There is not an issue with the engine getting enough air for combustion. There are all kinds of air gaps to suck air from. Ranger and Cutwaters Diesel powered do not have sealed bulkheads between the engine compartment and the rest of the boat. All the bulk heads are floating adding no structural strength to the hull. The air can be pulled into the engine compartment from the cockpit sole liner gaps, the cabin, or any of the many holes that are cut or gaps between the floating bulkheads. Getting air into the compartment is not an issue. The issue is air flow!! The only way the air in the compartment can get out is through the engines induction. Think of the engine as a variable speed engine compartment exhaust blower. When you are running lower rpm it is 150 CFM blower when cruising in the 3000 rpm range it is a 300 CFM exhaust blowers. At wide open throttle the D3 220 requires around 420 CFM of air flow to operate WOT. There are enough gaps to get the air in but there is no way to get the air that gets in (Hot air) out except though the engine. "IT COULD BE BETTER" is an understatement. There isn't any passive or power ventilation installed in any of the Fluid Motion Diesel powered boats to remove the warm air from the compartment. ( I would hope there is in the R43 with twin IPS drives and D6 engines) Most production boats of that size have auto blowers that power when the engine starts.
When I discovered this I called Fluid Motion and asked if they forgot to install the vent system in my C26. There are two large exterior deck vents located on the port and starboard side of the boat. The answer was, the vents are" fake, just for looks". The compartment would get "hot" after cruising for a few hours. The warmest area of the compartment was near the air intake of the engine.Why? Because this is where all the warm air was being pulled to. The engine is the exhaust blower sucking all the warm air to this area of the compartment. Diesels like warm air to operate efficiently. 70F to 80F is perfect. As the temperature of the air increases above 80F the engines efficiency starts to decline. Volvo recommends the temperature not to exceed 113F for combustion air. Further more they do not want overall temperatures in the compartment to exceed 120F when the machinery is operating.
The temperatures in my C26 before I installed a ventilation system would exceed 160F. This temperature measurement was taken 4 " away from the air filter. The air temperature measured in the aft section of the compartment would maintain 140 F . The engine was pulling air from the aft section of the cockpit. This air flow would enter through the gaps of the cockpit at ambient outside air be pulled in and by the time it would flow to the engine intake the temperature would increase 70F. Remember the only way the air comes in is the engine sucking it into the compartment the only way out is through the engine. When the engine is running there is a negative pressure in the compartment. The air flow is adjusted by the speed of the engine not a constant flow that would be provided by a properly installed passive system or a mechanical system that is normally found in diesel powered boats.
I installed suction passive vents the hose from the passive suction vents were installed 1' from the engine air intake. I installed 2 mechanical suction vents on the opposite side of the compartment one vent hose directly over the alternator to help keep it cool the other pulling air from open area in the compartment. The air temperature at the engine air filter dropped 40F and maintained between 115 F to 130F depending on what ambient temperatures were 75F to 90 F any time the air temperature was lower that 75F The temperature would be below 110F.
The Ranger and Cutwater boats were designed for the PNW. The issues I experienced would not be experienced there. I obtained a Sea Trial report done by Fluid Motion and Volvo. A C26 with a 200 HP D3 and the measured intake air temperature was 116F during the sea trial. The weather conditions 50 F ambient water temperature and 55 F air temperature ( Volvo recommends below 113 F) I boat in the Midwest and south. I have been cruising when air temperatures are 90F and the water temperature is 85 F. I would have to open the engine hatch to cool the compartment down.
The ventilation was needed and is needed in any diesel powered boat. As you said
tranmkp":1ryl0gzc said:
My OLD Albin had big Buick Roadmaster side louvers port and starboard. I dont see ANY sort of intake,
. I have never seen a Power boat that did not have a ventilation system installed. Passive or power that allows for proper air flow in the compartment.
The Rangers and Cutwaters are the first for me. The as found system installed in Rangers and Cutwaters works, as many owners and Fluid Motion have said. It could be better!!!
