anchor bridle

[psneeld]

I've struggled with this simplification thing since I've been on here. I get that most folks lack either the time or inclination to delve into this stuff in such depth, you're all here for recreation after all and this isn't your career so why make it into work. This is why I make suggestions like here, this was my career.

Yes ....most of us are here for recreation...that's why I try to keep it simple for the level most here need to be. They will study further if they see it as an important point and care to.

But don't assume for one minute that some here were not professional mariners for a big chunk of their lives or professional riggers or crane operators or engineers that don't understand the math, physics and practical use of lifting slings, bridles etc.

Imagine worrying about one breaking and have it come up through their helicopter rotor system....so more than a simple understanding probably happened at some point.

 

[Fish53]

Yes I get that we have a broad spectrum of talents here it's just sort of hard for me to know who knows what, which is why I answer questions. I'm not assuming you're all pencil pushing office types but neither am I assuming you're all accomplished professional mariners. If I respond to a question it's because I assume the questioner doesn't know the answer so if I'm somewhat capable I attempt to provide an answer. You should see a few of the exchanges I've had over the last six years, there's 8 on my blocked list, but conversely I have 82 thanks so I can't be that stupid or abrasive.

 

[OldDan1943]

I have never seen a bridle on a US Navy ship at anchor.

 

[Fish53]

You're not getting it correctly, assume you lose 10% at each splice and depending on the angle you lose another 25% you've lost 45% of the lines strength. It's the angle of pull or stress on the line which isn't directly in line with the load plus the lose at each splice. I have no idea of the total weight of your boat or the surge stress placed on the gear you anticipate so I certainly can't estimate any specs but a 25,000 lb. boat in 30kts of wind can exert over half it's total weight in stress on a maximum surge in open water. Oddly a single line rigged with either a float or a kellet will retain almost all of it's strength, which of course brings up deck fittings which will take up another thread. Honestly to me a bridle seems an unnecessary complication unless there's an issue on deck. I should add that cleats and chocks also reduce line strength as a knot does, 50%.

I was driving home from the store and something was bothering me about what I wrote and I realized I was incorrect. The strength lose is not cumulative, like a chain only being as strong as it's weakest link so it is with line. Two knots can't be added together to reduce strength by 100%. In rigging a sling there are most commonly splices which reduce strength by 10%, less in wire rope thus making sling angles the greater lose factor. The strongest way to rig this for the OP's situation would be short splices with thimbles at each end of each leg with the boat ends shackled into the deck fitting with an appropriate size shackle. the termination end would be spliced into the chain fastener of his/her choice. Personally I'd use a pear ring first but I don't know if they're available in stainless and I'm assuming galvanized is unacceptable. I apologize for my mistake in calculation but the strength lose is still considerable unless knots and short bridle legs with a low degree of angle can be avoided. And again the easy solution is a bit larger line size that will still fit deck hardware. I feel much better now.

 

[Fish53]

I have never seen a bridle on a US Navy ship at anchor.

The biggest reason for not seeing it on almost any vessel is it negates the ability to set two anchors.

 

[dhays]

You're not getting it correctly, assume you lose 10% at each splice and depending on the angle you lose another 25% you've lost 45% of the lines strength. It's the angle of pull or stress on the line which isn't directly in line with the load plus the lose at each splice. I have no idea of the total weight of your boat or the surge stress placed on the gear you anticipate so I certainly can't estimate any specs but a 25,000 lb. boat in 30kts of wind can exert over half it's total weight in stress on a maximum surge in open water. Oddly a single line rigged with either a float or a kellet will retain almost all of it's strength, which of course brings up deck fittings which will take up another thread. Honestly to me a bridle seems an unnecessary complication unless there's an issue on deck. I should add that cleats and chocks also reduce line strength as a knot does, 50%.

Yeah, I think I must be missing something.


My bridle is made up of two legs. Each leg has an attachment point at the ends. At one end is a cleat, the other end is a spliced thimble. Each leg sees tension in just one direction, without a bend anywhere along it's length. So all the tension is always directly in line with each leg of the bridle.


Wait.... I think I am finally beginning to understand what you are talking about. Correct me if I'm wrong.


