Engine Room Exhaust Fans

[Just Bob]

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!

 

[markpierce]

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.

*

*

 

[O C Diver]

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.

 

[markpierce]

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.

 

[Just Bob]

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.

 

[Ocean Breeze NL]

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

Congrats

Elwin*

 

[sunchaser]

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?

 

[markpierce]

Bob, where is all your electrical powering going?

 

[sunchaser]

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.

 

[Just Bob]

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.

 

[Just Bob]

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.

 

[FF]

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

 

[psneeld]

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.*

 

[sunchaser]

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.

 

[Tidahapah]

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.

 

[Phil Fill]

*
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

 

[Just Bob]

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.

 

[bshanafelt]

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

 

[Delfin]

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.

 

[FF]

"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.

 

[Larry M]

How about an AC generator off the engine? It would power all your AC loads while under way.

 

[Just Bob]

More good ideas. I like the AC generator off of the main, why doesn't anyone do this?

Already have full hydraulics with oversize PTO's on each main, this drives the stableizers, thusters and windlass, I built it to get all of the thrust we need at 600 RPM idle. Also don't want to start cobbling things together on a brand new boat. It's a clean and orderly ER that we want to stay that way.

 

[Marin]

Just Bob wrote:
More good ideas. I like the AC generator off of the main, why doesn't anyone do this?

Because if you've ever heard an AC generator load up with the power requirements from AC loads like a hot water heater, microwave, coffee maker, air conditioning unit, electric stove, etc.*you will understand why you don't want that load put on the boat's*main engine(s) in addition to the load of moving the boat.

 

[sunchaser]

Bob:

An AC generator has little tolerance for RPM variation to safely satisfy frequency and amplitude requirements required by ACs,* dryers, washers etc.* Your main engine is going to have a varying RPM. That is why the simplest and most popular approach on trucks, buses, RVs and boats is to use a big alternator or "cruise gen" to get a*useable 2000 -*4000 watts via a**battery bank with an inverter*supplying 110 or 220 volts.

 

[psneeld]

Not sure how huge of a deal this is.

If a person doesn't want to run a generator when underway....just use continuous duty 12V fans (on the big Sea Rays....they just used 12 automotive radiator fans bolted against the hull vents).* The Engine room cant be that big...yes on ships, tugs etc, HUGE 220V fans might be the norm...but then again they run generators while underway for a variety of reasons.


-- Edited by psneeld on Wednesday 21st of December 2011 06:43:36 AM

 

[RickB]

sunchaser wrote:
An AC generator has little tolerance for RPM variation

*Those days are long gone. Variable speed generators (VSGs) are becoming more common at the low end of power generation. The same technology that lets yachts to use shore power of any flavor and frequency from daylight to DC also allows a turbocharger or a propeller shaft, or even a microturbine to drive a generator at varying speeds.

Jet engines used to use complex constant speed devices to drive generators but now a small box of electronic bits does a far better job much more efficiently. The same technology that Boeing uses to produce electricity on the 787 is available on small boats.

Marin's note of how a conventional marine generator responds to a heavy load doesn't really apply. The typical marine generator operates at full rated speed and is capable of delivering full rated load as quickly as the governor can deliver fuel. The generator follows the load, it can't anticipate it and that fact creates the effects you see and hear.

A variable speed, electronically regulated, generator has an output relative to the speed it is operating. If it is operating at half speed, it can only produce partial power. It only produces as much power as is available at the input shaft when the load is applied. The generator control does not tell the engine to dump fuel in the cylinder to try and maintain a synchronus speed. If the VSG is driven by the propeller shaft and an additional electrical load is applied, the engine will add fuel to maintan shaft rpm but the electrical output follows the amount of power available, it is not driving it.

What this means in real life is that even if the shaft generator is a 50kW unit, you can't always get 50kW from it. You can only take off as much power as the propeller is not using. When the engine rpm (which determines power available) drops below a certain point, the generator can no longer supply enough power to be useful and will go offline. It will not act like a standard generator where a very heavy load can actually overload the engine and even stall it. The generator control only lets the generator convert the amount of power that is available at any given moment.

*

 

[Edelweiss]

RickB wrote:*

Jet engines used to use complex constant speed devices to drive generators but now a small box of electronic bits does a far better job much more efficiently. The same technology that Boeing uses to produce electricity on the 787 is available on small boats.

*_______________________

Interesting, that seems to be the norm now.* Even in home electronics*the input voltage is more often wide spectrum too.

I first noticed that change on a trip to Europe.* Not that many years ago if you wanted to use a U.S. designed device you had to deal with a converter.**You always had an issue with the electrical devices you took with you. *Now most devices use a switching power supply which accepts any AC voltage from 110 to 240 volts and 50 - 60 cycles and pumps out the appropriate voltage on the other end.**It just*boils down to the shape of the plug on the AC end of the cord now!!** Thank God for*the IC chips.

 

[sunchaser]

Right you are Rick on VSGs. My convoluted reply to Bob was for his "AC generator off the main" question.

I'd guess the biggest market for large VSGs to be wind turbines. 30 years ago a place where I worked replaced* a large HP DC drive shaft hoist motor with an SCR (Silicon cooled rectifier ?) drive from Siemens with much added safety and flexibility and fewer AC/DC drive compnents.

For Bob's vessel though, would a VSG drive be the way to go considering he already has a large battery bank and inverter. With a 200 - 300 amp alternator he should have all the power he needs to run his ER vent fans.

Bob, since you already have the 240 fans in place, it may be easiest to add a fan only*inverter to get you to 240 volts if your current inverter is not set up to do it.

Bob, you are to be applauded for tossing this subject up and let us all pontificate.*With your hard earned $$ and our great (or not)*ideas we can go a long way! I am sitting in my marina with*new pilot house OAs adjacent - a*50 to port and a*60 forward.*

 

[RickB]

If it were my boat and I wanted to optimize the system to conserve energy, I would stick with the inverter and power the fans with a thermostatically controlled "frequency drive."

*

*

 

[Phil Fill]

We have a 5 KW AC cruise gen of the main 671, which we use on longer cruises. The AC gen has an electric clutch that can be disengaged if not needed, and a clutch that regulates the RPM.* I did put a bigger sheave on the 671 so the gen does not brown out at lower RPM.* The 671 hardly knows its there so its almost free.** Usually when cruising we are using under 20 amps.* If higher we use the main gen set*as we can switch back and forth.* Small cruise gen are popular on sail boats and smaller boats/trawler with*air*conditioing.*
*
*We also have a high amp DC alternator, large house, three 8-D, battery banks, and 3000KW inverter which have very seldom used.* Being a live aboard and 58 ft we use a lot of AC power and DC. We are/have reducing the AC power demand to diesel/propane and DC. I do understand the need for an inverter if you anchor a lot but other than that it would seem AC would be preferred?**I am thinking of installing a small 1 or 2 cylinder gen for when at anchor rather than use the inverter or at least charge the batteries?*