Bob Agramonte of La Conner, WA, asks:

Sea water temps can be high in the South Seas. How will this effect your engine cooling?

Dan Streech responds:

The keel cooler on the N40 is supplied by the Walter keel cooler company of Jersey City, NJ. The sizing of the keel cooler is a team effort between PAE, Walter and Alaska Diesel (Lugger) and is based on the known heat rejection data of the engine at various loads, ambient water temperature and boat speed (water flow over the cooler).

We at PAE consider worst case scenarios when sizing the cooler on a new design. Our criteria for sizing the cooler are:
Seawater temperature: 85 F
Maximum heat rejection (meaning engine running at the full power output)
Boat speed: 6 knots

In actuality, the engine only requires about 35% of it's rated power to move the fully loaded boat at 6 knots, so there is quite a bit of reserve cooling available as the boat moves into the warmer waters. From previous experience, I have been aboard Nordhavns operating at normal cruising speeds in water temperatures exceeding 90 degrees without any rise in the coolant temperatures.

Since the engine coolant temperature is thermostatically controlled to 185 degrees, the gauge reading remains constant unless the conditions overpower the keel cooler - which has never happened.

The ATW project has many purposes and one of them is to thoroughly test our designs, concepts and assumptions. We may find some unusual combination of events (such as towing an Arab dhow in the Red Sea at 3 knots requiring full power in 95 degree water) which causes an overheating of the engine. This would tell us that future boats should have a larger cooler or avoid the above mentioned practice.

As an aside to your question, I will also mention that we are testing a new device on the ATW boat. It is keel cooler dedicated to the cooling of the hydraulic oil from the Naiad stabilizer system. Since our dry exhaust/keel cooled boats don't use any pumped raw sea water, the standard cooling system provided by Naiad is only usable if we install a special 12VDC pump dedicated to the cooling of the stabilizers. In our typical installation, the pump is activated by a relay when the engine is started. It has been our experience that the 12VDC pumps when run continuously only have a life span of from 500 to 1000 hours and therefore are a frequent headache. The prototype PAE designed and built monel keel cooler is on the supply side of the oil loop and therefore passively cools the Naiad oil whenever the engine is running. Unfortunately, we have learned that our Mk 1 design of the hydraulic oil cooler is not sufficient in performance, so we have developed a larger and more efficient MkII version for testing on a future N40.

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