filling, venting, sounding, filtering, supply and return (if required), and stripping, and should include stowage tanks and all other equipment necessary for the efficient stowage and use of the fuel. There should be no other joints in the fuel distribution and return lines other than those required to connect components.

For gasoline and JP-8 fuel systems, equipment in spaces subject to fumes must be ignition-protected, and fuel…