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Old 07-07-2015, 14:24   #1
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Mainship 400, stern low in the water

I've got a 2004 Mainship 400 that sits low in the stern to where the exhaust ports are approx. 1/2 submerged. My dinghy hangs off the stern but even with it in the water the ports are still partially submerged. Does anyone share this situation? What could be causing it (does ballast shift?)? Is there any problem with the exhaust ports being partially submerged?
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Old 07-07-2015, 14:58   #2
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Re: Mainship 400, stern low in the water

Assuming the bilge isn't flooded, where are your water and fuel tanks, and are they full?

The GB 42 had the water tanks in the stern and the waterline dropped 2" when they were filled.
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Old 07-07-2015, 15:14   #3
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Re: Mainship 400, stern low in the water

Fuel tanks are just barely aft of mid-ships but water tanks are about 1/2 way back from there so--could be the cause (They're full). Fortunately bilge is dry as a bone. I'll keep an eye on it the next time fuel and water approach empty. Seems, though, the design should have taken this into account??
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Old 07-07-2015, 23:50   #4
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Re: Mainship 400, stern low in the water

Most marine exhaust outlets are at or below the waterline when the boat is at rest. Once enough speed is attained, the exhausts are in open air. The important thing is to have exhaust flappers on the pipes where they go through the transom. These are rubber devices which will keep water from entering the engine exhaust system while moving in reverse or in a following sea or when the stern wave catches up to the boat when slowing down.
With the engines running, the exhaust pressure opens the flapper valves.
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Old 08-07-2015, 04:10   #5
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Re: Mainship 400, stern low in the water

Greetings and welcome aboard the CF, sailthentrawler.
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Old 08-07-2015, 06:27   #6
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Re: Mainship 400, stern low in the water

Quote:
Originally Posted by sailthentrawler View Post
I've got a 2004 Mainship 400 that sits low in the stern to where the exhaust ports are approx. 1/2 submerged. My dinghy hangs off the stern but even with it in the water the ports are still partially submerged. Does anyone share this situation? What could be causing it (does ballast shift?)? Is there any problem with the exhaust ports being partially submerged?

You might get more info from trawlerforum; several Mainship owners there.

Also, I think there's still a Mainship group on Yahoo somewhere...

-Chris
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Old 08-07-2015, 09:17   #7
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Re: Mainship 400, stern low in the water

Thanks all for your responses.
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Old 08-07-2015, 09:27   #8
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Re: Mainship 400, stern low in the water

Are you saying it is not sitting on it's waterline, or just looking at the exhaust outlets? Seems I see a lot of partially submerged exhaust outlets....
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Old 08-07-2015, 09:31   #9
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Re: Mainship 400, stern low in the water

The ports are below water (partially) and the waterline back to front slopes at the stern to where the tape line is also partly in the water--not straight and even from bow to stern.
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Old 11-07-2015, 12:27   #10
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Re: Mainship 400, stern low in the water

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Most marine exhaust outlets are at or below the waterline when the boat is at rest. Once enough speed is attained, the exhausts are in open air. The important thing is to have exhaust flappers on the pipes where they go through the transom. These are rubber devices which will keep water from entering the engine exhaust system while moving in reverse or in a following sea or when the stern wave catches up to the boat when slowing down.
With the engines running, the exhaust pressure opens the flapper valves.
The exhaust outlets on your vessel were designed to exit above the waterline.
If they do not, it may or may not present a problem, the real question is whether the exhaust run inside the vessel is properly executed to prevent seawater from entering the turbo/exhaust manifold area.
Mainship has been guilty of some really flawed exhaust systems, that have potential for catastrophic engine damage.
Rubber flappers are not the answer.
The solution is usually found in installing a "dry riser" at the turbo outlet to bring the spillover point to a minimum of 12" above the waterline.
Find some good reading on this topic at boatdiesel.com, or at sbmar.com
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Old 11-07-2015, 13:40   #11
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Re: Mainship 400, stern low in the water

sailthentrawler, this is an actual event, meant as a warning, only. Three years ago, my neighbor at the yacht club decided to mount his RIB on the canopy above his stern deck. He had a davit already mounted, so decided it was the obvious place to stow this bulky item on his trawler. As a result, his exhaust mufflers, which had been half submerged, were now fully submerged. One afternoon, deciding to warm up the engines, he started one engine, heard a "Pop", and being curious, shut down the engine and went to the engine room hatch on the aft deck to investigate. It took about twenty seconds to get there and open the hatch. He saw water rapidly rising in the engine room and called to his wife, who was down below, to get off the boat. By this time, less than a minute, the boat had begun to list heavily. He grabbed his cell phone and helped his wife off the boat, just as the stern went down, about two minutes into the incident. Having several large capacity pumps at our disposal, we went off to the emergency locker for the needed equipment. It took about five minutes to return with a Coast Guard type P-6 pump, a couple of electric submersible pumps, and all the other toys normally used for an incident as this. The stern was fully submerged, the cabin was filling, and within another fifteen minutes, only the tip of the bow was still floating, everything else was submerged, with the transom sitting on the bottom, fifteen feet down. Within a few minutes more, the dock was crowded with Harbor Police pump boats, salvage team and responding members. Late that afternoon, after multiple air bags had been deployed, the exhaust ports blocked, and continuous pumping of five high capacity pumps, the boat was raised and towed to a boatyard where it could be lifted on slings and set on the hard.

The back pressure of the exhaust was great enough to cause a loosened exhaust hose to pop off the exhaust flange at the transom. The resulting 6 inch hole below waterline was sufficient to immediately flood the engine room. As the stern sank, the pressure increased, speeding up the flow of water into the boat. Within minutes water was flowing through the scuppers, then into the engine room hatch and the rest of the boat. Nothing could have been done, short of blocking the exhaust outlet, which in minutes was ten feet below the surface and not a good place to physically have one's body. The good news, besides no one being hurt and the boat being fully insured, was that the dinghy floated off the coach roof and was recovered.

Back pressure is not a good thing for marine engines. The exhaust ports may be partially submerged, but that is merely (and probably) a symptom of bad design, weight management, or in this case, a bad decision. It can occasionally have freak consequences, such as this one. Something to keep in mind, though.
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Old 12-07-2015, 12:25   #12
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Re: Mainship 400, stern low in the water

Sailthentrawler, If you could post a rough drawing of your exhaust system with dimensions in relation to the waterline, it could help diagnose potential or already existing problems.
Also pulling off your exhaust elbow and take a picture of the turbo throat and blades can reveal some pertinent info.
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