A25 exhaust system

[kerrye]

This is a continuation of the discussion over on my 'First Splash' thread, but I thought it deserved a separate thread title of its own. For those who haven't read that thread, my Elastomuffler exploded in the middle of the lake the first time I launched my A25 causing the boat to rapidly fill with water. So, suffering from PTSD as a result of that event, I've been thinking about whether there are any ways to improve the exhaust system on an A25 such as raising the exhaust thru hull, installing a loop in the exhaust hose at the transom and/or installing a waterlift muffler. My conclusions at the moment is that there is no good process for substantially improving the existing system which is a gravity drain exhaust from the engine to the thru hull.
I took some measurements today. It looks like the bottom of my exhaust manifold is 6" above the waterline. It's about 3" above the cockpit floor and the cockpit floor is about 3" above the waterline. (measurements not exact--I did it with the boat on the trailer). My thru hull is mostly below the water line so once the boat is in the water, the exhaust hose is filled with water up to 6" below the exhaust manifold. Obviously, any failure in the hose will fill the boat with water via the thru hull. As long as the engine is running, there's no worry that water will enter the engine by backing up the exhaust hose, but once the engine is shut off, you have 6" to work with before water will get in the engine.
A loop at the transom and a waterlift muffler would stop intrusion of water via the hose but I can see no good place to install a waterlift muffler and definitely no place in which the drop from the exhaust manifold to the muffler would be any greater than the existing 6" drop from manifold to thru hull. And the water capacity of the muffler would have to be adequate to contain all the water in the 2" hose from the muffler to the thru-hull. That's not an insignificant amount. The other problem with the loop at the transom is that since that loop would be higher than the engine, there is a possibility of water reaching the level of the exhaust manifold and flooding the engine even with the engine 6" above the waterline.
I'm curious as to other people's thoughts on this topic. I'm attaching some pictures in the next post so people can see what I take to be the cause of my Elastomuffler explosion--the exhaust hose from the engine was far too long and inserted into the muffler all the way to the outlet end.

Given the fact that my existing hoses mate up in the current condition, I'm in a good position to experiment going without any muffler altogether which is what I think I will do initially. If it's too loud, I'll get a replacement for the Elastomuffle.

[kerrye]

Pictures

[kerrye]

Thoto of my exhaust thru hull which is underwater mostly.

[JT48348]

That thru hull does seem low given that you can't get a watertight muffler or loop in the exhaust system.

Would raising the exhaust thru-hull by 3"+ accomplish anything? Maybe not if taking a following sea.

[kerrye]

Any amount raised above the waterline will allow standing water in the exhaust hose to be that much closer to the exhaust manifold. I assume they put the thru hull with the top almost right at the waterline to maximize the distance between the water in the hose and the exhaust manifold. From what I can gather from reading various information about marine exhaust systems on the web, the 6" drop from manifold to waterline is marginal. Some places mention a 12" minimum but there's no way that's happening on an A25. I think that 12" minimum is typically used on a sailboat where the engine is not running while under sail and a following sea might drive up the exhaust hose. From the fact that many, if not most A25's are still afloat, I'm willing to think that a 6" minimum drop is acceptable.

[kerrye]

Here's a picture of the inside of the Elastomuffle looking towards the outlet end. The inlet hose was pressed up hard against that interior layer. So the water and gases had a hard time coming out of the inlet hose, then they had to reverse to fill up the inlet end of the muffler, then reverse to get out the slits in the outlet end.

I am completely ignorant when it comes to muffling principles, but when I look at this I can't see it serving much purpose besides increasing back pressure. I guess I'll find out once I hook the hoses back together and give it a try. I ordered some heavy duty hose clamps. The existing ones on the outlet end were so rusted they wouldn't move and I had to cut them off with a dremel tool and a cutting disc. Makes me think it might be useful to carry a 12 volt dremel tool on board.

[DesertAlbin736]

Sorry about all that off topic Titanic analogy trivia on the other thread. Note to moderator, feel free to delete it. I would myself if I knew how.

Probably the easiest and most viable solution would be to install a check valve as close to the thru hull as possible to keep as much water as possible from backing up in the hose & as little back pressure as possible needed to clear the hose when then engine is running. Certainly the fact that the floor boards are so close to the waterline limits options.

Having the exhaust outlet on starboard side changes a lot of things in that last bilge section. Here's ours showing the new Vetus raw water strainer I installed a while back that cured the problems we initially had with the raw water pump having trouble priming after the boat had been out of water. Our Whale manual bilge pump can be seen a lower left, the self-priming diaphragm electric bilge pump at upper right, and the muffler at lower right. Yours would be just the opposite.

