Raising the exhaust ports?

Good morning!

We are out on the hard here in Ketchikan, Alaska getting ready to begin some much needed maintenance and winter work on our new (to us) Albin Trawler 36. I'm trying to up the sea-worthiness game and am curious what the "great-and-all-knowing" forum thinks about raising the exhaust ports on the aft of our vessel.

It's about midline to the water now and served us fine during our delivery trip in August where we brought her up from Seattle (and her entire previous 38 years, no doubt) but we found salt water under the floor boards in the aft cabin (which we are investigating) and its causing us to rethink anything back there thats under the water line.

We are raising thru-hulls in other areas that sit midline with the water as well but wasn't quite sure what the deal was with something like exhaust. Any tips, suggestions, opinions or ideas welcome!

Much appreciated!

I just finished a major refit on a 1969 wooden boat and I'm here to tell you finding salt water in the bilge can create paranoia in me. My short story. Lots of money and time into a refit. The first 20 minutes out for sea trials, the boat hit a log (seeing as you are in Alaska you know all about this). I have a stern drive brand new merc engine and drive. The Bravo 2 was punched out of the water and up. You can imagine the dollar signs going off in my head when this occurred. Good news, after 5 more times on the water, an inspection of the stern drive and hull and through hulls immediately after the hit, nothing was found.

During refit, the exhaust system I bought (through the prop) couldn't be done so two exhaust large vents with flaps was install instead. I was informed this is what many of the fishing boats out here use. Your system on your boat may be used on commercial fishing boats, maybe go down the marinas in your area and talk to some of those guys about their exhaust set up.

I was warned that when slowing down to do it gradually to reduce slop into the exhaust vent, despite the flaps. My set up has produced a carbon monoxide problem in the boat (station wagon effect). So at my first servicing in the third week of November probably a ninety degree bent elbow is going to be installed at each vent, to take the venting into the water and reduce engine noise which is bad, I'm the loudest engine in the marina - embarrassing and irritating.

So I was having all manners of water in the bilge, not a great amount, the worst was about 8 buckets. The first batch of water was fresh water and of course I thought of everything I could, leak from the new fresh water tanks, etc. Eventually I narrowed it down to water coming in through my cockpit area, it isn't totally sealed up like you can find on glass boats. Fortunately I have a bimini that covers the cockpit with soft side walls that roll down. Once these were deployed, no more fresh water.

Then the genuine paranoia began. I went out on a bit of a brutal day to learn my boats characteristic's on a blowy day. When I came back in, about 8 buckets of salt water. I was afraid I did have unseen damage from the log strike. My new paranoia focus was on the new thru hull. After this incident (and all the salt water drained out), I went out on some glass smooth water days and running the engine at various RPM's (break in procedure) but not to WOT. When I inspected the boat looking for the source of the salt water incursion, the bilge was bone dry. Eventually I passed the 10 hour mark of engine break in and for the next 10 hours I could go WOT for brief periods of time.

When I went WOT (30 mph), I was taking some water over the bow even though the water was relatively calm. I also discovered a small amount of water under my V birth cushion at the tips. I began to suspect my anchor locker which did originally drain into the bilge and in theory had been sealed up and a drain through the hull added. When I talked to my refit guy, he said they had trouble sealing up the anchor locker as I have a number of wooden ribs and working around them and sealing in those areas was problematic.

So I have learned that most of the time, my paranoia is wrong. When I kept pushing to find the salt water incursion, it was much like a crime scene detective work. I would think such and such, then rule it out, etc., etc., etc.

Try to hit up every Albin forum, talk to the commercial fisherman in your area, and if there is a guy who has worked long term in the marine environment in your area, talk to him as well. I guess what I am saying is you might be right about the source of your salt water, but odds are good it might be coming in somewhere else.

PS: my boat is 1969.

Thats quite the story - it was pretty concerning when we noticed it but in monitoring the boat over a couple of weeks there seemed to be no change. There is weeping from the area of some of the outboard stringers that needs to be addressed but I am considering the shaft struts as well. Doubt those have ever been resealed. Of course the main issue is there is ZERO access to the struts in the aft section of the boat so we'd have to remove the floor or at the very least add access hatches. It seems foolish to not have access to an entire section of your vessel so we need to do something about it.

Long story longer: If we can raise the exhaust a couple of inches to get it out of the water it can be one step towards Peace of mind in these fridged Alaskan waters.

When raising the venting, you will be upping the noise problem very probably. My cockpit deck had to be re-done a bit. With the original old engine, one access hatch was okay. With the new engine, three more access hatches were added to improve engine accessibility.

