One more Bodge Job, then its Fishing Time!

With the platforms covering the lower half on the transom, there was now nowhere for the exhaust to exit below the engine's manifold. This is something of an issue, as the cooling water is injected into the exhaust immediately after the manifold to keep it cool, and if the exhaust runs straight uphill then seawater will seep back into the engine when its shut off. This is obviously an issue, so some engineering is required to move the water up and safely out of harm's way.

Fortunately, someone else has already solved this problem, when they invented the waterlift muffler. These use the pulses of exhaust leaving the engine to lift a column of water to heights well in excess of what we need here, and I set to making a temporary one.

As the water level covers the bottom of the exit pipe, a seal is made, and that water sitting in the bottom of the pipe is shot out with the next exhaust pulse. The process reaches equilibrium at high engine load, whereupon the water is shot out in super thin sheets, or even a mist, and thus the back pressure should be minimal.

The problem was what to make it from. I had some PVC pipe of about the right size, and I declared this suitable, but the main container/resonator part was less obvious. We had a look for paint buckets but couldn't find any that were empty, so I popped home and had a look for a strong container with reasonable heat and pressure resistance. All I found was a plastic petrol can, and whilst not quite the volume I was hoping for, I figured it should be strong enough, plus less prone to cracking than other plastics.

My home-made waterlift muffler

Two holes were made with a holesaw, and the pipes fit snugly into them. The surrounding area was degreased, and sanded with 60 grit, and the pipes glued with thick epoxy. I think the petrol can is vinylester, which isn't the best substrate for epoxy from what I understand, so extra care was taken to ensure a good bond.

The next day it was dry, and ready to fit after trimming the exit pipe.  This was then bent slightly with a heat gun (I don't reccommend this, buy the right elbow) as we only had a 45 degree elbow rather than a 90.

It performed entirely satisfactarily in testing; the noise reduction wasn't huge, but it was noticeable and took the sharp edge off the exhaust note. There was no problem with the lifting aspect, and a check after the engine was off confirmed that there was no danger of water ending up back in the engine, YUSS!

Under cruising power the water is largely atomised :{D

I'm unsure what could be done to make it quieter. I suspect incorporating baffles would help, as would a larger volume container. From what I have seen so far, I find no reason why this couln't be made from plywood and fibreglass, though I'd suggest incorporating a thermocouple and a basic heat alarm in case there are water supply issues. I think much of the sound level in this case is mechanical noise from the exposed engine; when this is boxed in I expect a larger reduction.

I plan to give this a good test before a redesign - its more than adequate for the moment. I was quoted around $300 for the correctly sized commercial equivalent, I can make at least twenty more prototypes for that sum and I'm sure I'll have something that's as good, if not better.

Rad work team, I'll see ya next time for more DIY adventures!