We need 0.075 m^2 /kW from the table.8 .95 kW × 0 .075 m^2 /kW= 0 .67 m^2
Circumference=π× 21. 3 = 66 .9 mm
66 .9 mm ×1,000 mm length =66,900 mm^2
per lineal m
66,900 mm^2 ÷1,000,000 mm^2 /m^2 = 0 .067 m^2
per lineal m of pipe
0 .67 m^2 required area ÷ 0 .067 m^2 per lineal m
= 10 .0 m of pipe
COPPER ORCOPPER-NICKELIS THEBEST
TUBINGMATERIAL Because it’s nonfouling
and has the highest heat conductivity, copper
or copper-nickel makes a superior material
for tubing, though care has to be taken to in-
sulate it galvanically from a steel hull and it
shouldn’t be used on an aluminum hull.
Copper-nickel is the first choice because it’s
considerably stronger than copper and also
resists internal erosion from fluid flow better.
For unpainted copper or copper-nickel tub-
ing, you can use Table 8-2 or 8-3 to find the
length of tube required. Note that in addition
to being more efficient at conducting heat
and being nonfouling, the wall thickness is
less than for the steel or aluminum tables.
Don’t use brass pipe or fittings!Brass is
copper alloyed with zinc, and it will suffer
from severe corrosion called dezincification.
KEEL-COOLERINSTALLATIONCONSIDERATIONS
Since keel coolers rely on seawater to cool
them, they should be located as deeply as
possible below the waterline. Too high up or
too close to the waterline, and the cooler may
roll out of the water or experience aerated
water flow, both of which reduce heat-
transfer (cooling) efficiency.
Keel coolers for stationary operation
should be mounted on the side of the hull or
the keel, not horizontally under the bottom of
the hull. This is because—for a horizontal
cooler when the boat isn’t moving—warm
water will not flow away by convection but
will be trapped under the cooler, which will
result in overheating. In addition, when hull-
side-mounted keel coolers are recessed, the
top of the recess should be angled to allow
free convective flow from the top of the
cooler (see Figure 8-9).
On tugs and towboats, the propulsion-
engine keel cooler should be located aft in
the underbody where the slipstream of the
propeller will accelerate water past the
cooler as much as possible.
When laying out the direction of water
flow through the keel cooler, try to set
things up so the flow runs from stern to
bow. This increases the apparent velocity of
the water flowing past the cooler relative
to the water inside the cooler. Clearly, water
in the cooler must flow in both directions
in some configurations, but keep this princi-
ple in mind.Chapter 8: Engine Cooling Systems and Their Exhausts
TABLE 8-2. KEEL-COOLER TUBE LENGTH (in./bhp) COPPER OR COPPER-NICKEL TUBE
UP TO 85°F (29.4°C) SEAWATER TEMPERATURE
ROUND TUBE, APPROX. 0.06 TO 0.10 in. THICK
Generators & Slow- Free-Running
Stationary Moving Under 8 Knots Over 8 Knots
Tube OD, in. in./bhp in./bhp in./bhp in./bhp11 / 8 1.^138.^565.^994.^794.^07
11. 00 9. 63 6. 74 5. 39 4. 58
(^7) / 8 0. 88 11. 00 7. 70 6. 16 5. 24
(^3) / 4 0. 75 12. 83 8. 98 7. 19 6. 11
(^5) / 8 0. 63 15. 40 10. 78 8. 62 7. 33
(^1) / 2 0. 50 19. 25 13. 48 10. 78 9. 17
(^3) / 8 0. 38 25. 67 17. 97 14. 37 12. 22
(^5) / 16 0. 31 30. 80 21. 56 17. 25 14. 67
(^1) / 4 0. 25 38. 50 26. 95 21. 56 18. 33
NOTE:Tubes are mounted so seawater flows freely around the entire tube surface.
NOTE:Square tube may be 78 percent of the length of round tube.