Is My Boat’s Internet Really This Slow?

So you're paying thousands each month for your superfast, superyacht internet connection, but when you check in with speedtest.net or testmy.net you find it's slower than dial-up. One problem could be the test itself.

Accurate for shore-based connections, these speed testing pages can be misleading if your important Facebook posts have to travel 35,000 Km to the nearest satellite and back in order to reach your audience. The problem is something called TCP.

TCP is a language used between two computers or devices on the internet. Like so many things about the internet, TCP is both clever and frustrating. Let's take the example of sending a cat pic to your friend Bob. Bob loves cats.

When you press the send button, TCP first divides the cat pic into manageable chunks. Next it sends a message to Bob's iPhone "Bob!" and waits for Bob's phone to reply. After a couple of back and forths, if everyone is happy, then the first chunk of cat data, let's say an ear, is sent to Bob's phone. Lastly, Bob's iPhone replies “ear here!”. Or something like that.

With many chunks of cat pic to send, and many messages per chunk, there might be hundreds of small messages involved in sending one cat pic. It is no wonder that people who know, say TCP is chatty. Now if you and Bob are at home or in the office, then no problem. But on a ship at sea, where each message and each cat chunk has to go all the way to space and back, then delays and gaps between all these messages mount up. It takes up to one second for each message to get from you to the satellite and back to Bob. And there are hundreds of them remember.

Worse still, TCP doesn't know it's chatting via satellite. It assumes the delays are due to congestion on the internet. In fact TCP slows everything down even further to make sure information isn't lost. That’s the frustrating bit.

The good news is, that during these long gaps and delays, hardly any of your precious VSAT bandwidth is actually being used. Most of it is free for other users on the boat, or other programs on your device to chip in, such as email and youtube.

The testing services use TCP. They  measure how long it takes to send a known chunk of data and work out the internet speed from this. But they don’t tell you about the gaps which are still available for everyone else on board to use.  They don't in fact report the true available speed for the boat at all.

The take away from this? There are better ways to test your boat’s VSAT speed. Oh and it’s much more efficient if everyone on board sends their cat pics at once rather than one by one. Message us at Acutec to ask us about improving your VSAT experience!

About the author

Jonathan is a professional engineer with a background in maritime communications and electronics. He founded Acutec Systems in 2004 and is managing director of the company.

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