So you want to build a warship – Part 5

Part 5 – Fitting Out
So far, everything seems to be coming together quite nicely.  We’ve clearly got the outline of a fine looking ship.  But looks can be deceiving, and we’re about to expose some problems caused by early design and construction decisions.  The choice of ship, while being a sleek and handsome design, presents its own problems when it comes to installing equipment to make her a fighter.

Just to recap, we’ve got a hull frame that’s 56.25″ long, just under 6″ wide, and about 3.5″ deep, deck-to-keel.  1/8″ ribs are spaced every 1″ (some are a little farther apart, to compensate for hull contour lines that don’t line up at even inches).  A solid oak keel, 1/2″ high and 1/4″ thick, extends from the very first rib to the 38th, where a pair of parallel skegs angles upward toward the waterline at the stern.  The skegs overlap the keel for a span of 3 ribs, making what should be a very strong point to eventually attach a recovery line.  The cap rail is in place, and the whole assembly feels feather-light, but incredibly strong.  No stringers are installed or planned.

Next on the agenda is to install propellers, shafts, and rudder while it’s still relatively easy to reach in between the unskinned ribs.  The expectation is that this job will only need to be done once – after the hull is skinned, it’s got to be a lot more difficult than it would be now.  Indeed, with the close rib spacing, it’s still a challenge for somebody with fairly large hands.

General layout of equipment is partly dictated by the plans, and also highly dependent on the need to balance and ballast the ship.  Locations of cannons, propellers, and rudder are specified in the plans.  To a large degree, these locations also dictate where other equipment, such as the rudder servo, can go.  Motors and propellor shafts are a little more flexible, however.  Not quite recognizing and appreciating this flexibility was the first major error in this ship’s construction.

I wanted to clear out as much space amidships as possible, for battery placement.  To accomplish this, as well as to be able to drive all four shafts from two motors, I chose a chain drive system, using parts from  Serv-O-Link Corp.   Serv-O-Link has a good selection of 1/8″ pitch Delrin chain and sprockets, as well as small gears.  The use of sprockets and chain would allow the final drive ratio to be “tweaked” by changing sprockets, plus it should be a simple matter to drive all four shafts, or just a pair, from a pair of counter-rotating motors, in a very flexible arrangement.  Also, the motors could be mounted parallel to the shafts in a sort of “folded back” configuration, instead of inline with them, making a larger space ahead of the motors for holding batteries and other equipment.

Ribs aft of Rib G were deliberately left with extra material at their bottoms to provide support for the propeller shafts.  Locations where each shaft is to pass through each rib was marked on the rib, but no holes were cut prior to assembly.  This presented a minor problem of having to drill what amounted to a hole over 12″ deep, through multiple ribs.  This problem was overcome by jamming a spade-style drill bit into a section of brass tubing to create an extension.  A short piece of rod, the largest diameter that could fit inside the tubing, was inserted into the drill end, to keep the drill’s chuck from crushing the tubing when it was tightened down.

Photo 1 shows the general layout, with propeller shafts set temporarily in place, as well as motors, batteries, and a stern cannon from another ship.  A problem which is visible in this photo, but wasn’t apparent to a rookie builder at the time, was the height of the #3 turret.  In the photo, it can be clearly seen that the top of the magazine is a good inch above the cap rail, and the barrels themselves are probably 1-1/2″ to 2″ above where they should eventually be.  Not only is this going to set the barrels to high, the weight of the cannon set up so high are going to hurt stability.  However, as can also be seen clearly in this photo, there is ample space for the accumulator to sit between the inboard propeller shafts if the ribs are cut down to allow it to sit deeper.  Right now would have been an excellent time to do this, but it wasn’t – when it was finally done, it was much more difficult, due to the work that was done subsequently.

Photo 1.
Test Fitting.


Propeller Shafts

One of the major successes of this particular construction project was the development of a very good  stuffing tube .  This design was used for all four propeller shafts, plus a shorter version for the rudder.

