how strong are stanchions?

[Burnham Bob]

SWMBO needs a shoulder operation. Getting on the boat from a pontoon is fine as she can grab the shrouds. However, from a dinghy is a different matter. From the stern we used to open the gate in the pushpit and use the boarding ladder. However, for several reasons it would be better to board from alongside using a fender step. But can a stanchion be used as a hand hold until she can reach the shrouds?? Must admit I've never really trusted them - maybe I'm wrong I've never put it to the test. The stanchions on a Trapper 500 are notoriously prone to leaking I am told and mine have been beefed up with solid stainless plates at the base which I believe is a common fix.

 

[Poignard]

The weak part is not the stanchion, or its base, but the deck. You could make a section of the guardrails detachable (using pelican hooks). Or how about a hardwood batten or two secured across the bottom part of the shrouds that she can get hold of?

 

[jwilson]

If when you left the boat you clipped/tied a right-length line either from the mast or a fitting midships on the coachroof to the top of the midships stanchion that would stop it bending outboard.......

 

[Halo]

Stanchions are strange. They seem far too weak to do a proper job. If you swing on them to climb aboard most would bend. I expect most people use them for balance and to hang things on. They also act as a single use safety device for falls. It seems they are a design which we have got used to living with rather than one which is ideal.

 

[Poignard]

If when you left the boat you clipped/tied a right-length line either from the mast or a fitting midships on the coachroof to the top of the midships stanchion that would stop it bending outboard.......

Good idea!

 

[dunedin]

Worth installing a rail gate like fitted to many modern high freeboard AWBs?
This could be a long term benefit.

 

[JumbleDuck]

Stanchions are strange. They seem far too weak to do a proper job. If you swing on them to climb aboard most would bend. I expect most people use them for balance and to hang things on. They also act as a single use safety device for falls. It seems they are a design which we have got used to living with rather than one which is ideal.

Agreed. Yacht stanchions are generally up to keeping toddlers on board while in harbour, but I have never seen one that would be any use at all if required to take a real load.

 

[ghostlymoron]

When a load is applied to the stanchion system, only the nearest one is subject to direct outward force. It is transferred to all the others by tension in the guardrails so that, within reason, the force of a falling crewmember can be resisted.
One stanchion on its own wouldn't stop anyone going overboard.

 

[JumbleDuck]

When a load is applied to the stanchion system, only the nearest one is subject to direct outward force. It is transferred to all the others by tension in the guardrails so that, within reason, the force of a falling crewmember can be resisted.
One stanchion on its own wouldn't stop anyone going overboard.

That all sounds a bit mechanically unlikely, though it's supposed to be the theory. The force on the stanchion is proportional to the sine of half the angle subtended by the guardrail, so to provide a significant inward force on an average shaped yacht the guardwire forces would have to be huge ... or the stanchion would have to bend out and increase the angle.

Let's try it. I'll visit your boat and we'll drop 100kg of sandbags through a metre and bring them up short with your guardrail. A pulley will be involved, of course, to provide a horizontal force. If no damage results, I'll give you a tenner. If damage results, you give me a tenner.

I'm not offering my boat for this test because I am sure there would be significant damage!

 

[PuffTheMagicDragon]

I see many, probably most, boats with loose lifelines. The lifelines should be taut so that a force to deflect them is not taken only by the two adjacent stanchions but by all of them, working as a team, not unlike a line of policemen with linked arms to hold back a crowd.
Regarding the proposed 'test' with a 100kg sack this is irrelevant to the OP's situation. In any case, a shockload like that would even bend a solid rail... but the rail would still serve its purpose of breaking a fall by slowing the trajectory sufficiently to prevent an MOB situation.

 

[JumbleDuck]

I see many, probably most, boats with loose lifelines. The lifelines should be taut so that a force to deflect them is not taken only by the two adjacent stanchions but by all of them, working as a team, not unlike a line of policemen with linked arms to hold back a crowd.

The line of policemen, like a motorway crash barrier, work by deflecting enough to allow the tension to have a significant inward component. How far are you happy for your stanchions to deflect?

Regarding the proposed 'test' with a 100kg sack this is irrelevant to the OP's situation. In any case, a shockload like that would even bend a solid rail... but the rail would still serve its purpose of breaking a fall by slowing the trajectory sufficiently to prevent an MOB situation.

It might bend a solid rail, but in every yacht I have seen I would expect it to rip some of the stanchions clean out. Two things people say:

"The guardrails and stanchions are there to catch me in a fall and save my life"

"No, don't ever pull on the guardrails and stanchions. They're not strong enough."

 

[Poignard]

If it were not for my crew objecting to it (and she has a half-share*) I would remove my guardwires and stanchions and just leave the pulpit and pushpit.

* I suppose I could remove them on one side

 

[PuffTheMagicDragon]

The line of policemen, like a motorway crash barrier, work by deflecting enough to allow the tension to have a significant inward component. How far are you happy for your stanchions to deflect?

The stanchions will only deflect as far as the lifelines can stretch; the looser they are, the further they will deflect. That is why we insist (as per ISAF Offshore Special Regulations) that stanchions are no further than 2,2m apart and that the maximum deflection shall not be greater than 50 mm when a force of 4kg is applied at the mid-point.

It might bend a solid rail, but in every yacht I have seen I would expect it to rip some of the stanchions clean out.

Not if the lifelines are tautened properly; having them loose is akin to having loose cap-shrouds and expecting them to support the mast effectively through the ensuing shockloads when boat is going through choppy seas. The major strain of the lifelines (if properly tautened) is taken by their anchoring points, usually the pulpit and the pushpit; if these are suspect and cannot be relied upon then you have a major structural/safety problem on your boat.