And many of the older boats were built like tanks, mine definitely so. Each access hatch I open is an encouragement to work out the arm muscles... lol.

If your Albin has a waterlift muffler, you should be able to raise your exhaust. But you still need to follow ALL the rules especially if you are anchoring in a seaway. A perfectly good marina to marina exhaust system can fill your engine in no time when anchoring out.
Whether your outlet is above or 1/2 below the WL, it can dip in and roll the water down the exhaust, fill your waterlift, and then fill your engine hobby-horsing while anchored. The answer is usually a waterlift muffler AND a gooseneck at the transom. Sometimes an inline checkvalve is used as a short term fix. Also flaps where the pipe exits don't work too well as they are pushed open when the transom dips unless that are covered with a transom mounted elbow of muffler.

I need to investigate more but so far as I’m aware the exhaust leaves each engine (FL120’s), hits an elbow that moves the respective hoses outboard to each side of the vessel, then it hits the waterlift mufflers and its a straight shot out to the transom.

albinalaska said:

I need to investigate more but so far as I’m aware the exhaust leaves each engine (FL120’s), hits an elbow that moves the respective hoses outboard to each side of the vessel, then it hits the waterlift mufflers and its a straight shot out to the transom.

Click to expand...

So, if they are indeed waterlift mufflers and the rules have been followed, and they are large enough, you could easily add goosenecks at the transom 12"-18" high that would preclude seawater ever running back towards the engine while anchored. I have even heard of water finding its way to the engine while docked stern to a busy waterway.


Cummins, John Deere, and the waterlift manufacturers all have good information on a proper wet exhaust system. Goosenecks can be bought from Vetus (plastic though) or easily made up from fiberglass "U" fittings, elbows, a few feet of hose, & clamps.

My main engine exhaust goes out stbd midship underwater via water lift muffler except for a little bit out at the stern stbd side, to verify cooling water flow.
Generator, out the port side midship under water via water lift muffler.
Both the main and generator exhaust are about 2 inches below the waterline.
Small main exhaust stbd side after, above waterline.
Good ER sound insulation but can still hear the main engine, underway.
Over all, a very quiet boat.

On our boat with 120 Lehmans the exhausts are 3/4 covered when the boat is loaded. In addition, OZ tends to squat as more power is applied leaving the exhaust opening totally submerged when at cruising speed and loaded. Has not been a problem for 5000hrs in all types of sea conditions. There is a fair amount of rise above sea level in the exhaust in the engine room before it exits through the lazarette and transom. I use to worry about it. Since then I have embraced the Alfred E. Nueman school of philosophy.

Tator

I am a little puzzled as to what problem you hope to solve by raising your exhaust ports and other thruhull levels. Lots of boats consciously put their exhaust ports under water with no problem.

The problem can be the plumbing from the engine to the exhaust port. If it is too low (ie not enough riser height or height in the loop after the water lift muffler) then water can back up into your engine.

Look at the two attached drawings of an acceptable exhaust system and the pic of a riser that doesn't drain, ie is doomed to fail. All courtesy of Tony Athens.

The first drawing shows the 12" riser height criteria, with no lift muffler. The second drawing shows an ideal lift muffler layout which due to the geometry will never let water fill up the lift muffler and back up into the engine.

The pic shows a riser that doesn't have enough downward slope to let the water drain out after shutdown. It sits in the riser and will ultimately corrode it out.

Admittedly lots and lots of boats don't meet these criteria and never get water inside the engine. But some do.

There are other things you can do to mitigate an exhaust system that doesn't meet these criteria. Sailboatps have a very high exhaust loop after exiting the lift muffler that gives enough protection. An exhaust flapper valve can help. Also a surge tube that can accommodate a wave will keep water from backing up too high.

David

I'd like my exhausts to be a little higher so they stay out of the water with full tanks and a few people on board. But from a water backflow perspective, they're fine. Being partly submerged isn't an issue if the system is well designed. I mostly worry about severe flooding in the event of a failure with the outlets partly submerged.

As an example, my system comes out of the mufflers, drops straight down about 18 inches, then runs about 12 feet to the transom with a slight down slope. It would take a lot to force water into the mufflers with that setup. Even a pretty good wave hit against the transom won't push water up the pipes with enough force to make a 90 degree bend and climb 18 inches after having traveled up 12 feet of pipe.

If you really want to learn about exhaust systems then go to TOny Athens' site,

www.sbmar.com

and look at all the articles he has provided for us to peruse free. Lots of explanation also.