Yanmar Exhaust - Bristol 32

[rgleason]

Josh suggested that I measure how much water is left in the muffler after using it and I found that there was about 1 quart. The engine reliably exhausts wet slugs when on lowest rpm idle and works well at high rpm too.
I have definitely noticed an increase in power from last year, and even possibly greater than when the engine was first installed in 2013. Will know more later. Also there is no sign of black exhaust as we had last fall.

[rgleason]

Bristol 32 with Yanmar 3YM30 Engine new 2" Exhaust system to replace the 40 year old 1.5" exhaust and leaking SS wet muffler intended for a Westerbeke W21, also the 2003 Yanmar was smoking at the end of the season and had lost power, due to a clogged exhaust elbow (8 years of use).

The new wet muffler is a fiberglass horizontal cylinder custom made from Centek X22022 Custom Muffler 2x2 Vernalift (Side In Top Out) 6.69" x 14.00" Compact Style, Black, $453.50 8 weeks for custom. Josh Vernon provided a scaled drawing for us. This has a water capacity of 1.3 gallons and the old one held only .3 gals.

We made two different cylinders to test the fit underneath the engine without having to move the engine, the 6.69" diameter x 14" worked, but I did have to cut a portion of the exhaust muffler platform towards the stern to be able to fit it all the way in.

This is the routing of the exhaust that I ended up with, rather than going over the top of the tank, I decided it would be better to go under the fuel tank and have the main upward slope all in one section of pipe so that the hydro exhaust part would work better. You will note that the top of the exhaust pipe occurs at 9'-8" directly underneath the cockpit seat, and then slopes down 2'-7" to the original integral 1.5" stern outlet.

I ordered 2"ID x14' Trident 250 Exhaust Flex Hose (w/wire) for $200 from Defender and used 12'-3" in the actual run. Also purchased (4) Clamp SAE 32 1-1/2"-2-1/2" ( 38-64 mm) $17 from Defender.

In the end we also purchased a new Yanmar Exhaust elbow and fitted it to the manifold, about $250. I did that rather than the better solutions suggested below, because I was short on time and not ready to mess with other custom solutions and wanted to get in the water.

Here is my report to Centek after a sea trial:

The motor sounds smoother and is more powerful, no doubt due to the 2" exhaust and the new clean elbow. There also is no sign of smoking which is particularly nice. I was registering 6.2 knots with my cell phone gps while under power at 2400 rpm but I think there might have been some current helping us.

I can honestly say we gained another 3 hp as in the fall I was able to push engine up to 3200 rpm (and more) with ease while pushing a boat that was heavily fouled at the end of the season. Also throughout the season I noticed that the engine had significantly more power than before with the 1.5" exhaust hose, because our prop pitch had been adjusted for the engine to reach 3000 rpm and now the rpm goes well above that. It was an expensive and time consuming improvement, but long overdue, and well worth it.

I also suggest you review all the posts below for good suggestions by others, and look carefully at the routing pictures in Post #30

The only other things we can do to improve this system are to perhaps install an in line one-way flap from Centek just before the outlet and to insert a foam plug on a lanyard to prevent stern waves from inundating the system. Attached is how the exhaust hose from the elbow makes its way past the transmission. I will need to watch that for chafe.

[rgleason]

I just realized that the dimensions on the drawing were derived from the drawing itself which was done before installation. The actual dimensions measured after installation at the boat are in Post #30

" This new route saves enough hose so that I could cut off 2'-11"' of hose from the 14'-8" length that I purchased=11'-9" this is 8" longer than the original 1.5" hose that went over the top of the tank and more directly to the stern exhaust without rising to the underside of the deck." The slope down is about 2'-6".

Sorry about the confusion.

Also the red plastic cutting board from Ace Hardware is to prevent stuffing box raw water being thrown on the bottom of our fuel tank.

[rgleason]

Here is a revised drawing showing the muffler routing more accurately. I believe I will be fitting a Centek 2" One-way valve #1200328at one of the two locations shown as Option 1 & 2. Josh from Centek advises that

I am glad to hear you have gained some new horsepower and everything is working great.

Our check valves are very simple and do indeed contain a rubber flapper. These units need to be placed horizontal for optimum performance. They are really most effective when stopping surges. I have not heard of any issues of longevity when it comes to the flapper so I don’t believe you will have any. In any case, we back our products with a 5 year “no hassle warranty” and we would gladly replace or refund if you would like.

.. at this price, I would say it is worth it. The added height in your exhaust should be enough to keep water from backflowing under normal operation and the check valve will keep any surges from passing through. Between the both of those attributes, you hopefully will not have to worry about your exhaust again!