Mast rewiring

How do I rewire my mast? Can you please help. I am trying to do some rewiring in the mast (Isomat): radar, coax, and a triplex wire for deck and steaming light. Are there internal conduits in the mast that extend below the side exit? Do I need to pull the mast? Gene Stoddard (#158, Swell Dish).

a. All masts are probably different. I have an Isomat clone (Cinkel Canada) and it has 3 extrusions inside the mast, 2 either side near the front and one aft.. They go the full length except that one or two (I forget which) are cut by the upper spreader supports. The extrusions each hold a plastic conduit tube and may be cut at whatever height one desires. I believe the only way to resolve wiring problems is to pull the mast. David Salter (Here’s my mast base, Pic 1) (#050, Opportunity).

b. We had an Isomat mast previously on our Corbin. It had two conduits, one fore and one aft. The wires within our conduits were bound together with cable ties every couple of feet or so. These wires flex snakelike back and forth across the conduit taking up much of the conduit space. We needed to take our mast down to get the wires out of the cable wraps and add another wire in the conduit. We disconnected all the wires, slid the entire bundle out, added a wire, attached it with cable wraps, slid the whole bundle back in, and reconnected everything. It was not as difficult as it sounded, and went quite smoothly. Hope that helps, Stephen Lefneski (#187, Toboggan).

c. I have an Isomat mast which I rewired several years ago. I had no conduits in the mast initially but Isomat sells various size conduits which can be slid up the mast from below into a retainer slot so they are fixed. In order to rewire your mast properly, and certainly to install additional conduits, the mast must be removed and put on sawhorses. Pull out all the old wiring and even remove the mast head temporarily for ease of pulling. Find the supplier of Isomat masts and accessories and purchase the new conduits you need. The conduits can be trimmed at the exact point where wires need to exit such as at the spreaders for spreader lights or radar domes before continuing on the the mast head. I would suggest signal wires be in separate conduits from the power wiring. If you have room in the conduit you might consider a spare wire for some future device or antenna you might want to install. Be sure to file smooth the holes where the wire exits the mast and that the wires are not pinched when exiting. All new wiring should be in double insulated sheaths and be tinned stranded wire of the proper gauge for the devices run. When the wires exit at the spreaders or at mast head they should exit at 90 degrees and make a slight bend down before heading back up again to the device. This will prevent water from entering the mast. Good luck with your rewiring. Jack Verheyden (#127, Kathrian).

d. There is no way you can deal with this mess without pulling the rig. The wires in the conduit will be impossible to pull out or use as pull throughs for new wiring. I rewired Two Pelicans mast down. The reason the wiring exit is higher than the conduit end is to form a drip loop. This exit would be the one to use for all the wiring including the radar if its cable is properly shielded. On deck I would mount an inverted U-shaped stainless steel conduit, one end attached by a flange to the deck where the wiring feeds below, the other end half the length of the U would be where the cables are fed in, then up and over the U and then down. With a suitably sized piece of pipe and a flange welded on the longer end you will have a barrier to sea water going below through the conduit. Plug the pipe after the wires are fed in, either with putty or with a piece of plastic tubing where the wires are fed through, one end inside the mast opening, the other slipped over the inverted shorter end of the conduit. Use the proper sized silvered copper wiring……expensive but a one time fix. Good luck, Jeremy Parrett (#101, Two Pelicans).

e. At the time most Corbins were being built, Isomat spars did not have conduits in them. Instead, they had two internal extruded tracks, similar to the sail track on the aft outside of the mast tube. Isomat would take the appropriate lengths of mast wiring, secure miniature slides every 12 – 18 inches along them, then “hoist” the wiring harness in one of the internal tracks, while fishing wires out of the mast tube at appropriate locations. With more complex wiring harnesses, they would split the bundle into two harnesses and use both internal tracks. There is no way to adjust the wiring on a setup like this unless the mast is unstepped. You may have something that’s been retrofitted, including a conduit (you should be able to see fasteners on the outside of the mast tube used to hold the conduit in place). In some cases, where advanced planning was employed, it may be possible to fish new wires through a conduit while the mast is stepped, but it is always easier while the mast is laid flat. In any event, your biggest issue may be the exit plate on your mast; a non-standard fitting for an Isomat spar and one I’ve never seen before. Good luck, Chris Reynolds, former owner of #083, Tamalmar, Corbin 39 pilothouse cutter.

f. The rewiring of a mast is much, much easier done with the mast down, especially if you are going to replace all the wiring. That being said, many times the wiring is filled with 3M 5200 at the base of the mast to prevent water from entering. To get wires out of 5200 is not an easy task if you don`t have access to it. There are internal conduits but the radar wire was big and often times did not make it inside the conduits. The radar cable usually goes out at the 1st spreader so it is about 20`long. Again, May I suggest that the mast be taken down for re-wiring. Have a wonderful day. Marius Corbin