The ship’s plans show a stand-off just forward of each propeller.  Each stand-off is apparently there to set the propellors’ locations, and provide a bearing for the shaft.  Stand-offs were build by soldering brass airfoil onto very short versions of the stuffing tube, as shown in Figure 1.  A small wood block was set between each airfoil, to set the angle – this block is fastened to a rib to create a strong support for the shafts.  Sections of 1/16″ brass tubing are inserted through the airfoil, through a small hole in the short stuffing tubes, to allow greasing of the bearings.  Note that the main stuffing tubes end where the shafts exit the hull.  This leaves the shafts exposed to water, where it is possible to pick up weeds.  This has proven to be much less of a problem than it might appear to be.

Figure 1.
Propellor Shaft Stand-off.



As noted previously, a shorter version of the stuffing tube was used for the rudder post.  This turns out to be overkill, since the rudder doesn’t need to turn nearly as much as the propellor shafts do.  Also, the upper end of the rudder post is above the waterline, so there isn’t any real need to provide a watertight seal.  However, materials were available and the design was working very well, so the same method was chosen to mount the rudder post, even though it is a bit over-engineered.  However, the diameter of the over-engineered rudder post just happened to match up very well with the space between the skegs of the hull frame, so centering was no problem at all and no spacers were needed – the rudder slipped very nicely between the skegs!

As for construction, the rudder was cut out of brass sheet and soldered to the post.  This particular ship used a two-piece rudder – a fixed forward piece, and a rotating section that is attached to the post.  The fixed section was soldered to the outer rudder post stuffing tube, making a complete rudder assembly that could be mounted into the hull as a unit.  Photo 2 shows the completed rudder assembly and the propellors with their hafts and standoffs, after the ship’s completion.

Photo 2.
Propellor and Rudder Details.

Control of the rudder provided an interesting challenge for a builder who had never seen a model warship before (or, for that matter, had even examined a R/C model boat!).  Therefore, the rudder control mechanics are a bit unusual.  Having lots of Delrin chain and sprockets available for the drive system, I decided to use the same method to control the rudder!  The servo is mounted on a wooden “carriage”, that really is only a pair of wood blocks that each end of the servo is screwed into.  Each block has a pair of 1/8″ holes drilled in it on either side, and a pair of 1/8″ brass rods are passed through the holes.  The rods are passed through a pair of expansion springs and mounted into brackets.  The springs force the servo forward on the rods, to keep tension on the chain.  One needs only to push the servo towards the stern to slip the chain on or off the sprockets.  Sprockets on either the rudder or the servo can be changed to get the best steering performance.  While this is an odd setup, dictated mostly by a combination of ignorance and materials on hand, nonetheless it has worked flawlessly.  The rudder and its control servo can be seen immediately after installation, in Photo 3.

Photo 3.
Test Fitting (another angle), Showing Rudder Installation.


Motor Mounting and Shaft Drive

As anybody who ever had a bike knows, a drive chain needs to be kept under tension.  To keep tension on the ship’s drive chains, a “floating” motor mount was built out of a piece of 1″ aluminum channel.  The channel had arcs cut out to keep the motors positioned, and holes cut in the bottom to allow zip ties to secure the motors to the channel.  A pair of larger holes were drilled, to allow cap screws to pass through the mount into captive nuts expoxied to the keel.  Coil springs around each cap screw, below the bracket, provide upward tension, which can be adjusted by turning the cap screws.  Backing the cap screws raises the bracket, under spring load – cranking the cap screws down all the way compresses the springs fully, and drops the bracket down to a point where the chains can easily be removed or installed.  Figure 2 illustrates the motor bracket assembly.

Figure 2.
Motor Mounting Bracket.

Attaching the sprockets to the motors was simple – the chosen motors have 1/8″ splined shafts, which grip the Delrin sprockets quite nicely.  The motors seem to generate pretty good torque, which is multiplied by the difference between the smaller sprocket on the motor and the larger sprockets on the propellor shafts.  Slippage of the driven (propellor shaft) sprockets was a problem for quite awhile, however, and various solutions were attempted.  What ended up working the best, and was quite simple as well, was to file a flat area on the propellor shaft, and place a dab of thick CA glue on it before sliding the sprocket over the shaft.  Obviously, it can’t be driven immediately – the glue needs to set up.  Once it has, though, there has been no more shaft slipping.

Motor Control

I chose to follow some advice that several veterans gave me regarding motor control:  Keep it simple, & don’t worry about intermediate speeds – you’ll find yourself going full speed forward or reverse most of the time, so speed control isn’t something that’s going to buy a lot.  The classic servo-switched forward/reverse circuit was installed as shown in Figure 3:

Figure 3.
Motor Control Circuit, As Installed.

