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chengkp75

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About chengkp75

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    Maine or at sea
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    Former cruise ship Chief Engineer

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  1. Interesting that they didn't cover the area around the bow thrusters with the teflon anti-fouling paint. Maybe the turbulence/cavitation causes it to erode faster.
  2. As I've noted, I made a mistake in saying that it was 20% volume per hour, when in fact it is per minute (as fans are rated in cubic feet per minute). To give an example of a cruise ship HVAC system, the Norwegian Sky runs two to three (depending on outside conditions) approximately 2Mw chillers (I don't remember the exact capacity), or about 4-6Mw of cooling, which is about 1100-1700 tons of cooling. I would like to see the link to high CO2 concentrations inside a cruise ship, as I have never heard of this before. Sorry, would like to continue this, but getting the call to take the ship out of port. Will get back later.
  3. You will see that I revised that figure in a later post to 12 ACH. If 20% volume is replaced every minute (as I revised my statement, and I cannot say why I made that mistake), then 60 minutes x 20% volume per minute = 1200% volume per hour, or 12 ACH. Recirculation, in all spaces, not just cabins, is not important to viral concentrations, except as a factor of the number of air exchanges. There is no data that even aerosolized virus can remain viable when transported a hundred feet or more in the return air duct from the theater, through the filter, the heating coil, the cooling coil, the fan, and then another hundred feet or more in the supply duct back to the theater. In cabins, it could be more of a factor, since the distance involved is very small. Each cabin has its own recirculation system, so aerosolized virus could be returned to the cabin, if it was present in the first place (i.e. by an infected person). It is interesting to note that design factors for hospital rooms use a 3-4 ACH figure, rather low, and this is due to the fact that higher ACH figures require higher airflow velocities, and these higher velocities can result in aerosolized virus being suspended for a longer distance, but not necessarily for a longer time. This was the result found in the Chinese restaurant case of covid spread, where the infected person was sitting directly under the AC vent, and the air currents moved his virus further than the accepted "cough/sneeze" radius of 6 feet. This may be the biggest change that HVAC systems need to make, is to be able to distribute the necessary cool air throughout the space, without creating high airflow velocities at certain locations.
  4. I have answered you on the thread "Ships Ventilation Systems". As for changes between heating and cooling with regards to the number of air changes, no this will not change substantially, if at all. The ship's HVAC system is not like a heat pump, where the same equipment does heating and cooling. The cooling is done by 3-6 large (1-2Mw) rotary refrigeration compressors, which then cool a fresh water cooling system, not the air directly. This "chilled water" is pumped around the ship to the various air handlers (including each cabin), and this cools the air. Heating is done in the air handler via a steam heating coil, the steam provided most commonly by an auxiliary boiler (used to heat fuel, oil, and domestic hot water), though some ships may have exhaust gas boilers that derive heat from the diesel engine exhaust gas. As I've said before, all the talk about going from recirculation of 80% of the volume, to 100% fresh air supply, really does nothing for preventing the spread of covid, unless the number of air changes increases. With a 12 ACH, whether the 80% of the volume is recirculated past a cooling coil, or whether it merely sits in the room, doesn't matter. To get rid of the virus, you need to exchange the air (bring fresh air in and get the possibly contaminated air out) as quickly as possible. The only thing that going to 100% fresh air supply will do is to increase the cooling energy greatly.
  5. Typically, 20% fresh air volume is used, which means 5 ACH (air changes per hour).
  6. The SSW heading was likely the shipping channel out to the point where you turn NW to clear Ushant. There are likely some sea trials to do, and possibly "swinging the compass" (turning in a circle and noting the variation between the magnetic and gyro compass at each point of the compass), which is done every couple years, and after any significant change in steel around the ship.
  7. Yes, and the answer to question #2 is in the avatar as well.
  8. No, all around the world. Suriname, Guyana, Honduras, Australia, Egypt, South Africa, Ireland, North Sea, South Pacific, Brazil.
  9. While another outbreak would cause a very bad PR situation, it would not likely break the company. Lawsuits for injuries or death at sea have a pretty high standard to meet showing negligence on the part of the carrier. Provided Cunard was following all protocols set forth by flag state, all port states, etc, then someone coming onboard and infecting a lot of people would not necessarily result in massive class action law suits. Now, since Cunard's ships are Bermudian flag, that makes them UK ships, and they could do cruises to nowhere out of the UK, but not the US or Europe.
  10. Spent 12 years in offshore oil in the 70's and 80's. Almost all of it on dynamically stationed drillships and semi-submersible rigs. Did all kinds of work from drilling for oil, pipeline backfill, deep sea mining (the cover story for the Glomar Explorer).
  11. I can't say for sure, but my guess is that this was a retrofit thruster, common in the 60's and 70's, as thrusters started to take off. I don't believe thrusters were in use in the 40's and 50's.
  12. That would be the Glomar Explorer, and dynamic positioning was the coming thing in offshore oil exploration.
  13. I can't say when cruise ships started to use thrusters, but they came into common service on ships in the 60's. As for azipods, a twin screw, twin high lift "Becker" rudder ships with bow and stern thrusters is no less maneuverable than a ship equipped with azipods. Azipods provide about a 10% increase in efficiency underway, and have a much smaller capital expense than the conventional propeller plant, which is the major reason for their use on cruise ships.
  14. They track the hours because part of the new laws is that there is a minimum amount of rest each crew member needs to get in any 24 hour or 7 day period, and the line can get fined if they violate this. And, again, the room and board situation is not as much of a perk as many believe. If the crew member has a family at home, he/she is still paying rent on a home (or a mortgage)(and even single crew would likely have a year-round home, unless they are living with the folks), and still buying groceries for the family.
  15. That is not quite correct. Their "wage" from the company may be only $100/week, and the rest from the DSC, but since the MLC 2006 went into effect in 2013, there is a minimum wage of $641/month (based on a 40 hour work week, and this increases annually), that the cruise line is obligated to pay.
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