Increasing a rode's caternary

[Franklin]

Ok....I think I see it now. I guess that's why I instinctively pull on the middle of a line between a pulley and a cleat when I want to tighten it. I guess when both lines go through the same pulley and attach at the same place, the bow, it is essentually one line.

I admit it, I was wrong

So I guess the only smart thing to do when others are doing the IBM or the BM, then do the BM with a lot of slack (to get beyond the 120 degree angle) and a kellet on both lines to keep them out of the keel, rudder and prop. I'm glad they don't do the BM here.

Thanks RichH and Tom for pointing out my ignorance I learned something today.

 

[DanW9494]

My limited experience says tighten it

I don't see the reason for loosening the rodes, if I'm understanding the thread.

The key premise to any safe anchoring set up is a set anchor. Allowing the wind or tide to change the rodes orientation 45* to the anchors orientation is an invitation to drag your anchor.

This is a poor man's temporary mooring field. The weak link will be the set of the anchor or the strength of the rode if the wind or tide changes to beam on.

There is a mechanical advantage to the lateral force. But, the skipper has to fight this force to keep the anchors set. You can do this by tightening the drawstring, which will keep the boat closer to the line between the anchors, if you think the setup is strong enough for the wind or tide. This will minimize the change in the angle of orientation while significantly increasing the forces on the rodes. Or you can drop a third hook upwind/upstream.

 

[Franklin]

Dan:

The point that took so long to become clear to me is that the pull on the anchors will be about 3 times as strong. Now in light conditions that's not a big deal, but in a strong current or a blow, I'd say that is a big deal. There is also the issue which we haven't discussed and that is tidal change. What if the tidal change is 20' like it is in some parts of the world?

Any anchor should be able to rotate 45 degrees without coming out. It's the 90+ angles is what pops them out IMHO.

 

[henkmeuzelaar]

It all depends on how you define "tightening the rode"....

Dan,

If you mean to increase rode tension to -- say -- 3,000 lb, then we all know what we are talking about. Unfortunately, very few of us do have a working tensiometer aboard. Moreover, when dealing with highly elastic rodes, interpreting tensiometer data is far from straightforward.

On the other hand, if you mean to straighten out the rode to the point that the catenary is more or less removed, you are embarking upon mission impossible for all the reasons enumerated by Tom.

By way of an easy to verify, above-water example: just look at the forestay. Wouldn't we all love to remove that ugly, performance-robbing sag?! Even with a nonelastic line you are only going to succeed in achieving your goal if the stay is nearly vertical (i.e. you are not fighting gravity) and wind-induced drag forces are negligible. A hell of a lot of practical usefulness that is going to have.....

Now, subsitute a piece of elastic nylon anchor rode for the forestay and tension it till it looks almost straight. Then ask a 10-year old kid to lean against it..... What do you think is going to happen?? Nuff said.



Have fun!

Flying Dutchman