Mixing synthetic and mineral oil

[jfm]

Dont they already have water cooled air coolers fitted , couldnt one be added or beefed up , you would expect the manufacturers would help out knowing they would be creating a more useful product to attract wider market ?

Nope, and as far as i know in the <30kva small boat sector no-one offers this. On the big ship stuff with turbo genset engines you'd have seawater cooled intercoolers of course, but that is a different class of kit

I think in the small boat segment genset makers want to build small and light, and therefore seawater coolers might make their gear less competitive. The choice anyway is Onan-Cummins, Kohler, Northern Lights and Westerbeke. Anything else aint good enough and none of those 4 offers a ready made solution to this problem afaik. Also, my thinking was (though I'm happy to hear contrary views) just ducting in air from outside, so not needing seacocks and seawater pumps, is probably just as good and simpler. The outside air is already 30-35degress; if you take engine room air at 80degrees and cool it with 26degree seawater you're unlikely to get a better result?

 

[Nick_H]

Duh, I've just remembered that the current gauge on the dash measures either domestic current or air-con current depending on which way the switch is set, so when I said that the genny stalled at below 40 amps, I was just reading the domestic load without adding the air-con current, which i'm sure would have put it over it's normal rating. Think i'd better lay off the G&T's for a day.

 

[ARE]

Anthony, thanks for that data. Please can you explain a bit more what you mean by "de-rate" and "max 50deg C"? Do you mean that naturally the engine produces less power 1% for every 5.5deg? In otherwords, the engines sensors know the quantity of air going in at WOT and the ECU naturally supplies less fuel becuase of the less dense air? Or are you saying the software measures the temperature and actually de-rates the engine via the ECU? (which is somewhat the same thing i suppose...)

I'm currently speccing a new boat and need to overcome this problem. On my last boat I had 2x 22.5kw Onan gensets (built 2010), with the 3.3 litre engine. Should be good for 85+ amps each and they were if in a cold engine room or with the engine fans running. But if I ran the boat then anchored, the e/r temp rose to 80deg (due to 6 tonnes of caterpillar cast iron at that temp) and the gensets engines would stall, not trip, at 60 amps, which is more like 20% derated compared with your stated 5%. For the hour before a meal when there is full on cooking in the galley, plus normal overhead of zero speed stabs and airco plus the 24v charger load, I needed around 75 amps to run the boat at anchor, so this was quite a nuisance (becuase i prefer not to run 2 gensets if possible).

Same effect occured on both gensets, so not a fault with one of them i think. I therefore put this down to hot intake air

Next boat, just going into build now, will have 2x 27kw (which is the same 3.3litre engine and just a bigger alternator). I plan to have ducted air, with switchable continuously rated fan, drawing outside air at say 27degrees (Mediterranean) and blasting it onto the face of the genset where the air intake is. Hence the genset will mostly breath air at 30deg. Does this make sense to Latestarter/you/other engine nuts on this forum please?

Thanks

The derate is based on two things, engine natural derate for air density and alternator derate for heat rise. together these give us the 1% for every 5.5C.

We state in our installation manual that the maximum air inlet temp should be 50C, above this the derate will be huge (Suspect this was the problem on your old boat)

The engine control is very basic, so it does not measure air intake temp or even have a ECU, It is a IDI mechanical injected engine and can make no allowances for high inlet temp.

The alternator control measures output voltage, frequency and field current. so as the alternator increases in temperture, so does it resistance. Hence you need more field current to make the same output. again this is up to a maximum inlet temp of 50C. We electronically limit field current in our control.

It would have been intresting to see what fault code your old generators stopped on, I guess it would be field overload or governor overload or maybe under frequency.

On your new boat I would recommend extra cooling fans as you say faced towards the generator inlet, Some boat builders have these on thermostat control, If I remember Fairline engine room fans only come on when the main engines are running?

Anthony

 

[jfm]

The derate is based on two things, engine natural derate for air density and alternator derate for heat rise. together these give us the 1% for every 5.5C.

We state in our installation manual that the maximum air inlet temp should be 50C, above this the derate will be huge (Suspect this was the problem on your old boat)

The engine control is very basic, so it does not measure air intake temp or even have a ECU, It is a IDI mechanical injected engine and can make no allowances for high inlet temp.

The alternator control measures output voltage, frequency and field current. so as the alternator increases in temperture, so does it resistance. Hence you need more field current to make the same output. again this is up to a maximum inlet temp of 50C. We electronically limit field current in our control.

