Contest: Use Radar To Determine Position

Ben Eriksen Carey Words 44 Comments

UPDATE: The contest is closed. I posted all the submissions and messages I received via email or Facebook in the comments below. The winner was drawn at random from all the correct entries, congratulations to Alex Rook. Thanks so much for playing. And don’t forget to check out the creative problem solving methods everyone used below. 

The correct answer is: 41° 7′ N x 71° 39′ W. 

Now you can watch a video of this delivery!


Read on to find out how to enter the contest. OR just skip to the last paragraph for contest rules. Its fun. Its puzzling. Its for sailors!

The weather during our recent training-delivery from Fort Pierce, Florida to Warwick, Rhode Island was, for the most part impeccable! We saw only one hour of light rain, conveniently while anchored in Norfolk Virginia! Winds remained abaft the beam for all but 15 fun filled miles of rail dipping close hauled sailing under reefed main and jib on the smooth, short-fetch waters south of Elizabeth City, North Carolina. Starry nights and moderate winds prevailed for much of the journey.

There was however, a surprising spell of fog that offered a fantastic hands-on opportunity to teach dead reckoning navigation and radar skills to our two students, Dorthy and Fred – new owners of Aviva, a Beneteau 423. As educators we could not have asked for a better teachable moment! We worked on determining multiple CPAs with EBLs and VRMs. We learned to identify radar conspicuous objects and use range arcs to fix our position. And we also kept frequent dead reckoning plots on the chart to help determine set and drift. We were busy!


Throughout the voyage we practiced other skills like: anchoring and docking; line handling and knots; safety and emergency procedures; rules of the road, lights and sound signals; vhf protocol; and perfected our triangulation and running fixes. We all enjoyed using flash cards to quiz each other. These methods of constant study and practice have enriched our sailing experience and while we are always learning a lot, the most important thing we have learned is that we have so much more to learn!

Now, here’s a quiz for you!

A wise sailor never relies on just one source of information to make decisions, but rather uses all available resources! So, start digging for clues in this blog post to determine Aviva’s lat/long position (within 1 mile of accuracy) based on our radar screenshot below. Email Teresa your answer. Please don’t post it on facebook or in the comments. Every correct answer will be entered to win a hardcover copy of The New Complete Sailing Manual. (Sorry Fred & Dorothy, you are not eligible!) The winner will be chosen randomly at noon on June 10th, so get your answers in now!


If you are interested in learning more about sail training opportunities for both coastal and offshore passages on your boat, please email Teresa.

Comments 44

  1. Dannie Hill

    Sounds like a great passage and a wonderful learning opportunity for the new owners. The best way to learn navigation is get out on the blue with a competent captain.

    I once made a non-stop passage on the outside from Hampton, VA to Ft Lauderdale with 15 foot following seas and 25 knots of wind abaft the beam and it was the best passage I’ve ever made. Only 4 1/2 days and we were not ready to stop.

    I’m now looking for a bluewater boat and will keep you in mind for a refresher. Great post.

  2. Pingback: SpinSheet | Can You Determine a Boat's Position with Radar? - SpinSheet

  3. Edward Teach

    From what I can gather you are on a port tack cutting into the wind as far as you dare. You dare in the ICW south of Elizabeth city. But you imply that the water depth is quite deep. Even though your are headed north by north east. You are prolly headed north or even north, north west. There is a land spit and a buoy to your starboard bow, and a buoy on your port quarter that is displaying a running rabbit, meaning a reflector. Unfortunately a sailboat with a radar reflector also displays as a running rabbit. The distance between the two possible buoys is 3.2 nm. The land is .7nm from the stand off buoy. The range from the two possible buoys from land is 225m. As there is not enough information as to the type of contacts displayed. The key to seaman’s eye navigation, or dead reckoning is the previous set of information. Are the contacts moving? Give me a running plot and I could thread a needle. I will take a pass on digging into the charts. Good luck to those who try.

    1. Teresa

      There is no need to know our previous plotted positions in order to solve this puzzle. Enough info is provided and there is only one possible answer that will match the radar plot.

      I’ll be posting the correct answer on June 11. I’ll also share what others had to say about it. You’ll see their creative problem solving techniques and if they were successful.

      Good luck “threading the needle.” I can’t wait to see how you work it out.


