Over the years, and with two different small diesels working in the tight quarters of the engine compartment of our 1978 Islander Bahama 30, we have consistently suffered from “overheated alternator syndrome.” Simply put, not enough airflow over the alternator results in ongoing repairs to this vital engine component. As the years have gone by, there seems to be more of an electrical demand on all boats and, without an onboard generator or a solar array, the alternator has to work harder to keep up with that demand. The generic 30-amp alternator on the old Volvo MD7A would soon stink up the compartment (and main cabin) with that hot metal odor. It was a simple system with no gauges, and somewhat limited knowledge on my part. I would have the alternator rebuilt every spring as a preventive measure, the technicians commenting on “overheating” damage.
Even with the best tension that I have been able to achieve with my Yanmar engine/alternator, I experience some degradation of the alternator/water pump belt during engine operation with a resultant belt “dust” contaminating areas of the engine compartment near the belt. I would be concerned about this getting sucked into the engine air intake as the air silencer on this engine seems to have little filter capability.
Hello Marc. Interesting that you mention belt tension and degradation. With 1,300+ hours on my Beta the engine water pump bearings went. The Canadian Beta distributor came to have a look as these pumps rarely fail. I had the pump/alternator belt far too tight! But there was no dust nor any indication of wear on the belt, and hasn’t been since the replacement. The air intake is, as shown in the photo, is above the alternator, not at the aft end of the engine as it would normally be. If dust was flying around in the engine compartment from the belt, it would get into the air filter wherever the air was being sucked in from. Thanks for the comment!
Bert,
I’m not suggesting your innovation lacks merit, just that air filtration would be a good idea. My engine really doesn’t have much air intake filtration (as best as I can tell); other engines may. Regarding the distribution of belt dust in the engine compartment, I never observed it aft near the air intake. The dust has always been visible, when present, around the alternator, water pump, etc. which is at the fore end of the engine installation. Regarding the water pump bearings, it might be better to have the belt a little too loose rather than a little too tight. Getting the optimal tension probably requires a belt deflection tension tool and I don’t have that.
Thanks for the comment Marc. Perhaps I didn’t chose the right words correctly in my article. The snorkel is connected to the air filter intake, not directly to the engine intake. The Beta 20 has a substantial air filter that I check annually and, in our sailing environment, seldom gets contaminated. Yes, it has been changed regularly over the years. Regarding the belt tension, my mechanic gave me a demonstration of the correct deflection of this particular belt on this engine. I’m happy with this. I’ve never had any belt dust visible, even when it was too tight.
Well @marc maybe lower temperature in the forward part of the engine compartment will help with belt life as well.
I wonder if adding that hose to the engine air intake could restrain air breathed by the engine and affect its performance or combustion quality. Using a larger diameter hose would mitigate that.
An alternative solution would be to extend the engine room intake ventilation hose all the way to the alternator area, and insert an electric ventilator un that hose, to force fresh air to the front of the alternator.
I thought about hose diameter as well. But the little Beta is rated at 3,700 rpm at max continuous output, I’m generally running it at 2,500 rpm where the maximum torque curve flattens out. Any faster and I’m just burying the aft end of the boat. If the air filter has that size hole for 3,700 rpm then extending that hole for an additional 24″ really won’t make any difference at 2,500 rpm. Yes, I also thought about putting an additional fan to blow that hot air around. But that’s another power drain and there isn’t a whole lot of room anyway. This was simply an experiment that has worked out really well. Thanks for the comment.
We sail an Outbound 46 & had the same issues with heat limiting Balmar 120a small case alternator output.
Ducted a 4″ flex hose to the front of the engine cover, Yanmar JH4TE, drawing cool air from below the engine and a 3″ duct on the rear wall of the engine compartment connected to a fan to pull cooler air over the alternator, hot air out of the engine compartment and exhaust it out a hurricane vent on the stern bulkhead.
Engine compartment temps dropped 31 C, alternator never gets above 70 C (I derate it to 70 amps for the single belt life) and the boat stays much cooler as much of the previously trapped radiant engine heat goes out the stern when motoring. We are in the South Pacific, this is important.
The 4 & 3″ sizes are probably excessive ,but I would not run an engine on a boat w/o a fan to vacuum heat out of the boat.
I’ve thought of a powered fan as well. But the set-up I have now works quite well. Obviously, I’m not in the tropics and would probably have to re-visit my solution if I was there (wishful thinking as the rain beats against the window, melting the snow!). Thanks for the idea!