AIS and radar from the hurricane season stragglers

Off Samana on VHF with Akira


Pinterest radar AIS aboarSunrise tinted the margins of Puerto Rico’s rugged profile with a warm glow. Making landfall on the west coast after a week of bumpy, on-again / off-again passage making from the Bahamas was a relief. Totem and her crew are the stragglers of southbound boats for hurricane season, long since expected to have the anchor set in Grenada…already a month in Puerto Rico, where we didn’t expect to stop at all!

Changing plans, unexpected events, and making the most of where you are: this may just be the definition of cruising. From the Bahamas, our intention was to pass through the various Virgin islands (Spanish, US, British) where we had places to go and people to see. From the BVIs, the focus would shift to a southbound track towards Grenada.

Unfortunately getting east from the Bahamas at this time of year is, in a word, unpleasant! We ran out of patience to wait for a system that would disrupt the prevailing easterlies. Ideally, that would allow us to take “I-65” (make easting to 65 degrees longitude, then drop south).  But there was no reprieve, and bashing into tradewinds isn’t very fun.

Enter Bruce Van Zant’s “Thornless” approach to routing from the Bahamas to the Caribbean. His alternative is to work along the coast of Hispaniola in daily hops, playing katabatic winds. Transit is made at night, when cooling air rushes out from the land and dampens trades to make easting easier. The trades pick up again by 10:00 in the morning: we’d aim to be settled in an anchorage by then, and rest until the evening settles the breeze again. In company with the family on their Manta 42, Akira, after the washing-machine seas south of Great Inauga it was a pleasant reprieve to follow this method along the north coast of the Dominican Republic—making progress at night, and tucking into anchor when the winds piped up during the day.

catamaran anchored Caribbean
Akira anchored off the lush coast of the Dominican Republic

Lush green hills of Haiti and the glorious aromas of tropical flora drifting to Totem were the first signs of a changing landscape. Balm to our parched souls after months in the flat, arid Bahamas, we watched longingly from the water. It wasn’t our plan to clear into the Dominican Republic at all, but remain on our boats during the brief stops and request safe harbor if pressed by officialdom. It stung to skip what is clearly a beautiful, fascinating place. It’s just the wrong time of year: in hurricane zone, during the season. As we watched a succession of early tropical storms marching across the Atlantic it was easy enough to be reminded that we needed to work towards safer water.

sailing watching coast through binoculars
Niall scans the Dominican Republic coast from Totem’s cockpit.

Steady progress across the top of Hispaniola was interrupted when Akira’s engines started giving them trouble. The cause was indefinite—a bad connection, probably, but definitely dirty fuel as well. Totem could well be next to suffer since we topped up diesel from the same source in Great Inagua. The prudent choice was to take shelter, polish fuel, and figure out the root cause of engine troubles. So much for our perfect weather window to cross the notorious Mona passage to Puerto Rico! A squall slammed through during the entry to Samana bay,  a timely reminder of our fragility with engine troubles on a lee shore. Tracking the squall with eyeballs and radar, we avoided it as best we could, and safely anchored a short time later off the town of Santa Barbara.

dolphins from sailboat after the squall
Mairen and Niall, dolphin spotting in Samana bay after the squall rolled by

If there was an MVP prize for gear that afternoon, it went to the radar. I’ve seen the question often enough: do you use radar? Or a variation: with AIS, why is radar really important? Not only is radar an essential tool, but it’s an entirely different one from AIS: here’s why.

Squall tracking

Our situation off the coast of the Dominican Republic is an excellent example of radar use for squall tracking. Even in daylight, where we can see the location and approximate progress of a squall, radar provides valuable insight into a squall’s course and speed, how it expands and contracts, the better to prepare and evade. That squall ended up packing 50 knots, and we wanted to be out of it ASAP for a host of reasons! Tracking squalls so we can try to avoid or minimize our exposure to them is our #1 use of radar. AIS has zero function here.

