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GENERAL INFORMATION

Marine engine noise should not be considered as solely a background disturbance that creates difficulty in radio or person to person communication What must be realized is that exposure to high levels of noise energy for a period of time will have physical impact. Short term effects may be characterized by ear or head aches, premature fatigue and high stress levels. With long term exposure, as would be expected, hearing loss becomes a factor.

On vessels with the pilot house directly over an uninsulated engine compartment, the noise level often exceeds the limits that have been set for safe work conditions by O.S.H.A., requiring some form of hearing protection to be used. This is why there is more attention given to noise control on our commercial fleet today. People are becoming more aware of noise problems and are seeking solutions

The noise energy created by marine engines travels to the ear in a number of ways. It may be airborne noise transmitted directly off the engine casing. It may be the inherent vibration from the engine that is being transmitted through the hull and bulkheads. It may be exhaust noise that is blown into the air or passed through the exhaust piping. It is important to determine the causes before action is undertaken, because there is not one simple solution which will remedy all of the possible causes of unacceptable noise levels

Airborne noise is that which is transmitted into the air (as opposed to the hull} from the engine casing or an exhaust casing. Airborne noise accounts for the major source of discomfort experienced by crews who work in close proximity to the machinery spaces in small and mid-size commercial vessels The design and construction of any vessel has a direct bearing on the noise levels that will be present. A primary concern to any noise control program should be the open passages between the machinery and the living and working areas. Noise travels most easily through the air or open holes, so air ventilation systems, exhaust piping, tightness of bulkheads and deckheads, etc, take on particular significance. Different structural materials will have their own acoustical characteristics, but an open hole will always allow noise to pass through most easily.

Vibrational noise, which is mechanical noise energy transmitted into the Structure of a vessel, is best treated through the isolation of the machinery from the hull. Isolators range from rubber padding to spring or rubber mounts, and up to the more sophisticated raft designs. V drives which absorb the thrust, but are connected to the main engines that are soft-mounted, are yet another means to isolate the vibration away from the hull. If the vibrational energy cannot be isolated at the source the alternative is to dissipate it along its path with damping treatments, These are surface applied or interlayers that are constrained within the girders, hull and other structural paths.

 

Insulation is used to combat the airborne noise. It should be designed to do three things:

1) be a barrier to block noise from escaping the engine room;

2) absorb noise while it is in the engine room;

3) dampen the vibrational energy that Is in the walls and ceiling of that room.

The barrier effect is accomplished through the use of high density and mass lead sheeting which is sandwiched between two resilient materials. The resilient materials must also perform the function of noise absorption Acoustical foam or fiberglass are particularly suited to be both a decoupler for the lead barrier, as well as being the absorption material. Absorption is accomplished by dissipating the noise energy as it passes through to the lead and as it is bounced back towards the noise source. Generally, lead core insulation is used on surfaces behind which people will be, and absorption-only material (no lead) is used on surfaces like hull sides, tanks, bulkheads against a fish hold, etc.

Outside of the engine room there are additional steps that can be taken to control particular noise sources, and these certainly vary from boat design. Often in smaller vessels the dry exhaust piping radiates significant noise, as well as heat. High temperature fiberglass insulation covered with an appropriate outside covering will minimize pipe and muffler shell noise, and at the same time cool the surface so that it can be touched. One of the largest interior surfaces are the ceilings, and their acoustical importance can be significant. Just as in a house with no furniture, carpets, drapes, etc., noise echoes from one hard wall to another, so does the same echo or reflection take place in a vessel which has hard finished walls and overhead. A ceiling which will absorb interior noise is definitely superior to one which will simply bounce noise. On the floors, carpets with acoustical underlayments will suppress noise from below, as well as absorb vibrational energy that's in the floor.

In short, there are many procedures and materials that can be used to keep noise levels under control in commercial vessels. It is important to understand what can be accomplished within a given vessel or with a particular noise problem. One solution simply will not apply to all of the problems, hence sound level reduction must be initiated with knowledge of the individual vessel and its owner's, operator's or designer's requirements understood.

MACHINERY AREA INSULATION

Material Ordering & Installations Procedures

For the sake of simplicity we have grouped the various boat designs into three categories We recognize that there are modifications and variations to these categories, and we will discuss those in depth on an individual basis

1) Pilot House Directly Over Machinery:

Boats with engine boxes
Boats with step deck
Boats with engine forward (cuddy)
Boats with engine under flush deck

2) Pilot House Two Levels Over Machinery:

Accommodation, galley, etc. over or forward of the machinery.

3) Platform Over Machinery:

On deck noise of major concern

1) Pilot House Directly Over Machinery:

Noise diminishes in direct proportion to the distance it has to travel before reaching the ear. Vessels with machinery directly under the pilot house will tend to have greater levels of noise, within that pilot house, than those with the pilot house removed some distance from the noise source.

