Ian McColgin
08-22-2009, 08:20 AM
Two neat things about Thursday’s ten hour sail from Branford to Hamburg Cove:
Cool DR in 50’ visibility through the morning; and
Solved the buoys that lean into the current phenomenon.
The latter first. Coming up the Connecticut against the river’s natural flow plus the ebb, I got a good look at two major buoy shapes behaving differently. The cans and nuns are deep buoys, almost twice as much below the waterline as above. These inevitably lean with the current since the mooring chain is at the bottom and they are pulled downstream.
The speed limit/no wake buoys, on the other hand, are a can set atop a larger diameter fat disc float, fairly shallow draft and the mooring chain attachment sometimes centered, sometimes off to one side in which case it exaggerates the lean into the current. These lean into the current. Still not a compulsive photographer and I don’t know how to post anyway but as we (Marmalade and I) took about a half minute to pass each buoy (barely ½ knot over ground) I got a good look. It’s the wave pattern. A boat moving through the water leaves its wake astern, essentially making a hole in the water into which the stern squats. But at about 4 knots (the current) the disc shape of the buoys makes a huge stern wave clutching at the downstream end and lifting that side. The buoyancy that might otherwise lift the upstream end is just enough in front of the buoy that it doesn’t lift, and the buoy tilts into it, with some of the bow wave (upstream end) slopping over the top of the float-disc. The mooring chain at the center of the underside is so close to the surface in these buoys that, unlike the nuns and cans, it exercises little leverage. The wave pattern dominates.
For the fog, I happily adapted a racing tactic.
A good RC (That’s Race Committee, not Roman Catholic!) will set the weather mark exactly upwind so absent current even tacks will get you there. In our not infrequent fog I short tack, never more than three or four minutes per, till we can really see what’s up. Of course, I’ll intuitively adjust the time on each tack a bit for current and expected wind shift, if any.
Thursday as I listened to the traffic on 16 and 13 - “I said go port dummy! Swing to due north, zero zero zero or 360 or whatever but turn now or you’ll die. I’m a tug with a loaded 200’ barge on my head and I can’t stop or even turn much if you keep moving into my track.” - while fueling I decided to stay out of the lanes and go where no heavies dare. Like thread the Thimbles and after that bounce off the coast. The wind was a bit south of east so the starboard tack was favored. This was going to be way too much tacking to DR each tack so, like a race course, I laid out desired targets at anywhere up to 5 mile intervals, usually more like two or three, and short tacked up that course by time. That way I only had to figure one current vector per leg rather than per tack. Even with the occasional 25% error in speed estimate (who can really tell three knots from four?) the distances were short enough that I could usually hear the bell, gong or hooter or see the refracted wave pattern of a rocky island. In one case the fog was so thick that after I circled the sound a couple of times without finding the buoy I daringly assumed it was the target and sallied forth.
The fog lifted to a good five miles in time for me to glimpse Fishers Island and tack out there for some bigger ebb to race us towards Saybrook and was virtually unlimited by the time we started the ever so slow slog upriver. Needless to say, the railroad bridge closed just as I was getting there. One smaller cat joined me in reaching back and forth waiting and a bunch of wusses with sails down and motors running milled about. Once it opened, there was the usual press of impatient folk from both sides all unsure of right-of-way in a strong current.
Cool DR in 50’ visibility through the morning; and
Solved the buoys that lean into the current phenomenon.
The latter first. Coming up the Connecticut against the river’s natural flow plus the ebb, I got a good look at two major buoy shapes behaving differently. The cans and nuns are deep buoys, almost twice as much below the waterline as above. These inevitably lean with the current since the mooring chain is at the bottom and they are pulled downstream.
The speed limit/no wake buoys, on the other hand, are a can set atop a larger diameter fat disc float, fairly shallow draft and the mooring chain attachment sometimes centered, sometimes off to one side in which case it exaggerates the lean into the current. These lean into the current. Still not a compulsive photographer and I don’t know how to post anyway but as we (Marmalade and I) took about a half minute to pass each buoy (barely ½ knot over ground) I got a good look. It’s the wave pattern. A boat moving through the water leaves its wake astern, essentially making a hole in the water into which the stern squats. But at about 4 knots (the current) the disc shape of the buoys makes a huge stern wave clutching at the downstream end and lifting that side. The buoyancy that might otherwise lift the upstream end is just enough in front of the buoy that it doesn’t lift, and the buoy tilts into it, with some of the bow wave (upstream end) slopping over the top of the float-disc. The mooring chain at the center of the underside is so close to the surface in these buoys that, unlike the nuns and cans, it exercises little leverage. The wave pattern dominates.
For the fog, I happily adapted a racing tactic.
A good RC (That’s Race Committee, not Roman Catholic!) will set the weather mark exactly upwind so absent current even tacks will get you there. In our not infrequent fog I short tack, never more than three or four minutes per, till we can really see what’s up. Of course, I’ll intuitively adjust the time on each tack a bit for current and expected wind shift, if any.
Thursday as I listened to the traffic on 16 and 13 - “I said go port dummy! Swing to due north, zero zero zero or 360 or whatever but turn now or you’ll die. I’m a tug with a loaded 200’ barge on my head and I can’t stop or even turn much if you keep moving into my track.” - while fueling I decided to stay out of the lanes and go where no heavies dare. Like thread the Thimbles and after that bounce off the coast. The wind was a bit south of east so the starboard tack was favored. This was going to be way too much tacking to DR each tack so, like a race course, I laid out desired targets at anywhere up to 5 mile intervals, usually more like two or three, and short tacked up that course by time. That way I only had to figure one current vector per leg rather than per tack. Even with the occasional 25% error in speed estimate (who can really tell three knots from four?) the distances were short enough that I could usually hear the bell, gong or hooter or see the refracted wave pattern of a rocky island. In one case the fog was so thick that after I circled the sound a couple of times without finding the buoy I daringly assumed it was the target and sallied forth.
The fog lifted to a good five miles in time for me to glimpse Fishers Island and tack out there for some bigger ebb to race us towards Saybrook and was virtually unlimited by the time we started the ever so slow slog upriver. Needless to say, the railroad bridge closed just as I was getting there. One smaller cat joined me in reaching back and forth waiting and a bunch of wusses with sails down and motors running milled about. Once it opened, there was the usual press of impatient folk from both sides all unsure of right-of-way in a strong current.