Saturday, August 4, 2012

Preparing for Take-off...

Sea Gem, like all Gulfstar 54 Sailcruisers, has two diesel engines, each driving a separate propeller.  This is unusual for a sailboat, even a big sailboat, but I love the configuration:  If one engine fails, we still have power, and the two engines make it much easier to maneuver the boat in tight spaces (with one engine in forward and the other in reverse, the boat turns very quickly).  The engines are located in a walk-in engine room located underneath the main salon, and I love that configuration as well:  I can maintain the engines and other mechanical equipment without encroaching into the living area, which would be required on most boats.

The downside of having twin engines located under the salon is that they generate a lot of heat, and this heat is transferred through the salon floor into the living spaces of the boat.  The result is that the interior can get very hot after running the engines, and the boat is often uncomfortably hot at anchor unless we run the A/C, which requires that we run the generator (yet another engine), and that means that the engine room never cools down.  (At the marina, we run the A/C off the grid.)

Although we will never be able to eliminate the problem of heat transfer from the engine room, we can reduce it by improving engine-room ventilation.  The faster we can remove the heat from the engine room, the faster it will cool down, and the more likely we will be able to sleep at night without firing up the generator.

Sea Gem's engine room has three 4-inch ventilation ducts that vent to outside the boat.  One is attached to an exhaust fan that runs only when the engines are running.  Unfortunately, the engines don't cool to room temperature as soon as we turn them off, so ventilation is needed even when the engines are not running.  For that reason, the other two ventilation ducts are connected to exhaust fans that can be turned on and off independently of the engine.  As a starting point for adding additional ventilation to the engine room, upgrading those two fans makes the most sense, as they provide additional cooling when it is needed the most: after we reach our destination and are trying to convert Sea Gem from "boat" to "house."

I did some investigating (slithering around in the far reaches of the engine room) and discovered that the two exhaust fans are 120mm (around 4.75") computer fans:

Our Old Fans
Upon further inspection, two deficiencies become immediately apparent: (1) at just over 2 watts a piece, the fans were far too weak to be useful, and (2) one of the fans was not working at all.  The result was half enough power to ventilate a computer, and nowhere near enough to ventilate an engine room.

The simple solution?  Tossing the half-broken and completely underpowered existing fans and replacing them with the most powerful 120mm 12-volt fans I could find.  And that is where things get interesting.

Most computer fans spin at around 1000 rpm.  Any faster, and they get too loud for the typical computer user.  A 120mm computer fan spinning at 1000 rpm moves about 25 cubic feet of air per hour: plenty for a 2-cubic-foot computer case, but woefully inadequate for a five- or six-hundred-cubic-foot engine room.  I figured that I could find fans that are maybe twice as powerful--enough to improve the situation, but no game changers.

As luck would have it, some computers apparently run as hot as diesel engines.  Enter the PFB1212UHE-F00, a screaming, 5500 rpm mad man that moves over 250 cubic feet of air per hour.  The rated output and power (48 watts) is at 12 volts--our battery bank is 13.2 volts, fully charged, so I'd expect the output to be around 10% higher, even--closer to 300 cubic feet per hour.  And, of course, there are two fans, and that should be enough to make a serious impact on our ventilation situation.

New Fans Pre-Installation 
Due to their freakish speed, the fans even came with a friendly warning:

A Serious Warning 
After installing the new fans, I flipped the switch, and--blew a fuse.  Oops.  No surprise--an appropriately sized fuse for 2-watt fans is going to be a bit small for fans that are twenty-five times more powerful.  After installing a larger fuse, I tried again.

The old fans, from their location deep in the engine room, were completely inaudible from the salon.  The new fans--not so much.

They started off with a gentle purr, but quickly grew louder...and louder...and louder.  At full speed, the fans screamed like a jet engine.  From inside the engine room next to the fans, it is too loud to hear anything else (why would anyone put one of these things in a computer?).  From inside the salon or the cockpit, the fans sound about as loud as a hairdryer or small vacuum cleaner--loud enough to notice, but not untolerable while waiting for the engine room to cool down.

Which, thanks to the new fans, should take no time at all.  Results to come.

1 comment:

  1. “They started off with a gentle purr, but quickly grew louder...and louder...and louder.” It could be that it really has the high power and capacity in giving a room good ventilation. Don’t forget to keep it clean, as it could affect its performance in ventilating the area. Additionally, it could also lengthen its maximum life expectancy.

    Staci Severns

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