It would have been intresting to see what fault code your old generators stopped on, I guess it would be field overload or governor overload or maybe under frequency.

On your new boat I would recommend extra cooling fans as you say faced towards the generator inlet, Some boat builders have these on thermostat control, If I remember Fairline engine room fans only come on when the main engines are running?

Anthony

Anthony
Thanks. Really appreciating your help here. Yes, Fairline e/r fans come on with main engines, though you can override that and switch them on at the dash when the engines are off. But with any boat in the 24m size bracket they are noisy and you cannot leave them running in an anchorage; they have to be turned off. Some people say run them for 5mins after turning the main engines off, which is fine but it doesn't solve the problem that there is 6 tonnes of caterpillar cast iron mostly at the 80deg jacket temp, some a bit cooler, and some like the turbos and exhausts a bit hotter. 6 tonnes at 80deg takes hours to cool down to below say 50degress

So I plan on next boat to use jabsco 24v continuously rated fan and 100mm ducting to suck in external air from the boat's side vents, with the ducting led to an outlet 100mm "nozzle" blowing straight at the air intake at the left hand side of the genset. From what you say this makes sense. BTW, i don't think cooling fans alone will work becuase they are just moving air around that is at 80deg; I think you need to duct air in from the outside so you are using 30deg air to cool the alternator and provide combustion air to the engine

Now your comments on field current being limited are enlightening. I hadn't realised this. Your limiting the field current in an over-hot genset will have contributed to my problem, so my choice to buy the 27kw model not 22.5 next time seems good, even though I only need 22.5kw of output. That said, I think my real problem was the diesel engine just not developing the power to spin the alternator once the air got to 70-80deg and demand got to 65amps, becuase oftentimes the genset stalled or dropped below 1500rpm (while i raced to switch something off like the airco!) without any fault code afaik

The upgrade from 2x22.5 sets to 2x27kw sets was surprisingly cheap btw, though they are based on the same unit

Thanks for the info

 

[ARE]

Anthony
Thanks. Really appreciating your help here. Yes, Fairline e/r fans come on with main engines, though you can override that and switch them on at the dash when the engines are off. But with any boat in the 24m size bracket they are noisy and you cannot leave them running in an anchorage; they have to be turned off. Some people say run them for 5mins after turning the main engines off, which is fine but it doesn't solve the problem that there is 6 tonnes of caterpillar cast iron mostly at the 80deg jacket temp, some a bit cooler, and some like the turbos and exhausts a bit hotter. 6 tonnes at 80deg takes hours to cool down to below say 50degress

If I remember correctly also the turbo's are very close to the generator air intakes?

So I plan on next boat to use jabsco 24v continuously rated fan and 100mm ducting to suck in external air from the boat's side vents, with the ducting led to an outlet 100mm "nozzle" blowing straight at the air intake at the left hand side of the genset. From what you say this makes sense. BTW, i don't think cooling fans alone will work becuase they are just moving air around that is at 80deg; I think you need to duct air in from the outside so you are using 30deg air to cool the alternator and provide combustion air to the engine

I think the engine room fans are set to extract air only and there is only passive inlet vents, Am I correct? If this is the case I would agree that fitting continuously rated fans directly at the generator air inlet is the best option.

Now your comments on field current being limited are enlightening. I hadn't realised this. Your limiting the field current in an over-hot genset will have contributed to my problem, so my choice to buy the 27kw model not 22.5 next time seems good, even though I only need 22.5kw of output. That said, I think my real problem was the diesel engine just not developing the power to spin the alternator once the air got to 70-80deg and demand got to 65amps, becuase oftentimes the genset stalled or dropped below 1500rpm (while i raced to switch something off like the airco!) without any fault code afaik

The upgrade from 2x22.5 sets to 2x27kw sets was surprisingly cheap btw, though they are based on the same unit

Thanks for the info

Ok, The 22.5 and the 27kW generator use the same engine (just more copper in the alterantor), so if you feed the 27kW with 80deg air you are still going to be limited to your 65amps ish. I checked with Kubota and extrapolating the derate curve I would guess that the engine derate for 80deg inlet temp would be around 50% (Kubota only show derate up to 50C on the derate curve). I guess this is what you were seeing on your old boat.

