The 104 Deptherm - The fishing odds are on your side every time you go out with a Deptherm, model 104, for two simple but important reasons. It tells you quickly and accurately what temperatures are below your boat and it also tells you how deep these temperature ranges go. Thus, if you have the temperature chart, you quickly know whether you're fishing in a spot where the fish are most apt to be. If your Deptherm shows the water too cold or too warm for the species you're after, you can quickly move just as the fish do. You won't be wasting the day in the wrong place.
Deptherm works like this: dropped on a line, growing pressure forces water into the tube as the instrument descends. The volume of water trapped in the tube serves as a depth measurement column and is read off the side of the tube calibrated in feet. The thermometer on the other side assures close temperature readings if the instrument is left down for 30 seconds.
General Application - Attach the Deptherm to line and let sink to bottom or any intermediate depth. Hold there for 30 seconds and return to surface. Read depth on the calibrated side at the top of the water column and temperature off the temperature plate. Invert instruments; press valve to release water. Shake until all water is out before using again.
Downrigger Application - Clip the Deptherm Model 104 to your downrigger ball for monitoring water temperature and depth at the downrigger. When raising the ball for re-rigging, check the temperature and depth. Temperature readings on the Deptherm will not change while ball is being raised due to a delayed reaction (1 to 2 minutes).