home boat selection disign fundation fuel cooling exhaust electrical engine propeller

In the picture above, the engine is directly cooled by outside water sucked-in by the waterpump. The water is cooling the cylinder and cylinder head where the heat is concentrated. When the engine is not on operating temperature, a thermostat within the cirquit is closed and the water is going out to the exhaust immediately.

Because the engine is located under the waterline, there is a risk that the cooling circuit will float the cilinder via the exhaustport (A). Therefore a airvent (B) is located behind the cooling outlet, far above the waterline.

inlet valve

Water strainer

On the left site you see the point where the cooling inlet is poking through the hull. I fixed it with glassfiber and epoxy. The inletscoop on the outside always must point backwards, otherwise, when sailing with an idle engine, a positive waterflow into the port will cause water pressure and possible floatation of water into the engine cylinder. For safety precautions, the inletport must be fitted with a valve (left). From the inlet the water is going to a filterunit (right).
The cooling water strainer (right) has a transparent cover, allowing easy inspection of the filter without dismantling. The cleaning of the filter will take only 30 seconds. Due to the large active surface, the filter seldom needs to be cleaned. According to the manufacturer, the filter always has to be placed above the waterline. When the cover is not tightly closed, air will be sucked in by the cooling pump. This can cause overheating of the engine. Therefore, the engine manufacturer advises to install the filter under the waterline ! And that's what i did. Annual inspection of the filter and the hoses is needed anyway.

transparent cover on waterstrainer

cooling pump

Like a human hart, when the waterpump stops there is no cirquilation. Therefore it must be kept in perfect condition. Driven by the engine, a rubber impeller behind the round coverplate is pumping water into the engine's cylinderhousing. During wintertime the impeller must be removed for inspection and stored seperately. If the impeller has no visible wear and tear it can be re-used at the start of the new season. Good practice is to use some grease before putting it in again. Never forget to open the inlet valve before starting the engine, otherwise the impeller will burn away in a few seconds.



On the left you see an inside scetch of the thermostat pictured on the right. The cooling water flows into the engine and is heated. The engine feeds hot water from below. When heated, the spring valve releases and the hot water can leave the engine. The thermostat is opening at a fixed temperature (operating temperature). Excess cooling water provided by the waterpump flows from left->right over the top. On the right side the water is leaving to the exhaust system . With an open cooling system as pictured above, the thermostat housing can be clogged by mud. It is recommended to connect the sensor on the thermostat housing to a manufacturer approved temperature indicator on the operator panel
airvent Eventually, the coolingwater leaves via the airvent. When there is no flow, the water level drops because on the top is an opening where air can come-in.

Water can also leave on top of the airvent when the engine is running. This water needs to be disposed of via a small opening through the outside hull.

PS: recently the ventilation hose brake loose. Within no-time i had thirteen buckets of cooling water in my boat.
I recommend to replace all original plastic hose clamps (see photo) with industrial steel hoseclamps like those on the lower hoses (left)

home boat selection design fundation fuel cooling exhaust electrical engine propeller

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