  4. Kiel

    Howdy Teresa,

    To be honest, I didn’t spend much time looking for the answer, but my quick-glance answer would be just off the coast of Block Island.



  5. Stefan

    Hey Teresa & Ben,

    now i know every RACON (B) along the Eastcoast! :/
    Took me some time but i think the position is next to Block island: 41° 7,25′ N 71° 39,5′ W
    …fingers crossed 🙂


  6. Matt

    That is a fun exercise – heck absent an “approaches to Block Island Sound” chart, with the proper deviation, etc. I’d ballpark it at: 41.128,-71.631 – en route to Great Salt Pond (which you didn’t stay in nearly long enough IMHO! 🙂 I’m guessing the bearing at roughly 50 degrees magnatic is a bell marking the SW approach to the island.

    Best regards, Matt

  7. Cheryl

    Hi Teresa,

    Thank you for the article you shared on Flipboard. We determined the Lat/Lon to be

    41 deg 7′ 20″ N
    071 deg 39′ 30″ W

    The boat is SW of Block Island. Did we get it right?


  8. Eric

    Hi Teresa-

    What a fun thing to do over my morning cup of coffee. The east coast is far from my stomping grounds, so I enjoyed exploring the charts.

    I’m a river tug captain in Western Alaska, virtually all of which are uncharted. Keen radar navigation skills are a must up here!

    What you do is inspiring!

    41*07’N / 71*39’W
    47′ of water

    * = degrees


  9. Alex


    I’m not sure if you remember us but my wife and I had started reading your posts right about brief time you were on cruisersforum and had started your blog. It was around the time you were worried about employment and we had suggested Edenton or Elizabeth City. But things seemed to have turned out well for you and we enjoy reading your blog, though on a sporadic basis. Last night I saw that you two had posted new entry and I wanted to catch up on it. That involved loosing a bit of sleep by the fun puzzle.

    I really wanted it to be by Cape Charles because I’d been there and had a really boring story to tell. Unfortunately the facts didn’t line up with the distances, not having a RACON and shape of the land mass. Nor did anything south of that from what I can see.

    But near Block Island does. The heading is about right but that online chart reader was devised by Satan. The distance from the RACON to you — one and a bit of whatever those NMs are — plus just about exactly two NMs from you to the other point equals (carry the zero, cross multiply — and get a new calculator). Three plus a bit of ninims or NiM or NMs. You know, you’d think folks would just use miles like we here in do in America.

    I put this on the NOAA/Google mashup because Satan’s map reader was working perfectly and ran a line from the RACON to the next marker and that about 3.2Nm then backed up two since that seemed like a good idea at the time.

    Anyway, I guess your position is 41º 7.260′ N, 71º 39.168′ W … mostly because that’s what google says.

    To be honest I read the comments and was promptly bewildered by the running rabbits and threading needles comment. While I can’t find anything on running rabbits, I did notice the charts says “RACON ( _ …)” just just happens to match the pattern you have on radar. I’m taking that as a sign; probably one that you need to close the seacock as you just crossed the 3 Nautical Mile No Discharge Zone (see note Z which we have hidden below).

    Anyway, thanks for the puzzle. Glad it was a good trip.

    Be well,


  10. ED

    Just a SWAG using the radar image only, not trying to read into any hidden hints, that may or may not be there. Thanks for letting me play.

    41°07’N 71°40’W


  11. Fred

    Hi Teresa,

    It was certainly fun and interesting, I hope you created lots of activity and lots of entrants to the contest. Maybe you could put a reminder on facebook and email, possibly a hint or two to create more activity if you need it.
    I was able to refresh with research and able to pinpoint the position more correctly to where I would determine the position to be and the correct way to express the position. Senior Sailors like me may not be totally computer literate as you can see.
    If I may I would certainly like to modify my previous answer to the following:
    Latitude 41 degrees 7.4 minutes North
    Longitude 71 degrees 38.7 minutes West

    In my first answer I tried to measure on my computer screen and it gave me different answers everytime I logged out and went back. Eventually I was able to print out the chart and found it much easier to plot the position on paper.

    fondest regards,

  12. Ken

    Teresa –

    Given that the radar is showing a RACON of -*** (morse code for letter B) within 1 NM the only I find on your cruise path appropriate would be Red “2” off the SW side of Block Island – very near Southwest Ledge: with SHU of 020M my guess your boat is around Longitude 72 degrees 39.5 minutes, Latitude 41 degrees 7.7 minutes.