What you are referring to is the increased load that the bridle leg would have in the system compared to a single line. So if the rode has 10,000 pound of force on the chain and it is connected by a 2 leg bridle and the angle between the rode and bridle is 30 degrees, each leg of the bridle will be taking about 1.15 x 5,000lbs of that force. In other words the inverse of the Cosine of 30 degrees, if I can recall my force vector calculations from college.


What was confusing me was the concept of the angle causing a loss of line strength. That isn't happening at all, but the load on the line is greater as the angle of the bridle from the rode to boat increases. (or the angle from the boat to rode decreases). The increased load would need to be taken into account when sizing the bridle line. Of course the heavier the expected conditions, the longer length of each leg I use. So that tends to be self adjusting.

 

[psneeld]

Yeah, I think I must be missing something.


My bridle is made up of two legs. Each leg has an attachment point at the ends. At one end is a cleat, the other end is a spliced thimble. Each leg sees tension in just one direction, without a bend anywhere along it's length. So all the tension is always directly in line with each leg of the bridle.


Wait.... I think I am finally beginning to understand what you are talking about. Correct me if I'm wrong.


What you are referring to is the increased load that the bridle leg would have in the system compared to a single line. So if the rode has 10,000 pound of force on the chain and it is connected by a 2 leg bridle and the angle between the rode and bridle is 30 degrees, each leg of the bridle will be taking about 1.15 x 5,000lbs of that force. In other words the inverse of the Cosine of 30 degrees, if I can recall my force vector calculations from college.


What was confusing me was the concept of the angle causing a loss of line strength. That isn't happening at all, but the load on the line is greater as the angle of the bridle from the rode to boat increases. (or the angle from the boat to rode decreases). The increased load would need to be taken into account when sizing the bridle line. Of course the heavier the expected conditions, the longer length of each leg I use. So that tends to be self adjusting.

That what was what I was trying to simply say back in post #21 , but it is complicated by rigging gear, etc. The line is weakened by some things but the actual WLL of the line remains constant.

 

[dhays]

That what was what I was trying to simply say back in post #21 , but it is complicated by rigging gear, etc. The line is weakened by some things but the actual WLL of the line remains constant.

Yeah, I was just not connecting the dots.

 

[markpierce]

I don't believe the forces are that great (concerning rode strength) to worry about even if waters are more violent than here:

 

[OldDan1943]

Mark,
I know this is totally off subject but, would you take a picture showing how you mount the anchor buoy to the bow railing of your boat please. Might help all of us.
IF you remember, what parts are required that would help too.
Thanks,
Dan.

 

[markpierce]

Mark,
I know this is totally off subject but, would you take a picture showing how you mount the anchor buoy to the bow railing of your boat please. Might help all of us.
IF you remember, what parts are required that would help too.
Thanks,
Dan.

Dan, I have not used an anchor buoy Anyway, an anchor buoy would be attached with a line to the anchor.

 

[OldDan1943]

Dan, I have not used an anchor buoy Anyway, an anchor buoy would be attached with a line to the anchor.

You do not use the black ball?

 

[BruceK]

...What you are referring to is the increased load that the bridle leg would have in the system compared to a single line. So if the rode has 10,000 pound of force on the chain and it is connected by a 2 leg bridle and the angle between the rode and bridle is 30 degrees, each leg of the bridle will be taking about 1.15 x 5,000lbs of that force. In other words the inverse of the Cosine of 30 degrees, if I can recall my force vector calculations from college....

At some point, all the load can be on one of the 2 legs of the bridle. The rope selected needs to be able to cope with that.
Similar to Industrial Law restrictions on lifting heavy objects. Just because 2 men take on the lift, it doesn`t divide the load by 2.

 

[Fish53]

That what was what I was trying to simply say back in post #21 , but it is complicated by rigging gear, etc. The line is weakened by some things but the actual WLL of the line remains constant.

We're actually using breaking strength here rather than WLL. WLL is a weight limit with a safety factor typically 5 to 1 for new, used nylon rope making 5/8 nylon have a WLL of about 1750 lbs. so I doubt the OP wants to spec this using WLL. I've explained as best as I can elsewhere so saying it all again here would just be boringly repetitive.

 

[Fish53]

Yeah, I think I must be missing something.


