Marine Engine External Exhaust Noise Suppressor With Swim Platform

This invention generally relates to a marine engine exhaust system and more particularly to a marine wet exhaust system, which substantially reduces noise, fumes and odor and is mounted on the external portion of the marine vessel, called the transom, and is installed in such a manner as to be functional as a swim platform, a boarding, or a life saving device, facilitating access to the vessel from the waterline, and providing a separate noise suppression chamber for each of a pair of marine engines in side by side orientation.

Present marine exhaust systems are subject to a variety of serious problems enumerated as follows:

(a) present day exhaust systems, designed to muffle sound, are installed internally within the hull of the vessel. Any breakdown of the composition with which the mufflers are constructed, or breakdown of clamps due to vibration and corrosion, can lead to serious consequences by discharging dangerous fumes and water directly into the interior of the vessel. Because of this danger and the use of the interior space, many vessels using high performance diesel engines are sold without muffled exhaust systems installed.

(b) the noise emissions from current marine engines have become intolerable, to an extent they provide a hazard to the operators and passengers of vessels, as well as the general public. Tests and studies show that marine diesel engines, at a crusing speed are operating at a sound level of more than 100 decibels within the immediate area of the vessel. According to the U.S. Department of Labor regulations, any noise level above 100 decibels is an impermissible noise beyond two hours of exposure. 115 decibels is the noise level of many vessels operated by diesel engines. If noise level exceeds 115 decibels, the permissible limit of exposure to that noise level is one-quarter of an hour, or less.

(c) exhaust fumes and odor, particularly of diesel engines emitting through the transom exhaust are drawn back into the cockpit by turbulant air flow through what is known as the "stationwagon" effect, thereby endangering and inconveniencing the boat's occupants. Ingestion of toxic exhaust fumes by boat passengers is well documented as a serious threat to public health.

(d) internal mufflers increase the heat level of the vessel. Heat levels on cruising vessels are extremely high, particularly with the high performance, turbo charged diesel engines now widely in use. Diesel engines operate most efficiently at temperatures approaching 200 degrees F. Turbo charges add substantially to heat buildup in the engine room. Considerable heat is retained in the current internal muffler systems, as when the engines are stopped, the muffler retains approximately one third of its volume in water, which rests in the muffler casing and retains heat of high temperature, thereby taking longer for the interior to cool, adding to the discomfort of crew and passengers.

Previous attempts to reduce the noise of marine engines, particularly diesel engines, reducing the odor and fumes from the exhaust systems of the engines, and preventing their backflow into the open rear, or cockpit, of the boat, and reducing internal muffler ambient heat, have been largely unsuccessful. No attempt has been made to solve the most serious problem of all, namely the safety hazard of internal mufflers, by providing a muffler system that is mounted to the exterior of the hull of the vessel, which thereby eliminates any hazard of discharging water or exhaust gases into the interior of the hull, and at the same time projecting the exhaust fumes at a distance farther aft of the vessel, directly into the water, thereby eliminating the flow of fumes and odor into the cockpit of the boat.

In U.S. Pat. No. 4,744,778 issued 5/17/88 to Porter, an exhaust muffler bolts on the transom and also serves as a swim platform. This muffler is a chamber that extends from one side of the boat to the other with exhaust gas exit ports in line with exhaust gas entrance pipes so that there is no athwart or transverse flow pathway forced on the gas to provide an elongate flow path through the muffler chamber for efficient silencing and gas scrubbing. And gas is not directed to exhaust along the center line. No special provisions are made for changing the exhaust vertical level between slow and planing speeds. Furthermore, the chamber of Porter makes no provision for the large mass of water that will accumulate in the chamber from both the surrounding water and the cooling water mixed with the exhaust. When running in reverse, extensions of the type shown by Porter will tend to dig into the sea and cause water to flow into the boat as well as into the chamber and the engine exhaust pipes causing serious problems.

Accordingly, there is a need for a simple, durable, inexpensive, but highly effective, marine exhaust system, which prevents and avoids internal breakdown, reduces substantially noise levels of the marine engines, reduces internal heat levels, provides a life saving and recreational attachment to the vessel, without interfering with engine performance, and without providing any known drawback.

It is accordingly an object of the invention to provide a marine engine exhaust system to fasten to the outside of the transom that directs engine exhaust transverse to the centerline and toward the centerline and provides exit ports substantially at the midline of the boat. This arrangement furnishes a muffler chamber length equal approximately to half the beam. The path length is further extended by a series of internal, perforated baffles for improved sound deadening action. The gas exit means includes an upper and a lower opening. The lower opening has occluding flap means for closing the opening automatically when in reverse to prevent water being forced into the exhaust chamber. The lower opening is open and exhaust gases are pulled out this opening near the water surface when the boat is on plane. This causes exhaust gas to be pulled into the wake, preventing it from swirling back into the boat in the "stationwagon" effect. The bottom surface of the chamber slopes upwardly from the point of attachment to the transom. When the boat is in reverse, this sloping surface acts as a planing surface lifting the stern and overcoming the tendency of the stern to bury itself in the waves when in reverse. This upward slope of the bottom surface of the exhaust chamber is reversed at the lower gas exit port so that any water in the chamber will drain out this port when the boat is lifted on plane or taken from the water. Since this is a chamber with substantial volume to achieve effective acoustic function, the volume of water would have a considerable weight, and could cause serious problems on freezing as well. The devices are to be employed in pairs in side by side relation with one device muffling a port engine's exhaust and a second device muffling a starboard engine's exhaust. The upper surface of each chamber is arranged to provide a sufficiently broad, flat surface to serve as a swim platform or boarding platform for recreational and safety purposes.

