Setting an anchor when tides do a 180 degree change

[Spade Anchor]

https://www.youtube.com/watch?v=l59f-OjWoq0

38 minutes is very interesting!

[reed1v]

If you set a heavy CQR on chain, it will reset itself fairly quickly in most bottoms(weeds excluded). Fairly common in roadsteads to have reversing currents. Big problem is if chain gets wrapped around the anchor. Not that common but does happen. Danforths can skip across the bottom if the boat is moving too fast with the current.

[sy_gilana]

Lots of advice above. Lots of stuff to wade through.
My personal 2c.
You did say 180 degrees, so there are two known directions, in this case a Bahamian Moor is probably best.
If there are changes in ANY direction, a genuine Bruce loves to be turned and turned, it just screws itself in further.

[knockabout]

try to pull in at 90 deg to the flow and set your rudder slightly off centre so you swing 180 not several 360 s /the pioneer river is challenging place to anchor/6 mtr tide range- shallow-sand over limestone shingle patches-prevailing wind is usually against the run out /the anchor moves in the sand till finding a hold in the shingle once pulled in to the shingle the holding is good/fitted 8 mm swivel to 6mm chain between anchor and chain to stop the chain twisting up/there may not be an accurate answer to your question /boats move differently have different windage different anchors / the wind changes/ tide height varies boat wakes can pull out an anchor set with short scope/if you can anchor safely clear of hazards especially expensive ones and be vigilant you may attain some degree of anchoring peace of mind (no guarantees)

[thinwater]

Think on the obvious for a moment.

How much force does it take to propel the boat at the 1-2 knots of a typical tide? No more than it does to pull a boat along a slip when moving it. For my boat, perhaps 10-20 pounds.

How much wind does a 15 knot wind load provide, with minor chop. I've measured this, about 75 pounds.

It's the wind that matters, far more than the tide. I doubt a power set anchor (about 250 pounds for me) is moved by a light tide. It won't even pull all the chain around unless combined with wind. That has been my experience. Yes, the tide can cause some interesting fouling problems, and if it is on the beam (because of the wind) the force will be greater. But not tide alone. It has to be combined with wind to cause trouble.

A wind shift is a different matter.

[JPA Cate]

The OP lives in an area with 4 - 6 meter tides.

Ann

[troppo]

Originally Posted by Ann T. Cate

The OP lives in an area with 4 - 6 meter tides.

Ann

Just on that point of speed of tide, one place I noticed a burst of water speed when the tide level reached the point where it flooded out from the creek proper onto wide mudflats. Since I am interested in stuff like this I stood in the bow with my watch in stopwatch mode and when something floated past, I clocked its time to travel to the stern of the boat (yes, running back so I could make sure it was more accurate). Then I calculated speed of flow.

Often it was about 3 knots but sometimes faster. Perhaps 4 knots. Even at 3 knots, I found the anchor rode to be very tight. More than I could easily haul in without motor assist. I could not think of any way to assess the force on it but would have liked to.

Louis

[leftbrainstuff]

At China Camp in San Francisco Bay an anchored vessel will be subject to full tide reversals and often wind against current.

Our Rocna resets itself and requires no input from us. We pay out approximately a 5:1 scope and dig in. The holding is mud which is key.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[sailorchic34]

Originally Posted by leftbrainstuff

At China Camp in San Francisco Bay an anchored vessel will be subject to full tide reversals and often wind against current.

Our Rocna resets itself and requires no input from us. We pay out approximately a 5:1 scope and dig in. The holding is mud which is key.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

My old bruce clone held there quite well at china camp. San Pablo bay (china camp is on the western shore) drains about 1/2 of California, so currents are a delight there. I have seen a few folks drag with CQR's or poorly set anchors on 2-1 scope.

Most of the SF Bay, San Pablo and the delta has fairly strong currents. Max ebb out the gate is many times 4 knots and sometimes exceeds 5 knots. I have sailed backwards near the gate.... Fun times.

