1. Does it really work? Doesn't the heated water just flow upwards in the hose for the sink?
Yes - the heated water does rise to water-line level in the hose where it comes to a stand-still before rocking up-and-down. This, however, has no influence on the cooling effect as an equal volume of water as that rocking up-and-down flows in-and-out through the heat exchanger situated in the skin fitting. Here, every single movement - large or small - of the boat's hull in the water pumps in the same volume of cold water into the heat exchanger as the volume of heated water that has just been sucked out. It is precisely at the orifice of the skin fitting where the heat exchange action occurs - not in the water standing higher up in the hose to the sink. It is for this reason that the inside diameter of the hose at water-line level must be a minimum of 1.5" while that of the orifice in the skin fitting is only 1" diameter. The resultant 2:1 area differential is very important as it creates an appreciable amount of additional turbulence in the orifice.

2. Is such a small heat exchanger coil really large enough to cool the refrigeration system?
Yes - in fact, even if only a piece of tubing the same length as that of the coil had been placed in the water outside the hull, it would still work! The heat, however, would then only be transported away by the "thermosiphon effect" of the surrounding water. In the skin fitting heat exchanger of the Isotherm SP, the water flow is also forced away by the self pumping action resulting in an appreciably higher efficiency level.

3. But if I close the seacock? What would happen then?
Turning off the seacock when under sail or engine makes very little difference. When crossing waves and splashing, new water is continually being pushed into the skin fitting even if the seacock is shut. The same thing happens if you are tacking and hear a "gurgling" noise indicating that the ejector effect is sucking the air down from the sink. It works even then! The orifice of the special SP skin fitting is so designed that lateral movement through the water creates a slight over-pressure on one side and correspondingly slight under-pressure on the other side causing the water to splash up into the heat exchanger inside the skin fitting, a principle that also works in planing motor boats. If the seacock is closed in harbour, the refrigeration unit will still operate but at reduced efficiency. This reduction in efficiency, however, is of little importance when shore power is connected but it is preferable that the seacock is open.

4. We sail in warm waters, won't the heat exchanger become blocked by external fouling?
How often must I clean the coil? This is an other good thing! You don't get fouling in the skin fitting for the sink if the seacock is open - this fitting is continually being flushed by water. In skin fittings for the engine, toilet or pumps, the water has no movement as they are often blocked by non-return valves, etc. Check this yourself when your boat is on shore next time.

5. If I accidentally block up the sink hose with an assortment of spaghetti, rice, potato peelings, etc., what should I do then?
If you were at home, phone for the plumber right away! If you are on your boat and happen to have an Isotherm SP onboard, all you have to do is to go sailing. Every single wave you plough through either under sail or motor results in very rapid and powerful pressure changes in the hose to the sink - so it cleans itself!

6. When in the West Indies, some mucous substance had to be continually removed from both the pump and heat exchanger of our traditional sea water cooled refrigeration unit. Surely this would also occur in an SP?
No, it would not! The water in the SP's skin fitting is always moving even when the refrigerator is switched off. In a traditional sea water cooled unit, the water in the system stops moving, for instance, each time the thermostat switches off the refrigerator and the water pump stops. This allows the fouling to start and increase rapidly particularly if light-penetrating transparent hoses have been fitted.

7. Our boat is used for long-distance cruising. When she's on shore for hull cleaning, etc, we usually live aboard. Could we still use our refrigerator?
Yes, it will still work and although it will require much more battery power, this is no problem as adequate shore power is usually connected in this situation. The SP heat exchanger coil becomes air-cooled using the "chimney effect" created by the flow of warm air rising up through the sink hose. It is important, however, that the drain plug for the sink is always removed after use to increase circulation of the air.

8. But what about corrosion?
The risk of corrosion must always be kept in mind. So-called "noble" metals should always be used for those components which, if they fail, would cause serious damage; when mixing materials consideration must be given to their position on the electro-magnetic scale; always fit a sacrificial zinc anode which compensate for the difference in potential. The electrical system of your boat must be checked regularly for current leakage. All Isotherm units have a separate earth and are carefully inspected during production for current leaks. If you have reasons to suspect that there could be a risk of galvanic corrosion aboard, the special sacrificial anode for the SP skin fitting should be fitted. Should there be considerable attack and material loss of the anode during a season, the reason for this must be found. The heat exchanger coil of SP is made of a copper/nickel alloy and the skin fitting itself of dezincification-resistant annealed brass certified by Lloyds. The hard-soldering of the connections is in silver.

9. How much less power does a SP or Magnum consume?
Isotherm SP is available in different versions, both with ASU - "Automatic Start Up" in combination with a holding plate, or with a traditional thermostat control and a direct evaporator. In normal northern European waters, an SP-type unit will have a 10-20 % lower power consumption compared to that of a corresponding air-cooled unit. In tropical conditions, however, when savings are most needed, power consumption can be reduced by as much as 30-50%. This efficiency increase is largely due to the greater difference between sea and air temperatures in these waters. Sea water temperatures are normally in the region of 77-86°F, whilst the air temperature inside the boat where the compressor is installed can be 85°, 105°or even 120°C.

10. We want to install both refrigerator and freezer onboard. Is it possible to fit two or more units to same skin fitting?
No, it isn't - each unit is separate entity and each requires its own heat exchanger skin fitting. These, however, may be connected to the same sink. It is also possible to have one or more heat exchanger skin fitting positioned below the waterline and connected to an existing or additional 1/2" diameter through-hull air-vent positioned well-above the water line.

11. We already have a working refrigerator aboard. Is it possible to rebuild it for SP?
Sorry - this is not possible. An SP unit is split into three separate parts, each pre-filled with refrigerant and special re-openable quick couplings. From both an economical and a liability point-of-view it is not convenient to re-build.