Bridle Line Sizing?

[Chotu]

What are you guys running for your bridle line sizing?

i was running 5/8” bridle with 3/4” anchor rode (all 3 strand nylon)

i ordered replacement cordage for the bridle when i ordered my new anchor chain and i mistakenly ordered 1/2”.

wondering if I will be able to get away with using 1/2 inch?

It looks and feels pretty flimsy compared to what I am used to, but I see the breaking strength is 5700 pounds.

[Chotu]

I think my post was unclear.

it looks like I’m talking about the anchor chain. I think that was confusing.

I’m only asking about the bridle. I was running 5/8” and mistakenly ordered 1/2”

what are you running for you bridle and what size catamaran do you have?

[barnakiel]

fine enough to be a fuse, fat enough to be easily handled under load


b.

[SailingHarmonie]

If you feel 3/4” line was sized properly for the rode, it seems 3/4 is needed for the bridle. The two legs of a bridle do not share the load evenly, they alternate it.

1/2” of the same construction is 25% the strength of the 3/4” rode. Even if you believe that the load is shared between the bridle legs completely evenly, it combined line is half the strength of the rode. Does that seem remotely reasonable to you?

[Chotu]

Originally Posted by SailingHarmonie

If you feel 3/4” line was sized properly for the rode, it seems 3/4 is needed for the bridle. The two legs of a bridle do not share the load evenly, they alternate it.

1/2” of the same construction is 25% the strength of the 3/4” rode. Even if you believe that the load is shared between the bridle legs completely evenly, it combined line is half the strength of the rode. Does that seem remotely reasonable to you?

it sounds reasonable, but that’s not how it’s done.

A snubber on a monohull or a bridle on a catamaran is not sized the same as the anchor rode.

It’s always smaller and designed to stretch like crazy, absorbing variable loads and smooths out the ride.

5/8” was something i liked, even though a lot of people on here said it was too big to properly do that “knot” where you just loop a spliced loop around to hold. I liked the greater strength of 5/8”. I’m still concerned that 1/2” is too flimsy and will break too soon

So.. i’m trying to see what other people are running

[SailingHarmonie]

Originally Posted by Chotu

it sounds reasonable, but that’s not how it’s done.

A snubber on a monohull or a bridle on a catamaran is not sized the same as the anchor rode.

It’s always smaller and designed to stretch like crazy, absorbing variable loads and smooths out the ride.

5/8” was something i liked, even though a lot of people on here said it was too big to properly do that “knot” where you just loop a spliced loop around to hold. I liked the greater strength of 5/8”. I’m still concerned that 1/2” is too flimsy and will break too soon

So.. i’m trying to see what other people are running

If you are running a nylon rode, which is how I read your description, you do not need the bridle to absorb energy, the long length of nylon will already do that. The math doesn’t lie.

But in any event you agree with me, the 1/2” is way too small.

Snubbers on chain rodes should be sized with a breaking strength similar to the WLL of the chain(*), and then made long enough to absorb energy of load surges. People who use these 2 meter long “snubbers’ are kidding themselves.

Having a snubber break under rough conditions could start a failure cascade that would be hard to stop. Basing the size of the snubber on the knot used is kind of a bad idea. If you need a snubber bigger than you feel you can attach, use a dyneema gasket or other attachment method, don’t downsize the snubber diameter.

(*) Yes, these are different things…

[tenchiki]

When using an all chain rode, the primary purpose of a snubber is to stretch to absorb varying loads (as said above). For a given amount of load-absorbing stretch, you need a longer snubber if it is a larger size.


Since you are using a nylon anchor rode, the primary purpose of the bridle is to keep the cat facing into the wind. In fact, you actually want less stretch in the bridle, to keep the "pivot point", where the bridle legs connect, to stay as close to the desired location (usually along the centerline) as possible. Since the stretch is coming from the anchor rode, you could even use dyneema for the bridle, though I'd still want some stretch in the bridle as a safety factor (especially if you are in very shallow water, where the amount of stretchy rode is less).


Also, if your 1/2" bridle breaks (not from chafe!), then you have probably exceeded the WLL of your 3/4" anchor rode.

[Chotu]

Originally Posted by tenchiki

When using an all chain rode, the primary purpose of a snubber is to stretch to absorb varying loads (as said above). For a given amount of load-absorbing stretch, you need a longer snubber if it is a larger size.


Since you are using a nylon anchor rode, the primary purpose of the bridle is to keep the cat facing into the wind. In fact, you actually want less stretch in the bridle, to keep the "pivot point", where the bridle legs connect, to stay as close to the desired location (usually along the centerline) as possible. Since the stretch is coming from the anchor rode, you could even use dyneema for the bridle, though I'd still want some stretch in the bridle as a safety factor (especially if you are in very shallow water, where the amount of stretchy rode is less).


Also, if your 1/2" bridle breaks (not from chafe!), then you have probably exceeded the WLL of your 3/4" anchor rode.

thanks!

this is Catamaran. Not mono. My bridle is 25ft long

it’s interesting. I did look at the WLL and the breaking strength of all the sizes.

WLL is in the hundreds of lbs. breaking in the mid 1000s.

