Welded lifeline stanchions on a steel hull - pipe or flat bar?

I think your numbers are a little off!

A 25mm x sch 10 wall pipe has a Z = 1.06cm^3.
A 40 x 4 FB has a Z = 1.07cm^3.

The question you must ask yourself is this, are the stanchions for show, or to suit a purpose? I design in the commercial field, not leisure. Thus my design criterion is the latter.

So, the weight of a person, fully suited up, say 80-90kgs, falling over onto the top of the stanchion, so a 2g load. What does this, at a height of the stanchion translate to, as a bending moment. Then apply a suitable factor of safety.

So, as an example, if the stanchion is 750mm, this is a bending moment of 1.2kNm. With a 25mm dia pipe the stress, with a FoS of say 3 = 3331MPa....a little over i would say!

If you use the min req'd from SOLAS of 750Nm, the stress would be 2122MPa.

So, you really need to think whether you want aesthetic, or functional stanchions. Which is why up fwd at least most vessels have bulwarks, for commercial craft, as the side plate offers the extra stiffness req'd.

 

I was going off of the circumference of a circle, hence approx 78mm if rolled out flat.

The hull has 200mm high bulwarks (actually 175mm plate plus 20NB top pipe), total 200mm from deck ignoring any deviation from vertical which is greater up the bow of course. Stanchions weld to top of bulwark cap pipe so total length is either 550mm if a wire top lifeline or 525mm if a welded 20NB pipe top rail.

I want functional stanchions; if I just wanted pretty ones I'd buy thin tube ones from a yacht store. If I have to go to Sched 40, fine. Ditto with T sections. Thwartships dimension will cause me some problems if I go over 25mm but not insuperable ones, however I would greatly prefer not to exceed this pipe diameter or FB width.

PDW

 

Are the lifelines or welded top rail as PDW is considering not taken in to account? I don't remember ever seeing a stancheon bent significantly outwards, even on very lightly built charter boats, where as I have seen many bent inward...which is a good reason too to have them strong. Just interested in the calculations.
Nick.

 

It is hard to say for sure without seeing the construction drawing, thus can only generalise and surmise to the arrangement.

 

If you have either wire or pipe lifelines then some load is going to transfer from a direct hit on a stanchion into the lifelines and spread the impact across other stanchions. This works for impacts in the outward direction as the wires have to stretch (assuming they're tensioned to take out the slack). It doesn't work for impacts in the other direction (hitting a jetty for example) as the wires contribute nothing. A pipe top rail would help but how much???

Anyway. Here's a piece of the bulwark; as I said 200mm from the deck to the top of the capping pipe. Plate is 4mm.

PDW

 

Have you considered U shaped channel? It could minimize the crews exposure to hard edges.

 

How about instead of drilling holes and running the wire through the pipe, you weld something to the outside of the pipe for the wire to run through, leaving the pipe sealed. Put them on the outboard side so people wouldn't snag them walking by. Depending on what sort of finish look is acceptable, I can think of several things that might work. A short piece of tube, a threaded nut, a washer, links from a chain....there's all kinds of possibilities.....






















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I've seen stainless steel rings welded to the inboard side of the stanchions. Of maybe you could use small ring bolts, that way it'll be even easier to drill a hole in the stanchion, shove in the ring and weld in. Or just butt a small ring against, a nice quick tack weld around where it touches the stanchion, Bob's yer uncle. Paint the mild steel stanchions, and if you just slap on paint on the SS rings it won't matter and will weather off pretty quick anyway.

 

I saw a boat recently with the stancheons coming down inside the bulwarks but stopping short of the deck, the base being welded to a small bracket off the bulwark and the stancheon welded to the inside edge of the bulwark tube. It looked good, the scuppers were clear and the arrangement looked stronger than if welded on top of the tube.
Might give the stancheons a bit of extra protection as well when moored.
Nick.

 

Yeah, that's one of the other possibilities I'm considering. Half links of 316 chain welded to 316 pipe for stanchions. Lot of work compared to drilling holes in FB though. Worth considering if FB isn't going to be adequate. Then again drilling an oversize hole and welding in say a short length of 10NB pipe wouldn't be a lot harder and a lot neater. This drilling and then welding is what I'm trying to avoid because when it comes down to it, I'm lazy. However, if it's the better way to go, I'll probably do it.

PDW

 

Little late to the thread
PDW what if yet have you decided on ?
Couple easy ways to deal with the mild steel cap rail and rusting. cut out top half pipe couple inches long and replace with stainless half pipe or use next size up stainless pipe split in half and weld on top of existing cap rail.
I wouldn't use flat bar railing nor cable railing, hurts to much when you land on it, pipe or round tube is bad enough. Pipe or tube top rail adds a lot of strength and give a lot better feeling of security but it does add weight
Tom

 

Funny you should ask. I just finished drilling all the holes, next step is to weld them all in place.

25x10 FB with a top rail of 20NB Sched 40 pipe, all in 316. 2 intermediate wire lifelines. You might be able to go over the top, total height is 775mm, but you'll have a really hard time sliding through.

I wanted 25x8 FB but wasn't possible, nobody had it, so I went up a size. Shrug.

If bruising becomes an issue I'll slip some split lengths of poly pipe over them. The 2 stanchions P&S where you board are 20NB Sched 40 with half links welded to them to terminate the wires, nicer to grab than the FB.

If it all gets severely bent that's what welders, grinders and lever blocks etc are for.

I had to make a 3 wheel roller bender to get the long gentle curves in all the pipe for the aft deck area so I'll probably use it to pre-bend most of the top rail, reduce the strain when welding it in place.

PDW

 

Yep a roller bender is nice for that kinda work, I used a pipe bender about every 3" very slight bend, works but takes a while .
Now that I have had some on hand experience working with 6061 pipe "tough stuff" I could have used it and been about 50 lbs lighter vs the galvanized steel pipe I used on mine

 

I did the same thing when making the curved pipe for the transom cap rail. Took me most of a day to bend, fit, bend, fit..... and that was only 1.5m of pipe. So I spent most of a week building the roller bender and also a small T shaped bender I call my rail tweaker for making adjustments in place. Probably not a productive use of time but what the hell, I've got the bender for the next job (which will probably be making arches to support netting to keep the birds & possums out of my garden).

The roller bender is a simplified version of one posted on rec.crafts.metalworking by Ernie Leimkuhler (sp??) many years ago. My version can be made with not much more than a welder and a grinder with cutting wheels, though I did use my lathe to turn some of the parts. I'll post a picture if you're interested.

PDW

 

Please do post a picture
Nick.