Using EBL on radar to track a squall
Using EBL on radar to track a squall

This snapshot shows a squall to the southeast of Totem’s position as we sailed up the Atlantic last year. Placing an EBL (electronic bearing line) on the squall’s radar footprint made it easy to track: was approaching or retreating? With the EBL holding a fixed position relative to Totem, this shows we’re moving away on our course to the northwest. Eyeballing the footprint shows how it’s growing (or not), but additional marks can be laid on the squall’s footprint as well.

Per the cruiser version of Murphy’s law, all this action (hello cargo ship at speed!) is happening at two o’clock in the morning: it was probably challenging pick out the squall at that hour with eyeballs alone.

Chart accuracy

Radar can help validate that your charts for remote-country-of-the-moment are reasonably accurate. Charts are fallible (witness the recent tragic, avoidable loss of  the catamaranTanda Malaika on a reef in French Polynesia). We’ve had errors of up to a mile in countries from Mexico to Tonga. Whether you overlay radar on your chartplotter or compare ship-to-shore distances on different screens, this is a great safety aid. Again, AIS has zero role here. I’m trying to think of where we have seen aids to navigation with an AIS signal outside the USA… there were some oil rigs off Brunei… others probably exist but I can’t recall them. Such aids may be present and growing in developed countries, but not most of the places we’ve been cruising. The bamboo stick on a coral head is more likely to suggest the pass in an atoll.

This snapshot of the south coast of Phuket, Thailand, shows radar overlay on OpenCPN helping validate the accuracy of our charts. The Thai coastline lines up well, as do the blips that match with boats and buoys.

Radar testing of Phuket
Radar testing off Phuket

Spotting vessels

Using radar to see other boats, in particular for collision avoidance, the why most people confuse the value add of radar compared to AIS. And yes, both radar and AIS are very helpful tools for identifying and avoiding other boats.

Florida coast: the yacht UQ($@ passes offshore from Totem during an overnight coastal transit.
Florida coast: a radar blip and AIS data show the yacht XYZZY passing offshore from Totem during an overnight coastal transit.

Leave the USA, and how many boats use AIS? The further from the developed world you go, the less it is used, up to the point where it’s a surprise to see a boat that actually is using AIS. AIS is mainly useful for big ship avoidance at sea, and has pretty much nothing do to with avoiding coastal traffic… which, it turns out, is where most of the boats you’re trying not to hit are located. Case in point: most of those blips on the radar screenshot of Thailand are other boats. Only four have an AIS signal.

Sailing through Sri Lanka, Totem skirted coastwise around the south of the island in the dark night of a new moon. One fleet of fishing boats after another dotted the radar. The smaller boats were difficult for our radar to pick up, but careful tuning and a watchful eye usually tipped us of. They DEFINITELY didn’t have AIS, however… the boats were inconsistently lit, if they were lit at all, and had probably never heard of COLREGS.  This situation repeats itself all over the world! Radar was a meaningful help; even more important, though, was eyes on watch all the time to avoid fishing boats and their nets.

Radar vs AIS

For boaters in North America with relatively limited experience, I can see how they may confuse the radar/AIS case. AIS is so common on boats! Charts are accurate now! What, squalls? They have a lot of safety nets, and not a lot of squalls. But spend any time in the tropical belt, and squalls rule: tracking them is key. I think that’s hard to appreciate when you haven’t experience this, just as it’s harder to appreciate trying to navigate an obstacle course of small fishing boats (or FADs, fish aggregating devices) on a moonless night. There is nothing at all interchangeable about radar and AIS. They are different tools: different sources of information to help clarify some navigation situations.

Would you go without?

There was a stretch in Southeast Asia where Totem didn’t have a working radar. A near lightning strike was the likely culprit in failure of the installed unit. Between being remote, and low on funds, it took a couple of years to replace. This was particularly stressful at times as the incidence of lightning is high in the Malaysian waters we subsequently sailed through: a radar to assist with squall tracking was sorely missed!