My bridle is made up of two legs. Each leg has an attachment point at the ends. At one end is a cleat, the other end is a spliced thimble. Each leg sees tension in just one direction, without a bend anywhere along it's length. So all the tension is always directly in line with each leg of the bridle.


Wait.... I think I am finally beginning to understand what you are talking about. Correct me if I'm wrong.


What you are referring to is the increased load that the bridle leg would have in the system compared to a single line. So if the rode has 10,000 pound of force on the chain and it is connected by a 2 leg bridle and the angle between the rode and bridle is 30 degrees, each leg of the bridle will be taking about 1.15 x 5,000lbs of that force. In other words the inverse of the Cosine of 30 degrees, if I can recall my force vector calculations from college.


What was confusing me was the concept of the angle causing a loss of line strength. That isn't happening at all, but the load on the line is greater as the angle of the bridle from the rode to boat increases. (or the angle from the boat to rode decreases). The increased load would need to be taken into account when sizing the bridle line. Of course the heavier the expected conditions, the longer length of each leg I use. So that tends to be self adjusting.

I don't want just keep repeating myself, I explained the mechanical properties of rope previously with reference to the uneven loading of the fibers when rope is loaded at an angle or subjected to bending under load, I respectfully suggest you consider rereading that or doing some research on your own if you're interested. As I said I'm not convinced this is a good idea but I'm not aware of all the factors and and it ain't my boat.

 

[twistedtree]

Wait.... I think I am finally beginning to understand what you are talking about. Correct me if I'm wrong.


What you are referring to is the increased load that the bridle leg would have in the system compared to a single line. So if the rode has 10,000 pound of force on the chain and it is connected by a 2 leg bridle and the angle between the rode and bridle is 30 degrees, each leg of the bridle will be taking about 1.15 x 5,000lbs of that force. In other words the inverse of the Cosine of 30 degrees, if I can recall my force vector calculations from college.

Exactly. That's the confusion. Fish53's "simplified" explanation confused things a bit because he described it in terms of reduced capacity rather than increased load. Both get you to the same result - the line brakes sooner than you might expect.

 

[psneeld]

You keep repeating yourself because I believe people are discussing 2 different points.

I sure am.

And as far as WLL vs breaking strength... good luck in any TF ground tackle discussion involving chain, shackles, etc...etc...

And I am pretty sure I am not making myself clear because this is worth a whole chapter in a book trying to be explained a couple sentences at a time.

 

[psneeld]

Exactly. That's the confusion. Fish53's "simplified" explanation confused things a bit because he described it in terms of reduced capacity rather than increased load. Both get you to the same result - the line brakes sooner than you might expect.

I agree, now we can discuss whether recreational boaters should be calculating ground tackle components based on WLLs or breaking strengths.

And what do boating experts seem to think based on book, magazine and manufacturer table references.... :

 

[Fish53]

Exactly. That's the confusion. Fish53's "simplified" explanation confused things a bit because he described it in terms of reduced capacity rather than increased load. Both get you to the same result - the line brakes sooner than you might expect.

How could you possibly define load either decreased or increased under such widely variable conditions as anchoring? Load could be anywhere from zero to the maximum total weight of the vessel, more if surge were calculable. Total capacity is definable within a a fairly reasonable range when all the factors of the system are known. We're not lifting a known load with a crane here.

 

[twistedtree]

How could you possibly define load either decreased or increased under such widely variable conditions as anchoring? Load could be anywhere from zero to the maximum total weight of the vessel, more if surge were calculable. Total capacity is definable within a a fairly reasonable range when all the factors of the system are known. We're not lifting a known load with a crane here.

I think we are talking about different things. I'm just referring back to your warning that the angle between the lines in a bridle will reduce the effective capacity of the lines. The way you described it confused Dhays, but he sorted it out. What happens is that whatever load is present on the rode, there is greater tension in the lines that are at an angle. Your subsequent lifting sling illustration showed it well. And re your comment above, I agree that the load will vary from nothing to very big. But what ever that load is, it will create a greater tension in the legs of the sling.


So I think we are in total agreement?

 

[psneeld]

This now reminds me of the which came first discussion..."the chicken or the egg".

I get your point Fish, I also see it from the other side.

