Mooring line design

Hello to all,

Considering the title, I am searching for the proper up-to-date literature taking into account the latest calculations about forces - and overall, energies and powers - encountered dynamically by our boats at anchor (of course in reasonably sheltered areas) against the winds and the seas.

Through so many testimonials, the breaking consequence on the lines, either all chain or mixed, put fondamental questions about the weakest link, which can be so different from the deck to the bottom.

I red with really great benefit the following calculating sheet produced by Mr Alain FRAYSSE: http://alain.fraysse.free.fr/sail/rode/rode.htm

Thanks in advance for contributing and please make prior assumption of design calculations and engineering concerns, not of maintenance failures.

Patrick

 

Patrick
Did you want to discuss anchoring or mooring systems? And what size vessel ? Class requirements are quite specific and they work.

 

Hello Mike,

My purpose is to consider anchoring in heavy conditions and reasonable shelter with a sailing boat (my 35 footer for instance).

At the moment, I am considering Alain FRAYSSE's work as probably the most complete to evaluate such a design, as follows:
http://alain.fraysse.free.fr/sail/rode/rode.htm

But, I wonder if some feedbacks are available, especially validating the calculated forces encontered on the line.

Breaking lines and security are to be considered in that way towards possible improvements.

Kindly.

Patrick

 

With mooring lines chafe is the obvious failure point.

Normally chafe is caused by poor design, poor deck layout. A mooring fairlead is designed to deflect the line and lead it to its cleat. A fairleed must not be used as a turning block.

Mooring lines must be flexible..stretch. Low stretch yacht braid type mooring lines tear hardware out of the deck, shatter winch pawls and generally cause problems.

Stretch is particularly important when mooring lines are short. The stern line on a sailing yacht is always the shortestest mooring line when tied alongside. This line takes a very heavy load. And since it is short it must stretch or the deck hardware will be overloaded.

Since your boat will be correctly designed and have 4 cleats on each side and 4 fairleeda on each side chafe should not be an issue.

The stern fairleed shall provide a correct lead to your primary winch.

Chafe at the dockside, bollard end of the mooring line ,is addressed by double covering the end of the mooring line. This cover is made of a chafe resistant material. Chafe caused when the dockline must bend, deflect, over the Concrete edge of the dock is addressed with lengths of fire hose that are always on the mooring line and can be positioned as needed.

The diameter of mooring lines must match the capabilities of you self tailing winches on deck and the line carring capicty of your cleats.

If large diameter lines are used you may not be able to ease a heavily loaded line while it is on the cleat

Three strand is cheap and easy to work with. Docklines shall be black. White suffers from UV deterioration and looks old very fast.

http:// subir fotos a internet

 

Stern mooring line leed to primary winch is critical for competent boat handling



http:// subir fotos a internet

 

I'll lend you a book to read that should help at the level you need to understand, I sent you an email via BD net.

In sand or mud when using a snubber to take the shock loading you wont much exceed the max holding force of the anchor prior to it dragging (the force varies as the anchor resets and then drags and resets and so on...)

Chain rode by virtue of it's weight reduced the shock significantly and it's further reduced by using a snubber across a length of chain which is often just a length of nylon rope of much smaller diameter than that required for a rode. Or use a rubber snubber both work well and are less hassle and risk that mucking around with weights. There are very good guides an the chain size you should use.

Chain is self stowing, tremendously robust and gives a beneficial catenary. It's also immune to chafe.

Beware anchor comparisons, the holding results are not necessarily linear by weight and a slightly larger much cheaper plough anchor for example, can significantly outperform a supposedly superior design one size down and even perform better in weed rock and mud while easily matching performance in sand.

You might want to look at what weight allowance was made for anchoring gear by the designer. But hefty ground tackle is very good insurance.

 

The old fashion CQR anchor is a good anchor. Its especially desirable because it nests , well on the offset stemhead roller of a sailing yacht. Other good anchors like the bruce are difficult to nest .

Something to remember is that when you loose your anchor while on a cruise ,
it may be impossible to purchase a replacement of the same style. Your stem head anchor handling gear should be versatile enough to handle other style anchors.

 

Hello to all,

Thank you for yours inputs.

Do you know such cells used on a sailing boat in the range 30 - 50 feet that produced measurements especialy during heavy conditions and the relative published literature ?

Following my thread, these data are to be compared to calculated ones.

I wish you all calm and secure anchorages.

Kindly.

Patrick

 

For small craft wind loads in sheltered anchorage have a look at this study:

http://www.practical-sailor.com/issues/37_17/features/anchor_testing_rode_loads_10784-1.html

 

Thank you Mike.

I didn't succeed in sending you an email at your indicated adress.
Please confirm it at pecf.blosse@wanadoo.fr

Kindly.

Patrick

 

Hello to all.

Thanks a lot Mike: I finally received your pdf file.

I had some personnal discussions with Alain POIRAUD and Alain FRAYSSE.
The first because I equiped my 35 footer with SPADE anchors (steel and aluminum) and the second concerning his excellent public calculation sheets allowing simulations to design anchoring suitable line.
http://alain.fraysse.free.fr/sail/rode/rode.htm

My aim at this point is to try to compare the results between theorical design and pratical measurements especially during heavy conditions because of possible well known breaking line conditions.
In my opinion some improvements are then possibly to be foreseen, if any.

If some of you sailors are french fluent, a glance at a thread dedicated is of possible interest at: http://www.stw.fr/forumstw/quest_answers.cfm?quest_id=48188&st_row=1&rep_st_row=321&topic_id=22

Smooth anchoring to all.
Kindly.

Patrick