Exhaust System For Tunnel Stern Boat

Abstract

In a tunnel stern boat having a propeller in the tunnel and a spray plate and rudder aft of the tunnel, the exhaust from an inboard engine is piped to a transom opening from which it is guided downward and directed under the spray plate into the high speed stream of water thrust aft from the propeller.

Description

THE INVENTIVE IMPROVEMENT

Exhaust systems for small marine craft have generally been relatively noisy. Marine engines generally emit larger quantities of exhaust than comparable land vehicle engines, and marine exhaust is relatively wet so that muffling has been either unsuccessful or excessively expensive. Various arrangements for underwater exhaust have not reduced the noise substantially.

The invention involves a discovery of a simple way to exhaust underwater from a tunnel stern boat to achieve a muffled and quieter exhaust. The invention aims at simplicity, economy, reliability and longevity in a quieter marine exhaust system.

SUMMARY OF THE INVENTION

The inventive exhaust system is applied to a tunnel stern, planing boat having an inboard engine, a drive shaft turned by the engine and extending into the tunnel, and a propeller in the tunnel turned by the drive shaft. A spray plate is arranged to extend aft of the transom closely over the stream of water thrust aft by the propeller, and a rudder is arranged below the spray plate in the stream. There is an opening through the transom, and an exhaust pipe conducts exhaust from the engine to the transom opening. Means aft of the transom opening guides the exhaust downward in the region of the spray plate to direct the exhaust into the stream of water under the spray plate.

DRAWINGS

FIG. 1 is a partially cut-away, fragmentary elevational view of a preferred embodiment of the inventive exhaust system;

FIG. 2 is a partially cut-away, stern elevational view of the exhaust system of FIG. 1;

FIG. 3 is a partially cut-away, fragmentary side elevational view of an alternative preferred embodiment of the inventive exhaust system; and

FIG. 4 is a fragmentary stern elevational view of the exhaust system of FIG. 3.

DETAILED DESCRIPTION

The inventive exhaust system is applied to a tunnel stern boat 10 having a tunnel 11 housing a propeller 12 supported by a strut 13 and turned by a drive shaft 14 that extends into tunnel 11 from inboard engine 15. An engine 15 turns propeller 12, a high-speed stream of water is drive aft from tunnel 11 relative to boat 10 to propel boat 10 as is generally understood for tunnel stern, planing craft.

Spray plate 16 extends aft from transom 17 closely over the stream of water thrust aft by propeller 12. Spray plate 16 is aligned with the top of tunnel 11 so that the propeller stream flows smoothly under and generally tangent to spray plate 16, A rudder 18 is arranged under spray plate 16 in the propeller stream to steer boat 10 as is generally known.

An exhaust pipe 19 conducts exhaust from inboard engine 15 to an opening 20 in transom 17 above spray plate 16. Another opening 21 is formed in the after central region of spray plate 16 and cowling 22 is generally angled downward and aft from spray plate 16. A shroud 23 is secured tightly to transom 17 above spray plate 16 to fit loosely over the top of spray plate 16 so that exhaust passing through transom opening 20 is substantially confined by shroud 23 so that it passes through opening 21 and is guided by cowling down into the propeller stream.

Shroud 23 is preferably formed of a resilient material such as resin-bonded glass fibers to have a muffling effect on the exhaust. Shroud 23 is preferably sealed to transom 17 but not secured rigidly to the top of spray plate 16 to allow for manufacturing tolerances and flexure of spray plate 16 under the pressure of operation. With shroud 23 fitting loosely around the top of spray plate 16, a small amount of exhaust escapes downward around the juncture between shroud 23 and spray plate 16. However, such exhaust escape is directed into the propeller stream and is well-muffled and relatively quiet. The main exhaust passage through opening 21 in spray plate 16 also directs the exhaust fumes into the relatively fast-moving and turbulent propeller stream which tends to mix the exhaust thoroughly into the water for quieting effect. Experience shows that the inventive exhaust downward into the top of the propeller stream of a tunnel stern boat is much quieter than the ordinary underwater exhaust from the hull of an inboard engined craft.

Some alternatives for the inventive exhaust system are illustrated in FIGS. 3 & 4. The differences are a pair of exhaust pipes 24 conducting exhaust gases to twin transom openings 25 above spray plate 16. Instead of a shroud covering spray plate 16, a pair of pipes 26 extend from transom openings 25 downward to a pair of openings 27 located in spray plate 16 astraddle rudder 18. Portions of pipes 26 extend through and below openings 27 to form cowlings 28 directing exhaust gases through spray plate 16 and into the propeller stream.

Persons wishing to practice the invention should remember that other embodiments and variations can be adapted to particular circumstances. Even though one point of view is necessarily chosen in describing and defining the invention, this should not inhibit broader or related embodiments going beyond the semantic orientation of this application but falling within the spirit of the invention. For example, those skilled in the art will appreciate how the invention can be adapted to various tunnel stern craft and will appreciate the various ways that exhaust can be directed into the propeller stream of such a craft within the spirit of the invention.

Claims

I claim:

1. A marine exhaust system for a tunnel stern, planing boat having an inboard engine for driving a propeller recessed in said tunnel, said system comprising:

a. a spray plate extending aft from the transom of said boat closely over the stream of water thrust aft from said tunnel by said propeller;

b. said transom having an opening;

c. an exhaust pipe for conducting exhaust from said engine to said transom opening; and

d. means aft of said transom opening for guiding said exhaust downward to the region of said spray plate and for directing said exhaust into the water under said spray plate.

2. The exhaust system of claim 1 wherein said spray plate has an opening and said guiding means encloses a space between said transom opening and said spray plate opening for directing said exhaust through said spray plate opening into said stream of water.

3. The exhaust system of claim 2 wherein said opening in said spray plate is in the central after region of said spray plate.

4. The exhaust system of claim 2 including a cowling generally angled downward and aft from said spray plate opening.

5. The exhaust system of claim 2 wherein said spray plate has a pair of said openings.

6. The exhaust system of claim 2 wherein said enclosing means comprises a pipe extending from said transom opening to said spray plate opening.

7. The exhaust system of claim 1 wherein said transom opening is above said spray plate, and said guiding means comprises a shroud secured to said transom and fitting over said spray plate.

8. The exhaust system of claim 7 wherein said shroud is formed of relatively resilient material to muffle said exhaust.

9. The exhaust system of claim 7 including means for sealing said shroud to said transom, said shroud being loosely adjacent said spray plate.

10. The exhaust system of claim 7 wherein said spray plate has an opening in its after central region beneath said shroud so that said exhaust passes through said opening into said stream of water.

11. The exhaust system of claim 10 including a cowling generally angled downward and aft from said spray plate opening.

12. The exhaust system of claim 11 including means for sealing said shroud to said transom, said shroud being loosely adjacent said spray plate.