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Old 12-20-2011, 06:28 AM   #21
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RE: Engine Room Exhaust Fans

How about an AC generator off the engine? It would power all your AC loads while under way.
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Old 12-20-2011, 06:21 PM   #22
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RE: Engine Room Exhaust Fans

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.
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Old 12-20-2011, 10:25 PM   #23
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RE: Engine Room Exhaust Fans

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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.
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Old 12-20-2011, 11:04 PM   #24
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RE: Engine Room Exhaust Fans

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.
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Old 12-21-2011, 05:42 AM   #25
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Engine Room Exhaust Fans

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
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Old 12-21-2011, 05:46 AM   #26
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RE: Engine Room Exhaust Fans

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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.

*
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Old 12-21-2011, 08:07 AM   #27
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RE: Engine Room Exhaust Fans

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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.
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Old 12-21-2011, 09:02 AM   #28
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RE: Engine Room Exhaust Fans

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.*
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Old 12-21-2011, 09:11 AM   #29
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RE: Engine Room Exhaust Fans

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."

*

*
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Old 12-21-2011, 09:36 AM   #30
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RE: Engine Room Exhaust Fans

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?*
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Old 12-21-2011, 12:21 PM   #31
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RE: Engine Room Exhaust Fans

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RickB wrote:
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.
Right, but wouldn't if follow that if the main engine was also driving an AC generator sized to run AC appliances like hot water heaters, stoves, and whatnot, as these loads were applied the main engine would have to work that much harder to combine the load of the generator with the load of moving the boat?**If that reasoning is correct,*you'd either need a larger engine to maintain the same propulsion power while powering the loaded-up generator, or you'd need to accept less propulsion power with a smaller engine whenever a significant load was put on the generator.
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Old 12-21-2011, 12:55 PM   #32
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RE: Engine Room Exhaust Fans

The temperature in my engine room stays quite comfortable while we are under way as the engines draw in fresh (relatively) cool air from outside. When we park up and switch off, the temperature shoots up as the heat soaks out of the engines.
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Old 12-21-2011, 04:08 PM   #33
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Engine Room Exhaust Fans

Wow you guys are amazing, I'm glad you're not billing me for the advise!

My inverter is a Victron "Quattro" 24v 5000w. I do not believe it will supply 240v, I believe I can pair it with a second and produce 240, but it would seem that the DC feed would be enormous.

I was talking today to a Krogen 52 owner who moves a lot of Krogen 55's and 58's and he says Krogens theory on boats this size is two gensets, with the smaller be essentially a disposable one. Assuming one is good for several thousand hours, I'm not so sure this s crazy.

I'm still going to work on getting power to my existing fans and house bank without the genset.


The other advantage I see to this is some day in the future if I can replenish house bank with wind and sun, we could stay at anchor for some time with little genset use.

-- Edited by Just Bob on Wednesday 21st of December 2011 05:15:35 PM

-- Edited by Just Bob on Wednesday 21st of December 2011 05:16:13 PM
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Old 12-21-2011, 07:18 PM   #34
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RE: Engine Room Exhaust Fans

Quote:
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Right, but wouldn't if follow that if the main engine was also driving an AC generator sized to run AC appliances like hot water heaters, stoves, and whatnot, as these loads were applied the main engine would have to work that much harder to combine the load of the generator with the load of moving the boat?**If that reasoning is correct,*you'd either need a larger engine to maintain the same propulsion power while powering the loaded-up generator, or you'd need to accept less propulsion power with a smaller engine whenever a significant load was put on the generator.
*That is correct, you can't create energy, you can only convert it. The shaft generator can only convert horsepower that is not being used by the propeller and it does take fuel to do that.

Shaft generators are usually sized to produce X amount of power at 100 percent shaft rpm or power (if a CP wheel) and a more or less linearily decreasing amount of power down to about 50 percent of engine power. You can't just add a shaft generator to an existing powerplant that is already required to produce 100 percent power to move at X speed and expect the speed to remain the same. You can't add a shaft generator to an engine that burns X gallons per hour at Y knots and expect to burn the same fuel at the same speed and produce Z kW as well.

Where a shaft generator would work on a trawler yacht would be on one that is grossly overpowered but normally operates at low speed so that there is a large margin of "reserve power" available to convert to electricity.

Given that most trawlers don't cruise at constant rpm for extended periods the chances are that the shaft generator would frequently trip due to rapid rpm and load changes. To negate this problem, a shaft generator can be paralleled with an inverter or smaller generator to share the load. Either method means that load management is still as important as it is on shore power. If you only have a 30A shore power supply you know you won't be running the hot tub, the dryer, and the galley oven at the same time and having a shaft generator doesn't automatically eliminate that issue.

Now, if you have lots of space for batteries and still need a lot of AC power, it might make more sense to keep it simple and just install a very large alternator on the main (if it is big enough) and feed inverters through the batteries. You can parallel inverters to support large loads and use the batteries to provide "peaking" power when needed or to make up for short term main engine power reductions.

The bottom line in all this stuff is that you are trying to change the fuel in the tanks to heat and lights or cold or some other more useful form and the means to do that are as varied as the reasons to do it. It is all a compromise and no one method is better than another for all people all the time.
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Old 12-21-2011, 09:40 PM   #35
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RE: Engine Room Exhaust Fans

Quote:
Just Bob wrote:
My inverter is a Victron "Quattro" 24v 5000w. I do not believe it will supply 240v, I believe I can pair it with a second and produce 240, but it would seem that the DC feed would be enormous.
*Pretty sure you can't pair 2 - 120 volt inverters to make 240 volts. Inverter power consumption is based on 120 or 240 volt load, not the capacity of the inverter. I drive a 16,500 btu airconditioner with a 5,000 watt 12 volt inverter. The inverter could consume 420 amps at 13.2 volts to produce 5,000 watts. But running the AC unit, it only consumes about 120 amps at 13.2 volts.

It would be helpful if you could post the amp draw of the fans, so we could bloviate better.*
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Old 12-22-2011, 07:14 PM   #36
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RE: Engine Room Exhaust Fans

I'll be able to post that fan amperage draw next week when I get to the boat.

Just for knowledge, I checked Victron's website and this inverter can be paralleled with another to produce 240v. Not sure I want to (read can afford) that option, but I guess it's nice to know it's there. I think I would prefer to see if I can change the fan motors to 120.
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Old 12-23-2011, 04:22 AM   #37
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RE: Engine Room Exhaust Fans

"If that reasoning is correct, you'd either need a larger engine to maintain the same propulsion power while powering the loaded-up generator, or you'd need to accept less propulsion power with a smaller engine whenever a significant load was put on the generator."

This might be a hassle if the engine was properly sized and working hard and efficiently.
With most pleasure boats the engine is way oversized

A TT using 3gph at cruise is perhaps using 45 HP certainly under 60hp.

With frequently 120 or 135 hp farm engines , another 20 hp for 10KW would not require a vessel slow down.
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Old 07-05-2012, 04:45 PM   #38
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Just Bob: curious as to where you've ended up with all this, having just seen this thread for first time. I am an OA owner (older, 52ft). I think the problem you face stems from the design decision to use Delta-T system at all...but that's another story and now you have it irrelevant anyway. But to 'design' for full-time genset use these days is crazy...your boat is just not that big ! Do you now have a solution to the engine room ventilation problem that doesn't require the genset to be run?
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