Around the same time as we finally replaced the radar, a new AIS unit was put in. When we left the USA in 2008, only receivers were available for private boats: we could see commercial ships, but couldn’t send our own signal. Receiving AIS is great, but since installing the transponder we’ve noticed commercial ships alter course a tiny bit, from miles away, to ensure sufficient sea room. It’s tremendous peace of mind.

I’d prefer to never to go without either of these very useful tools on board.

Meanwhile on Totem

So…. our path has meandered more than hoped. It’s been nearly a month in Puerto Rico already! That’s another story.

Sailing route through Antilles on PredictWind
Our Totem’s track from the Bahamas through Puerto Rico

Slow though our progress may be, the unexpected is to be anticipated in the cruising life. Stopping in Samana Bay introduced us to people, flavors, experiences that have added to our world.

The agent Chicho, who made himself invaluable during our whirlwind stay: interpreting to ease our rusty Spanish, greasing the skids for us to go ashore (despite not clearing in officially, something he also facilitated), pointing us to some truly spectacular barbecued chicken (the same that the Trio Travels crew sent us to, oh wow, it was SO good!), helping us with a side fuel purchase (again, not cleared in!), and talking story (he worked on the wreck of a pirate ship just yards from where we anchored and was full of fascinating information). Boats going to Samana: if you anchor out, this is your guy.

Our intrepid, gregarious self-starter agent in Samana. Thanks Traci for the pic!
Our intrepid, gregarious self-starter agent in Samana. Thanks Traci for the pic!

The opportunity to pick up fresh fruit and vegetables, and a pack of kids to help carry it all back to Totem (not to mention, make it more fun! Our girls loved especially loved hanging out with Emma from Akira).

kids shopping in Samana
Our first grocery since the Bahamas: yay fresh produce! Kids a big help to carry it all back to Totem.

Soaking in the bustle of the local market, and slowly remembering how to stumble along in Spanish.

Happy bustle (and sweeeeeet sweet pinapples) of the Santa Barbara market
Sweeeeeet sweet pinapples at the Santa Barbara market

Above it all, the kindness of our fellow humans.

Ferried back to Totem by a helpful panga, coco frio in hand
Ferried back to Totem by a helpful panga, with BBQ takeout for Jamie coco frio in hand

27 Responses

  1. Hi Jamie&Behan – glad you got through this years skin cancer check. They can be a worry. Bit concerned about your progress though, with Hurricane Season and still so far to go. Take your points about the recent grounding in FP. They had three things against them – lapsed insurance, relying on only one source of navigation, and approaching reef at night. You have one, being late. Be careful if/when something else moves against you. Just concerned.

    1. We’re worried about our progress too! Thanks for being in our corner, Bruce. We’ve been near hurricane holes (daysail from a great one right now) during our time in PR. It will be more worrisome to me when we head south. BUT- that’s also where all the TRS action has been: south! Ahh…. we’ll get there. TM… that’s a complicated issue. Really ONE thing that needed to be different- daylight arrival for visual navigation. It’s really the only way to enter a lagoon in the South Pacific; they didn’t have to go in after dark.

  2. Hi Guys and Gals,

    We agree with your review of radar vs AIS. Up in in AK with have been using the radar seldom except during foggy mornings. However AIS has been invaluable as most fishing and larger pleasure boats have them here.

    However radar on a chart plotter of any type makes an ideal backup to what you see (or don’t) and can confirm that charts and the hard stuff line up.

    When we were in the Caribbean we did use the radar exactly as you described to track squalls but getting the settings right to make it useful took a bit of time. My experience using radar in airplanes was invaluable since storm cells is all you can track with inflight radar not traffic at all.

    Keep enjoying. We get a lot of it from your posts.

