DEPRESSION SERVO CABLE RETAINING DECK

One area of concern with rotating cannons is that of the depression servo cable. The depression servo sits on top of the magazine cover, and its cable course over the edge, and down to wherever the builder has routed the rest of the cable run to the radio box. Our trouble is that the cable is forced into unpredictable snags and twists as the cannon rotates, and usually finds some way to get caught up in the rotation drive, be it chain, O-ring or steel cable.

Various methods have been tried to prevent this. There are spring-loaded cable tensioning devices that attempt to keep the cable under constant restriction, forcing it to remain straight and level at all times. There are rubber bands doing similar jobs. And there are various types of supports that try to keep the cable near the deck.

In my H-39, I decided to make use of a 2 layer approach. I built a deck that supports the servo cable, and keeps it from falling below into the rotation drive. Everything below the cable deck is prevented from interfering with the cable, and the only thing above the deck is the cable itself, and a bit higher, the main deck. The deck is nothing more than a slightly flexible, clear plastic sheet, about .060" thick. It is in 2 pieces, and taped to its supports. Its flexibility allows it to be installed and removed quickly and easily.

To understand how it works, and how it should be installed, you have to understand the geometry of the Standard, or Indiana cannon. The portion of the cannon that needs to be dealt with is everything above the ball valve. This is mainly comprised of 2 discs of plastic, about 1" tall each. They are stacked one over the other, with the lower measuring 2 7/8" in diameter (the manifold), and the larger at either 3" or 4" in diameter (the magazine). For most cases, ships equipped with depression and rotation are BBs and CAs, and utilize the 4" magazines. The manifold has 2 1/8" or 1 5/16" groves cut into its outer surface. The rotation O-ring or cables rest in these groves in constant contact with about 50% of the groves' circumference, and under tension.

It is here where we have our problem. The depression servo cable can drop into the open area near where the rotation drive and groves meet, and be pulled into the contact zone. This damages the cable and sometimes the rotation drive. It almost always throws the turret indexing off, requiring a trip to port to clear the mess and reset the turret index.

The cable deck interferes with the interference! It eliminates any open space that has the potential to allow the cable to drop. Setting it up is simple in theory, though it requires careful execution.

The cannons and blast shields must be in the hull during the setup. The blast shields need to be of a type that are firmly mounted, and not free to move around. In the H-39, the blast shields are .060" plastic, held in place with a few rib-mounted screws and 1"-2" overlapping ends. The rotation system may be removed, and might actually make the installation of the deck easier.

Cut a strip of balsa beam that will fit between the blast shields when placed beamwise in the hull and mounted to the underside of the magazine. I used a piece of handy 5/16" x 5/8" balsa. Push it up against the underside of the magazine's overhang. This beam will help you determine where to position the deck's mounting flanges. You can hold the beam in place with one hand, or tape it there.

Move one end of the beam against the blast shield, and make a mark with a pencil by drawing along the shield using the beam as a guide. On dual cannons setups, make marks on each shield ahead of the forward cannon, between the 2 cannons and behind the rear cannons. On a single cannon setup, make marks ahead of and behind the cannon. Using a flexible ruler, connect the marks and draw a continuous line. This line represents the level of the magazines' bases. When you connect the marks, do so with the blast shields mounted in the hull. When they are mounted, they warp and bend. If the lines were drawn outside of the hull, they would not be true and level when bent and installed.

The deck will need to extend 1" beyond the manifolds lengthwise in the hull. So your supports will need to as well. At this point, it might be well to note that the blast shields to which the supports are affixed will need to be 1 piece units. If you have a joint in this region, either replace the shields with a single unit, or permanently join them. A joint in this region leaves the possibility of a round passing through and rupturing an accumulator, as has been seen more than once in the Midwest Battle Group.

The deck supports are 1/8" by 1/4" flexible balsa strip. Cut them to length and glue them to the blast shield. To position them correctly, press them against the shield with one of the thin edges facing upwards. The top edge of the strip should be about 1/8" below the line you drew on the shield. Try a dry fit first, and when you are satisfied with how it looks, glue it in place permanently. The H-39 shield/deck support assemblies have been in and out of the hull, under tension and without, many times with no trouble. There is a third support that needs to be built. It is a simple block of wood. It should be 2" wide, and as long as the gap between the magazines on a dual cannon setup. It will be glued to the accumulators and its top should match the level of the side supports. Use a straight edge to verify the height. On single cannon setups, you can fashion 2 blocks to do the same job, or use shield-to-shield strips to do a similar job.

Look at the first picture to see the basic parts. You'll notice the ship's framing, a cannon support plate and associated hardware, main deck and blast shields. The cannon itself is seen head-on, with accumulator at the bottom, the manifold and rotation grooves, and the magazine and depression servo/cable above that. These should be familiar to you. The cable deck is green. The deck supports are red and attached to the dark blue blast shields. The tape that holds the deck is light blue, and can be seen at the junction of the cable deck and blast shields, just above the deck supports.

You now have the supports needed to mount the deck. The deck itself is made of 2 pieces of flexible plastic (preferably clear, so that you may see what's below it) that are taped in place with electrical or masking tape. The drawing shows you the basic shape. It follows the curve of the blast shield along one side of the hull, and the cannons' manifolds along the centerline. It presses up against the underside of the magazine.

The next picture shows the setup from above. It only shows one half of the cable deck, outlined in black.

Carefully trim the cable deck a bit at a time until the shape is correct. First trim the inner arcs where they come against the manifolds above the rotation drive grooves. If you have a compass, plot the center points of the cannons (measure from magazine leading edge to leading edge to find their separation distance), and draw an arc that is 1/4" bigger than the arc of the manifolds. There needs to be a gap between the edge of the cable deck and the manifolds so that no binding occurs. Once you have this complete, trim the edge of the deck where it meets the blast shield. You'll have a short length of decking between the 2 manifolds, and fore and aft of them. It is tempting to cut these to match the centerline of the ship. Don't. Leave it about 1/2" to 1" on the opposite side of the centerline so that both halves of the deck will overlap.

At the blast shield, the cable deck rests on top of the support and is held there by a strip of tape that is half on the deck, and half on the shield. At the ship's centerline, the port and starboard decks overlap about 1", resting on top of the center block, and free floating at the ends. The entire exposed joint areas are taped to eliminate any edges that might snag the cable.

So, with five pieces of tape, the deck is secured. As the cannons rotate, you'll hear a swishing sound as the magazines slide on the cable deck. As long as the undersides of the magazines are smooth and have no protrusions, there will be no binds. The depression servo cables should be set so that they have enough slack to allow your maximum planned rotation travel, and then a few degrees more. The remainder needs to be anchored to the cable deck. This keeps the cable from trying to get between the magazine and the deck. The critical point in the deck fitting is with the block between the 2 cannons. It is here that the cable will bind up if there is a low point. Be sure the block pushes the deck up against the magazines.

The depression servo cable also needs to be taped securely to the along it length as it lays on the magazine cover, and down the side of the magazine. This prevents snagging on the upper deck, and keeps the cable low against the cable deck, forcing it to bends in some semblance of order at the cable deck level.