Buying a satellite communications system can feel like reading a spec sheet in a foreign language. Kilobits, voice channels, certifications, service tiers — it’s a lot of detail for what is, at heart, a simple question: what does this vessel actually need to do?
Here’s a plain-language way to think it through, without the jargon doing the deciding for you.
Start with the job, not the spec
Before comparing data speeds, it helps to be honest about how the vessel operates. A few questions usually settle most of the decision:
Is this your primary way of reaching shore, or a back-up to something else? Do you mostly need voice and messaging, or do you depend on data — email, weather files, reporting, crew internet? And critically: are you legally required to carry GMDSS safety equipment, or not?
Those three answers point at the right family of system far more reliably than a feature checklist.
The three tiers, in human terms
The Lars Thrane Iridium range steps up in capability, and each tier suits a different centre of gravity.
The LT-3100 — the voice-first satellite phone. This is the straightforward, dependable option for vessels whose core need is to stay in touch: voice, SMS, and modest data, with global coverage and competitive airtime. It’s the natural choice as a primary line on smaller commercial vessels and workboats, as a crew-calling phone, or as a reliable back-up on a larger vessel. If “we just need to be able to call and message from anywhere” describes the job, this is usually where to look.
The LT-4100 — Certus® 100. A step up in data, with two voice channels and IP data of 22 kbps up / 88 kbps down. This is for vessels that have outgrown pure voice and want usable data — email, weather routing, light operational traffic — without moving to a full broadband package. It also comes in a LandMobile variant for vehicles and fixed installations ashore.
The LT-4200 — Certus® 200. The most capable of the three, with three voice channels and IP data up to 176 kbps up/down. This suits vessels that lean on connectivity day to day and want headroom: more simultaneous calls, faster data, a system comfortable as the communications hub of the vessel.
The honest guidance is to buy for how you operate, not for the biggest number. A trawler that needs a reliable voice line and the occasional weather file is well served by the LT-3100; paying for Certus 200 throughput it never uses is just ballast.
Then ask the GMDSS question
Running parallel to those three tiers is a separate, non-negotiable question: is your vessel required to carry GMDSS — the Global Maritime Distress and Safety System?
If it is, you need a type-approved GMDSS system, full stop. That’s what the “S” variants are for: the LT-3100S, LT-4100S, and LT-4200S add the SOLAS-approved distress and safety suite — Distress Alert, Safety Voice, Maritime Safety Information — along with Ship Security Alert System (SSAS) and Long Range Identification & Tracking (LRIT). They do everything their standard siblings do, plus the regulated safety layer that keeps a mandated vessel compliant.
If you’re not GMDSS-required — much of the fishing, workboat, and leisure world — then the standard systems are exactly right, and you don’t pay for certification you don’t need.
So the choice is really two decisions, not one: how much capability (3100 / 4100 / 4200), and GMDSS or not (standard or S).
The things that are the same across the range
It’s worth knowing what doesn’t change as you move up and down the line, because it’s the part that makes living with the system easy. Every system uses a single coaxial cable between control unit and antenna, with generous separation so the antenna goes where the sky is clearest. Every one carries a large 4.3″ display for clear day-and-night operation, a built-in webserver for setup and maintenance, and a build rated for the temperature extremes of life at sea. The platform is consistent; what you’re really selecting is the right amount of capability on top of it.
When in doubt, describe the voyage
If the spec sheet still feels abstract, the shortcut is to describe a typical voyage to your dealer in plain terms — where you go, how long you’re out, who needs to reach whom, and what the regulations require of you. The right system tends to pick itself once the operation is on the table.