Technical Specifications Defined and Reviewed

The noise and vibration specifications define the noise and vibration qualities that are to be met in the delivered product. These should be set to the standard of the buyer, within the limits of what the builder (supplier) has agreed to produce.

Typical objectives of noise and vibration limits consider passenger and crew comfort as well as protection against fatigue, hearing loss, and skeletal damage.

Vessel specifications must consider the critical modes of vessel operation for the owners. These may include maximum power, transit/cruise speed, loiter, at anchor, dynamic positioning (DP), etc.

J&A consultation on specification development ensures a good match between the technical description of the owner’s requirements and the practical means by which a shipyard can comply with such requirements.

Noise Limits may involve include: dB(A), Speech Interference Level (SIL,  STC, Underwater Self-Noise, Underwater Radiated Noise, and in-air detectability). Vibration specifications may include velocity and/or acceleration limits, Impact, g’s and/or Structure borne Noise Limits.

Subjective goals of specifications may relate to:

  • Protection against hearing loss, neural and skeletal damage, fatigue and miscommunication

  • Protection of machinery, structures, and electronics

  • ·Signatures: noise in air, noise underwater, thermal signature

 J&A is familiar with such specifications and the necessary means of respecting them for a wide variety of vessels, from small 30’ to 40’ pleasure and workboats, to medium 40’ to 200’ pleasure, passenger, and workboats, to large 200’ to 300’ yachts, passenger vessels and workboats, to very large 300’ to 500’ super yachts, passenger and workboats.

A major choice for noise and vibration specifications, as for other portions of the specification, is the choice between a vessel performance spec and specification for the means of achieving the required noise and vibration performance or a hybrid spec including a combination of performance and means (some work for the lawyers on the hybrid approach!).

Many of the vessel classification societies (ABS, Lloyds, DNV, RINA) have detailed specifications for noise and vibration in a range of vessels. These specifications include a range of limits from “Good” to Excellent”, and include instruction on the means of measuring, equipment used, and details of the boat operation during measurements. Such “Comfort Class” specs may be a good starting point for specification generation of a new vessel, however fine tuning is appropriate in most situations.

The gross range of categories to which specifications apply are:

  • Vessel Types: displacement, semi displacement-planing, air cushion, hydrofoil

  • Application: pleasure, work, passenger, research, military/police

  • Material: steel, aluminum, composite, wood, hybrid

  • Machinery: gas turbine, diesel, gasoline, electric

  • Propulsion: propeller, waterjet, ducted propeller, Z-drive

J&A’s experience with many combinations of the categories above gives us a deep capability to advise any of the parties to a vessel specification, whether on the side of the seller (builder, designer) or the user (vessel owner or operator), regarding appropriate and feasible limits.

EXAMPLES

  • Large US Built Yacht - J&A participated as the noise and vibration specialist in contract design specification for a large (280’) US built very quiet yacht. Our work for the builder included discussions with the builder and the buyer of noise and vibration limits and a formula for damages and non-acceptance in case of excess noise or vibration.   

  • Fast passenger Ferry - J&A consulted with a Pacific Northwest shipyard in bidding a 40-knot ferry in a competitive bid. J&A advised on quiet noise levels that could be achieved by practical noise abatement treatments (Cost and Weight). The shipyard won the bid and built a quiet vessel.

  • 85’ Fast yacht - J&A consulted for an owner to a shipyard for construction of a large sport yacht (50+ knots), with excellent noise and vibration comfort. Conditions included underway, at anchor, voice privacy, and wave impact (“chuckle”) at anchor, all in a weight critical construction. The contract, with quiet levels and low vibration limits was signed, and a very quiet boat was delivered within the specification.

  • 87’ Great Lakes Research Vessel - A small Great Lakes research vessel, originally constructed with little attention to noise and vibration control, was tested by J&A and a set of noise reduction measures was developed. Those measures were presented as a “means specification” document in the bid package for noise reduction refit. That specification document turned into a contract, and a much-improved vessel resulted.

  • Large Sail Yacht - J&A was the noise and vibration consultant for the design specification of a 160’ sail yacht. Noise and vibration levels significantly below those of past projects of the shipyard were negotiated into the specification, and resulted in design and delivery of a yacht much improved over the prior experience of the shipyard, and resulted in a new standard for their following projects.

  • Large Tug Specification Relaxed Treatment - A contract under negotiation specified a combination of acoustic treatments on the decks.  J&A’s calculations determined that the specified floated floor could be eliminated while still reaching the required quiet noise levels. The J&A position was accepted, money and time were saved, and the noise limits were complied with.

  • Small Tug – Specification Refused - A small tug was specified to meet a quiet ABS standard, with construction specified to have rigidly mounted Diesel engines. J&A calculations showed that the specified noise limit could not be achieved unless the engines were elastically mounted. The rigid mounting was used but the noise limits were relaxed to the J&A recommendation.