Irish Mist":2rcjn3hb said:
My understanding is just gas boats have blowers to clear the engine room of fumes. They are not required on a Diesel engine. All my gas boats with twin engines I only ran the blower before starting then turned it off.. I don’t know much about anything but I have never had a heat issue from lack of a blower and been boating 40 + years . In fact this form is the only time in my life I have ever heard of a boat having a venting issue.
Inadequate engine compartment ventilation as been a problem for many boat builders for years. Blowers are not required in diesel powered boats as they are in gas powered boats.Gas powered boats have bilge blowers that draw from lower portions of the bilge, where smelly and, sometimes, explosive fumes reside. Diesels have ventilation fans that pull warm air from the upper sections of the compartment to lower the compartment temperatures.
I monitor my engine compartment temperatures and I have not had what an average boater would call an issue. "Its warm in the compartment but everything works " I have experienced elevated temperatures in the engine compartment beyond what I would want a piece of equipment operating in. Lifting a hatch and inspecting the engine and monitoring the compartment temperature is not a method that assures me or a engine manufacturer that the compartment is running within specs. When you open the hatch you remove the warmest air from the compartment. Remember bilge blowers suck cooler air where the vapors are present, exhaust ventilation blowers pull air from the top of the compartment where the warm air is present.
( A learning experience for me) example : Late 80's early 90's I worked for a Regal dealer in Massachusetts. I had several customers that owned 19' and 21' with hard start issues. The owners would cruise and notice slight misfires and then when they shut off the engine it would not restart. When I would test run the boats and began to notice the misfire I would open the engine hatch and check for cylinder misfire shorting cylinders, check for ignition timing changes suspecting ignition amplifier malfunction and other checks but found nothing. I would shut the engine off and experienced a normal restart. Most of my troubleshooting was done with the engine "cover or hatch open" I noticed a warm compartment from the 142F to 165F engine heat syncing the compartment but no where above 120 F. What I finally determined the issue was fuel percolating in the carburetor and Vapor locking. The compartment temperatures where exceeding 140 F and the compartment ventilation was not sized properly. When I was troubleshooting the issues I kept opening the engine hatch to do engine inspections this lowered the compartment temperature and eliminated the Fault. Solution was to add additional ventilation to the models affected. This became a marine industry issue. Many boat manufactures started increasing the size of ventilation ports and the engine manufactures started installing fuel cooling exchangers to keep the fuel from boiling.
Diesels also have issues with running performance if the fuel or air temperature rise to levels above specification or there is an inadequate supply of air or fuel. Volvo rates the engine HP at 76F and claim derate above 113 F. At 113 F the effected power loss is minimal. This is why they recommend temperatures not exceeding 30 F above ambient this keeps the temperature in proper range maintaining rated HP. With proper air circulation and ventilation a boat running in 85F ambient should operate in a compartment temperature of no more than 115 F. If your 31' Ranger is operating there or +/- 10F you are in good shape and have no need to "worry about it". In my case which is not what the thread is about ( C26 ) I stated my issues with lack of ventilation. I see after 1 hour of operation 60 F above ambient not just one time but I monitor all the time. If the ambient air temperature is 60F I see 120F to 125F, If the ambient air temperature is 80F I see temperatures 140F to 145F. If I increase engine rpm to high cruise ( engine operating temperature usually increases to 185F from 178F) I will see additional air temperature increases of 5F (65F above ambient in the compartment). I have seen as high as 162F air temperature before I installed additional ventilation. I compared my results to the results from the Fluid Motion factory Sea trial of the 2014 C26 with a 200 HP D3 Volvo. The day of the sea trail Ambient air temperature was 55F and sea temperature was 51 F. The recorded engine compartment temperature at the intake was 116F, the recorded compartment temperature at the high point Fwd 116 F, the recorded high point aft 116 F. These numbers are consistent with my numbers of 60 F above ambient 30 F more than the recommendations.
