Estimating current

[psneeld]

I see in many threads and hear horror stories on the docks about marinas with 5 knots or more ripping through them.

My old home marina that I also operated an assistance towboat out of...and did many dockings with tow and rescued many others who crashed.... had about the worst daily current max that I ever saw between NJ and the Keys on the ACIW. The average max including the worst for the month was 2.5-3 knots.... only worse during hurricane or Nor'easter flooding.

I know places in the far New England, Pacific Northwest and am familiar with the Anchorage/Kodiak area of Alaska with 20+ foot tides have some pretty severe currents.

Just for reference and I apologize for not being able to post or link the videos that show many of the pilings wagging back and forth...but the wake around the pilings and docks are evident and the local ICW buoys are pulled 1/3 to 1/2 underwater'

Here are a few stills.... remember this is around 3 knots of tidal current (something almost nobody tried to dock in)

 

[ScottC]

Wow, if I were to approach a marina with that much visible current, I would look elsewhere. My thrusters could not come close to correcting for that!


Reminds me of a lesson learned in Utrecht, Netherlands. We were traveling on a narrow canal and had to pass a garbage collection barge. The barge used thrusters intermittently to hold it against the concrete wall for each garbage collection stop. We had just come through a curved tunnel under the city streets, with boats behind us, so turning around or backing up was not an option. I decided to try to time it so I could pass the garbage barge between thruster "thrusts". That strategy didn't work. A thrust hit us just as we were passing and threw us against the opposite concrete wall. It popped one of our fenders (which we always have out in a canal). Fortunately, the other fenders held and there was no damage to the boat. But it was violent. It was only a garbage barge, but it was close. This has given me new respect for keeping the maximum distance possible from large ships (typically cruise ships) that are not tied to the pier in a harbor. They could be getting ready to let loose with a thruster at any time. I have noticed that they are not always attentive to giving a blast when pushing away from the pier in Italy. In one case, I called the ship on VHF to confirm it was safe to pass.

 

[boomerang]

This was the lower Cape Fear river bringing the boat home last spring. As you well know, Scott, we normally cruise at a very modest RPM for the best mileage ,which is 6.3-6.5 knots. When we came out of the ICW at Southport, our cruse dropped to below 3 knots. I remember seriously contemplating switching the AIS to the no-transmit mode so nobody would see how little headway we were actually making. It got better the farther upriver we got, but only after being passed by a tug towing a barge.

 

[Hippocampus]

City dock in Charleston and savanna also have interesting currents at times for docking. But most impressive I’ve seen was in the bay of fundy. Don’t much mind a decent current on my bow docking but any other direction is just plain scary.
A lot of places are now seeing torrential rains at times. Often they will augment coastal currents. What was interesting in the US SE was the spots where current is mainly wind driven. A nearby bay (they tend to be very shallow) will force water into the nearby ICW producing a very local current. Same wind may drain water of the next bay. Effect is larger than moon effects. Weird. Travel along and within 5-10nm May have it with you, against you, strong and weak. All without leaving the ICW channel. Coming down (N to S) don’t recall anything but mild currents.

 

[boatnbump]

I remember coming out of Charlston going south down Wappo Creek. The tide was moving I worked to get through there. It was a little scary. After that through the marsh's we would go around a corner and the wife would say wow we a flying. 9 knts Around the next and down to 5 knts

 

[Hippocampus]

Last boat had a paddle wheel for speed through the water and gps for SOG. Between the two if you did a circle you could get a reasonable idea of current and set.
Trick I was taught was to turn on track and keep your rudder angle the same. Deviation of the oval from a circle is informative as is variation in speed at constant rpm.
Current boat doesn’t. One of my very earliest boats had nearly nothing so I carried a knot stick. The ultimate low tech. A rigid disc with a metal rod out of it. That I’d was attached to a thin string. Other end of the string ended into a clear tube. At the base of the tube was a spring. On the tube was a scale of knots you could read off. About as basic as counting knots as they sped off a reel. But it worked and was surprisely accurate. May actually buy another like it for kicks and giggles. Now I guest. Either using spit or a small piece of something biodegradable. I know the length of my boat and have a stopwatch function in the Iwatch. Rough guessimate. From watching pots and buoys over the years kinda know from that as well but accuracy is probably lousy and even worse.
Still it’s amazing how in coastal settings how 2-3kts can really screw you up.

 

[psneeld]

Again, I have never seen any marina including Charleston City (where my buddy docked his sailboat for the last 10 years and I have been to dozens of times) with a current any more than 2 knots..... if even that. 2 knots scare most people when docking (at least where I have taught and done boating). I wouldn't dock my trawler in a slip at places that had a 2 knot current. Alongside a dock with a parallel 2 knots, even 3....no problem as long as I have help to get one line on.

Most people overestimate currents by a longshot. Marina managers are some of the worst and so are old salts. I am not one because I have actually measured currents for a project involving a prototype water generation machine and several bridge projects using GPS and their current measuring devices.

Shawn, I agree the lower Cape Fear River was definitely in the top 5 currents I dreaded to fight along my cruising...fortunately never had the inclination to dock there.

ScottC...a lot of people refused to dock their boats at my marina and theones there almost always timed the tides or tied to the fuel dock T head till it abated some.

