Catamaran Anchor Bridle

[DesertIsland]

Firstly sorry for the long post. I am attempting to provide all the required information for my situation to make sense to someone who has the patience to read it all!

I am planning to replace the factory fitted bridle on my Fountaine Pagot Astrea 42. She is 12.58m LOA (just under 42ft) 7.2m beam (just over 23.5ft) and just shy of 15000kg fully laden.

Currently each leg is approx 5m long, fixed to each bow through the cross beam brackets with a bowline and having a shamefully inadequate snap shackle where the two legs join as the connector to the chain. To be fair, it works, however it is, to my mind, completely inadequate for anchoring in anything other than benign conditions. I would provide a photo however I am not on the boat until a week today.

My first instinct was to replace it with a longer bridle than currently installed and go 20mm Dia nylon anchor plait or similar and a proper anchor hook. However I came across an article in Practical Sailor which has caused me to pause, reconsider and seek further information/ advice.

I therefore searched and read all the posts I could find on the subject here on YBW, many either highlighted as good info or were written by Jonathan Neeves. Whilst I have learn’t a great deal, as yet, I do not feel I have a clear enough plan to move forward with purchasing and install. Therefore I am reaching out to the vast knowledge here and would value feedback on my current thinking and suggestions of improvement.

My current plan is to:

1. Fit an eye bolt fixing for each leg of the bridle such as the one from Wichard or a commercial lifting rated one like this. I am thinking M12. My concern with the commercial lifting one is if it will stand up to the high corrosion environment it will be in.
2. The rope I am currently planning to use is 12 or 14mm ‘Liros Handy Elastic’ as it has a quoted working stretch of > 20% (i’m thinking good for absorbing the snatch loads).
3. Each end of the bridle will have a eye splice with a stainless steel thimble and a shackle to connect it to the eye bolt.
4. Each bridle leg will have a Unimer U-Cleat mooring compensator.
5. The finished length of each leg (with the U-Cleats in place) is planned to be 7m.
6. The middle of the bridle will have a stainless steel thimble eye spliced into it.
7. Use a chain hook shackled to the thimble to connect to the chain. The chain we have is 100m of G70 8mm galvanised chain.

My math ability is not bad (even if I do say so myself ) however I have been unable to make enough sense of the formulas I have found relating to snatch loads and diameter of bridle rope to get meaningful results with which to make an informed decision on sizing for my situation.

I really quite like the idea of the bridle plate designed by Jonathan Neeves and being able to run the bridle lines back to the aft cleats however I think it is not practical for me to install fixings low down on each bow. Therefore the rope would come from and go back to the ends of the cross beam creating a near 180deg turn in the rope where it passes through the bridle plate. This (rightly or wrongly) I feel would not be good for the rope and would weaken it. Although I am certainly open to be convinced.

 

[Neeves]

Use 12mm dynamic climbing rope, it has an extension to break of approximately 40%. Run from the transoms to turning blocks on the bow and then to a simple chain hook (or bridle plate - its neater). When you buy the rope have eyes sewn into one end and this can attach to a shackle and then to the chain hook. You have an approx deck length of 11m, so if you commence at the transom you have elasticity of the deck length and for every day usage you will have the extra from each bow to the shackle/chain hook, say an extra 5m (each side). If you buy 'even more' and start at the transom and deploy 11m +5m but bought, say 30m each side you have an extra 14m carefully stored in a bag on each transom that you can deploy as conditions get tough. Use a sheet winch.

Surely your cat has bob stays holding a prodder - ?? use them to run from the chain hook with a bridle plate (I have other options) to the strong point defined by the bobstays on the bows (at the waterline). You may find that though you don't have the bobstays, nor prodder, the reinforcing for same was built into the bow. We reinforced the bobstay termination, at the bow waterline, with 10mm aluminium plates and extra glass.

Based on the layout described in the PS article, that introduces the bridle plate, the arrangement benefits scope - appreciably. The rode, in terms of scope, is 'attached' at the waterline, not at the bow roller, and this means a scope calculation based on depth of water + bow roller distance above the water - can remove that last dimension - you only need calculate using depth of water. (Its all clever stuff ).

Snubbers are all about elasticity - the more the better - more means a stretchy rope (and dynamic climbing rope is the most stretchy) and length means more stretch.

If you were in Sydney, Australia I could lend you 30m x 12mm x 2 of climbing rope to try - but you do not say where you are located.

When we started on the above concept, or half way through development, we used 12mm dynamic ropes. We were 11.5m x 7.5m beam and 7t cruising weight. We bought 12mm new rope but subsequently downsized to 10mm rope, 30m each side. We use 6mm Armorgalv coated High Tensile chain.

