Catamaran vs monohull: navigation equipment that changes

Two boats of equal length can require very different installations. A cruising catamaran spreads working positions, engines and steering gear across a wide platform; a monohull concentrates much of the equipment along a narrower hull and may operate with substantial heel. Neither description proves that one needs a more expensive brand. The useful comparison is where the crew works, what the sensors measure and how the installation will be maintained.

#The differences that change the quote

#Screen size: use the watch position

Start with a full-size paper template and the distance from the watchkeeper’s eyes. A broad catamaran console can accommodate a larger display, but a raised screen that requires leaving the seat or stretching across controls may be less useful. Check the saloon view separately: a screen indoors is not permission to abandon an effective lookout.

On the monohull, test reach while braced and while working lines. On either vessel, ask the crew to change chart scale and select a route using a demonstration unit. Consider physical controls or a supported remote when wet touch operation is difficult. These are installation decisions, not a rule that every cat needs 16 inches and every monohull needs nine.

#Depth in one hull or two?

A second catamaran depth sensor can be useful, but only if the readings remain identifiable and the systems are designed to coexist. Ask how source selection works on each display, whether the chosen sounders can operate together without unacceptable interference, and which reference each readout uses. Two numbers silently alternating in one field make a system harder to understand.

A sensor under the port hull does not measure a rock beneath the starboard hull. Nor does a downward sounder reliably reveal what lies ahead. When entering unfamiliar shallow water, combine charts, tide, observations, appropriate speed and a plan to stop or retreat. On a monohull, an offset labelled “below keel” must reflect the actual loaded geometry; on a cat, record both keel and sensor locations. Use the depth-refit worked example for reference arithmetic, not as a universal offset to copy.

#Pilot selection needs the steering drawing

Do not multiply or divide a monohull pilot package by two to equip a cat. Request the real linkage layout, loaded displacement, ram capacity where applicable, full travel and mounting constraints. The Raymarine drive-selection reference and hydraulic pump guide illustrate why steering type and hydraulic volume are selection inputs. An installer must apply the chosen manufacturer’s instructions to the actual vessel.

For either hull type, ask what happens when the pilot computer loses heading or the network fails. Confirm the route back to manual steering and the physical disengagement procedure. A premium display package leaves this mechanical question unanswered. Remote support, an accessible drive and a documented spare-parts plan may be more valuable than another screen.

#Cable length, cameras and engine identity

Trace cable routes before requesting a firm installation quote. On a cat, a sensor close in a straight line may need a much longer route through service spaces and across the bridgedeck. Measure the full route and voltage at the far end under load. The network drawing should show terminators, power feeds, switches and accessible junctions; do not improvise extra network power feeds without the manufacturer’s approved arrangement.

Cameras can help with blind quarters and docking, but test their field of view and latency and keep the lens-cleaning route practical. For twin engines, verify the display labels by observing one engine at a time through an appropriate commissioning procedure. A neat “port” label is not evidence that the data actually comes from port. Leave a source and device-instance record aboard.

#Worked example: a 42–46-foot cruising cat

Assume a raised starboard helm, a sheltered saloon chart position, one functioning depth source, and a pilot and VHF that can be retained. Start with Axiom+ 12 at the helm and Axiom+ 9 inside, then assess Quantum 2 and AIS700 for the passage brief. The large-boat hardware basket also includes an i70s sensor pack and totals A$14,265 at the stated date; omit that A$2,569 pack when the existing instruments already meet the brief. These are the same core boxes as the 50-foot monohull example. The difference is where they go and what connects them.

Keep the inside screen available for planning without assuming it replaces a lookout at the helm. Locate the independent battery-powered chart device where the crew can reach it after a helm failure. Measure the cable route from the raised helm down through the service space and across to the saloon, not the straight-line distance between screens. A supported RayNet switch and the required instrument-data adapters remain outside the hardware subtotal.

For this one-depth-source example, label the readout port sensor, starboard sensor or the actual installed location, and record its reference. Do not fabricate a second sounding by displaying the same network source twice. Add a second sensor only after defining how each hull's readings will be distinguished and how acoustic interference will be managed. Sensor location and hull suitability need a survey; the illustration is a station plan, not a drilling template.

A twin-helm cat changes the brief again: each working helm may need accessible depth and pilot standby controls. A third large plotter is not necessarily the first purchase. Check which controls can be reached from each helm and what remains usable if the shared network fails. The 32-foot and 50-foot monohull plans use the same functional priorities, while the catamaran installation guide covers the wider hull-specific decisions.