I think you are always exceeding the WLL but you never get to the breaking strength.

is it chain? Is it rope? Yes. It is. It’s both. There’s no need to worry about if I’m connecting to chain or rope because I’m connecting to both. probably best for everyone’s imagination to just think all chain however

this summer, I broke 5/8” in a freak event. The boat went through a 180° wind shift. Coupled with a huge acceleration of wind. A big gust from a front. The storm of the summer. The boat picked up serious speed and moved about 200ft. Then the anchor reset. BAM! During that event, a mega yacht, a commercial tugboat, and about half a dozen boats dragged and one half of my bridle blew up into shreds. The great thing about using knots is I just cut off the part that blew up and retied the same line on. Fixed in 10 minutes for $0

[Chotu]

I posted this in the multihull section hoping that some other people with Catamarans might be able to chime in and let me know what size bridle cordage they are using. I haven’t seen anyone that actually has a bridle and is using it on Catamaran in here yet. Where are you guys?

I remember reading that other people used half inch on big Catamaras. I already have half inch. Ordered by mistake. I don’t want to go waste money just because I’m paranoid. Hopefully some data will come in on this thread and confirm or deny my paranoia

[Miyalk]

Hi Chotu, we have a FP Bahia 46", we have a 20mm 8 plait polyprop bridle. I made the 2 'legs' 7.5m long, (same as the beam). Not sure how that compares to american sizing!

We use the same bridle for mooring and anchoring. (boat lives on a swing mooring.) Has been fine in 50k winds. I replace it every couple of years.

[GordMay]

Symmetrical* Bridle/Sling Load calculation:
Load on Each Leg = [Total Load ÷ # Legs] x Load Tension Factor
Load on Each Leg = [Total Load ÷ # Legs] ÷ Load Reduction Factor

Tension Factor [TF] = Length of Each Sling Leg ÷ Distance to Load Connection

Reduction Factor [RF] = Distance to Load Connection ÷ Length of Each Sling Leg

“TF” Load Tension Factor at:
Leg Angle 30° = 2.000
45° = 1.414
60° = 1.154

“RF” Load Reduction Factor at:
Leg Angle 30º = 0.5 [sine of the angle]
45º = .707
60º = .866

Leg angle is the “inside” angle, between a line on the beam of the boat, and the bridle leg.

* Symmetric loading occurs when the load is shared, equally on each leg, because the center of loading is placed, equally/centrally, between the pick points, on the boat.
Asymmetric loading occurs when the centre of loading is not equally spaced, between the pick points, so the bridle and fittings will not carry an equal share of the load. The bridle leg, connected to the pick point, closest to the centre of loading [smallest leg angle] will carry the greatest share of the load.

WLL of SYMMETRIC Bridle Assembly = WLL of bridle rope x [D ÷ L] x 2
Where:
D = Distance from C/L of boat to anchor rode connection point
L = Length of bridle leg
2 = Number of bridle legs

[catsketcher]

Gday Chotu

You could probably use the 1/2 inch somewhere else, but it may be fine to use.

You can certainly use a too thick bridle. Ifr the bridle is short then the loads are higher and the cat swings quicker. Also you lose load absorption. We had this problem using 12mm polyprop on our 4000kg cat. It did not give enough to allow for load absorption in large gusts.

I have to make up a couple of bridles. One will be a short one for anchoring in lighter winds (up to 20 knots) in shallow water. The other will be longer and use thin nylon to ensure it stretches enough to cope with gusts and has enough give. Too thick and you don't get enough elasticity.

I find I need to adjust the bridle length to get the boat's natural frequency (of swinging in the wind) to be exactly compensated by the natural damping of the bridle. No one can tell you what your cat needs, but if you get the bridle length and line thickness sorted right then you will sail around very little in a big breeze.

You will have to replace the nylon pretty quickly unless it is black. White nylon does not like the sun.

[AiniA]

I used 1/2" on a 40,000 lb monohull with all chain and it worked fine. I replaced it after two+ years out of an abundance of caution. I worked fine but a cat is different so don't know if my experience translates.

[team karst]

Originally Posted by Chotu

thanks!

this is Catamaran. Not mono. My bridle is 25ft long

…..



this summer, I broke 5/8” in a freak event. The boat went through a 180° wind shift. Coupled with a huge acceleration of wind..,,,Fixed in 10 minutes for $0

Where did the line break? At a splice or thimble or mid section? Is there wear at whisker lines?

[rslifkin]

1/2" is probably a little on the small side, but not unreasonable. Even if you go bigger, the 1/2" bridle would be good to have around for light to moderate weather when you're on all chain and not into the rope portion of the rode, as it'll give you more stretch. And then maybe a 5/8" or 3/4" bridle for when bad weather might be expected or if you've got a lot of rope rode out and don't need the extra stretch.

In general, you can always get more stretch with a bigger (stronger) line by just making it longer.

Personally, I like to limit how much extra chain is let out after a snubber or bridle is attached so that the snubber/bridle can't stretch more than about 15 - 20% without the chain going tight. That greatly reduces the risk of failure due to overloading, and it also gives you a sizing gauge. If you're pulling it tight regularly, it's time for a bigger (and probably longer) bridle as you're hitting the limits of what the current one can safely provide for stretch.