Why does exhaust exit the transom right at the waterline?

[Luhrs28]

Hi guys!

On my Luhrs 28' the original transom exhaust tubes/flappers are exactly halfway below the waterline, when the boat is at rest. Why? Is that to quiet the exhaust? If so I don't really think it works because when I'm going along at any decent speed the entire exhaust tubes are out of the water. (because of the transom wake)

The reason I'm asking is because I'm putting a new Mercruiser 5.7 (gasser) in soon, which needs 4" tubes. (my original ones are 3"). What I'm thinking of doing is raising them so they exit the transom maybe 2" above the waterline.

The reason I want to do this is because in the current location if one of my exhaust hoses or tubes springs a leak at 3am bigger than my bilge pump can handle my boat will sink right at the dock. If I raise them above the waterline that can't happen. I'm going to install in-line mufflers so I don't think noise is going to be a problem.

What do you guys think about this?

Thanks,

Bert

 

[cyclops2]

Re: Why does exhaust exit the transom right at the waterline?

Because Great Grandpa did it that way.
It sounds race engine like.

All the inside piping is pitched downward slightly.

If the water freezes. Boat shop makes a bundle off of us.

 

[Don S]

Re: Why does exhaust exit the transom right at the waterline?

It's not ususally a problem, even if it freezes if only part of it is below the water line it won't hurt anything.

If the water freezes. Boat shop makes a bundle off of us.

No, that means you should have had your boat out of the water and drained it if it's a problem.

 

[Bondo]

Re: Why does exhaust exit the transom right at the waterline?

Hi guys!

On my Luhrs 28' the original transom exhaust tubes/flappers are exactly halfway below the waterline, when the boat is at rest. Why? Is that to quiet the exhaust? If so I don't really think it works because when I'm going along at any decent speed the entire exhaust tubes are out of the water. (because of the transom wake)

The reason I'm asking is because I'm putting a new Mercruiser 5.7 (gasser) in soon, which needs 4" tubes. (my original ones are 3"). What I'm thinking of doing is raising them so they exit the transom maybe 2" above the waterline.

The reason I want to do this is because in the current location if one of my exhaust hoses or tubes springs a leak at 3am bigger than my bilge pump can handle my boat will sink right at the dock. If I raise them above the waterline that can't happen. I'm going to install in-line mufflers so I don't think noise is going to be a problem.

What do you guys think about this?

Thanks,

Bert

Ayuh,... I think I'd drop in the new motor, 'n leave well enough alone...

If ya think yer hoses are gettin' Iffy, Change 'em...

The motor sure won't care...

 

[Luhrs28]

Re: Why does exhaust exit the transom right at the waterline?

I just thought of another benefit to raising the outlets. I'd be able to see that I've got raw water flow. As they are currently the exhaust gas pulses are bubbling the water so much at idle I can't really tell if there's raw water exiting.

 

[Tahorover]

Re: Why does exhaust exit the transom right at the waterline?

I have no issues pushing 500hp out of two 3" pipes.

 

[cyclops2]

Re: Why does exhaust exit the transom right at the waterline?

Have your temperature guage checked after the engine warms up. I am always doing a quick look at the gauges every few minutes. Also make sure your OVERHEATING ALARM is working at the correct temperature. Both are simple checks that WILL SAVE your engine.

At WOT I check temperature every 5 or 10 seconds. At that heat generating level. POOOFF goes the engine.

I agree with you below water exhausts are not very comforting. But ALL stern drive are under water & do just fine.

Your call. Above water DOES SOUND a lot better.

 

[cyclops2]

Re: Why does exhaust exit the transom right at the waterline?

Tahoe makes a very good point.
Once the engine water is mixed into the exhaust the VOLUME OF HOT GAS & BACK PRESSURE DROPS tremendously.
So unless you race for money or trophies, 3" should do fine.

people that run DRY exhausts have a need for larger, shorter & straighter pipes.

Enjoy you bigger engine.

 

[Luhrs28]

Re: Why does exhaust exit the transom right at the waterline?

Thanks for the replies. I think I'm still going to raise my outlets a couple inches. I just hate the idea that any more hull penetrations are below the waterline than absolutely necessary.

Bert

 

[Don S]

Re: Why does exhaust exit the transom right at the waterline?

Just make sure you still have the proper down angle on what ever exhaust setup you have.