[Rhodes22-list] Chain/Rope Rode

[DCLewis1 at aol.com]

Bill,
 
To respond further to your anchoring issues:
 
- Your experience with anchoring is useful, and interesting, but we need to  
know what type of bottom you were typically anchoring on/in, the typical wind  
current, sea state, and what your anchoring requirements.  For example, if  
the bottom is mud, your grapnels may not work well at all, but if it’s dead  
trees and boulders, it could work well. Also, if you are dealing with day  
sailing - why would you want to go sailing on a really crummy high wind, heavy  
seas day - but cruisers have to deal with that.  Finally, if you’re  daysailing 
and anchoring for a short while to enjoy the day you may not need the  same 
confidence a cruiser needs when he anchors off a rocky coast with the  intention 
of sleeping through the night.  My point is, your results may be  
representative for day sailing in your locale, but it may be inappropriate to  generalize 
for the rest of the Rhodes community.
 
- Regarding the anchoring of fishing boats that you reported: I assume  you’
re talking small 16 ft to 20 ft boats.  They don’t have the windage or  current 
problems sailboats do.  Many of them can be rowed home.  They  have an easier 
problem. 
 
- Regarding the windage, current, and swell forces: Seems to me you could  
make a stab at estimating those forces.  I’m sure the anchor manufacturers  etc 
do over specify - it’s in their interest to sell a larger anchor, but more  
important, they will be liable if their systems don’t perform.  We might  try to 
figure out the windage, hull drag, and bouyancy forces, it  would be 
interesting, but then we’d have to crank in some safety factors to be  sure the 
systems used by the vessels could perform - and we’d likely be right  back with 
Fortress et al.
 
- Regarding a catenary “going away” when the anchor rode is stressed.   Not 
right.  As I believe Robert said, a catenary is a solution to a type of  
problem where you have forces at 2 ends of a flexible whatever (rope, wire,?)  and 
there is a distributed force due to gravity (or buoyancy, or both).   When you 
see the lines attached to a towed vessel sag you are seeing the effect  of 
the gravitational forces - the deflections are obvious.  If the ropes  jerk 
taught it doesn’t mean the catenary has gone away, those same gravitational  
forces are still there; instead it means the non-gravitational forces have  
suddenly become much greater relative to the gravitational forces, so the  deflection 
that you see, and associate with a catenary, is much less - but it’s  still a 
catenary, and it’s still there.
 
- Regarding anchoring from a beach having the same physics as anchoring 75'  
off shore: they are likely different problems if the standoff from each  
anchoring point is the same.  The difference is the difference in height  between 
the anchor and the boat deck (point of anchor line attachement).   The anchor 
at the beach is about at the height of the boat deck, primary forces  are 
nearly horizontal.  The anchor 75' off shore will be many feet deeper  than the 
deck is high (hopefully), so there will be a significant vertical force  on the 
anchor rode, and perhaps the anchor’s shank, if the weight of the rode  can’t 
offset the vertical force coming down from the anchor line.
 
- With regards to your concerns about large yachts anchoring and their  
chains just going straight down: I’m sure they could blow it.  The flukes  could be 
fouled with the chain as you suggest, they may not have actually set  their 
anchors, they may not even have found the bottom and the anchor may be  just 
dangling.  All sorts of possibilities.  But the fact that the  chains go down 
from the deck as opposed to out laterally is not conclusive  evidence the anchor 
isn’t set and holding.  Rather it means the weight of  the chain is much 
greater than the forces that would pull the anchor line  taught.  To understand 
this just take a close look at the San Francisco  bridge.  Those main cables 
that support the great weight of the structure  are relatively vertical near the 
top of the structure, but then the  catenary asserts itself and the cables 
become more horizontal and continue to  their anchor points at the end of the 
bridge.  The large yachts you  describe are anchoring with large (eg heavy) 
cables and you can only see  the part of the cable that’s very near the top, just 
like the suspension of the  San Francisco bridge, the chain may loop off in a 
catenary to a point that’s  ultimately horizontal at the anchor point- or even 
before the anchor point, but  all that’s underwater and out of sight.
 
Finally, I think there's an implicit presumption here that the entire rest  
of the boating world has engaged in some type of swindle in perpetuating the  
desirability of a metal chain rode, or that they've been too ignorant to spot  
the swindle for what is a very long time.  I think there have been too many  
people involved with all types of boats for too long for that type of situation 
 to occur.  Yes, some people don't use metal chain rodes, and get away with  
it very well given their usage, locales, etc, but when push comes to shove and 
 you really want it right in what could become a tight situation (e.g.  
standing off a rocky coast in a storm and needing catch a nights rest) I'd  vote 
for the metal chain rode.
JMO.
 
Dave