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Old 12-18-2011, 04:03 PM   #1
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Engine Room Exhaust Fans

Several of you were a big help with some issues earlier in the year during the build process of our new Ocean Alexander 54 Trawler.* Well she's built and we've enjoyed getting to know her over the last few months.* A few things have come up now that we're using her and I'm trying to form a final a opinion a few issues, so there will be a few different posts under different subject headings.* The first is engine room temperature and (almost)/continuous*running of a genset.

*

We were surprised to get the boat with AC powered engine room exhaust fans - 240v no less.* This obviously means we have to run the genset to*ventilate the*ER.**The house/inverter batteries will keep the house systems running about 12 hours, so there is no need to run the genset during a normal days run, except*the ER temp climbs higher than John Deere said it should be, their*recomendation is 30 degrees above outside air temperature, well that can vary quite a bit depending on whether it's 40 or 80 outside, but none the less*I find I'm*running a genset just to run the fans to maintian that temperature delta.**

*

This is our first trawler and the first boat of this size.* Many I've spoken to have said*it is not unusual to run a genset continuously on a boat this size.*** I*installed two gensets, a 9kw and 15.5kw.* Is it someting I just need to get used to?

Thank you!
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Old 12-18-2011, 06:00 PM   #2
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RE: Engine Room Exhaust Fans

Got no gensets.* Nevertheless, don't mind having an engineroom exhaust system if nothing more than bringing in cooler air while "dipping" into the engine room.

Notice the stainless-steel louvre underneath pilothouse window.* There is one on the other side.* One's for intake, the other for exhaust.

Your boat seems well equipped.

*

*
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Old 12-18-2011, 06:40 PM   #3
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RE: Engine Room Exhaust Fans

Couple of simple options:

Change the fans to 12 volt.

Run the fans off a 12 volt 240 inverter.

*

Personally I would contact JD about the ER temperature requirement. If it's 20 degrees outside, I can see no logical reason to keep the ER below 50 degrees.
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Old 12-18-2011, 06:59 PM   #4
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RE: Engine Room Exhaust Fans

Quote:
Just Bob wrote:
This is our first trawler and the first boat of this size.* Many I've spoken to have said*it is not unusual to run a genset continuously on a boat this size.*** I*installed two gensets, a 9kw and 15.5kw.* Is it someting I just need to get used to?
*My engine's alternator*provides sufficient power for all needs while it is running.* No need*for a genset unless staying in place for several days*with no outside power source.* Don't have a genset since that's not in*my plans, but consider I have no air conditioning, and stove*uses propane.
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Old 12-18-2011, 07:08 PM   #5
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RE: Engine Room Exhaust Fans

Thank you, I'm waiting for Delta T, the fan manufacturer to tell me if they can change the fan motors to 24v DC and still have enough power to move enough air. It unfortunately will require a lot of re-wiring as the controller at the helm is AC powered as well.

When I questioned Ocean Alexander as to their thinking on the design, they also said they assumed a genset would be running all the time as well. Most folks in this size/type boat say the same thing. I'm still trying to figure out if I'm just thinking too small because of the small boat (39' so relatively speaking) I came out of.
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Old 12-18-2011, 07:15 PM   #6
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RE: Engine Room Exhaust Fans

Great couple of pictures there Bob..awesome job on your O/A..*

Congrats

Elwin*
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Old 12-18-2011, 08:29 PM   #7
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RE: Engine Room Exhaust Fans

Yes, get some fans that can run off 110 or 12/24 volts. My ER fans are 12 volt and do a bang up job. Or, get a 110/240 V cruise gen that runs off the engine to power the fans/inverter.. You do not want to be running your genset except sometimes at anchor, this is an obvious mis-design on OA's part and they are trying to back away from their design.

Is there sufficient combustion air coming into the ER?
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Old 12-18-2011, 08:29 PM   #8
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RE: Engine Room Exhaust Fans

Bob, where is all your electrical powering going?
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Old 12-18-2011, 08:40 PM   #9
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RE: Engine Room Exhaust Fans

The other reason you don't want to run your genset all the time is it will have insufficient*load on it and suffer a premature death.
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Old 12-18-2011, 09:36 PM   #10
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RE: Engine Room Exhaust Fans

All good comments, thank you.