Unfortunately as an assistance tower I didn't have that luxury so ilearned fast. The first time I exited the towboat slip I hit a pilingso hard it cracked the side deck alongside the pilot house of the Shamrock. The second time, my crew pushed off a pilingbut was leaning against a pilothouse window and pushed so hard it broke the window. Figured I was short for excuses and from then on planed and drove a lot better. Within the year I figured how to get boats in their slips under tow despite that current. Not all that hard, just required good planning and some decent maneuvering. The towboat didn't have a thruster and thus I have a hard time when people say there are situations where no thruster means no docking. Would I lover to have one or more thrusters? You betcha!!!...but it can be done. I felt a lot better (took the pressure off me) when my boss broke 2 pilings one night when trying to get into the slip next to my trawler with the 42 foot aluminum ex-fishing boat turned towboat. I did tell him I would kill him if he hit my trawler instead of pilings.

 

[psneeld]

I remember coming out of Charlston going south down Wappo Creek. The tide was moving I worked to get through there. It was a little scary. After that through the marsh's we would go around a corner and the wife would say wow we a flying. 9 knts Around the next and down to 5 knts

Yep, one of my top 5 current areas to avoid when running foul.

 

[ScottC]

Last boat had a paddle wheel for speed through the water and gps for SOG. Between the two if you did a circle you could get a reasonable idea of current and set.

I love my "old-fashioned" paddle wheel for exactly the reason you mention. I am finding that, in warmer waters, it gets fouled more frequently and I have to go swimming to free it up. A run in rough weather can also free it up, if I'm "lucky."

 

[Bmarler]

I love my "old-fashioned" paddle wheel for exactly the reason you mention. I am finding that, in warmer waters, it gets fouled more frequently and I have to go swimming to free it up. A run in rough weather can also free it up, if I'm "lucky."

Mine was removable for cleaning. Gotta have some big stones to open the big hole in the bottom of the boat though, so I didn’t do it often.

 

[Portage_Bay]

Mine was removable for cleaning. Gotta have some big stones to open the big hole in the bottom of the boat though, so I didn’t do it often.

I used to do that on a paddle wheel sensor that was 4 ft below the waterline. I kept a length of hose on hand to stuff over the thru hull fitting while cleaning the paddle wheel. I still got wet but the inflow was minimized and I could take my time cleaning the paddle wheel. I preferred the hose method to stuffing the blanking fitting in the hole.

 

[psneeld]

My old sailboat in the 80's had a clamshell on the opening that when you pulled it .... it stopped 90% of the inflow, then you stuck the plug in that was supposed to be tethered to the speed/transducer thru hull till the paddlewheel was cleaned.

 

[Hippocampus]

Yup every one I had had a flapper valve and a blank plug. Cleaned it regularly. Not a biggie. Use sailcote on the o rings. Used transducer paint on the unit and paddles. Had an ultrasonic one from airmar it sucked. Went back to old school. Also liked knowing water temp. Told me when I was in the Gulf Stream or a breakout.

 

[Gdavid]

Mine was removable for cleaning. Gotta have some big stones to open the big hole in the bottom of the boat though, so I didn’t do it often.

I have found that the heal of my foot plugs up the paddle wheel hole quite nicely while also allowing me to reach out and grab a toothbrush from the head to scrub the wheel clean because I forgot to grab something ahead of time.

 

[ScottC]

Yup every one I had had a flapper valve and a blank plug. Cleaned it regularly. Not a biggie. Use sailcote on the o rings. Used transducer paint on the unit and paddles. Had an ultrasonic one from airmar it sucked. Went back to old school. Also liked knowing water temp. Told me when I was in the Gulf Stream or a breakout.

I have an Airmar cap for the Airmar transducer, so I guess I could do this while the boat was in the water if I were quick about it. Too chicken to do this, however, for something that's not really that critical.

 

[Old Sea Dog]

Removing a paddlewheel speed transducer can be intimidating at first. Do it enough and it becomes routine. Had Datamarine speed and depth instruments on my Cal 2-27. Would remove the speed and insert plug when I was not traveling. Saved wear and tear on the paddlewheel components.

 

[psneeld]

Paddlewheels were probably why I started to estimate current more accurately, then when GPS came out and I was into a trawler with a very narrow speed range based on engine rpms I all but lost interest in them.

Between their questionable accuracy and their propensity to foul easy were the 2 biggest reasons for me. I did competitively race sail so I know there were some better/more accurate ones out there but for my budget sailing I never sprang for a better one for my boats.

 

[PM]

My boat's previous owner brought the boat (36 foot Albin, single 120 diesel) up the Mississippi. He was having a sandwich on the flybridge and noticed a peculiar tree on the bank. He had a leisurely lunch leaving the bridge several times for whatever reason. When he finished his lunch he noticed that in comparison to the tree he had progressed maybe 50 feet.

pete

 

[jgwinks]

I have an Airmar cap for the Airmar transducer, so I guess I could do this while the boat was in the water if I were quick about it. Too chicken to do this, however, for something that's not really that critical.

It looks scary but really no big deal. Just pull the 'ducer out with one hand and the plug in the other for a quick change. On mine I'd get maybe a half gallon of water.

 

[MYTraveler]

I was slow trolling at perhaps 1 knot (over water, not ground). Because the current was approximately 3 knots, I was actually traveling backward, so we kept our watch out of our cockpit, which was conveniently where the action was. We watched the cliff on our starboard side disappear forward as we continue moving, relative to earth at least, backward.

By luck, I went to the galley, just aft of the main helm station, just in time to see another vessel, approaching from our port, on a collision course with us, oblivious to our presence. I took evasive action and avoided hitting him midship. But had we collided, it would have been his boat hitting mine, though not easy to prove. Irrelevant though, since he was cutting across my port bow. At least that is my understanding of the rules. What did I miss?

 

[psneeld]

Hmm, interesting situatin but not sure if anything matters in rthe rules but relative motion.

If crossing your bow in open watets from the port, he was obliged to go behind you or slow to let you pass.

If in a narrow channel or following a traffic zone then those rules apply which have different conditions for stand on, give way.