Searay sundancer 400 1999 cat 3116

[Morgan1957]

Hi anyone everyone
I have the searay 400 sundancer 1999 Just had a servayer on the boat today and he queried the under water exhaust system
And the possibility that water could back fill up the exhaust to the engine
Is this a possibility or dose the system have a no return in the exhaust
Any help would be appreciated or a contact at Searay maybe
Thanks

 

[Strecker25]

Hi anyone everyone
I have the searay 400 sundancer 1999 Just had a servayer on the boat today and he queried the under water exhaust system
And the possibility that water could back fill up the exhaust to the engine
Is this a possibility or dose the system have a no return in the exhaust
Any help would be appreciated or a contact at Searay maybe
Thanks

Never heard that being a problem on the larger boats. Ours is similar to that boat (410 with 3126’s) and the highest point in the exhaust riser is way above the water line.

He may just be sharing experiences from smaller gas powered boats. The 370 of similar vintage had big problems with water intrusion back up the log style exhaust manifolds

 

[fwebster]

I have been around diesel powered 370, 380,400, 410. 450 and 460 Sundancers and owned, operated and maintained a 450DA for 26 years, all with under water exhaust outlets, and I have never seen or heard of one ingesting water thru the exhaust outlet.

The reason is primarily because of the exhaust port outlet design. It creates a venturi effect as it passes thru the water under the hull. This means that the exhaust outlet under the hull creates a vacuum under and behind the outlet so it is "sucking" water and exhaus out of the port rather that pushing it back into the engine. The exhaust on boats with the underwater exhause outlet actually surfaces quite a distance behind the boat. Plus Ryan is correct, the exhaust system in the boat is part of the engine design and is well above the point where it can ingest water from under and behind the boat. Even on smaller diesel Sundancers, the 370, and 380, water ingestion does not happen.

I think you just happened to find a surveyor that probably has no or very limited experience with diesel Sea Rays but has proably "read-up" on water ingestion in smaller Sundancers with V-8 gasoline engines.

While the underwater exhaust outlets are not prone to problems; however, if you hit an underwater obstruction they can be dislodged and fall off/lost. That is a rare occurrence, but it gets expensive because will require a haul out and sourcing a replacement. Also, if you hit something shallow enough to impact the exhaust outlet, you likely will also have prop, shaft, rudder and even strut damage.

The Diesel 400DA is a great boat……enjoy it!

 

[Stee6043]

I think that was also only ever a problem with gas engines. Specifically horizon 7.4's I believe. I've never heard of it with diesels.

 

[ttmott]

The exhaust arrangement on the diesel 400DA provides not only the underwater but also the bypass that is above the water line. You can completely remove the exhaust system with the boat in the water without risk. Any happenstance of a vacuum or reversion situation (can't really happen with a diesel engine) would draw air from the bypass. Plus, all of the exhaust system inside of the boat except for the tube coming up from the bottom is above the water line. As @fwebster Frank says, hull speed forms a vortex behind the underwater exhaust nozzle and will draw the exhaust from the engine.

 

[Jaybeaux]

An interesting sidebar to @fwebster comments....We hit a partially submerged log in our 420. After stopping and assessing any vibration or any other damage, all was good. We ran for 1/2 a season. I noticed that my fuel consumption on one engine went up (as best can be determined on a mechanical CTA). Later that year we pulled the boat for detailing and we were missing the exhaust port on one side...the side that was suffering from higher fuel consumption. As Frank says, the port creates a suction to help pull the exhaust gas out of the engine, thereby reducing backpressure.

Physics is cool.

Jaybeaux

 

[Stee6043]

Physics is cool.

Jaybeaux

Well...I mean...not so much the part about your underwater exhaust port being ripped from the bottom of the boat by an object "not in motion"

 

[Strecker25]

The exhaust arrangement on the diesel 400DA provides not only the underwater but also the bypass that is above the water line. You can completely remove the exhaust system with the boat in the water without risk. Any happenstance of a vacuum or reversion situation (can't really happen with a diesel engine) would draw air from the bypass. Plus, all of the exhaust system inside of the boat except for the tube coming up from the bottom is above the water line. As @fwebster Frank says, hull speed forms a vortex behind the underwater exhaust nozzle and will draw the exhaust from the engine.

can confirm, I pulled the entire exhaust system while in the water and the waterline is like an inch below the top of the vertical fiberglass tube running through the bottom of the hull. I had a pump handy the first time I did that