Controlling the Hunley

How did the crew control the Hunley?

E	xcavation uncovered the lever used to control the Hunley's dive planes in the forward location occupied by Lt. Dixon, the commander, a very different mechanism from that depicted in the historical material.

Nearly nothing more has been published about the control mechanism since the discovery in late 2002. Based on study of the few pertinent photos, I've come up with a speculative reconstruction using simple linkage rods as illustrated in the accompanying animation. The mechanism has five major parts.
o	The tiller itself (green in the graphic) bent for the offset connection to:
o	A long control rod located under the bench and mostly not visible in the graphic
o	An offset lever attached to the aft end of the control rod (shown in blue)
The first three parts are bolted together and rotate as a unit.
o	An offset lever fixed to the rudder control (in blue at the top). This mechanism rotates as a unit with the rudder exterior control arm, ghosted in the animation.
o	An articulating linkage rod (also in blue) connecting the under-bench assembly with the rudder mechanism that runs through the aft tank

As the tiller is moved to port or starboard, the linkage rotates the rudder control so that it moves in the same direction, turning the boat in that direction. Notice that the mechanism depicted clears both the propeller shaft that penetrates the aft bulkhead and the inter-tank pipe (black at the lower left) that runs the length of the cabin. The bench, crank, and prop chain gear are shown for reference. The linkage rods in blue are located aft of the flywheel (not shown) against the aft bulkhead.

The apparatus in motion, looking forward

See the rudder mechanism pop-up, linked below, for a discussion about how the rudder linkage moves the rudder.

The following material is from steering speculation prior to and soon after the discovery of the tiller. Our discussion group considered two major possible arrangements for control of the rudder:

o	A wheel, tiller, or other control was located forward and operated by the commander. This is the setup shown by Alexander and by Lake in the historical drawings.
o	The control was located aft and operated by the seventh crewman who in addition to cranking was responsible the aft ballast tank controls.
The major support for the second possibility is the lack of evidence of an internal linkage mechanism. Alexander's drawing showed cables set high in the cabin but no signs of such an arrangement are evident. There has been mention of rods located under the crew bench and something is visible in a published photo. This may also be associated with an air circulation system. I strongly favor the first possibility. I picture the commander seated to look out the forward view ports, one hand on the dive lever and one on the wheel. I think control required a rapid response by the helmsman to the situation visible outside, and I don't think that kind of response would have be possible with relayed commands. In addition to the communication problem, it would not be possible for the seventh crewman to crank and steer simultaneously. Short of re-organizing the currently accepted crew positions, the second possibility seems highly unlikely to me.

A look at the cabin cross-section helps define the problem. A linkage along the top of the cabin must allow for the the two hatch openings. The entire upper port side must consider the heads and backs of the crew. Nearly the entire lower starboard side and the floor must permit free movement of the crank and foot room for the crew. This leaves two possibilities for routing the linkage:

o	The part of the upper starboard quadrant closest to the hull
o	Under the bench

Kevin Wilcomb provided these early speculations. Although the most recent information contradicts some details, much is consistent with the mechanism suggested below.

Kevin's early steering speculation draws on 18^th century locomotive technology. A single control rod runs beneath the bench, supported by brackets. (I've ghosted parts of the drawings that clearly don't match the known mechanisms.)

Steering speculation sketch, Copyright 2001 Kevin Wilcomb

According to Kevin, with the exception of the gears in the compensation mechanism, all of these parts could be scavenged from the brakes and other locomotive gear in service at that time. The next figure presents Kevin's later reconstruction.

	He's replaced the the aft section tiller rod pictured above with a gear and rocker assembly. He offers that this increases the range of the rudder movement and thus maneuverability of the boat. (Kevin places the linkage forward of the propeller gear in this early drawing. It appears actually to be aft of it.)
	These graphics Copyright 2001 Kevin Wilcomb and used with permission.

At the beginning of the second excavation session, the Friends of the Hunley described the area under the bench as "heavily concreted and the sediment has a lot of iron in it". They expected to find personal effects of the crew here, thinking it a logical place for stowage. The space could have served both purposes if any control linkage was protected.
In November 2001, near the end of the second excavation session, the Friends provided a photo to the press showing a tiller in the forward hatch section. Two weeks later they reported the tiller rod as hinged at the bottom and attached to connections leading back into a pipe that runs under the bench. Aft, it runs over the bulkhead to the rudder. The description is a little confused and I've attempted to match it to my own thoughts. Mark Ramos sent me information about various small boat helm's from a Power Squadron maintenance manual. In particular, the "lever-and-rod steering, the oldest and simplest system" with a pivot and bell crank, seems close to the Hunley mechanism. The under-bench part of the mechanism pictured is essentially the same as the equivalent part depicted in Kevin Wilcomb's drawings above.

Mark Ramos thinks an angular feature above the aft bulkhead discernable in some photos and shown in some of the renderings on these pages suggests a chain cover or guide. Connecting the lower and upper control rods with a chain would facilitate routing the linkage around the prop shaft and provide for optimizing the control ratio. A simple connection like that on a bicycle however rotates the rudder control in the same direction as the tiller resulting in a reversed rudder (move the tiller to port to turn starboard). Intuitive steering requires a more complex chain reversal mechanism. For this reason, I favor the linkage rod mechanism described above.

On the archaeology page I once speculated that the Hunley was originally fitted with a rotating, vertical steering mechanism similar to those depicted by McClintock and Alexander. If so, we might consider why it was changed to the tiller. A small horizontal wheel, as depicted by Alexander, would provide little advantage without a low-ratio gear. Such gearing would make it difficult for the operator to determine rudder position by looking at or touching the wheel. A horizontal tiller, as drawn by McClintock, could provide both leverage and position feedback, but would not have much clearance in the cramped available space. The vertical tiller provides mechanical advantage, good position feedback, uses the space well, and probably was worked more intuitively in combination with the diving plane lever that operated with up and down motion.

What do you think? E-mail me with comments

How did the rudder work?