A25 cautionary tale

[kerrye]

Today’s events: Since Jasper is here for a couple of days we decided to take a 10 mile jaunt on the canal, passing through the Waterloo lock to Seneca Falls where we could spend the afternoon and evening reveling in the presence of dead feminists. We approached the Waterloo lock with about a 1 1/2 or 2 knot current running towards the lock and the weir feeding the generating station. The lock master informed us on the radio that the lock was empty and it would take 10 minutes to fill it before he could let us in. So I alternated between drifting towards the lock a few dozen yards then reversing back upstream. After about 8 minutes of this I put the boat in forward and immediately it sounded like a rod was going to go through the side of the block. Damn. Not a great place to lose an engine, right above a weir. I put it in neutral and revved it up and backed off. Even worse, clattering to beat the band. I made a quick decision, the Waterloo courtesy dock was just downstream of us, upstream of the weir. I figured the engine would hold together long enough to get there so I accelerated downstream so I could turn up into the current and dock. As soon as I turned upstream the noise went away. WTF? Mystery self healing connecting rod? Did a stick drift down into our prop jamming in the crab line catcher and wacking the hull when in gear, washing out when the current was flushing through? Why did the knock increase with engine rpm’s when in neutral? Did I not have it in neutral? Bizarre. In any case we decided to forego the section to Seneca Falls and return to Seneca Lake, on which trip the engine performed flawlessly. It must be my summer for weird unidentifiable knocks and clatters. (I do have a back up outboard in case you were wondering).

[kerrye]

Holy crap! I just figured out what was going on. Exhaust outlet is about half submerged with no one aboard. With 3 aboard it is under water. Exhaust manifold is just an inch or two above the waterline. None of this is a problem when going forward with high engine rpm’s as cooling water is blown out with the high exhaust pressure. However when the engine was idling and I was backing into a 2 knot current, water was being forced back up the exhaust pipe and not being blown out because the exhaust pressure was so low. Finally it got so high that some water backed into the lowest cylinder causing the knock, because as every hydraulic engineer knows, water is not compressible. It disappeared when I accelerated and turned up stream because the water got blown out of the exhaust once it was on the downstream end of the boat without a 2 knot current flowing into it. Damn. Not something I ever imagined might happen. Time to make some changes in the exhaust system.

[kerrye]

Looks like I’ll be doing this: viewtopic.php?f=28&t=9596&p=66781&hilit=Exhaust#p66781

[WillieC]

Ok. That settles it. I have spent a lot of time reading about exhaust systems and hydrolock and wonder how in the heck did these boats ever get built this way.
Kerrye, thank you for this timely reminder. I like Hetek's pictures. This is my winter's project or should I move it up?

Do keep us posted.

[kerrye]

The one downside to Hetek’s system is that it’s easier to fill it up and have water get into the engine that way.

[WillieC]

I need to look more closely at Hetek's system. Looks like a lot of parts and clamps to leak.
There's got to be a simple ABYC or good boat system method to do this for our goofy A25s. What I understand is a loop is needed, something like 12" above water line. And it should be vented? We just have to figure out where to put that sucker. I have been thinking about exhaust piping using PVC. If you can use rubber, why not PVC? I know how to make it bend into just about any shape. (I am sure it has something to do with burn characteristics, though I think burning rubber would kill me just about as quickly as burning PVC. Just as soon NONE of it burns.) We really need to solve this one for the ages, A25 specific. Loss of cabin space be damned. Kerrye's story about the rubber muffler exploding opened my eyes. Whenever I see one, I give the serious dad talk.

Hetek, how is your system working? What would you do differently?

Kerrye, why do you say Hetek's system would easily fill with water? Long engine start cranking?

[kerrye]

Yes

[kerrye]

And it’s about time someone else started having exhaust problems as I’m getting seriously tired of being the bad example

[kerrye]

One thing to keep in mind: my boat has a Westerbeke 42. Same engine was OE in Catalina 36 where many suffered a quick demise due to a high exhaust loop causing high back pressure and poor compression in last two cylinders. Anyone have any idea how to predict back pressure from height of exhaust loop.

[hetek]

My exhaust system was technically designed by Vetus. The Vetus catalog has calculations, formulas and examples to design a proper exhaust system. However, I have yet to see how it works. My boat has been trailer bound since.