These and other features, objects and advantages of the present invention will become more apparent when the following detailed descriptions of preferred embodiments of the invention are read in conjunction with the drawings.

FIG. 1 is a schematic top view, looking down on the invention as it would be installed on the transom, showing a typical baffle configuration and direction of water and exhaust flow.

FIG. 2 is a perspective view of the invention viewed from behind the port side of the boat.

FIG. 3 is a perspective view of the invention on a boat viewed from behind the starboard side of the boat.

FIG. 4 is a schematic top view of the invention as it would be installed on a boat of wider beam than in FIG. 1.

FIG. 5 is a perspective view of the installation of FIG. 4 with a portion of the starboard device cut away.

FIG. 6 is a cross sectional view taken on line 6--6 of FIG. 3.

FIG. 7 is a cross sectional view taken on line 7--7 of FIG. 3.

FIG. 8 is a cross sectional view taken on line 8--8 of FIG. 3.

Referring more particularly to the drawings and initially to FIGS. 1-3, there is shown a boat 12 having side walls 13 and a transom or rear wall 11 with engine exhaust pipes 10 extending through transom 11. Ordinarily, these pipes run adjacent the side walls just above the water line and may have covering flaps to prevent ingress of water when running in reverse or in a following sea. It is the usual practice to pump seawater along with the exhaust gas through the exhaust system for cooling. A starboard silencer 1 and a port silencer 21 of the invention are fastened to the transom 11 side by side. Each silencer has a lateral sidewall 15, a central side wall 16 and a rear wall 17. A top surface 18 which is generally flat to serve as a swim platform and a bottom 19 connect the sidewalls and rear wall which define an inner acoustic chamber 20 when applied to the transom which serves as the forward wall of the chamber 20 when the silencer is sealed against the transom by sealing means such as caulking or gaskets.

Each silencer is mounted on one side of the transom so that the lateral sidewall 15 is substantially in line with the side 13 of the boat for hydrodynamic efficiency. It is located vertically so that the lateral exhaust pipe 10 is enclosed by the lateral portion of the acoustic chamber 20. The rear wall 17 of the silencer has no lateral exhaust ports. The upper exhaust ports 5 and the lower exhaust ports 9 are located close to the central sidewall 16 so that exhaust gas leaving the port 10 must change direction ninety degrees and move toward the centerline of the boat and then change direction ninety degrees again to exit through the exhaust ports 5 and 9. This provides a long outboard muffler that doesn't extend a great distance beyond the transom. It can be as long as half the beam. The path is extended and diverted by a plurality of perforated baffles 4, 7, 8 for enhanced noise reduction. An exhaust scrubber 2 of fibrous material may further enhance operation. Access plates 3 provide access to the interior for service and adjustment of the plates to provide maximum noise reduction with minimal resistance to exhaust gas glow. With diesel engines, it is important to avoid restriction of exhaust flow because this interferes with correct operation and produces noxious emissions. The central sidewalls 16 of the two mufflers are shown against one another with the top surface seam 22 between the two covered by a trim strip 23 shown partially broken away. Alternatively, the two mufflers may be molded in one piece with a common central sidewall 16.

For commercial economy in molding a product that will be more versatile in fitting a number of boats of varying beam, the preferred embodiment has a width between lateral sidewall and central sidewall small enough to fit the narrowest beam for which the product is designed, when the two central sidewalls are juxtaposed. A top extension 24 extends centrally beyond central sidewall 16. As much of these top extensions 24 is cut off as is necessary so that the two top surfaces of port and starboard mufflers will meet in a butt joint seam 22 to be covered with trim strip 23.

It will be seen in FIGS. 4 and 5, where the two mufflers are installed on a boat with broader beam, that the two central sidewalls 16 shown in phantom in FIG. 4 are spaced apart and extensions 24 span the gap therebetween to form a complete top surface. A vinyl trim strip 23, shown partly broken away, covers the seam.

The housing is preferably molded of glass fiber reinforced plastic. The baffle plates may be of perforated plastic or metal. As best shown in the cross sectional views, FIGS. 6-8, the bottom 19 slopes upwardly from its attachment to the transom 11 except at the central wall where the exhaust outlet ports 5 and 9 penetrate the rear wall 17. This upward slope provides an upward thrust on the transom when in reverse which overcomes the tendency to dig in and spill water into the boat. The bottom 19 also slopes toward the central sidewall so that any water in chamber 20 drains out lower exhaust port 9. This reduces the weight when on plane and prevents damage from water trapped in the chamber freezing in winter layup.

Stainless steel angle brackets 25 bolted to muffler 1 and transom 11 with through bolts 26 hold the muffler securely in place. Sealant 27 in the form of calking or gaskets provides a gas tight seal. Lower flap 6 pivoted on pivot 28 is pushed closed in reverse preventing water from entering chamber 20 when running in reverse. Since lower exhaust port 9 is underwater at low speed, gas normally exits through upper exhaust ports 5 at idle or low speed. At high speed, flap 6 is pulled open and the force of water rushing past port 9 creates a vacuum, sucking exhaust gas out port 9 and into the churning wake where it is pulled into the water, well behind and below the boat, thereby preventing the gas from entering the boat. The stop 29 holds the flap at the bast angle to ensure this suction effect, which delivers exhaust at a level about two feet below that of conventional exhausts. For clarity of illustration only a single baffle with perforations 30 is shown in FIG. 7. These baffles may be attached to upper, lower or rear wall of the muffler.

The above disclosed invention has a number of particular features which should preferably be employed in combination although each is useful separately without departure from the scope of the invention. While I have shown and described the preferred embodiments of my invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that certain changes in the form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention within the scope of the appended claims.