Waypoints for crossing the Rio Dulce bar at Livingston, Guatelama

Sunday, March 15, 2020

015-50.000 N
088-43.800 W

Ahoy from the crew of the BlueJacket!

As you may remember, the last time that we crossed the bar into Livingston, Guatemala we had a terrible time. We had to be pulled across using 2 dinghies with 15 HP motors. This was despite using the same waypoints that we've used for years. The problem is that channels shoal, shift, etc and there's no economic incentive for the government to survey as locals make good money assisting boats across the bar. As a result, I decided that I would undertake surveying the bar so that we wouldn't get stuck again and for the general good of the cruising community.

After a bunch of research, I found a device called the SonarPhone T-Box made by Vexilar. It consists of a transducer and a box which turns into a WiFi hotspot which provides depth data to up to 8 wireless devices. The transducer can attach to the transom of the dinghy by a suction cup or there's a permanent mount that you can attach. I used the suction cup, which worked fine.

To map the bottom I used my iPhone with the Navionics Boating app. The app is free, but you have to buy a yearly subscription to their charts, which is relatively cheap. The basic concept of the app is that you connect to the SonarPhone device and then drive back and forth across the area that you're interested in mapping. As you drive, you can see the area that you've mapped showing up in darker blue and contour lines get drawn or modified. I spent about 1.5 hours transversing the area and then went back over the area which I thought would provide the best route across the bar. When you've completed mapping an area, the app will upload your data to Navionics and they will process it and combine it with other data from the area. The charts should be corrected to MLW, as it utilizes nearby tide stations, and it had one in Livingston.

The following images show the output of the Navionics app. I miscalculated the transducer offset by about 3", so there's actually a little bit more water than is shown here. But, it clearly shows where a 5' channel runs through the bar. The shallowest section (between waypoints 1 & 4) is about 0.1nm long and the shallowest that I saw was 4.3' MLW. Note that it doesn't matter which side you keep the sea buoy on, as there's plenty of water at the buoy.

Here are all of the waypoints that I generated. "S" is the start and "F" is the finish, which is by the sea buoy. Click on the image to the right for a high resolution version.

S: 15-49.663 / 88-44.343
1: 15-49.766 / 88-44.197
2: 15-49.789 / 88-44.204
3: 15-49.826 / 88-44.160
4: 15-49.835 / 88-44.125
F: 15-49.963 / 88-44.017 (near sea buoy)

We crossed with a 1.6’ tide and saw no less than 6’2”.

To simplify things, I would average waypoints 2&3 and use the following to cross the bar:

S: 15-49.663 / 88-44.343
1: 15-49.766 / 88-44.197
2-3: 15-49.807 / 88-44.182
4: 15-49.835 / 88-44.125
F: 15-49.963 / 88-44.017

Note that the waypoints often used (and which we have used) are:

Inside the bar: N 15 49.299 W 88 44.734 
Outside the bar: N 15 50.100 W 88 43.960 

are between 88 and 127 yards to the NW of the above waypoints, which clearly places you in shallower water.

We hope that this helps getting across the bar!

-- Geoff & Sue s/v BlueJacket

Log ID: 2295