I operate a sport fish boat in Dubai in the United Arab Emirates. Our water temperature exceeds 95º for most of the year. This creates an ongoing problem with excessive marine growth of different mollusks in my sea strainer along with the condenser seawater circuit of my air conditioning. The problem is so bad I currently keep a spare set of hoses that I swap out twice a year. The condition is not as pronounced with other sea water circuits. Do you have any ideas?

Mark

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Dear Mark,

Air conditioning thru hulls and associated water circuits will accumulate marine growth faster than other thru hulls because the water pump running constantly provides oxygen rich nourishment that enhances marine growth.There are some tricks to help reduce marine growth. One is to cut up a piece of ½ inch copper tubing and place the pieces in your sea strainer. The copper will react with the sea water producing a copper oxide in the water making an environment not conducive to mollusk growth. You can also have your thru hull and strainer basket sent out for copper plating which will help keep them from fouling.On many larger vessels the condenser sea water circuit has valves and plugged tee fittings next to the intake and overboard to accommodate plumbing a cooling tower to the vessel during haul-outs. An acid bucket, a circulating pump and a 50/50 mixture of muriatic acid and water can be connected to the cooling tower port. This will allow you to clean and dissolve all the critters growing in your system.This would be much simpler than changing out the hoses. As always, care must be taken when using dissimilar metals around aluminum.

Rich

This article appeared originally in the March 2006 issue of Dockwalk.

The vessel I have been running for the past two years is under going a refit. The air conditioning has not always met our expectations. When we have had the system checked by a technician he reported that the system was operating properly considering the restricted air flow. His recommendation is to increase the grill size. Now that the boat is being refit, how do I know what size of grill is required?

Daryl

Dear Daryl,

Restricted air flow on both the air return and supply is definitely one of the most common problems that reduces the performance of air conditioning on a vessel. Restricted air flow allows the compressor to operate at low suction pressure reducing the BTU capacity of the compressor. Also with restricted air flow the discharge air is colder than normal, sometime presenting problems with sweating ductwork and blades of the discharge grill.

A rough rule of thumb for sizing a return grill is to look at the evaporator fin coil area and use that size as the minimum size for the air return. The discharge grills should be sized by dividing the CFM of the blower by 7 to get the minimum discharge grill size. For example, a 16,000 BTU evaporator moves about 500 CFM of air, divide by 7, which equals approximately 70 square inches of grill area. It is always recommended to use a larger grill than the above formula, reason being the larger grill will have a slow air movement across the blades, lessening the air noise.

When designing a proper air delivery system for air conditioning, the goal is to be able to walk into a room, have it maintain a constant desired temperature and not be able to determine directly where the cool air is coming from. To achieve this air is ducted into a transition box, which is used to slow the velocity down and distribute the air evenly across the blades of the grill at low velocity.

Rich

This article appeared originally in the March 2006 issue of Dockwalk.

I am the engineer on a 130 foot vessel that is going to based in the Baltic region. The current heating system is chilled water using reverse cycle. From my experience reverse cycle does not perform well in cold water. What would be my alternatives to provide more heating capacity for the vessel?

Ingo

Dear Ingo,

Yes, you are correct, chilled water air conditioning that uses reverse cycle for heat works well in warm waters but in 40ºF seawater it provides limited capacity in heat mode.One simple method is to incorporate resistant water heaters into the chilled water loop of the vessel. The resistant heaters are available in many kilowatt capacities and can be staged on thermostats in the same manner as the chiller for power management.Another method of increasing your heating capacity is to install a diesel fired water heater that would be piped into the air conditioning chilled water loop. One company that produces this type of heater is Webasto of Stockdorf Germany.And yet another method that we have used in conjunction to resistant water heaters is to install a water-to-water heat exchanger with one side coupled to the chilled water loop. The other side is coupled to the fresh water side of the vessels generator with isolation valves. This will allow the heat of combustion from the generator to be used in heating the vessel. This is an extremely simple and low cost method for increasing the heating capacity without increasing the vessels electrical demands.

Rich

This article appeared originally in the December 2005 issue of Dockwalk.

We have a chilled water system on our vessel that has a small leak in the water loop that requires topping off every three days. So far I have been unable to locate the source of the leak. When I find water drips I don’t know if it is condensation or a source of the leak. You must have experienced this type of problem before. Any suggestions?

Dennis

Dear Dennis,

Trying to locate a leak on chilled water piping when there is condensation present is very difficult. When we are presented with this problem, we put a water soluble florescent dye in the water loop and let it circulate in the system for a period of time depending on the size of the leak. The water that has been treated with the dye will emit a florescent glow. After the florescent dye has had sufficient time to circulate and leak out with the water we use a high intensity blacklight shined in the bilge to locate the general area of the leak within the vessel. Then we start shinning the blacklight on the air handlers, drip pans and the assorted piping to locate the exact leak.This method of leak detection with an ester oil dye we have also found to be the best way to find the smallest refrigerant leak. This type of dye is also available for hydraulic and engine oil leak detection as well.Another method to locate the leak is to turn the chiller off for a couple of days and let things dry out or put the system in the heat mode. With the lines and air handlers dry finding the leak is much easier than when operating in the chiller mode.

Rich

This article appeared originally in the September 2005 issue of Dockwalk.