Note that the motors are wired in series, so that they turn in opposite directions.  The switches are operated by a cut-away wheel on the servo – moving the servo one way closes one switch, moving the servo the other way closes the other switch.  The motor(s) are connected through the “C” (common) pole of each switch, through the “NC” (normally closed) pole, to the same terminal of the battery.  When the servo activates one of the switches, it breaks the C-to-NC connection, and closes the C-to-NO (normally open) connection.  This connects the motor to the opposite terminal of the battery, completing a circuit and driving the motor(s).  Operating the servo the opposite direction closes the other switch, completing a similar circuit, but with opposite polarity, driving the motor(s) the opposite direction.  The circuit is not polarity-sensitive; it works the same regardless of where the battery and motor(s) are hooked up.  If the direction of rotation is not what you want, simply reverse the battery connections or motor connections.  Also, most radios have a switch to reverse the servo direction.  A schematic diagram of the motor control circuit is shown in Figure 4.

Figure 4.
Motor Control Circuit Schematic.


Now For The Important Stuff!

Our whole reason for being is to to be a gun platform.  Therefore, we have to install guns!  A couple of mistakes were made in this project, that I swear will never be made again if I can help it:

  1. When I figured I was about two weeks from being ready for cannons, I decided to check around and see what was available.  To my shock and horror, the best I could come up with was a set of new guns “around September” (this was March)!  This certainly would not do!  As luck would have it, I managed to make contact with Phil Sensibaugh, of the Midwest Battle Group, and he was nice enough to sell me a pair of used 3/16″ triple Indiana guns and put me on the list for a third new one.  I was able to install turrets #1 and #2 in a reasonable time, and eventually got #3.  The lesson I learned was: Make sure you have the guns before you build the ship – build the ship around the guns!
  2. Space and clearance was a real issue in the tapered bow of USS Pittsburgh.  I mounted #2 turret over the top of #1, about 1-1/2″ higher, so that everything would fit.  This made rotation very unreliable, as the #2 rotation groove lined up about an inch higher than #1, and the cable wouldn’t stay on like I’d hoped it would.  The height of turret #2 did nothing for stability, in a ship that’s pretty narrow to begin with and wants to roll.  I ended up having to cut and grind some material out of several ribs so that I could set #2 turret in at an angle, and also ground off a corner of a “L” fitting attached to the #1 turret’s actuator for clearance.  This got the turrets at the same height, which cured the rotation problems and helped stability.

I developed an interesting mounting method for the Indian cannons.  What I had seen, and written in other peoples’ recommendations, was to epoxy the cannons to a mounting board or frame, that is then attached to the hull of the ship.  I wasn’t keen on epoxying anything onto my guns, plus I didn’t think I had extra room below them for a mounting board.  What I did instead was make use of some of that eight feet of aluminum channel that I had to buy for the motor mounts and fabricated some custom gun brackets.  I cut slits in the bracket to pass a hose clamp through, and drilled a bunch of holes in a random pattern on the bottom/top side of the bracket.  The brackets were attached to the hull of the ship inverted, that is with the channel down, and the flat surface up, using epoxy. The holes drilled in the channel were to allow the epoxy to have something to grab hold of.  A hose clamp gets threaded through the slits, and clamped around the guns’ accumulators!  Some care and precision was needed to make sure that the bracket lines up on the point where the center of the cannon needs to be, but once it’s done it’s a nice solid mount, with just a little give.  Also, it’s easy to adjust the position of the cannon, and very easy to remove it for service.

However clever this arrangement was, there is no denying the fact that it would have been easier if done first!  Everything else is secondary, but the guns have to fit or you don’t have a warship!

With the cannons, propellors, shafts, drive motors, rudder, rudder control servo, and motor control servo and wiring installed, USS Pittsburgh is ready to be skinned.  The CO2 delivery system was assembled per Safe, Effective CO2 Delivery.  Items such as the adjustable regulator rack and various fittings were left unattached, so that they could be moved around as needed to balance the ship.

Skinning the hull, decks, and superstructure will be covered in the next article of this series.

Part 6 – Skinning the Hull; Decks, and Superstructure