    Thanks and if I’m wrong I certainly look forward to learning from my error.


  13. Dennis

    Very intriguing! It took me a while, but I am pretty sure you were at the following location:

    41 – 07 – 22.649’N 071 – 39 – 29.04’Wht off the Southwest Ledge Lighted Whistle Buoy, between that and Block Island.



  14. Andreas

    Hey Theresa,
    I love these kinds of puzzles, so of course I had to figure out your position. Here’s my bet:
    41°07.5 N
    71°39.0 W

    If you’d like to see my reasoning:
    My first guess was somewhere north, I guessed that’s where the fog is. The first place I zoomed after studying your track had a RACON B buoy, just as in the radar screenshot. That was southwest of Block Island, with the racon and the island 4-5 nm apart (as in the screenhot), and something could be the marker SW of the island. This made me quite confident that I got the right spot. Then I just did my best to match the distances in the radar screenshot with the map.

    For the rest, keep up the good work. It’s a pleasure to read your writing about sailing. And I really look forward to see your film.

    Greetings from a Norwegian living in Belgium, still on a high after spending a few days on the sailing cargo ship Tres Hombres (hot tip: Google them).



  15. Bill

    I’m going to guess SW of Block Island at approximately 41d 07.542’N and 71d
    39.389’W. I must admit that at this location I can’t justify the target SW
    of your boat at the time – so I’ll just assume it was a large boat.


  16. Jeremy

    Hi Teresa & Ben,

    I love the blog. Keep it coming! Here’s my read on the radar plot:
    SW of Block Island, N41 07.4′ W71 39.0′


  17. Darren

    Hi Thersa,

    The racon was a real give away as well as your heading and isolated land mass.

    My answer is: 41°07.48′ N, 071°39.50′ W, its south west of Block island.

    Hope i got this would love a book to brush up on some skills.

    Holding thumbs.

    Kind regards


  18. Chris

    Hi Teresa,

    In response to the navigation quiz that Benji posted on the blog… I don’t have dividers in front of me at the moment (I typically don’t keep nav tools in my classroom), so I’ll email you the exact lat/long later this week. In the meantime, I can say with a fair degree of certainty that you were about 2 nm due SW of the R’4′ just off the SW tip of Block Island.

    I wish my radar had that type of resolution 🙂


  19. Rob

    It looks like a position of approx 41 07.2192 N, 071 39.1310 W headed north into Block Sound atop Southwest Ledge, with the RACON aft to port being Southwest Ledge Lighted Whistle Buoy 2, the land off the starboard bow being Block island, and the small echo 1/2 Mi off the land being Southwest Point Lighted Whistle Buoy 4.

    but hey, I am just guessing . . .


  20. Fred

    Hello Teresa,
    Great idea, fun and interesting for sailors to do.

    Radar position : 2 and 1/2 nautical miles southwest of Block Island.

    Chart position : Latitude 40 degrees 08′ and 50″
    Longitude 71 degrees 37′ and 10″

    I used your radar plot and Charts # 13217 and 13205 in my estimates.

    Hope I get close, while the eastern seaboard is a very large area. If i am incorrect it would be fun to start over and correct the position. Thanks for
    the opportunity.

  21. Peter-Paul

    Hello Teresa,

    My answer would place the Aviva at these coordinates:
    N 41 07.276
    W 71 39.232

    And now the story for how I got there. I recognised the racon B signal on the radar screen (long short short short), given my unfamiliarity with the US coast I went searching for a light list which I was able to find with the USCG. For the Atlantic coast there are multiple documents so i started with the first volume ( and searched for “Racon: B” and plotted what I found on a google map. This gave me this screen:
    Given the shape on the radar screen and the track around Block Island after leaving Warwick, I assumed that the Racon B signal on the radar screen was that of “Southwest Ledge Lighted Whistle Buoy 2” at position 41 6 22.649N 71 40 14.042W. And that the position of Aviva would be 1.3 nm northeast of the buoy and this gave me my answer which I stated above 🙂

    I have zero experience as of yet operating a radar and I have doubts about my answer due to the dotted circle and line on the radar screen and whether or not these are any indication of heading on the vessel. And i’m unsure if my estimated position corresponds correctly with what i see on the radar screen.