The fan's would need to move around 2.2m3/per min per generator

I hope this helps

Anthony

 

[jfm]

If I remember correctly also the turbo's are very close to the generator air intakes?

I think the engine room fans are set to extract air only and there is only passive inlet vents, Am I correct? If this is the case I would agree that fitting continuously rated fans directly at the generator air inlet is the best option.

Ok, The 22.5 and the 27kW generator use the same engine (just more copper in the alterantor), so if you feed the 27kW with 80deg air you are still going to be limited to your 65amps ish. I checked with Kubota and extrapolating the derate curve I would guess that the engine derate for 80deg inlet temp would be around 50% (Kubota only show derate up to 50C on the derate curve). I guess this is what you were seeing on your old boat.

The fan's would need to move around 2.2m3/per min per generator

I hope this helps

Anthony

Thans Anthony, really useful. In reply:

1. Yup, turbos close to intakes, esp on one side of engine room (cos Onan intakes are not handed, as you know)
2. No, Fairline fans include both blowers into engine room and suckers out. But that doesn't change what i should do - I need a fan blowing straight at the genset intake, literally with the 100mm blower nozzle 50mm placed from the face of the genset squirting directly at it
3. Yup, i fugured that even with 27kw gensets but using the same engine, I'll have the same problem becuase the diesel engine aint making anything like its 36hp and it doesn't matter how big an alternator you bolt to it. On your figures (thanks very much for that Kubota data and extrapolation) it is making 18hp, which is 14kw which is 60amps(before losses), QED!! So mainly I need to get the cold air supply to increase that 18hp back up to 30hp or so. But i think I'll go for the 27's anyway, for good measure, and to help in case I hit a limit with field current
4. Thanks for the 2.2 m3/min data. The 100mm jabsco continuously rated blower fan promises 7 m3/min. Some will spill over the sides of the genset but better to have too much than too little!

This sounds like a solution I can be confident in. Thanks very much for the hard data. I'll report back (next summer!) on how it worked out.

 

[ARE]

Thans Anthony, really useful. In reply:

1. Yup, turbos close to intakes, esp on one side of engine room (cos Onan intakes are not handed, as you know)
2. No, Fairline fans include both blowers into engine room and suckers out. But that doesn't change what i should do - I need a fan blowing straight at the genset intake, literally with the 100mm blower nozzle 50mm placed from the face of the genset squirting directly at it
3. Yup, i fugured that even with 27kw gensets but using the same engine, I'll have the same problem becuase the diesel engine aint making anything like its 36hp and it doesn't matter how big an alternator you bolt to it. On your figures (thanks very much for that Kubota data and extrapolation) it is making 18hp, which is 14kw which is 60amps(before losses), QED!! So mainly I need to get the cold air supply to increase that 18hp back up to 30hp or so. But i think I'll go for the 27's anyway, for good measure, and to help in case I hit a limit with field current
4. Thanks for the 2.2 m3/min data. The 100mm jabsco continuously rated blower fan promises 7 m3/min. Some will spill over the sides of the genset but better to have too much than too little!

This sounds like a solution I can be confident in. Thanks very much for the hard data. I'll report back (next summer!) on how it worked out.

No problems with suppling technicial info.

Just out of interest - was it your old boat I supplied generator autostart on low batttery modules for?

Anthony

 

[jfm]

No problems with suppling technicial info.

Just out of interest - was it your old boat I supplied generator autostart on low batttery modules for?

Anthony

No that wasn't me. I didn't know about those gizmos. Can you supply some tech info on them please?

To manage weight and packaging logistics, i am deliberately not speccing loads of house batteries. This is fine, except i have to take care overnight at anchor. All deck lighting is LED but my problem is fridges and freezers, of which there are quite a lot, all running off inverter/batteries overnight. In a long hot night the house batteries have taken quite a beating by morning and so a genset autostart would be an interesting idea. Do you have a link please?

An alternative would be a time switch module. Do you have one of those?

 

[ARE]

No that wasn't me. I didn't know about those gizmos. Can you supply some tech info on them please?

To manage weight and packaging logistics, i am deliberately not speccing loads of house batteries. This is fine, except i have to take care overnight at anchor. All deck lighting is LED but my problem is fridges and freezers, of which there are quite a lot, all running off inverter/batteries overnight. In a long hot night the house batteries have taken quite a beating by morning and so a genset autostart would be an interesting idea. Do you have a link please?

An alternative would be a time switch module. Do you have one of those?

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