anchor sizing

[Ross]

I have seen those tables but what I wonder is whether or not anyone has tested the theoretical figures in a real anchoring situation.

 

[sailingdog]

Ross-

I'm pretty sure no one wants to be messing with a strain gauge during a storm...

I have seen those tables but what I wonder is whether or not anyone has tested the theoretical figures in a real anchoring situation.

 

[Ross]

Dog , If the instrumentation was in place before the storm then the recording of the data would be automatic and the analysis could be done when the storm had passed.

 

[sailingdog]

Yes, but it does become another possible point of failure in the ground tackle setup and would probably require inspection during a storm. While the data collection might be automatic, the inspection of the gear isn't.

Dog , If the instrumentation was in place before the storm then the recording of the data would be automatic and the analysis could be done when the storm had passed.

 

[Franklin]

Has anyone ever placed a measuring system on the anchor rode measure and record the actual strain on the system in a storm? If they have what were the results?

Ross, before I decided to anchor out in Ike, I did some calculations. Found out that in winds 130 knots hitting a solid flat surface would put a force of about 52lbs on it. So I then calculated that I have at max, 50 sqr feet of surface exposed stern to (I was testing the theory that you don't swing on anchor when stern to). Then I figured another 10 sqr feet of the mast exposed. Then figured that neither of each is flat so only take about 80% of that and I figured that was actually a safe number was it mostlikely would be a lot less.

So, in 130 knots, which of course if I did get up to 130 knots, it wouldn't be 130 at water level, I came up with the following presure on my anchor system:

mast and rigging: 800 lbs
stern and cockpit: 2080 lbs.
total : 2880 lbs.

Now when I was out there and had to pull on the rode, it wasn't anywhere near that much so my numbers were very safe indeed. I figure it was about 600-700 lbs of force on the rode. I come up with this number as I could mess with the bridle when the pressure was in half, but I couldn't budge it when all the force was on one line.

Of course, when you anchor from the bow, the pressure veries as you swing and expose more hull.

 

[Ross]

Franklin,Your 80 percent gave you a good safety factor. I bet a riding sail would reduce swing on the rode.

Dog , Strain gauges are never a part of the structure they just measure the deflection of the structure. The failure of the strain gauge would only represent the loss of data and would in no way hazard the ship.

 

[sailingdog]

Ross-

True, but there are always unintended consequences to doing things... adding complication to a system often causes things that would otherwise be okay, to go very badly wrong.

 

[Ross]

Dog, Don't bother trying this Mainesail probably will.

 

[sailingdog]

I was going to let him anyways... he's got more anchors to try out than I do.

Dog, Don't bother trying this Mainesail probably will.