Exhaust System and Ventilation

As noted earlier, the exhaust system for the Yanmar engine is 3 inches in diameter and the exhaust comes off the back of the engine. This means that the entire exhaust system must be replaced. The engine has the exhaust manifold on the starboard side of the engine. Pearson put the water-lift muffler on the port side of the engine compartment. It is unwise to put the water-lift off axis with respect to the manifold because when the boat heals, the manifold may be below the water-lift, allowing water to drain from the water-lift into the valve train. In order to avoid this problem, I glassed in a new platform just behind the manifold for the new water-lift. The accessory platform adds a considerable length to the engine. In order to allow sufficient space for the water-lift, I had to mount the accessories to the port side of the platform. This allowed just enough room to fit the water lift in the starboard corner of the engine compartment. The exhaust hose must make a sharp bend under the injection elbow where it is redirected aft. Normal hose would be very difficult to bend, so I ordered the more flexible series 252 hose. This hose is a slightly more expensive than the stiff hose that is normally used, but will make installation much easier. Items purchased for the exhaust system 1. 3" Series 252 hose - $12.39/ft (15 ft) = $185. 2. Muffler # 1500034 - $170.40 3. 3" White Exh. Fitting # 1200298 - $52.40 The engine comes standard with a typical water injection elbow. I ordered my engine with an optional high-rise injection elbow. This will provide a little better protection for the exhaust manifold from water intrusion. It has a sharper bend than the stock elbow, reducing the turn that the hose must make. It is made from a non-magnetic material, probably bronze. This should last much longer than the typical cast-iron elbow supplied by most manufacturers. The list price for this part is about $900. I'm not sure how much this increased the price of my engine. It is undoubtedly one reason the Yanmar engine is so much more expensive than the competition. I found that the generic hose clamps shown in the photos don't work with these hoses. They aren't strong enough to clamp down hard enough to seal the hose on the hose fittings. I had to refit the hoses with T-Bolt clamps, available only from a propeller specialty shop.

The photo to the left shows a method I used to bend the exhaust hose. I first lifted the aft end of the engine a couple of inches with a cable winch. Then I slipped a piece of scrap wood with a round hole cut in it over the hose. I used the wood piece as a lever to bend the hose into position. After the hose clamps were attached, I used a hand-saw to cut the wood lever free. I was initially concerned about having the exhaust come off the transmission end of the engine, but this turned out to be easier to install than I expected.

The photo to the right shows the exhaust hose in position. There is ample room to route the hoses.

Good ventilation is necessary if the engine is to run well. Turbo engines in particular require air-flow to work well. This is often overlooked requirement. I was never happy with the vents installed by Pearson just behind the cockpit. I always had a problem with water intrusion and the hoses were just screwed into the sides of a rough hole cut in the combing. I replaced the deck plates and added optional hose adapter rings to the new plates. The hose adapters require a larger hole. I re-cut the holes using a 4 ¾" hole saw and ran new hoses into the engine room. I have yet to find dorades with built-in water traps that are small enough for this installation, so water intrusion is still a problem.