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As we sailed from St. Lucia to Sint Maarten we were happy to find that, for much of the trip, we had a favorable current of about a knot or so helping us along the way. This was especially appreciated because it almost always seems as if the current is flowing to make our travels more difficult as opposed to easier (for example between St. Vincent and St. Lucia). In some parts of the world the currents are so strong that if you don’t plan your routes to travel with them, you just won’t make it. Fortunately we don’t need to be quite that mindful of the currents down here.

How can we tell if we have a current influencing us, other than just by feel or perception? When they’re both working, we have two methods of measuring boat speed on board ZTC: a paddle-wheel speed transducer which measures speed through the water and our Garmin 546 chartplotter which, among other things, tells us Speed Over Ground (SOG). If the numbers on both of these devices are equal then there is no current influencing the boat. If, as in the photos below, the SOG (5.8 knots, labeled in the pic as GPS Speed) is greater than the speed through the water (4.2 knots), we are being pushed along by the current (or surfing, which in this particular case, we were doing a bit of that too). The opposite would of course be true if the numbers were reversed. Unfortunately, the paddle-wheel on the speed transducer is notorious for getting clogged and almost certainly will not function if we have been at anchor for a few days unless we dive under the boat and clean it. That’s not a huge deal but we do need to remember to do it which is why I said “when they’re both working.”

As nice as it is to have a current helping us along on a passage, there are times when I do not appreciate this happening. Because boats only steer when there is water flowing past the rudder, a boat which is simply being “pushed along” by a fast-moving current has no steerage. There were times in the Intracoastal Waterway (ICW) where, when we were waiting for a bridge to open, we were being pushed along towards the large metal structure by the current. In this situation the only way to regain steerage is to move faster than the current, in this case towards the bridge. Not something that is at all intuitive. I was reminded of this the other day when the Simpson Bay Bridge tender kept telling us to get closer to the yet-to-be-opened bridge. Fortunately, in this case, there was no current effecting us but it does still make me a bit nervous to be put in situations like that. Sailboat masts and closed bridges do not tend to get along all that well.

8 Comments

  1. Sailboat masts and bridges do not get along full stop……..

    ……Like what happened to me once when we were racing round a mark of a course and the symmetric spinnaker halyard decided to jam fully hoisted….and the sheet and guy also decided to let go to full extent with no way to let it blow out.

    …..with an 6 knot incoming tide and a fast approaching 30 ft high bridge with a 40 ft high mast upriver…….. I will leave you to work out the interesting result ;).

    …….interesting learning curve!

    I’m glad I wasn’t the one on the helm that day.

  2. You can probably hear the gnashing of teeth, even from there. “We just dive to clear the paddle wheel” you say. Grrrrrrrr!

    For some it is different, the paddle wheel fouls within 3 weeks yes, but the water is murky, it is bitterly cold, the tide is like a mill race, and I don’t swim (I sink, despite many instructors and helpers!). So, no log for most of the season, every season.

    I hope you really appreciate and enjoy the freedom to “just dive and clear it”!

    🙂

    Mike

  3. I recall a time when I was circling to wait for a local bridge to open. There were some tourists walking across the bridge. They stopped in the middle to watch us. One of them said “I wonder why they are going in circles?”, and the bridge tender stuck his head out and said, “They’re waiting for you (fools) to get off the bridge so I can open it!” The tourists moved along.

  4. Have you had the opportunity to “race” ZTC? in good winds, what have you gotten her up to?

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