Ohio Class, Ballistic Missile Nuclear Powered Submarine, USS Kentucky SSBN737

Splitting the hull, and fitting bulkheads:

The very first step in this process, is to put the hull into water. Allow the hull to roll, and settle. Now, using a permanent marker, mark the top most part of the hull. Why all this? Well.. since we have made this hull from epoxy and glass fiber, no matter how careful we have been, then there will be a little more resin here and there, than in other places, giving it an uneven balance. Why force our self to use weights and flotation material compensating for this later, when this small step does the job for us?

The Ohio hull splits right at the middle (Between black and brown area). Very very carefully draw a line around the main part of the hull at the exact middle! At the bow, follow the outline of the sonar dome and travel over the hull, leaving the entire sonar dome as part the lower half.
At the tail section we need to go across the top and to the other side as well, leaving all rudders fitted to the lower half. (This is the only way we can ensure proper rudder control, and fixture) This type of cutting is called a "Z" cut. Then, using a thin cutting disk, separate the two halves all the way around.

There are a number of reasons why I did not choose to make the sonar dome a part of the upper half, though it would mean that the cut would travel under the hull, thus making it harder to spot. Leaving the dome on the upper half would:

  • Make it harder to put down the top half when removed,
  • cause the forces from any impact to be absorbed by the lighter half of the two hull parts,
  • complicate the front most MBT and bow thruster pump orientation,
  • make an unbalanced hull when sailing without the top in test situations.
Splitting the hull along the length IS pretty tricky. I drew a line with a marker, and build the setup in the picture.
The sledge holding the drill could slide, and the hull could not move anywhere in the box it was sitting in. The sides of the box was shaped to match the shape of the hull, so the aft and bow end also could be cut using the rotary cutting disk. Be careful not to run the disk too hot, as this might damage the epoxy / PVC.

Not in picture: Below the rear end of the drill, there is an aluminum bar supporting the drill to a firm hold, as it's very important that the drill can not get out of alignment!

After cutting the whole thing, and using a knife to cut the foam within, the two halves came apart. I haven't seen the inside mockup for about two years, so this was a rather big step.

The wooden stick served as a guide back when there was nothing else to guide the mockup's, keeping them aligned along the center axis.

After digging out the expanded polystyrene, the hull finally looks like something that will end up being a sub, and the last stretch of the project can begin. Now it's time to put together all of the components produced for the last many many month.

The duct tape that formed a membrane between the mockup and the resin let go real easy, so the removal of the mockup's was done quickly. (Still the small white balls was all over the hose afterwards..)

A close look of the aft section. This area will house the aft MBT later, and shortly I'll fit the rudders and dive planes as well.

The edge around the entire cut need to be filed and in two spots repaired, as the disk did wobble a bit. However, I'll wait with this until the two halves are more stable, so I can get a better view of where I need to take action.

I had to see how it looked with all of the WTC's in it, missing is only the not yet constructed pressurized air system / tank. I also got into thinking about how to fit the WTC's. The original idea with a series of disks forming walls, holding the WTC's need to be altered a bit, since the brown PVC tube bents slightly after cutting it, making the sub too thin at the middle. In other words, both the top and the bottom half need to be supported into right (round) shape.

This might give the impression of a lot of waste space, but keep in mind that the air system including the air tank is still not produced. There will still be some space to spare though, and I'm thinking about making a third WTC for periscope control, bow thruster pump, receiver, and some electronics.

Next I'll drill a series of drainage holes in the very bottom of the sub. The diameter of these holes should be app. 0.2 (5 mm), and close to 2 (5 cm) apart. They should all be aligned down the center line, so that they are placed in the lowest place possible. (As this is a "wet hull" sub, the hull is flooded during operation.)

This completes the splitting of the main hull, and now it's time to fit the missile deck.

Take the missile deck, and temporary put on top of the sub. A line is then drawn around it, and then the missile deck section is removed yet again. Now a second line is drawn inside the outline, and the area left is cut out. The distance between the two lines should be such that the main hull sticks app. 1/4" (6mm) past the inside vertical edge of the missile deck. This enables us to glue the missile deck on to the mail hull, without the glue strip being visible from the out side.

First we need to cut out the part of the main hull which is under the missile deck. We need the space for stuff, and we need to reduce hull weight as well. Another reason to cut this section of the main hull, is that it allows us better control of any entrapped air.

The electrical jig saw proved to be perfect for this job, but the blade did run rather hot! Besides that, I have noticed that cutting resin and fiber cloth really wears down the cutting tools. This blade was dead afterwards..


Here's a view of the finished job, and all three major hull parts (main hull upper and lower part, and the missile deck).