Snubbers are consumables, like your chain and sails. They wear out. Usually they fail unexpectedly. Life of elastic ropes are based on numbers of cycles and the amount of stretch of each cycle. So building a stretchy snubber/bridle where you want stretch means that you are intentionally, our unwittingly reducing life of the bridle/snubber - carry spares.

Elasticity of rope is more correctly determined by the weight of rope - not its diameter. Elasticities quoted might be to a WLL not at failure.

This also works for monohulls - a bridle is not restricted to multihulls

Viking Anchor in Israel and Ukraine (what a combination ). I think are sourcing bridles and snubbers and have bridle plates (and Boomerang), to my designs, made in Ukraine. I think the snubbers have sewn eyes at one end. I have no commercial interest in Viking - I'm just flattered that someone wants to follow my ideas. However check - both locations are less than ideal - things may have changed.

If you send me a PM with your email address I can send you a couple of articles you may not have seen. But keep other correspondence to the Forum, for the benefit of other(s) . If anyone else wants articles - send me an email address by PM. (I've just sent a stack of links to a YBW member and we may make an Armorgalv 8mm HT chain rode to replace his existing 10mm rode) - I'm happy to help

Mull this over and then ask the questions raised

Jonathan

Edit - if your snubbers/bridle do not fail then either you anchor infrequently or anchor only in benign conditions (and you really don't need a snubber). Alternatively your snubber/bridle is too beefy and you are not enjoying elasticity - you are not stressing it. If you do need a snubber then it will be cycled under tension and it will break. We have not broken climbing rope but did break 2 earlier iterations. When they fail they do so with a sound like gunshot - its not something that happens and you know nothing about it.

Its a bit of a compromise - snubbers work because they are elastic (but work as a team with the rest of the rode). To be elastic they will be much weaker than the rode - if you go for strength you lose elasticity.

But snubbers make your time at anchor more comfortable - the rode is the ultimate fall back.

Its a good idea to have a short length of rope at the bow roller secured in such a way that if your snubber fails the short strop keeps the snatch off the windlass (a sort of chain lock - but it can be designed with a bit of stretch).

If your snubber fails you can easily replace the failed snubber as often the chain hook (or attachment point) is just forward of the bow - because a lot of your snubber is inboard down the side deck.

Jonathan

 

[DesertIsland]

If its not a good idea to run the bridle from the current fixing point to the chain hook/plate and back to a fairlead on the cross beam (due to the sharp change in direction of the rope), I like your idea of going from the stern over the bow to the chain hook without returning to the bows, simple, yet I hadn’t thought of that. Thank you. And yes it would enable quite a long bridle. What do you think of the idea of the fairlead in the following picture (not my boat but a sister boat) to guide the bridle?


This following picture is the only one I can find that sort of shows the bowsprit and bridle on my boat. I can get a better one on Sunday if it helps. As you can see I do not need bob stays with that beefy bowsprit! Where the stripe is on the inside of the hull is actually a sealed (and filled with foam) area which, I think, extends approx half way up the hull. Therefore I cant fix any fittings into that area without a lot of work cutting access into that area on the inside.



Thank you for the very kind offer of a loan of rope however I forgot to say I am in the UK (currently). We have been marina based up until now however next spring we are starting a leisurely sail to Australia (planning to take 5-7 years but could be more) initially by sailing to the Med next year. Most of our time will be at anchor.

I will start looking for 12mm dynamic climbing rope. My initial quick search only came up with sizes up to 11mm but I will look in detail tomorrow.

 

[Neeves]

If its not a good idea to run the bridle from the current fixing point to the chain hook/plate and back to a fairlead on the cross beam (due to the sharp change in direction of the rope), I like your idea of going from the stern over the bow to the chain hook without returning to the bows, simple, yet I hadn’t thought of that. Thank you. And yes it would enable quite a long bridle. What do you think of the idea of the fairlead in the following picture (not my boat but a sister boat) to guide the bridle?
View attachment 166011

This following picture is the only one I can find that sort of shows the bowsprit and bridle on my boat. I can get a better one on Sunday if it helps. As you can see I do not need bob stays with that beefy bowsprit! Where the stripe is on the inside of the hull is actually a sealed (and filled with foam) area which, I think, extends approx half way up the hull. Therefore I cant fix any fittings into that area without a lot of work cutting access into that area on the inside.

