Depth of Waterlift Muffler - Any Fudge Room?

[bristol27]

I am working on the exhaust system for my Beta 14 engine. There's a standard requirement for a waterlift muffler to drop 12" (or 9" in Beta Marine's instructions) from the outlet of the exhaust mixer elbow to the top of the water-lift muffler body.

When planning the location of my water-lift muffler, I originally had this slightly incorrect as thought the measurement was to the inlet on the water-lift muffler which is 3" lower than the top of the body. Now, when measuring from the top of the water-lift muffler body to the top outlet of the exhaust mixer elbow, I find that I only have 6" drop between the two. There really aren't any other locations where I could place the muffler that would be any lower than this 6", as I built a diesel tank in the bilge.

I plan to have a valve at the transom that I will always open when the engine needs to run, and close after the engine has stopped. My thinking is that I will make this a habit, so any water flowing back into the engine won't really be an issue and this 12/9" drop requirement is less important. I've attached an image of the area so you can see what I'm working with

My question is - is 6" drop OK or is it wholly unacceptable to breach this 12/9" drop requirement?

[Triton106]

I believe the main reason for the 12" verticle drop from the exhaust elbow to the top of the water muffler lift is to prevent the water trapped in the lift from flowing back into the engine. Therefore, the distance you should be concerned about is the one from the top of the inlet (not the outlet) of the lift to the lowest point of the exhaust elbow bend (not the outlet). If you can get close to 12" that would be ideall, 9" is ok, 6" would be cutting a little too close. If there is any kind of wave action the resulting rocking and rolling of the boat could cause the water to flow back into the exhaust manifold. This situation could be especially problematic if the lift is not directly below the exhaust elbow. If that is the case you should definitely reconsider the lift location or design.

An alternative you could consider is to install a Vetus type lift under the engine as Tim has done many times on Glissando and other projects he worked on. Google Tim's website and you should be able to locate several examples. Hope this is helpful.

[Carl-A259]

Could you install a couple of elbows in the exhaust before the muffler to raise the exhaust to just below any overhead obstruction and then it drop to the muffler?

[Quetzalsailor]

Read your instructions again (and again). The fellow who installed our Yanmar and a waterlift without sufficient height difference between the manifold and the muffler used a length of pipe, a nipple, to raise the injection elbow to the required height. Worked just fine for the years before we owned the boat but the nipple fatigue-failed in our first year. Sprayed water and exhaust all over the engine compartment.

Hmmm. I picked the broken bit out of the engine fitting and stuffed the broken nipple back into the fitting. It's been 6 seasons. I think a little preventive maintenance is in order/overdue and maybe a bit of engineering to add a brace.

I think Yanmar's instructions cover this detail.

[bristol27]

The solution I've come to (both from your and Beta's input) is to add a SS pipe extension to the already "high rise" exhaust. This will raise the exhaust mixing elbow to the required 9" above the muffler. I would have preferred to place the muffler in a lower location, but the limitations in the engine room and below cockpit area prohibited this.

Thanks for everyone's input, I appreciate it.

Edit: For future reference, here's a link to the project section on my site that goes into more detail about the exhaust set-up process - http://www.bristol27.com/projects/exhaust