15 feet too short for storm bridle?

[sailingunity]

I have a 47' Ketch, 32000 lbs dry.

I found this storm bridle on my boat - it's only 15 feet long and made of 3/4 three strand. Knowing what I know about snubbers this seems way too short, but before I throw it out I thought I would ask for some second opinions. Mantus' website would imply that 26 feet is the ideal length - other places I've seen more like 60 feet is the best length - more stretch is better right?

[rslifkin]

I'd call it too short. For bad weather, I'd want big lines for strength, then add as much length as it takes to get enough stretch.



For your boat, 3/4" is a reasonable size for a storm bridle, but I'd be looking at 30+ feet long, probably 40 or 50 considering the load is split between 2 lines at times, reducing the effective stretch.

[Benz]

I'd cut off that rusty hardware, whip the ends, and use them as ghetto dockline.
I'm personally against bridles for monohulls: when there's a storm coming, I usually have two anchors out, one at each side of the bow, each with a single snubber. A bridle just causes more confusion. If I think I might snap a snubber (it's happened), I can have a second one pre-attached, ready to take up the slack when the first one pops, rove in exactly the same way.

[rgleason]

Some good calculators are here https://www.cruisersforum.com/forums...ml#post3553060


I like Snubberhead

https://www.snubberhead.com/anchor-s...ize-calculator


Going with 3/4" may a little too inelastic to reduce anchor loads adequately unless you have a longer bridle. Note that you should replace this gear regularly due to chafe and being stretched past 20% breaking load.

The calculator shows a double bridle of 5/8" x 30' would work "cocktails out of stems" and shackle and hook wll of 1629 lbs. down at the anchor.

You could go to 3/4"x 40" for the same result. (See the graph in the calculator.)


This calculator assumes a 1 knot boat speed at anchor.

[thinwater]

It's just worn out in every sense. Trash it or make a mat from it.


Yes, too short, but I'm not going to wade into that. Do look to see how the chafe gear fit; judging from the wear marks, it is needed. In fact, there may be a better way to route the snubber.

[Shrew]

Nylon line has stretch characteristics based on amount of stretch per foot. Less feet, less stretch. The only way to take the big hits out is to use a lot of snubber.

My snubbers are around 25 feet and too short for real storms. We automatically put out 10 feet and feed out more when the wind picks up and reduce it when the winds die.

My next set of snubbers will be 30 feet.

Stretch is also based on size. A 32,000 lb boat will have dificulty stretching 1"+ line.

I wouldn't consider 15 feet of 3/4" a storm snubber on a 32K lb boat.

[rgleason]

As an Example:

After using Mathias AnchorChainCalculator, to learn about the chain size and length I had selected, I found the length of rope rode needed to attach the boat, from the loose end of chain to the bow using
sin(bow angle) x depth = 295feet.

NER Premium 3 strand 1/2" 7,500 lb x 20% break strength= WL 1500 at 12% Stretch

Total stretch at WL of 1500 lbs = 295ft = 35.4 ft of stretch

Use the Mathias Wagner's AnchorChainCalculator app to get the Anchor Load in say 40.2kn BF8 with

vesssel displacement=11500lbs
chain=1/4"
max length= 0 feet
wind= 40.2kn Beaufort 8
Anchor Depth=0
Vessel Velocity=0
Anchor load found AL=395.7 lbf

Use the formula to solve:

WS(Working Stretch) * AL(Anchor Load)/WL(Working Load)
= 35.4ft (from above) * 395.7lbs/1500 lbs
= 35.4ft * .2638'
= 9.33 ft of stretch

So for a 11,500lb boat with a certain type of wind profile, 1/4" x 40' chain in I think it was 10' of water, the single bridle could be 1/2" x 36' and would stretch up to 9.33 feet at 40.2 knots with an anchor load of 395 lbs.

For a bridle, Frye's Formula says the bridle line should be 70% of the size of a comparable single line.

However all of this has to be adjusted to the boat and existing conditions as needed. Use common sense, it is free and readily available in most cases.