Engine Boxes:

Noise does travel in all directions, not just straight up. If an engine sits well up into the box (at least half of it), then appreciable reduction will be achieved by insulating the box only. If the box just covers the top of the engine, then it will be necessary to insulate the entire floor, in addition to the cover, to gain significant results. Frequently, there are fuel tanks alongside of the engine, which make it difficult to reach the overhead areas. In those cases there are approaches to be used, for instance, creating an engine-box-like structure below deck or hanging acoustical curtains from the deck level down. In new construction, plans should be made early on the methods that will be used to acoustically insulate a vessel.

Step Deck or Flush Deck:

From an acoustical position these two layouts are about the same. Spot insulation on hatch covers only will not provide significant reduction in noise levels. The entire engine room overhead has to be covered with lead core insulation. Frequently, noise levels forward of the engine room in this type of layout are severe. It is recommended that the forward bulkhead also be covered with lead core insulation. Hull sides do not require lead core material, but absorption insulation may increase quieting.

2) Pilot House Two Levels Over Machinery:

Airborne machinery noise is usually not objectionable in this design. Noise in the pilot house can come from adjacent exhaust stacks and sometimes from vibrational noise sources. Exhaust stacks can be easily insulated from noise and heat during construction phases, but often they are difficult to get at after construction is completed. Lead core insulation is used in these places, either in the wall or on the exhaust pipe side of the wall. In those situations where the exhaust stack is also used as the air intake stack, engine noise will be present directly behind or in the pilot house. Those areas between the pilot house and the machinery area will be the noisiest Lead core insulation is recommended for the engine room overhead and the forward bulkhead (if the crews quarters are forward), and absorption material may be applied to the hull sides.

 

3) Work Platform Over Machinery:

If engine/generator noise is objectionable on the work platform, then lead core insulation should be applied to the engine room overhead only. If noise is from on-deck generators, winches or exhaust, we would prefer to address those problems on an individual basis.

 

II, INSTALLATION

What to Install:

Machinery area acoustical insulation should be used to do three things: stop noise energy from penetrating the walls surrounding the machinery and absorb, in the engine room, as much of the noise energy as possible. Acoustical insulation will also dampen the vibrational energy that is in the hull, bulkheads, and machinery area ceiling. The use of limp, pliable and heavy mass lead sandwiched between two soft materials causes the noise energy to be reflected or bounced back towards the machinery source. The soft materials will be either acoustical foam or acoustical fiberglass which also serve to dissipate the noise energy in their layers of air pockets The lead stops noise from passing into the living and working areas, while the absorption material dissipates and reduces the volume of noise in the engine area. Lead core insulation is used on those surfaces behind which people will be, and absorption material (acoustical fiberglass or foam without lead) will be used on hull sides and aft bulkheads.

Insulation materials made of lead/foam or lead/fiberglass have essentially the same acoustical qualities. Lead/foam is considerably easier to handle and to cut to size. Lead/foam is rated as fire retardant or self extinguishing, whereas lead/fiberglass is virtually unburnable. If lead/fiberglass is selected, we recommend that sections be made to dimension (see section on ordering materials) so that the edges may be wrapped. Fiberglass has one weakness in that it tends to separate from itself. Wrapped edges keep it intact.

All insulation materials are provided with a covering. Mylar is the most common surface coveringg and it is used because of its strength. It will not significantly interfere with noise absorption. The covering is needed to protect the foam or fiberglass from spills, leaks or absorption of fuel fumes.

The amount of absorption achieved is a function of the thickness (not the density) of the absorption materials. See our price list for the different thicknesses available Assuming that there are no interferences, we suggest the use of two-inch thickness or more of both the lead core insulation and the absorption only insulation.

How to install:

Insulation has to be attached to the vessel in some manner. This may be accomplished through the use of adhesives, mechanical fasteners or by covering the insulation with pegboard or perforated aluminum. In those designs where the pilot house is directly over the engine (flush decks, engine box, etc.), adhesive is usually the only fastener. Screwed-in battens or large washers can be used to augment the adhesive. In steel or aluminum vessels, insulation is often made to correspond to the height of the angle stiffeners which support the insulation along with the adhesive. An alternative to stud welding is mechanical fasteners called Hanging Pins. These pins are large headed (2"x 2") nails with force fitting washers. The head is adhesive fastened to the vessel, and then the insulation is forced over the nail. The large lock washer is put on to support the insulation. They are generally used on 13 to 17 inch centers.

 

 III, ORDERING

The lead core insulation and the absorption insulation are available either in sheets or in made-to-dimension sections. We offer the latter service, because it is often less expensive to order made-to-dimension sections. It may be less expensive because of the savings in labor and wastage In cutting sheet material, or because one does not require full sheet sizes (36 ft2). Engine box designs and metal vessels with parallel stiffeners are particularly suitable to made-to-dimension ordering. Lead/fiberglass insulation may be best with wrapped edges, i.e., made-to-dimension sections. Remember, eventually you have to measure the vessel and the individual panels that will be put in place. It may be easier for you to provide us with the measurements of the individual panels. Just number them #1 through... We will be happy to help you with this decision.  You can price the material by determining the total square footage required and multiplying it by the appropriate cost per square foot found on the price list. Instructions for cementing are found on the container.