Steering and throttle cable routing

Control cable routing is often a bit of an afterthought. In a small, simple boat, it's often OK for the designer to more or less ignore the engine controls, and trust that the builder will know how to install them. That approach doesn't work so well for a larger vessel, like the Starwind 860 trimaran, in which the exact routing of each control cable must be planned out to avoid conflicts.

The mechanical connections between the Starwind 860's engine and helm include:

  • Pull-pull cable steering, using two 6 mm Dacron lines
  • Throttle and shift, each of which is a standard Morse, Teleflex or similar control cable

There will also be an electrical harness for the engine instruments, and a separate electrical harness for the real loads (radio, lights, etc.).

Pull-pull steering requires that we run the steering cables in perfectly straight line segments, with turning blocks (probably 29 to 38 mm Harken Classic or similar) wherever the cable bends. This is a bit more work to install than push-pull cable systems, but push-pull creates a huge dead zone that drives the helmsman insane, and its cable can't be bent around sharp corners. Pull-pull is easier and cheaper than hydraulic steering for a boat of this size.

The throttle and shift cables must have a fair lead off the engine, sufficient slack to handle the engine's steering and tilt movements, and a reasonably straight run without any kinks or sharp bends. The only alternative here would be fly-by-wire, which to my knowledge is not yet available on 60 hp outboards.

We could route all these cables under the cockpit sole. In the Starwind 860, though, there are two 140 litre fuel tanks and a battery bay under the sole, and the control cables would have to run above them- making it hard to remove a tank or battery without first disconnecting the controls. So we'll run them under the seats instead; there is enough room under the starboard cockpit seat and entry step for all four control cables and the engine instrumentation wiring harness. The corresponding space on the port side will carry the main wiring harness.

The beauty of working in true 3D at the design stage is that we can easily check for conflicts. Will the captain's legs bump the steering lines when he sits down? Not anymore, after tweaking the line runs a bit.

Are there any points where a control cable will have to take a sharp kink, which would cause it to bind or wear out? Again, nope. Planning this out in 3D ensures that we can leave enough room for appropriate curves in the throttle and shift cables.

At the engine end, we can tweak the alignment of the control cables until everything looks roughly as it should. Since the engine has not yet been chosen, some of the detail here will be left as "figure out in the shop". The bisector lines at the bends near the bulkhead are pretty much fixed, though, allowing those turning blocks to be laid out now.

The rope steering system used in the Starwind 860 is a slightly beefed up version of that described by Harry Bryan in WoodenBoat 227 (Jul/Aug 2012 p48).




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