View attachment 166012

Thank you for the very kind offer of a loan of rope however I forgot to say I am in the UK (currently). We have been marina based up until now however next spring we are starting a leisurely sail to Australia (planning to take 5-7 years but could be more) initially by sailing to the Med next year. Most of our time will be at anchor.

I will start looking for 12mm dynamic climbing rope. My initial quick search only came up with sizes up to 11mm but I will look in detail tomorrow.

Very quick answer to your concerns of the angles through which the rope has to turn and you idea of using the fairlead. The fairlead is probably going to be a point of abrasion or stress. But still use the fairlead but hang a block, single sheave, off the fairlead, use nylon tape to attach the block. You may need another block on the bow itself where the snubber turns from the deck to go to the black fairlead (or block). That's what we did but our sheave hung off a horn cleat (used for mooring lines). You then have a frictionless, or nearly so, turning point. Run from transom through stanchion bases, to turning block and then to a simple chain hook. You can still have excess bridle if at the transom you run through another block. Normally the over long bridle is stored as you would a sheet but when in use you run from the aft located turning block to a sheet winch. You can then extend the bridle at your leisure (except you might need to go to the bow to extend the chain).

Climbing rope is difficult to knot. If you order rope the manufacturer can sew an eye or this can be done by a local sailmaker. You can knot - I have used a halyard knot - but once tied and stressed it cannot be undone and you need to cut the knot off.

In Australia retired climbing ropes used in gyms are stored and then go to land fill. They are sometimes used as tie downs on Utes (pickup trucks) and other miscellaneous uses - BUT they must not be used for safety applications. But you can pick up used ropes easily. I gather its more difficult in the UK and they chop them up - so they are useless and then go to land fill. Go to your local climbing walls and see if you can persuade any of them to save a couple of ropes - the higher the climbing walls the longer the ropes. Point out to the gym that in landfill they will decompose over centuries and your rebirthing them saves the environment. I have a gym not far away that uses 30m ropes but others only have 15m ropes. Here ropes are good to test ideas out - they come free (you might want to contribute to their Xmas party) and once you are comfortable go buy new rope. The gyms cannot sell these ropes as selling implies responsibility for what they are selling, If the biggest you can find is 11mm - go for 11mm but you need length - so find gyms with high walls. So find your walls - there will be a number of them - go and speak to them and see if you can persuade them to save a couple of lengths when the ropes need to be retired. Finding a source then gives you assess to the spares I mentioned in my first post on this thread (and they make good mooring lines/springs) - so if you are offered 4 ropes - go for it!

I note the restriction on not having a bow securement point at the water line.

To keep the bridle length forward of the bow short you could go from my taped on block, to the chain hook/bridle plate (we can discuss later) and then back to the bow - say to the central bow roller. This way you double the length beyond the bow but its only 'using' half the length - if that makes sense. So you have say 11mm down the side deck, 6m to chain hook, 6m back from chain hook to termination point (at say bow roller) and then any extra you have stored in a sheet bag at the transom. Now you have plenty of elasticity - but it does not mean you need a huge bridle (or snubber) forward of the bow. This is an intermediate step we used when we developed our system but we moved on quickly to the bridle plate with the Low Friction Rings. So... on benign days you simply attach the chain hook (and the hook will sit just forward of the bow) on bad days you extend extra from the transom and the chain hook might be 10-15m in front of the bow.

Its breakfast here - this evening I'll see if I can find images of our blocks when attached to the bow/fairlead/horn cleat - and other assorted ideas.

I'll send the articles this evening to the email address, they are big files otherwise I'd post them here. They are repetitive - but may give you ideas.

The best chain hooks come from the lifting industry - the lifting industry rejected as dangerous the chain hooks sold in chandlers decades ago.

Again keep asking questions or make observations.



Jonathan

 

[Neeves]

I had a quick look for our early use of a single block, one sheave, attached with tape to the bow horn cleat to feed one arm of the bridle forward. I had not realised we updated this practice so early - at least 8 years ago.

Your idea of using the fairlead on the cross beam reduces the 'width' or angle of the bridle. You are looking for separation to minimise the impact of yawing and reducing the angle reduces the opportunity - maybe not much - but when the chips are down we want all the help possible.

Yawing is a major factor in anchors dragging - tensioned from one direction and then another. The yawing may have nothing to do with the vessel - it might be the wind veering (and we would deploy 2 anchor in a 'V' or fork - adding to the benefits of a bridle). You will find some people criticise use of 2 anchors in a 'V' - maybe they have not experienced a yawing wind.

If you don't believe a yawing wind - just watch vids of aircraft landing - the aircraft do not yaw to entertain the passengers!

Jonathan