Back in August, I wrote a pretty detailed article on construction of a dinghy tow harness for use with my Highfield 330 Dinghy being towed behind catamaran sailboat. That article is here. Today, with completion of a 500 mile tow, I can share images and videos of the tow underway as well as lessons learned on the construction and use of the dinghy tow harness.
First – everything worked fine. We drove the boat Fort Lauderdale to St. Augustine, round trip, most of it in the ICW, with two big sections in ocean. On the southern journey, the Southern Boulevard ICW bridge was closed for several days and after waiting for a while, it became necessary to tolerate some bad weather going out West Palm Beach and back in at Hillsboro Inlet. This provided a pretty rugged test for the dinghy tow harness. Going out West Palm Beach, the waves were big and nasty and no time for filming. Classic inlet stuff with big crests and large waves. We made 2.2 knots as the ocean beat up the big boat, and sloshed around the dinghy in big seas. When things calmed down a bit, I was able to film the dinghy tow harness in action in “rough” seas. I must say that on video, the ocean looks much calmer than it was in person.
Back to the design
Recall the dinghy tow harness connects in 3 points and the center point is designed to only take a load if one of the port/starboard connections fails. See the prior blog for excruciating detail, but the math on how long to make the center connector, worked out to be solid.
Things came loose
Did I expect things to come loose? Definitely not.
Did things come loose? Demonstrably yes.
Trip was 3 weeks and the first time on the trip that I found a disconnected carabiner was after waking up in an anchorage in the middle of nowhere north of Cape Canaveral. When did it come loose? Probably in the 15 miles stretch of rough water north of Haulover Canal. I recall hitting several good size yacht wakes and next day, one of the carabiners was loose! A couple hundred miles in before a disconnect, but yet there was a disconnect!
In the spirit of good engineering, a problem that cannot be reproduced, is not a problem, so reconnect, push on, keep an eye on it and see what happens. These carabiners are massive, with strong springs and they are hard to get attached to the dinghy. They should be even harder to have them come off of the dinghy due to wave action!
We made it to St. Augustine, had a great time in the city and prepared for the return trip. A day or two in, hit the same 15 mile stretch before the Haulover Canal. Again rough, NASTY weather, squalls, pouring down rain. Get to the turn for the Haulover Canal and … a carabiner is loose! This time, the other side, so the problem is reproducible and it isn’t the fault of the specific carabiner! No time to fix it there, towed the dinghy using only two connect points through the canal and onto smoother water on the inside.
How can these things come loose?
Hypothesis, later confirmed: The propensity of the carabiner to come loose is related to the orientation of the carabiner on the dinghy! I switched the carabiners to the “right” method and for the rest of the way home of 200+ miles, including ICW and ocean in rough seas, no failures.
Spring side of carabiner needs to be pointing “down” or toward the “inside” of the dinghy
Here is a collection of images and videos of the trip.
First one shows the dinghy tow harness after the starboard carabiner came loose and the starboard rope then wrapped around the port rope. It towed fine here as planned with the middle connector picking up the load.
Next picture shows the “good” carabiner orientation. If this way, it stays put. If reverse the orientation, experience says that the carabiner can find its way loose after many miles and getting bounced around in choppy waves.
Orientation of the middle connection didn’t matter. The port/starboard would come loose if the spring was “up” or “to the outside”. If the spring is down, it stays put. WHY? I don’t know, but I can say what when it came loose on the ICW, it was at a point of yacht wake and big bouncing. Something happened to allow it to slip loose and I was amazed to see it happen in real time. No fear here, would have to loose two at the same time for it to be a problem, but was still interesting to see. Bottom line, with the spring to the inside, hundreds of miles in test, and no failures. Getting that orientation right when clipping on the carabiners from above, in the water, takes some effort.
For videos, here are links to youtube.
Towing dinghy in ocean in pretty rough water.
And for the final video, again towing the dinghy in ocean, in calmer water.
From here, made it the last 8 hours to Hillsboro Inlet and home. Once switched the dinghy tow harness to have the springs toward the inside, no more disconnects.
Why don’t you lift the dinghy onto that set of davits on back of boat?
The big boat has a dinghy lifter, that doesn’t work. Its in the process of bring repaired and all the electronics have been replaced. The hydraulic cylinders are still a TBD and that means I can’t lift the dinghy. Completing this project really can’t come soon enough. Towing a dinghy 500 miles can be done, but it is WORK. The dinghy is something to complicate every bridge, every docking, every anchoring. What more it also means that the dinghy gets marine growth and cleanup after a 3 week trip, is real effort.
Final thoughts – Speed and fuel
There are many good jokes that roughly say that people with yachts don’t need to worry about the price of fuel. I still measured it and found it interesting to see observe that towing the dinghy causes the big boat to slow 0.7 knots (a 15% loss in speed) vs. lifting the dinghy. Towing the dinghy also causes a 26% hit to fuel efficiency. This was more than I expected. This isn’t a fast boat, so the dinghy has a larger effect than it would on something more substantial.
Fun times, let me know if you find things interesting.