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Working Principle · Schematic

Equipment Guide · Satcom — FleetBroadband

FleetBroadband — Holding a Dish on a Satellite 36,000 km Away

The ship's broadband rides on one geostationary satellite parked over the equator. A gyro-stabilised dish inside the white radome stares at that fixed point in the sky while the ship rolls, pitches and alters course beneath it — and every link problem on board comes down to three things: how high the satellite sits (elevation), where it sits against the bow (relative bearing), and what part of your own ship is in the way. Tap a step or press "Play", then take the tracking simulator north and watch the funnel eat your link.

El / Az / link: el 18° · dish locked · link OK
sky — one satellite, fixed sea Inmarsat I-4 geostationary · 35,786 km L-band beam — fixed az / el for this position elevation horizontal (horizon) orbit view · not to scale equator el 90° overhead el ~5° at 76°N move away from the equator → satellite slides down the sky funnel shadow aft · below el ≈14° — no line of sight funnel foremast cargo deck radome · ADE gyro-stabilised dish inside coax terminal SIM phone · data BDE — below deck plan view N sat az (true) shadow turns WITH the ship the satellite does not
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A satellite parked in the sky

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Key —
Tap a step
Worked example — the link died at the wheel-overrel brg = az − hdg
Common mistakepower-cycling the below-deck terminal because “the internet died” after an alteration — the fault is geometry, not electronics. Check the satellite's relative bearing against the shadow sector first.

A ship at high latitude sees her satellite at azimuth 152°(T), elevation 18° — low enough for the funnel to matter. The installation record shows a funnel shadow of 160°–200° relative, effective below 25° elevation. Steady up on 340°(T): rel brg = 152 − 340 + 360 = 172° — inside the shadow, and the link drops the moment she settles on the new course. Ease to 320°(T)? rel = 192° — still inside. It takes 305°(T), rel = 207°, to clear the sector — or simply accept the outage and make the important calls before the wheel-over. One line of arithmetic, done at the chart table, predicts the whole event.

Working principle — explained in our own plain words with our own schematic from general marine knowledge (not copied from any OEM manual). Conceptual; varies by ship/model. Reviewed and verified by a Master Mariner.