As to where the power is going; the boat is a 24 volt system so everything DC on the house runs off of the house batteries ( 4 8D ) which also power the inverter. The two biggest continuos draws on the inverter are refrigerator/freezers. All of the helms electronics come out of the 24v house system as well. The only thing the engine alternators do is keep the engine batteries up. They do not recharge the house batteries, these are genset or shore power only.


As to underloading the gensets, I too was concerned over that, which is why I installed the smaller 9kw, so it would be better utilized for light load charging or overnight use of a single air conditioner.
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Old 12-18-2011, 09:39 PM   #11
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RE: Engine Room Exhaust Fans

Thank you!

We studied and shopped for about 5 years before we settled on this boat. Generally we are very happy with the design and build quality.
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Old 12-19-2011, 04:24 AM   #12
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RE: Engine Room Exhaust Fans

The only thing the engine alternators do is keep the engine batteries up. They do not recharge the house batteries, these are genset or shore power only.


THat is something I would change instantly.

ADD an alternator , at least a truck 125A or far better a bus 250, 300A unit and a smart voltage regulator with battery temperature monitoring. And a SOC meter.

Also look at Sun Frost for fridges with 1/2 to 1/10 the power requirements
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Old 12-19-2011, 06:26 AM   #13
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RE: Engine Room Exhaust Fans

Most commercial boats I've run ...that's really the first thing you do when you get onboard...fire up the genset.* So much runs off it.* Lights, heat/air, blowers, etc.* Not running engines or gensets is kinda a sailor...greenie boater sort of mentality.* I like peace and quiet too...but if a main is going to run..usually the genset is a wisper*in comparison if mounted correctly.

I guess*running one is just the cost of doing business in commercial circles.* But if you are going to have one...having systems on board that use it for power and cost less because they are simpler or cheaper offset the costs of running and replacing the genset.*
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Old 12-19-2011, 07:28 AM   #14
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RE: Engine Room Exhaust Fans

FF's points are valid.

Commercial is not an OA, although it can be set up that way. Today's, and yesterday's for that matter, alternators, inverters*and cruise gens*will allow*the main(s) to supply all the normal (non AC) power you may need in a large trawler yacht. This includes extra freezers assuming they are not the inefficient ones.*Many vessels* are intentionally*set up this way with the genset used for an hour or two a day for house battery charging, water makers and clothes washing. My genset has 1/4 the hours as the main.

Since Bob*assumes he must*run his vent fans when the main is running, then a spare set of installed fans is required,*no matter what the power source. Having been on many wet exhaust vessels where ER fans are not required to run with the main, I'd question this base assumption with ER natural ventilation an area of interest.*The 54 OA should not need much more than 140 HP to do hull speed, hardly a big heat generator.
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Old 12-19-2011, 11:07 AM   #15
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RE: Engine Room Exhaust Fans

Bob,
I have 2 x 240 V ER fans on my boat and run them from the inverter outlet.
My alternator keeps the bats toped up when I am steaming and so don't require the gen set when under way even when I don't have my 5 KVA 240 V belt driven cruise alternator on line.

This is probably another option that you could look at for cruising load. A belt driven or other means 4/5 KVA cruise alternator. Limited to your cruising RPM unless a variable speed drive (expensive) is used.
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Old 12-19-2011, 03:04 PM   #16
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Engine Room Exhaust Fans

*
Larger boats tend to run a generator when they are not plugged into dock power.*I would not be to concerned about a light load as you will probable have enough amp load periodically while under way, heat, hot water, micro wave, whatever, and the gen is set for high RPM.* If concern put a load on*it!* Turn on the heat/AC*and open the windows!*

*


-- Edited by Phil Fill on Monday 19th of December 2011 04:37:08 PM
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Old 12-19-2011, 03:29 PM   #17
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RE: Engine Room Exhaust Fans

Great points each of you. I think the analogy to a commercial boat is very appropriate and I think it is how the manufacturers think of larger more complex (read power hungry) boats. But that is not to say we have to keep it that way. I think there is a compromise.