DSCN1991.JPG

And the difference in through hulls between boats as noted on the other thread: Upper left Kerry's boat, our 1971 boat at upper right, lower left the semi-displacement 1977 A25 we almost bought but didn't. It highlights the difference between the early full displacement hulls and the later semi-displacement DeLuxe models. For some unknown reason the owners of the '77 A25 decided to add a piece of rubber hose to the exhaust outlet. Have no idea why they did that. In any case, we've never had any trouble with ours, but there must be other A25's out there that have run into similar issues.

A25 exhaust thru hull comparison.jpg

So here you go, here's your solution, problem solved!

centek check valve.jpg

http://www.defender.com/product.jsp?pat ... id=1656822

Here's a better price for the same thing from JMS

http://www.jmsonline.net/centek-industr ... fgod7nQA0Q

[DesertAlbin736]

The existing ones on the outlet end were so rusted they wouldn't move and I had to cut them off with a dremel tool and a cutting disc. Makes me think it might be useful to carry a 12 volt dremel tool on board.

I've used my Dremel tool with cutting disks more times than I can count, like triming the though bolts on our hard top off flush with the nuts on the underside, and many other uses. Have to check how much wattage they use & how big an inverter it would take, or just use it when plugged into shore power.

[WillieC]

I just bought a cheap used 12vdc/120vac plug in inverter. Not the recommended pure sine wave for electronic equipment, but I am planning to use it to keep my laptop with Seacharts charged up and for the battery drill charger. LOW TECH. Should work for a dremel too. Now back to the muffler!
Mine is a fiberglass tube, I assume it is a waterlift in that its operation matches BetaDon's description and one of the links you posted, Kerry. Don't think it is big enough to hold all the water in the hose to the through hull, but mine has a slight hump under the stbd aft cabin that I think I should eliminate since, as you noted, it will raise the water level in the system, thus closer to the exhaust elbow. Sorry I don't have pictures. Will take some next boarding.

There she sits! Note: No following sea will flood engine at this angle. (Stupid smart phones, or operator.)

IMG_0257 (2).JPG

PS. Steve, don't worry about the Titanic piece. Great info, and mildly relevant!

[kerrye]

I've seen that muffler listed on Defender and 'check valve' in the description has puzzled me. It seems as if the listing combines both the muffler and the Centek check valve erroneously.

[kerrye]

If you have a waterlift muffler, it's capacity should be listed somewhere online so you could check to see if it holds enough to contain the hose water. If it can, you could put a loop in the hose at the transom to prevent water flowing down the hose. If I were you, I'd check to see the distance between the bottom of your exhaust manifold and the water level in the muffler. From that, you could probably calculate how much additional water in the hose beyond the capacity of the muffler it would take to flood your engine. The engine wouldn't flood if there was no point in the hose which was higher than the bottom of the exhaust manifold, assuming your thru hull is below that.

[kerrye]

After reading a number of descriptions of that part, some of which called it a thru hull with flapper and others referred to it as a muffler, I decided it was just a check valve and ordered it thru Discount Marine Supplies for $80 plus shipping. It looks like cheap insurance for an A25 if it does work as a check valve.

I did look at their mufflers and the ones which appear similar to DesertAlbin's muffler are described as for above waterline use only. I'm not sure exactly what they mean by that but based on my experience, at least when the engine isn't running, my muffler would be filled with water even though the engine is above the waterline. I'm not sure if they intend to imply that such a muffler should not be used in those circumstances.

[DesertAlbin736]

No, this Vernalift muffler similar to what's in my boat that I mentioned earlier is designed for engines located on or below the waterline. Add the check valve & you'd be fail-safe.

The Vernalift muffler was designed originally for small auxiliary propulsion engines installed near or below the water line in sailboats. In the early 70’s the quieting capabilities of lift mufflers were recognized. The Vernalift™ Group expanded to include new and larger engines.
Features:

Application: Inboards, Sailboats & Generators
Fuel type: Gas or Diesel
Waterline: Above or Below
Sound rating: Better
2" ID Inlet / Outlet 17.5" long x 10" Diameter

muffler.jpg

http://www.defender.com/product.jsp?pat ... id=1248544

[2manyboats]

Kerry; I have the 38 Beta in my 25 with a waterlift muffler installed. I will try to get pictures and info tomorrow.

Wayne

[kerrye]

Thanks that would be useful.