46' Post SF Sinks

How long is a piece of string? For example, who knows.

Also tragic things happen in a boat's life that might not mean anything at the time. For example, suppose previously in the boat's life they were running at cruise and the engine ate an impellor. Hot exhaust with no water flow could've got the muffler much hotter than it normally gets, yet the alarm went off, they stopped or slowed the boat and shut down the motor before any damage, yet the fiberglass muffler was compromised or weakened. Only to show up later. Or suppose the boat wasn't winterized properly and water froze in the muffler cracking or weakening it.

My theory is excessive backpressure. If the exhaust was weakened, it would've cracked the muffler and broken maybe some small pieces off or the main piece would've still been attached at one side. For a hole that size to be blown out completely, I think something was blocking the exhaust exit and a lot of pressure built up. I've started up SF with 8-12" exhaust and watched a 3 gallon buckets worth of leaves and floating crap come out of it, if it's sitting in a corner slip in the marina where the debris settles. A floating basketball, beachball, dead animal, any of that could've floated in there.......or maybe Rcrapps forget his fender wedged up in there! hehehe Fuel is a bit far fetched IMO, the muffler is pretty far back from the engines riser and has water sitting in it all of the time.

That doesn't make any sense, usually fiberglass will show some signs of failure...spiderweb cracks, softening, something. With the gen set out of the picture, and the fact that the slip she was in was extremely tight, I really don't see how anything big enough could get into the exhaust port to cause a back pressure blow out. If something was inside of the exhaust port it was put there intentionally.

It does show signs of failure...lots of old cracking........it's just they are all on the INSIDE, where the water flows year after year......the paint on the outside has concealed them.

You realize you are talking about a 30+ year old fiberglass muffler that has been subjected to how many hot and cold cycles???

Jimbo

Any animals swim in those waters that could have gone up the exhaust and died? Very strange set of facts. All that has been said seems logical but speculative. Why the huge failure rather than progressive? Did the owner notice soot in his bilge water, or an increase rear bilge light when running? The BANG still indicates imo a back pressure issue. Has the forensic surveyor been there yet?

This would be a lot easier to understand if she had underwater exhaust with a slow idle bypass at the water line...then I might be able to buy the back pressure scenario. But then again, I'm not the sharpest knife in the drawer when it comes to this forum.

If a few people stood in the cockpit on that side of the boat and the boat was full of fuel, the exhaust would've been completely underwater.

By golly Capt J, I do believe you might have solved the mystery! That makes perfect sense...If I were a betting man...I'd put my money on that theory. And you thought you were just another pretty face Capt J.

You asked a dumb question and you got a logical answer to your dumb question. There is no need for sarcasm.

Jimbo

The exhaust configuration on my 1998 50 is not that much different. So I would be very interested in knowing the cause. Thankfully I have not heard of this kind of event here on the east coast with a Post

No. Post here if it might interest others.

Sure looks like a failed seam at the bottom. Dead easy to prove one way or the other and much faster than weeks of speculation from afar ... maybe not as much fun though.

Is one scheduled?

I would think the insurance company would retain one, no?

Depends on the value. That often determines how much time and effort the insurer will spend.

This was a 30 year old part from what I've gathered. Not unrealistic to think the insurer might make some claim of lack of maintenance and care. Perhaps that's the real reminder here to all of us to keep an eye on and maintain every aspect of the boat.

We don't know and probably never will know the specifics of this sinking. I lived on a lake where muskrats were a major threat to boats and boathouses. They'd chip away at styrofoam and they'd eat bellows of inboard outboards. Leaking bellows was the leading cause of sinking there. And how often dealers wanted to replace them but owners said "Not now. They'll make it another year at least."

I don't think I have ever heard of any fellow boater changing mufflers as a maintenance item - you?

I have, but because the baffles have gone in them and suddenly the boat was too loud.....but not all that often.

When the exhaust goes underwater while the motor is running is a different story as it already has momentum going to exhaust. BUT, upon startup is a different story. I've run a bunch of SF to and from the boat shows with all of the boat show gear in them and exhausts underwater. When you start the engine, a lot of times, when it fires, it shoots water and spray 4' out of the exhaust and is quite violent when it first fire and the water builds enough pressure to come out. That kind of backpressure on an old muffler with old seam......the other thing is the boat was sitting on the hard for 6 months, 2nd startup since being launched.....possible frozen water in the exhaust did some damage to the muffler......

I would chaulk it up as a freak incident/accident that very seldomly happens. I'd chaulk it up to excessive backpressure on a weakened old muffler. Otherwise perhaps some on Tony Soprano's boys had something to do with it!

I've known one boatyard to check them. Actually talked to, make that listened to, a customer who was furious because of the things they told him needed changing and muffler was included. They bought an old boat that had been sitting out of the water for 6 years or so and was auctioned as a result of a mechanic's lien. They wanted the boatyard to get the engines running for them and just launch it without doing anything else. The boatyard pointing out the hoses that were destroyed. So launched it and towed it away.

Now otherwise I haven't heard of checking the muffler but really there is nothing that doesn't need to be checked over time.

I think most are only replaced as Capt J pointed out when sound gives them away. I did once have one collapse on a car. It was parked in snow and after I drove it a while suddenly I could only run about 30 mph. From the ice to the heat.

The exhaust must have been (almost) completely blocked, when backpressure on idle has caused the explosion, but how realistic is that?

I focus on the explosion, not the actual state of the exhaust...

I’m also triggered by Ralph’s suggestion ‘something got ignited somehow’…but diesel…it’s not that easy to ignite…