    1. Thank you Victor, I’m glad to know you enjoy the posts. I have a screenshot that you’d probably find entertaining from a friend currently in Alaska; his chartplotter shows the boat WELL inland. Radar could confirm. Although the tragic bit of that anecdote is that the “land” was a glacier which has receded. 🙁

  3. Another great post, Behan. Our Lagoon did not come equipped with radar but we could have really used it in a few cases. We did install an AIS transponder and that helped a lot.

  4. Hi Behan from the yacht XYZZY in your AIS track off the FL coast! Two people PM’d me to say, “you’re in Behan’s blog! We were waving but you couldn’t see! Hope all is well, and our paths cross again soon! Deb & Dennis Jansma

  5. “Leave the USA, and how many boats use AIS? The further from the developed world you go, the less it is used, ” Things are changing, in South East Asia, AIS is mandatory in some countries now – excellent way for local customs (and bad guys) to follow your location. Mandatory for foreign cruisers paying customs entry, but local boats not so strict. Give it time and AIS/GPS will be mandatory for people walking around, oh wait, that exists already via cell phones.

    1. Times were changing already: we were in SE Asia when Thailand began to require foreign boats to be equipped with AIS, and it was the Singaporean requirement to transpond that prompted us to get a transciever. But the *reality* of boats using AIS? Singapore, as you’d expect, there are approximately a gazillion (technical word, ha!) targets- it’s insane (our reciever would crash when it hit 1,000 targets in a 5 mile range, we had to keep it to two miles). But the pic of Phuket kind of says it all – they made AIS mandatory fro boats, and there are probably a couple of hundred boats in the area of that radar footprint, and four of those boats have an AIS target. FOUR. I think it’s going to take a while. LOL re: carrying our personal targets around on phones! Sad but so true!!

  6. Thank you for this. S/Y THATHANKA. AIS registered as ‘YOGANE’. Safe passages to beautiful encounters with good hearts.

  7. Ha well this was a timely post for us as our boat took a lightning strike last week that knocked out our radar among a whole lot of other electronics. We’ve been sitting here debating about whether to go without or try to replace it here in the Bahamas, my feeling is that it’s been pretty valuable especially during night passages so I’d like to replace but obviously sourcing it here and insurance are the two big variables in the final decision. Your post also made me realize that if we do get a new one, I need to really dig into maximizing it for squall tracking! Did not know you could do all of that with radar. Take care, Totem Crew!

    1. Sorry to hear it Brooke! That’s a bummer. May be easier to deal with in Florida or the Caribbean than George Town. I heart our radar! But you wouldn’t have go to without for too long if it’s awkward to replace in the Bahamas.

      1. Thanks, Behan! Yep, I just got off the phone with a few surveyors, who all said that repairing all of this in GT will be nearly impossible so it sounds like we might be backtracking to Florida for repairs before continuing on. But, as y’all have shown so well these past few months, setbacks are setbacks and they happen often in cruising and sometimes they even have upsides to them. (Like restocking on all the good IPAs if we do go back to the States…one can only drink so many Kaliks!) 😉

  8. 1. How do you supply power for continually using radar? We found that our nighttime power usage, even with LED everything, still averaged 10 amps and once solar shut down around 5:00PM, unless we wanted to recharge our batteries once or twice a night we didn’t think we could power a radar unit as well.

    2. How many crew do you have on watch to allow a constant radar watch?

    Keep up the good blog postings.

    Fred & Judy

    1. Our particular setup is Garmin digital radar connected to laptop and overlaid on OpenCPN. The radome uses milliamps in standby and about 3 amps in use. The laptop requires up to 4 amps, but usually much less (when the screen is off). Underway, the laptop and OpenCPN are always on, but not always looked at (and screen goes off after 5 minutes or so). At night, in fog, or squally conditions the radar is on or in standby. Radar on time depends on conditions and risks. Radar is on during squalls (relatively short lived) and on full time along a busy coastline at night. With less need (offshore at night, we switch between standby and on, every 15 to 30 minutes (again depending on risks), and then back to standby after a few minutes of scanning. Total power isn’t great.

