Aligning shipboard antennas with SatPointer on Australian waters
Working communications on a vessel that pitches through a Bass Strait crossing or rolls idly in a Cairns marina come down to one stubborn detail: the dish must point at the right slice of sky and stay pointed there. Australian commercial operators, charter skippers and offshore crews running tuna longliners or reef tourism cats know that a stable satellite link is no longer a luxury. The Australian Maritime Safety Authority expects many vessels to carry systems that rely on satellite reception, and the Australian Communications and Media Authority keeps a close eye on which bands are usable where.
The trouble is that a ship is not a rooftop. The platform tilts, swings and vibrates, the horizon is rarely flat, and the choice of mounting point is limited by radar masts, cranes, tuna towers and exhausts. SatPointer is a free web tool that turns Google Maps and up-to-date orbital data into precise pointing figures for any chosen berth or anchorage. Feeding it the vessel's position lets you pull the exact azimuth, elevation and polarisation skew needed for reception, uplink, downlink or mobile satellite links before anyone climbs the ladder with a wrench.
What follows is a working method for fitting SatPointer into a shipboard antenna alignment workflow, from picking the mount and the satellite, through gathering numbers and managing vessel motion, to verifying the link and looking after the rig between voyages.
Planning the antenna mount on an Australian vessel
Before any software opens, decide where the dish will live. A spot on the flybridge hardtop, the mast platform or a custom pod above the wheelhouse will give different results, and SatPointer's value starts with giving you a number for each candidate. The location typed into the tool becomes the basis for every figure it returns, so a wrong pin means wrong angles on the deck.
Look for a mounting pad with an unobstructed dome of sky between roughly 5° and 60° elevation, depending on the satellite. On many Australian charter boats the obvious choice, the tuna tower, is also the worst, because the upper spreader shadows the lower sky. A lower position, often forward of the radar scanner, usually keeps the antenna clear of the radar's near-field interference and lets a single coax run reach the radio rack without crossing power cables.
Key items to weigh when choosing a mount:
- At least one metre separation from radar scanners, HF antennas and high-power VHF coax
- A flat pad large enough for the dish plus the footprint of any radome or pedestal
- Access for periodic bolt checks, paint touch-ups and cable gland re-sealing
- Drainage so saltwater does not pool around fasteners
- A clear path below decks for the coax, power and any control cable
Drop the GPS coordinates into SatPointer twice, once at the pad and once slightly offset, to see how sensitive the angles are. Coastal cliffs at Jervis Bay and the lee of Magnetic Island can mask lower elevations, and a few metres of height often decides whether the link works at all.
Choosing the right satellite for your operating area
The satellite that suits a Sydney Harbour charter may not suit a vessel on the North West Shelf. SatPointer's database lets you browse available birds and inspect beam coverage before buying hardware. For domestic voice and data the Optus fleet is the natural fit, while Inmarsat and Iridium handle safety services and Antarctic routes.
For offshore fleets between Broome and Cairns, a Ku-band beam over the Timor Sea and Gulf of Carpentaria often beats a transcontinental footprint, because the dish can be smaller and the link margin more forgiving in tropical rain. SatPointer shows the estimated dish size for each beam at your pin, which is a useful sanity check.
Pulling the pointing numbers from SatPointer
With a location and a satellite chosen, SatPointer's interface is straightforward. Select the bird you intend to track, click the map at the vessel's position, and the tool returns azimuth, elevation, polarisation skew and the estimated dish size for that beam. For Australian users, common targets include Optus for domestic traffic, Inmarsat and Iridium for safety services, and Ku-band birds used by offshore fishing fleets for weather and crew welfare links.
The figures are static, which is the point. They tell you where the satellite sits relative to your hull when the vessel is level and heading north. A SiriusXM dish alignment walkthrough uses the same principles for a different orbit and is worth skimming if you have never aligned a dish by numbers, even though SiriusXM satellites aim at the Americas.
Write the figures on a waterproof card and file a copy in the radio log. Moving between home berths, say Cairns to Fremantle, changes the angles noticeably.
Accounting for pitch, roll and heading
Static numbers assume the ship is flat, which the Coral Sea rarely allows. A 1.2-metre dish on a free-swinging pedestal can lose lock in moderate swell, and even a stabilised system needs accurate baseline angles.
Two approaches are common. Smaller operators use a manually aimed dish on a swing bracket and accept drop-outs in heavy weather. Larger vessels run a gyro-stabilised pedestal that holds the beam on target automatically. Either way, the starting alignment is set using SatPointer figures, with the vessel moored in calm water and trimmed close to even keel. Crews then enter the SatPointer angles into the pedestal's control unit as the home or stow reference.
For setups that use an azimuth rotor to track the satellite as the vessel yaws, SatPointer pairs well with automated solutions. A guide on automated dish pointing explains how the same data feeds a rotor controller, freeing the operator from walking to the mast with a compass. The logic is identical whether the rotor sits on a tin shed in Bendigo or the afterdeck of a 30-metre prawn trawler at Bundaberg.
Verifying the link once the hardware is fitted
With hardware installed and the dish roughly aimed, the next job is to confirm the numbers produce a lock. Connect a sat finder or a laptop running the modem's diagnostic page, then make small adjustments while watching the signal-to-noise ratio or Eb/No reading.
Tools and references worth keeping on board for this stage:
- A handheld sat-finder with audible tone, rated for the band in use
- An inclinometer or smartphone equivalent for mast angle
- A magnetic compass, declination-adjusted for Australian waters
- A printed SatPointer snapshot of the vessel's pin, dated and signed
- Contact details for the satellite operator's help desk
Lock the mount only after the best signal holds steady for several minutes. Salt spray, wind and crew movement can each nudge a marginal alignment, so what looks good at the dock may fail at sea. Mark the final azimuth and skew with a paint pen so a relief skipper moving between Cairns and the Whitsundays can repeat the alignment.
Looking after the rig between voyages
Australian waters are not gentle on metal. Salt air, tropical UV and the occasional Pilbara dust storm attack connectors, paint and stainless fittings equally. Re-check the alignment at the start of each trip, especially after a cyclone season run or a long stint alongside in a tidal berth where the pad may have shifted.
The familiar failures include a skew setting that has rotated because the locking bolt was under-torqued, a hazed radome that has dropped signal by a few dB, a new radar or solar panel creating a fresh shadow, cable water ingress at a deck gland, and corroded mount bolts that have let the dish drift a degree or two.
Keep a small spares kit aboard, including a spare LNB, self-amalgamating tape, a spare gland, a torque wrench for the mount bolts and a printed SatPointer cheat sheet. With those on hand, a lost link halfway across a crossing from Port Hedland to the Indonesian border becomes a one-hour job rather than a day-stealer.
For skippers and engineers ready to begin, head to SatPointer, drop a pin on your home berth, and let the tool do the first round of maths before you climb the mast. The numbers it returns are the difference between a quiet radio watch and a wet afternoon spent chasing a signal by guesswork.