So here is how out see it as of now:


1. Increasing the size of the alternator and tying it to the house batteries seems like the most logical first step.
2. Checking the amount of natural air flow in the ER. My air intakes are large but inboard in my walkway, which is good for most reasons but they don't get a lot of air past them at 7-8 knots.
3. Double checking the 30 deg delta between ER temp and outside ambient.
4. I'm going to try to increase my house bank by at least 1 more 8D.
5. Still seeing if the ER fan motors can be changed to 24v DC
6. Changing refrigerators and or freezers is not an option, nor does it need to be, they are new and fairly efficient.

Having just taken delivery of the boat in the last few months, we still have many projects planned, one of which is the installation of solar panels to try to give us a little more freedom from the genset.

Thank you all!

There will be other issues to discuss.
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Old 12-19-2011, 04:34 PM   #18
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RE: Engine Room Exhaust Fans

When sizing a large frame bus or truck alternator, make sure you factor in a couple of things:
- clearance in the engine room
- good venting/cooling
- mounting brackets on the main.
- enough belting to spin the thing when loaded up
- a good regulator
- the correct guage of wire between the alternator and the bank
- fuses for all


good luck
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Old 12-19-2011, 05:28 PM   #19
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RE: Engine Room Exhaust Fans

Quote:
Just Bob wrote:
Several of you were a big help with some issues earlier in the year during the build process of our new Ocean Alexander 54 Trawler.* Well she's built and we've enjoyed getting to know her over the last few months.* A few things have come up now that we're using her and I'm trying to form a final a opinion a few issues, so there will be a few different posts under different subject headings.* The first is engine room temperature and (almost)/continuous*running of a genset.

We were surprised to get the boat with AC powered engine room exhaust fans - 240v no less.* This obviously means we have to run the genset to*ventilate the*ER.**The house/inverter batteries will keep the house systems running about 12 hours, so there is no need to run the genset during a normal days run, except*the ER temp climbs higher than John Deere said it should be, their*recomendation is 30 degrees above outside air temperature, well that can vary quite a bit depending on whether it's 40 or 80 outside, but none the less*I find I'm*running a genset just to run the fans to maintian that temperature delta. *

This is our first trawler and the first boat of this size.* Many I've spoken to have said*it is not unusual to run a genset continuously on a boat this size.*** I*installed two gensets, a 9kw and 15.5kw.* Is it someting I just need to get used to?

Thank you!
*I took a little bit different approach in providing for ventilation for the engine room. *If the inlet air temperature for combustion is ambient, and any batteries in the E/R are kept cool, higher temperatures otherwise don't really seem to be negative. *I simply used a 24 vdc fan to provide air that can be easily picked up by the CAT for combustion with a separate pick up to blow cold air over the batteries and another over the refer/freezer compressors. *There is sufficient air capacity left over to push waste heat up a raceway built for the dry stack, exhausting outside. *The system seems to work just fine. *E/R temperatures might be 105 degrees when it is 70 degrees outside, but the combustion air is 75 degrees and the batteries are around +3 degrees outside temps.

This approach means we run the genset to power the stove, or recharge if we are at anchor for a couple of days. *The E/R fan just runs off the batteries when the engine is running.
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Old 12-20-2011, 05:05 AM   #20
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RE: Engine Room Exhaust Fans

"Limited to your cruising RPM unless a variable speed drive (expensive) is used. "

Simplest might be to use hydraulics to power the gen set loads.

Hyd on the main and you have a 6KW cruise generator at low cost.

A big advantage is the gen set hyd power can be used while docking on hyd bow and stern thrusters with no need to operate the main engine above idle to produce big power to the thrusters.

Makes a "get home" setup , hyd power to the shaft rather EZ, ,,,might even allow the folks that insist on an oversized inefficient engine "in case they try to run from a storm" to use the correct size engine and add power for emergency flank speed from the gen set.
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