The weight removed from the top half of the main hull by cutting out the area below the missile deck was app. 1/3.

Detailed view of the aft end of this step. Next is to fit the hulk heads in the top half, and prepare for missile deck fitting..
Notice that the hole in the top half of the hull follows the inside outline of the missile deck. At the ends, it'll be clued straight on, but down the side (along the "crack"), the glue line is some what further up, why the hole shows this in it's outline.

Strange view? Well...yes. It's a look down the hole for the sail, seeing the very bottom of the sub about 19 cm (7 inch) below missile deck surface. The hole down there is one of the drain holes, of which there are app. 25.

Notice the reinforcements of the gathering between the main hull tube, and the green-like bow part. It's split at the very bottom allowing water to drain undisturbed.

This is a look inside the top half of the main hull with the missile deck test-fitted on, seen from the bow.
Notice the hole for the sail in the missile deck, and the aft end app. 188 cm (74 inches) away!
It's a boomer all right...

Now let's make and fit the bulkheads..
The bulkheads serve two purposes. First is to stabilize the hull, and second is to work as a mounting bracket for the WTC's and MBT's later on. The material chosen for this task, is a 10mm (0.4") thick plexi glass sheet. (Seen on the picture with the protective coating still on one side, and the marked up surface facing up.)

It's a tricky material to work, but when done right, it's strong, light, and relatively inexpensive. The disks was cut using a plate cutter, and afterwards the inside hole was cut. Notice that the inside hole for the WTC is off center, this is so in order to lower the
center of balance to be below the center axis of the sub. (Thus giving upright stability)
The inverted top to the right shows the completed bulkhead tops that go into the top half of the hull, thus stabilizing the structure. When these are fitted, then the missile deck can go on.

This image shows the original bulkheads, made of plexi glass. Later these was replaced by some made in a plastic kind of material. Plexi glass is just to brittle, I found out.. the hard way.
Fitting the bulk heads are pretty straight forward. The two long aluminum bars on the sides of the upper hull part, ensures that the hull part will have the right width afterwards. The small aluminum pieces that the bulk heads are standing on, ensures the right location of the bulk heads. The masking tape just holds it all in place, until the resin has cured.

Remember to rough all the edges prior to gluing.
This image shows the indexing plates that will extend down and into the bottom half, when the sub is assembled.
They also serve to add strength to the structure, right at the gathering between the brown main hull pipe, and the green self-made part.

Why are the indexing plates not in the bottom half? Well.. this way they'll even serve as legs when the top is put down somewhere, ensuring that the edges of the upper hull part are kept intact, and clean.
The original bulkheads were of plexi glass, but it proved too brittle in the end, so a mold was made from them, and new ones was cast in a plastic-like material.

The mold was made by putting the nicest of the original ones in a box, and pouring silicone over them. After curing, the mold was used again and again to produce all of the bulkheads.
Back at the dock, brass brackets was made by hand, to go over the modules and support the modules as well as possible.

The funny "fork-shape" at the lower end allows hoses and wires to run next to the weights.
Left: Notice the holes in the bulkheads. They will support the push-rods for the rudders.  The tunnel in the middle will support hoses etc.

Right: This gives a nice overview of the fitted bulkheads, allowing the weights to sit at the very bottom. The "fork-shape" allows hoses and wires to run next to the weights through out the sub, front to back.

Left: A view of the fitted bulkheads towards the bow area, and at the fitted air tank.
The two bulkheads closest to the camera are for the MBT1. (Later removed)

Right: This shows the WTC2 and the MBT2
(Later removed) at their places, resting in the bulkheads, and with the brass bracket in place. (But not bolted yet)

NOTE: The number of bulkheads was heavily reduced in the stage two rebuild because the dive system was changed from two ballast tanks to one, central ballast tank.
The bulkheads all have a small brass nipple with an M3 thread inside drilled into the top. This allows the brass bracket to mount.
The H shaped support bracket holds firmly around the bulkheads. The space between the lower end of the bulkheads matches the width of the support brackets bottom piece, thus locking it.

NOTE: The H bracket is not glued to the bulkheads, but to the module. This is for illustration only.
The H bracket is glued to the module, and now the module is ready for the final piece of mounting: The brass bracket. The brackets was made from the same tube as the modules them self, as it proved strong and just flexible enough.
Here the brass bracket hold the module, missing is only the M3 brass bolts.

This method gives a strong and secure fit of all modules. They can not slide, turn, or rise out of their bulkheads. Water, hoses and wires can pass, and the hull is supported as well.

Notice that the very top of the H bracket arms grasp the brass bracket as well..

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