Most diesel powered boats there is no reason to monitor the compartment temperature because they have passive designed system that uses intake and exhaust vents sized according to engine size and compartment area. Many of the upper end diesel powered boats not only have passive systems but also have auto systems that turn fans on when temperatures exceed max temperature requirements exhausting the compartment air so it lowers and maintains the requirements of Volvo, Yanmar, Cumins, Caterpillar .... and also follow the guidelines set by the ABYC. Next time you go out on the water try to find another inboard power boat that does not have exterior engine compartment ventilation. Inside the cockpit ventilation designed by Fluid Motion technically makes the cockpit the engine compartment. Enclosure use with this design is not recommended by ABYC. ( Blow boats don't count most starve for air when they are running) (Cutwaters don't count, the large vents on port and starboard are Fake.)
Boatagain":2rcjn3hb said:
I watched the engine temperature carefully, it never budged out of its typical range. Both engine and generator (and A/C) ran without a hitch. I don’t think it was just luck, I’ve done similar trips before.
I don't doubt that the engine ,generator and air unit ran without a hitch and that is why John Livingston responded as he did. My question is what was the estimated engine compartment temperature that your equipment was running in with Ambient air temperature of 95F being pulled into a compartment through gaps in the cockpit with an engine running at and radiating 180F + with a turbo radiating 800F + and a generator producing 140F+ and the only way the warm air is removed is through the air intake of the engine. May or may not meet recommended specs by Yanmar or Volvo, or what is recommended by the generator manufacture and probably doesn't follow the ABYC recommendation. It did do want you required it to do, get you across the bay. For most average boaters that is all that should be required. If it works don't fix it. This is also the attitude most manufactures have too. Its a boat ! As long as it runs, pumps and shifts and people have fun who cares what the longevity of the equipment is! It's hard to pinpoint all the different equipment failures that owners have to operating the equipment in high temperatures. But, if the compartment temperatures are known and maintained and the equipment is operated at or below recommended requirements that element can be eliminated as cause of failure.
The original poster of this thread stated the previous owner ran with the the hatch propped open a bit to keep the compartment cooler CB 31. He asked" Do most folks with similar engines not worry or should I add a blower to help keep temps down? " I guess the answer is most folks don't worry. I should have left the comments to the CB31 owners that can honestly state what the compartment temperatures are. I based my comments on a different model with the same design ventilation. My opinion is not apples to apples to the model in question. If it is warmer than recommended specs my opinion is install an exhaust fan. If you don't know find out, don't install a fan or additional ventilation if it is not needed.
ALICE J":2rcjn3hb said:
Curious to know what effect the high temps have on the alternator. While the alternator normally gets hot from charging, how does the added engine heat affect the output? Does it further reduce the alternator output and/or reduce the diode lifespan? There was one Tugger who placed a blower next to the alternator in an effort to extend the output in amps. Not sure if it worked? As an aside the Mase generator (not made anymore) used water to cool the air around the air cooled diesel and the alternator eliminating a generator blower.
Heat effects reliability. Most electronic devises installed in marine engine compartments are rated not to exceed 160F. Relays, ECM, pump motors, marginally sized electrical wiring, fuse capacities.... Heat increases resistance so there would be a loss of power or efficiency from the alternator if it is trying to generate capacity and operating in a warm compartment. Extracting heat via a blower may help with the efficiency of the alternator and increase the alternators longevity. Many larger output alternators have a external regulator that helps maintain the internal temperature of the alternator. It turns the alternator off when it reaches a peak temperature usually around 220F to 240F. There is no question reducing the air temperature in areas where mechanical or electrical equipment are operating is always good advise.
Once again I have made a simple answer to a simple question a long answer to a simple question. "Make a short story Long" I consider myself the average boater. I have a working career history in Mechanical Reliability Quality Control and Marine repair. I tend to carry these experiences and theories into my average boater advise. If it just works make it better!!