The Vetus design dictates lengths and diameters of exhaust hoses, distance between exhaust elbow and waterline, distance of discharge above waterline, minimum rise of transom riser... Mine passes on all accounts.

The only thing I didn't use is a Vetus waterlock. However the one I did use has the same internal volume of a similar Vetus model.

Agreed about "all those connections" but it is what it is. I double clamped all just to be sure. The A25's design and measurements almost perfectly matched one of the Vetus designs in the book so that's what I built.

I recall that the design was necessary due to my engine's exhaust elbow being 6" above the waterline. Kerrye's exhaust elbow only an inch or two above the waterline screams "vented loop", according to Vetus.

[hetek]

Hey! Vetus has the catalog online! Here:

http://viewer.zmags.com/publication/6af ... afeb8e9/84

Page 85 (the right side) has everything I mentioned. I built the system in the diagram on the left. Kerrye would need the system on the right due to the lower exhaust elbow (the one with the vented loop).

I omitted the muffler because the waterlock should be enough of a muffler on it's own.

Note the title of the page: "Preventing water running back to the engine". Says it all!

[WillieC]

Now I gotta read all that stuff. Again! (Thanks for the links.)

Trailer bound boat!!?? What's that all about? Sounds almost like I thought my summer was going to go.

[hetek]

My "trailer bound" is self-imposed, temporarily.

My interior is currently gutted to the bare hull sides and I just put in all new cabin windows and weatherstrip. I have new hull liner ready to go and marine grade Sapele plywood just waiting for the table saw.

I thought of splashing her as-is and day sailing but it would make it more difficult to do the interior fitting. I still may. I'll make a final decision after the weekend.

I know... I know... The Summer isn't waiting for me.

[DesertAlbin736]

Seneca Falls... now that brings back some memories. Was that the CS1 lock you're talking about? Does your exhaust system not have a check/flapper valve? I could imagine that at idle raw cooling water could back up behind a check valve in that situation & not be able to force it open & blow the water out. Perhaps the solution
in that situation when in neutral is not let your RPMs drop below 1,000 or 1,500. When I first looked at a 1978 A25 Deluxe for sale in Phoenix (first intro to Albins) I was concerned about how low the exhaust exit was, seemingly below the waterline. I was all like WTF is with that? That was one among several reasons why we walked on that deal.

Aside from your exhaust system problem I'm intrigued by the article in BoatUS mag's latest issue about doing part of the so-called "Triangle mini loop". Future bucket list item? That's as we sit at anchor on a cold wet day on Lopez Island in Washington's San Juan Islands.

[WillieC]

Here are some more links to make it more confusing. This may be why I haven't done this yet.

https://www.centekmarine.com/wp-content ... pdf?x88641

I post this because we have a Centek Vernalift 1500038 muffler on the WillieC. (These instructions look a lot like the Vetus'.) Centek's handy-dandy installation guide shows the canister type lift muffler installed, not the straight through type we have. Kill me now. I am pretty sure our MD17C exhaust manifold and top of exhaust elbow is at least 6" above the waterline. I will double check next trip out.

The installation instructions state that the exhaust hose from the muffler should run downhill from its exit to the transom fitting. Hard to do on the A25 as the muffler is below the water line, but the canister type mufflers exit the top of same and rise to a point where they can flow downhill.

Page 84/85 on the Vetus catalog is also confusing. Their schematics show up to three muffler/lifts/locks. Are those variations on the theme, use the one that applies, or do I need three devices in my system? Confusing, once again, to say the least. And just for giggles, how much back pressure is specified for my 45 YO engine that was installed originally with an oversized radiator exhaust hose and NO concern for flooding the engine?

I understand Kerrye's concern about hard starting, or yahoo operator error who forgets to release the engine stop knob and cranks for fifteen seconds and can't understand why it is taking so long to start...oh, yeah, I forgot. All that raw water pumped cooling seawater stacks up in the system until it starts hydrolocking the rear cylinder. But isn't that an inherent concern on a "properly" installed system? We prevent seawater from forcing its way back into the engine, but turn around and load it up if we have to crank too long. It's always somethin!
Fortunately, this new engine rebuild is an easy starter. Amazing what proper compression will do for these old beasts.

Hetek, get that boat in the water put a ton of hours on it and get back to us!