Two things people say:

"The guardrails and stanchions are there to catch me in a fall and save my life"

"No, don't ever pull on the guardrails and stanchions. They're not strong enough."

People do say a lot of things. Under normal circumstances the lifelines only serve as a gentle reminder of potential danger when one's thighs come into contact with them. Under abnormal conditions they absorb the initial impact and help to prevent MOB.

 

[JumbleDuck]

The stanchions will only deflect as far as the lifelines can stretch; the looser they are, the further they will deflect. That is why we insist (as per ISAF Offshore Special Regulations) that stanchions are no further than 2,2m apart and that the maximum deflection shall not be greater than 50 mm when a force of 4kg is applied at the mid-point.

The less the stanchions deflect the higher the loads will be in the guardrails. I suppose to some extent it would depend on the shape of the boat; the curvier the guardrail the better. 4kg is about an order of magnitude too low for any realistic emergency load, of course, so I guess the 50mm deflection limit is just a way of saying "don't have them too rattly in the their sockets"

The major strain of the lifelines (if properly tautened) is taken by their anchoring points, usually the pulpit and the pushpit; if these are suspect and cannot be relied upon then you have a major structural/safety problem on your boat.

Sorry, but from a structural engineering point of view that seems most implausible. The crew member falling downhill and landing on the lifeline is exerting a force outboard which has to be balanced by a force inboard. Typically the front attachment is at about 30[/sup]o to the centreline, and therefore provides an inward load equal to half the wire tension, while the back attachment is more-or-less fore and aft and provides no inward force at all. If, as you say, the lifelines are taut, there is going to be little scope for outboard movement and a huge proportion of the load is going to be taken by the stanchions - most of it by the two nearest the point of impact. The lifeline can't provide any more inwards force there unless it gets tauter and it can only get tauter if the stanchion tops move significantly out.

One day I'll get this modelled properly. Meanwhile, why not demonstrate your confidence in your setup with the 100kg-of-sand-bags-through-1m drop test. What harm can it do?

Under abnormal conditions they absorb the initial impact and help to prevent MOB.

Maybe. But I don't think your stanchions will survive it.

 

[lpdsn]

4kg is about an order of magnitude too low for any realistic emergency load, of course, so I guess the 50mm deflection limit is just a way of saying "don't have them too rattly in the their sockets"

Race crews like to slacken the guardrails as it makes it more comfortable, if comfortable is the right word, to hike. This rule will be to limit that.

 

[James_Calvert]

I swing against my guardrails as hard as I like when getting out of my dinghy alongside. Doesn't harm the Stanchions or their bases. I've got a boat with a pinched in stern so I guess I'm effectively pulling at them when they are already in the shape of a drawn bowstring, with the horns of the bow being at the pulpit and pushpit.

The stanchions are a little loose in their sockets, so they can deflect a bit as necessary. It all just works and I don't understand how/why other boats have flimsier arrangements. The stanchions themselves are 1 in ss tube set in cast ally bases bolted through a grp/balsa/grp deck with nothing more than halfpenny washers under their nuts.

As an aside I've had the boat over 30 years and I am probably now personally about 50% heavier than I used to be. The stanchions are still fine...
but my upper body strength is not as effective as it used to be.

 

[William_H]

If when you left the boat you clipped/tied a right-length line either from the mast or a fitting midships on the coachroof to the top of the midships stanchion that would stop it bending outboard.......

Yes reinforcing the stanchion that she need to pull herself up on seems like a good idea. Perhaps y6ou could add another stanchion to make a gap of person size as a permanent gate entry. This would halve the load on the stanchion if she pulle don both at once. (and be a lot more stable.)
However I was also thinking of perhaps another post/tube clamped to the stanchion out board so that it extended down the side of the hull about 30 cms perhaps with a pad of some sort on the end resting on the hull. A clamp then with a spacer to the base of the stanchion and another clamp nearer the top of the stanchion. This would transfer the outward pull to the base of the stanchion. (much stronger). This might look bad but would be a temporary measure with no damage/modes to the boat itself. good luck olewill

 

[Poignard]

If I were having a boat built I would not have guard-wires around the toe-rail at all. Instead I would have either guard-wires or, preferably, tubular rails mounted inboard, around the periphery of the coachroof. The sort of strong arrangement that pilot boats have.

 

[JumbleDuck]

Race crews like to slacken the guardrails as it makes it more comfortable, if comfortable is the right word, to hike. This rule will be to limit that.

Ah, that would explain it.

I swing against my guardrails as hard as I like when getting out of my dinghy alongside. Doesn't harm the Stanchions or their bases. I've got a boat with a pinched in stern so I guess I'm effectively pulling at them when they are already in the shape of a drawn bowstring, with the horns of the bow being at the pulpit and pushpit.

The stanchions are a little loose in their sockets, so they can deflect a bit as necessary. It all just works and I don't understand how/why other boats have flimsier arrangements. The stanchions themselves are 1 in ss tube set in cast ally bases bolted through a grp/balsa/grp deck with nothing more than halfpenny washers under their nuts.

Not a Chuck Paine design, by any chance?

 

[Kelpie]

If it were not for my crew objecting to it (and she has a half-share*) I would remove my guardwires and stanchions and just leave the pulpit and pushpit.

* I suppose I could remove them on one side

Kelpie had no stanchions, nor pushpit/pulpit, when we got her.
At first I found it all quite liberating, and wondered whether fitting them would make it hard to get past the side-deck-mounted shrouds. But after one season without them, I went ahead and fitted them. It makes a far bigger difference than I expected. Maybe it is purely psychological, but I feel far happier on deck now. Oh and I can drop my large genoa with it going straight over the side too.