    Anyway, thank you for this little puzzle! I look forward to hearing if i’m even remotely close!

    Kind regards from The Netherlands,


  22. Bob


    I’ve enjoyed your blog and found this contest fun!

    I’m guessing your position at the time of the Radar shot is N41 07.40 W71 39.40 or a little over 2.5 nm SW of Block Island, RI.

    Here’s how I came up with my answer:

    When you said fog, I figured it had to be Rhode Island because we’ve sailed (and motored) thru Pea Soup where you can barely see the lookout in the yellow oilskin on the bow of the boat from the helm. I saw the letter B Racon signal on the radar and first guessed the approach to Narragansset Bay near Brenton Point, and in fact there is also a B Racon buoy there. However, there are other land masses that would show up on the Radar within 6nm of you, so that couldn’t be it. I showed it to my wife Ann and she said the land looked like Block Island, and sure enough there is a R2 Racon B buoy there too. I took the measurements along with a buoy R4 on the chart which appears on the radar, and plotted the location.

    This was a fun quiz – looking forward to seeing how we did!

  23. Andrew

    It looks to me like the Racon is light #650, the Southwest Ledge Lighted Whistle Bouy 2. The land mass is Block Island. Best position I can figure is 41° 7’18.61″N 71°39’12.64″W. I freely admit I could be off since it’s my first time trying something like this, and I was using Google Earth instead of charts. Great blog.



  24. Olaf

    Hello Teresa and Ben,

    Thanks for giving me a bit of a challenge on a Sunday-night.

    My answer to your location at the time of the radar image is:
    41 deg 07.3649N / 071 deg 39.2430W

    If I would have to describe it, you were near Block Island, between the
    two WHIS/Racon beacons, between the top of the letters ‘So’ of Southwest
    Ledge marked on the NOAA RNC map you pointed to in the blogpost.

    How I found it: It took me a little while matching the radar image with
    the surroundings on Google maps. The shape of Block Island near Warwick
    was a good candidate but I also checked for similar shapes near Norfolk
    and Elizabeth City (with no good match). Then the task was getting the
    position right. The boat was doing 20 deg magnetic, and the NOAA map
    showed a significant variation of some 14+ degrees W. Ho-hum. The map
    viewer from the NOAA website did not scale to the point of matching the
    radar image and the lat/lon lines were inconveniently outside of the
    viewing window. Then I noticed that the RNC chart could be downloaded.
    In the zipfile was a file I had no reader for. Some Googling pointed me
    to the opencpn software, which read the map fine and scaled it to
    something comparable to the radar image. Now I had to rotate the image a
    little bit to get a better match between island and the two WHIS
    markers. When that roughly matched I had a fix for your position. I
    noticed that the RACON dash-dot pattern on the NOAA map matched the
    radar image, which finally confirmed to me that the location must be
    near Block Island.

    Best regards from the Netherlands,


  25. Rich

    Hi Teresa!

    I really enjoy reading your advice and of your adventures!

    I think I have the answer here, but please give me some wiggle room because I am using my laptop monitor as a set of dividers! 🙂

    Your were 2.5 nm SW of Block Island. The RACON buoy to your SW is R “2” FL R 2.5s RACON (-…). The object off the landmass about 1/2 nm should be buoy R “4”.

    I have your approximate position as: 41 degrees, 08 minutes N; 071 degrees, 39 minutes W.

    Best wishes for continued success!
    Your Fan,

  26. Micheal

    Not a practical question. Nothing within 15 miles of elizabeth city is going to give that profile with a heading of 20 deg Mg. Unless all the day beacons don’t give a profile to radar? You need the last fix and or DRP unless you’re guessing.


    1. Teresa Carey

      Micheal, it is a practical question. There is enough hints in the blog post to figure it out. I can’t give any more hints now but you will love seeing how others figured it out when I post the answer on June 11. People are very creative in problem solving!

  27. Edward Teach

    Running rabbits are quite common, They can confuse any image. That’s why I wanted more info.
    For those who don’t know what a running rabbit is, I will try to explain. It is a contact that displays as if it is either running at you or away from you. It is factious, and can be misleading at first glance. They generally spiral but not always. That is why you must study it and wait for changes.

    I found a link but it isn’t very helpful without an explanation.

    Thanks again for letting me play, I guess I should have broken out the calipers.Congratulations to the winners.


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