[Cheechako]

My luck with dual anchors has always been bad. Once I set a Bahamian Moor, in of all places the Bahamas. I was at that little island with the Iguanas on it. (forget the name) Anchored in the channel which gets a lot of current thru there. Next AM, the two rodes were twisted entirely. Top to bottom. Go figure. Now here's the problem, how do you retrieve that?
When you get the rode snubbed up tight the anchor wont break free because the two anchors are apart and all you are doing is pulling the anchors in deeper. It took us a long time to get it sorted out.
Something similar seems to happen each time I try two anchors. I will not set two anchors unless there's a hurricane coming at this point.
Another example is in the dead of Thanksgiving night, gale blowing outside the harbor, tide change going on and a lot of current (PNW), we noticed the boat was swinging very close to the rocks. OK, we'll solve that by putting out a stern anchor. Rowed the stern anchor out, set it and got back on board. The pressure on the stern and bow anchor then puled the bow anchor free and it started dragging. Arghh! We abandoned the stern anchor and rode and tied a fender to it for retrieval next day. Then pull the bow anchor quickly and headed out into the channel. Spent the next 5 hours in steep breaking seas getting to a better anchorage.

[thinwater]

Originally Posted by troppo

I could not think of any way to assess the force on it but would have liked to.

Louis

How much power does it take to drive the boat at the same speed? 1 hp ~ 35-45 pounds, depending on the prop etc. Less with outboards.

Another way to estimate forces is the attach a thin line and measure the stretch. Then stretch the same line with weights attached.

I use a load cell, since I do a lot of testing, but the line method gets used occasionally when the geometry is weird.

[troppo]

Originally Posted by thinwater

How much power does it take to drive the boat at the same speed? 1 hp ~ 35-45 pounds, depending on the prop etc. Less with outboards.

Another way to estimate forces is the attach a thin line and measure the stretch. Then stretch the same line with weights attached.

I use a load cell, since I do a lot of testing, but the line method gets used occasionally when the geometry is weird.

Wow! I'm going to give them a go.

[RaymondR]

I set 2 anchors pretty regularly. The second on an 18mm poly line which is in 10m sections with thimbles in each end. I shackle a number of them together and unshackle and unwind from the main anchor chain whenever needed. A bit fussy but I like to sleep well at night and have the boat stay where I leave it. I have twin bow rollers which help, almost never use bow and stern setup.

[Toys_with_time]

Originally Posted by Cottontop

Consider a Bahamian moor if anchoring where there are strong tidal effects.

Bahamian Mooring : by S.Bryant [Anchors and Anchoring] - VisitMyHarbour articles

How do you do a Bahamian moor if you are on a cat with an anchor bridle?

[kerrydeare]

Originally Posted by troppo

I have been wondering about a specific aspect of anchoring ... if an anchor needs to be set by reversing the motor, what happens at change of tide when the anchor pops up out of the bed and has to reset itself? Does the motor have to be used every tide change to keep power setting the anchor? ...

Considering that securing the boat is perhaps the most fundamental skill, no anchoring question is "stupid" or "trivial." Problem is that at my advanced age, I hesitate to enter such discussion based solely on time considerations.

If you find yourself compelled to anchor in a significant tidal stream with no access to a permanent safe mooring, you are probably best served by two anchors (mentioned earlier under "Bahaminan" or such). We have had very good success with a pair of the older style Danforth (or "patent") anchors of the High Tensile variety. I am not even sure these are still available for purchase as new items, but that's another issue.

Set one of these on the ebb (with a sufficient amount of chain), hammer it in with the engine, and then drop back twice your swing to set the second, motor forward with vigor and drive the second anchor home. Avoid setting off both bow and stern: this won't really work well. Set both off the bow allowing for the complications of the rodes messing with your keel, and you will be secure.

Best bet: avoid this situation in the first place, and if you cannot, pick a strong permanent mooring.