So without going into detailed calculations of one's entire ground tackle and deck handling equipment...the average boater is most likely going to some "recommended size" chart and maybe upsize....and also hope the boat was designed and built to withstand whatever anchoring situation they fall into.

Sure if you plan to ride out hurricanes or are rebuilding a boat for adventure....then do most or all of the calculations that are necessary to build a "storm proof system". Or if they are just interested and then yes, they may lean all about the physics and rigging involved.

 

[Fish53]

I agree, now we can discuss whether recreational boaters should be calculating ground tackle components based on WLLs or breaking strengths.

And what do boating experts seem to think based on book, magazine and manufacturer table references.... :

As WLL varies by component, even by differing chain types it seems difficult to use WLL. A more workable system for recreational boaters would be start with the rough holding capacity of the chosen anchor and work upward using the safety factor of their choice, 3 to 1, 5 to 1, 12 to 1. It's important to realize this is a system, makes no sense having an anchor and rode with a capacity of 5000 lbs. when the deck gear can only handle 500. WLL: Working Limit Load /Safe Working Load (SWL)/Normal Working Load (NWL) is the load that the rode can safely support without fear of breaking. Usually marked on the equipment by the manufacturer and it is often 1/3 to 1/4 of the Minimum Breaking Strength (MBS) for chain and 1/10 to 1/12 the Minimum Breaking Strength (MBS) for rope.

 

[Fish53]

This now reminds me of the which came first discussion..."the chicken or the egg".

I get your point Fish, I also see it from the other side.

So without going into detailed calculations of one's entire ground tackle and deck handling equipment...the average boater is most likely going to some "recommended size" chart and maybe upsize....and also hope the boat was designed and built to withstand whatever anchoring situation they fall into.

Sure if you plan to ride out hurricanes or are rebuilding a boat for adventure....then do most or all of the calculations that are necessary to build a "storm proof system". Or if they are just interested and then yes, they may lean all about the physics and rigging involved.

Well enough tit for tat to satisfy me, I'm going to go out and try to get my truck stuck in the mud so I can spin my wheels for a purpose.

 

[psneeld]

As WLL varies by component, even by differing chain types it seems difficult to use WLL. A more workable system for recreational boaters would be start with the rough holding capacity of the chosen anchor and work upward using the safety factor of their choice, 3 to 1, 5 to 1, 12 to 1. It's important to realize this is a system, makes no sense having an anchor and rode with a capacity of 5000 lbs. when the deck gear can only handle 500. WLL: Working Limit Load /Safe Working Load (SWL)/Normal Working Load (NWL) is the load that the rode can safely support without fear of breaking. Usually marked on the equipment by the manufacturer and it is often 1/3 to 1/4 of the Minimum Breaking Strength (MBS) for chain and 1/10 to 1/12 the Minimum Breaking Strength (MBS) for rope.

I too have been saying this for decades....

 

[diver dave]

You do not use the black ball?

,

Why yes, I flew one last w/e. And, it was quite the learning curve. it was a plastic, two piece affair, that interlocked. From a distance, it looks like a ball. From the deck, it looked like a drunken sailor. The flag halyard I used was a twisted mess, and I was even afraid it wouldn't come down.
Maybe an actual ball works better??

 

[dhays]

At some point, all the load can be on one of the 2 legs of the bridle. The rope selected needs to be able to cope with that.
Similar to Industrial Law restrictions on lifting heavy objects. Just because 2 men take on the lift, it doesn`t divide the load by 2.

True Bruce. I was just trying to figure out the forces on the bridle leg when it was in an equal configuration so that I could make sense of what Fish was patiently trying to get me to understand.

 

[psneeld]

Thus theoretical boating...and there is practical boating.


If experience is a great teacher...then reading a million articles, posts, books, and hearing sea stories that describe what seems to work and what doesn't to me trumps all the calculations in the world that are momentary, theoretical, a guess by golly, etc...etc...


Sure numbers are a great start... but as pointed out...the boat is moving and surging...so just what load is used to determine your tackle strength? To me, if the weakest component in any form or angle or anything is still 2X stronger than what my anchor is expected to hold in the bottom I think I am over....then I feel pretty good about going to sleep.