      We used to have older radome and green screen CRT display. We had the same general pattern of use with standby and on – but this setup consumed a lot more power. As long as we approached nighttime with batteries in charge state, our house bank was large enough to supply the power through the night. I do recall some longer/squally passages where it was challenging to manage though.

      As to watch keeping, we normally have 1 person only. For us, constant radar watch (and AIS) means it’s on standby or on and the watch keeper comes down below to check the radar, on a time pattern that matches assessed risk. Moving between cockpit to nav station every 10 or 15 minutes – keeps the crew awake and active. It is important at night to dim the screen (laptop or chartplotter) and/or set to nighttime color scheme, so as to not impair night vision with every chart check.If particularly rough out or busy with traffic, then we are likely to have 2 people on watch.

  9. Hello Behan & crew! Thank you for the great write-up of your experiences with AIS & radar use. The screenshots are very helpful for understanding the situation at hand. Doppler radar’s capabilities appear to fit right into collision avoidance/local weather tracking you discuss. See: .

    AIS, radar, GPS, satellite weather and the other wonders we have today go with the caveat that the best nav. aid is still our noggin.

  10. Hi Jamie & Behan,

    Hope your delay game works out! I can’t help but recall the tale told by a guy I introduced to sailing about 35 years ago. He eventually ended up buying a Westsail 43 and keeping it in the Caribbean. Except that he was a school teacher, so he sailed in the summer and worked when everybody else was cruising. He had almost three days warning when what was eventually a Cat 5 hurricane began to develop and threaten a potential landfall in the BVI. His inclination was to immediately head to Venezuela where he had just come from. Made the mistake of calling his insurance agent, who informed him that he was uninsured if more that 30 miles from an authorized hurricane hole. So he took his boat into the totally enclosed lagoon on Culebra. As the hurricane got closer the lagoon filled up with at least 100 boats.(and this was nearly 30 years ago) Even though his anchor held through the initial winds somebody eventually dragged down on him and took out his anchor. Fortunately he washed ashore on a sandy beach and was able to get off the boat. But with 165 knots of wind you can’t stand up, so he rolled over until he eventually found a log to hide behind. When the eye came through he realized that he had to find better shelter, so ran uphill and got in an old stone house. But with the wind shift even it started to lift, so he had to leave and weather the rest of the storm in the open. Took 2 weeks to get a flight home.

    Moral of the story– with the number of boats that now stay in the Eastern Caribbean through the summer, there basically aren’t any hurricane holes left– unless one can tie into the mangroves before everybody else arrives.

  11. Always excellent posts! Love it! Great stuff!
    We’re off to the exumas: trying to stay within 300 or so of our Fort Lauderdale hurricane hole.

    Can’t wait for the mid October wind shift to take the 25 to the 65.

    Glad the CA is out!

    Great photos too!

    Be well you guys!


  12. Hi Behan – FWIW , my view is that you’re right ; these are totally different tools, so AIS and radar cannot be compared. Our radar on ATEA is pretty hopeless and rarely used, but I’d love to upgrade if funds ever allow, and it needs to be visible at the helm to have much value.

    The other benefit that you don’t mention is blind navigation – using a radar clearing line to keep one safe off a headland, sandbank or other obstruction is invaluable. Not to mention plotting targets relative motion on a dark night – is it drawing forward, or on a steady bearing? This makes all the difference!!

    New radar for us, hopefully one day! All love John

    1. A big yes to all the other uses!! Getting radar dome only (and using existing nav laptop for display) kept it a lot more affordable, if that would help on Atea. Ours is in the nav station, and I don’t feel at all like I’m missing out by not having it at the helm. Nav view provides info we need, eyeballs get the rest done in the cockpit. Thinking about places where the radar would tell us “something” was there (fish aggregating device? Dugout canoe?), and then it was up to eyeballs (that aren’t compromised for night vision) to keep lookout from the helm.

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