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Old 09-06-2017, 10:40   #1
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Checks, Runs and Baby = more strength?

Given similar situation, comparing a smaller taper cross section mast, against beefy extrusion no taper, ( both masthead)-- will the baby stay, checks and runners if set up correctly give more mast support in addition to sail shape control, or is this a trade off, and generally weaker than a stand alone?

I know rig design is usually coupled to overall hull design as well as intended usage such as racing vs cruising and an identical hull design with the 2 polar opposite options is unlikely. But it is interesting to me, I am no engineer, so I appeal to the NA and engineer types who may have a stronger understanding of the forces involved to enlighten me

Which is the stout choice? More wires or bigger stick?
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Old 09-06-2017, 10:50   #2
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Re: Checks, Runs and Baby = more strength?

The "bigger stick", AKA higher/larger section modulus is far, far stronger. Part of the reason for runners, checks, babystay, backstay, deck chocks, butt position, etc. is to assist with holding the mast up via keeping it in a controlled shape. But the extra wires are also there BECAUSE the tube itself is more bendy (fragile) & racers use this to an advantage in that you get much, much greater control over the shape of the mast. Which gives you much greater control of the shape of the sails, the main especially.

On some boats/classes of boats you literally adjust not only the above mentioned wires while racing, but also the tension on the various shrouds. And by "while racing" I mean in between tacks, or even during an upwind or downwind leg. All in the name of altering the shape of the sails for a tiny bit more speed. And on a Star boat for example, there are enough mast controls to practically turn it inside out. Which also means that if you **** up, the mast falls down. Whereas with a stiff tube, short of breaking stays, rarely does a mast suffer a gravity storm.
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Old 09-06-2017, 11:54   #3
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Re: Checks, Runs and Baby = more strength?

I do not think your question can be answered in a brief 'A is better than B'. You requested a closed ended answer to an open form question. This is how I feel it.

It is sort of like when we ask which is better mono or multi. Or whether blonde or red haired people are more sexy.

Look at the specific boat and how she will be used. Look at the materials and technology at hand and then build accordingly. Mind the budget (unless you are Bill Gates).

I would love to have a carbon monocoque mast and zero or next to nil wires to get mast stiffness. But this is an expensive technology limited to some racers and very expensive luxury boats (and a handful of small dinghies).

If your available materials are thin-walled alloys or anything else that does not offer much stiffness, you will end up with plenty of wires that keep the extrusion in column. No freaking way out.

So these are material and technology choices derived from whatever drives your build. None is better, they are just different, not superior / inferior or anything.

It is only when you apply the technology to specific use when you can say A is better than B. But you must define the use and the existing limitations (e.g. cost) up first.

Bueno. My take that is.

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Old 09-06-2017, 22:48   #4
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Re: Checks, Runs and Baby = more strength?

So if we have a beefy extrusion that stands alone and does not require running backs or babystay do we benefit by adding checks, runners, and a baby stay in terms of adding strength and redundancy or are these really all about changing sail shape with controlled mast bend? I remember Hal Roth ran with running backs in heavier weather, and often a baby and runners prevent mast pump, so there is some stability and strength increase, I guess what I am asking is is it worth adding on for mast support in rough conditions?

Lets say someone just throws some running back stays on. Should a rigger or original naval architect/the boat manufacturer be consulted before doing this? I mean is it possible to create a point load on the mast that is not designed into the rig and actually cause a possible failure if there is not an equal or appropriate load from a fore stay on the other side say for example a "staysail" removable type?

I see running backs on masthead setups and I can only assume they are mainly a supplement with a baby stay to stop mast pump in lumpy conditions, These running backs on the masthead setup are also adding significant stability and strength not just preventing mast pump right?
These do not usually have a matching forestay at the point they join the mast, so maybe that is not so important?
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Old 10-06-2017, 00:48   #5
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Re: Checks, Runs and Baby = more strength?

Its all about compromise.

Adding runners and an inner babystays in general adds considerable strength to the rig. Adding inner forestays with a sail on it may increase the load on parts of the rig that were not designed for it.

Trying to build a stick that has a sail carrying inner forestay (not solant stay) with no runners sometimes ends up with a lower safety factor than the same spindly rig with runners.
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Old 10-06-2017, 05:43   #6
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Re: Checks, Runs and Baby = more strength?

If you are talking any normal alloy spar then look at your wires as two different functions: some add stiffness to otherwise extremely flexible spar while others carry sails or counterbalance SIDE loads induced by such sails.

Runners balance the side load from sails flown on inner forestays. A sudden pull from an inner forestay could otherwise pull the stick out of column. Once too far out of column, the spar collapses.

At the dock in stable conditions the spar is in balanced conditions. In waves and with some sails hoisted, you may (or may not) need extra support. Hence the runners and any other semi-standing rigging. There are ways to have runner-less inner forestays too (e.g. with some swept spreaders)

Give or take. If the wire is there, there is a reason. Other than that any extra wires are only weight aloft and drag. There is no benefit in excess.

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Old 11-06-2017, 01:54   #7
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Re: Checks, Runs and Baby = more strength?

Checks, Runs and Baby = more strength?
No more strength but more stability for sure, and you can choose where to put that stability. That really matters with a thin-walled fractional rig but if your stick is thick-walled and a masthead as is the case for many cruising boats, then you're into diminishing returns.

Have a bit of fun: get a wooden block, drill a hole in it to stand a long piece of dowel (1 metre) about 1cm thick. This is your mast. Epoxy on some wooden spreaders so that it somewhat resembles your rig and then attach 'rigging' in the same way from the dowel to the wooden block. Then start pushing the dowel around and see how the different bits of 'rigging' affect its bendiness and position of bend.
I think that will display to you that in a simple masthead without cutter-type forestays etc, there is no real point in adding extra rigging.
I converted a masthead rigged 32 footer into a 3/4 rig many years ago and designed the rigging positions using that method. It didn't fall down!
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Old 11-06-2017, 16:17   #8
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Re: Checks, Runs and Baby = more strength?

I am a fan of runners and babystays for offshore work, they really are the best way of dealing with fore and aft loads. And they add redundancy and stability to any rig. Sure you can sweep spreaders, add fore and aft lower, or use aft led intermediates but these are all compromises that considerably add compression loads on the rig.

There is a reason most high level racing boats use runners.

You do have to be a little bit careful, overtensioning runners or using a staysail or stormjib on an inner stay can do nasty things to rig load in some cases. The positioning needs to be chosen with care.

When I set up Snowpetrel 1 for the run to Antarctica I added dyneema checkstays from the spreaders and a babystay with a storm jib. The rig didnt need them to stay up, I had sailed her hard for years without any of these. But having them there gave me lots of piece of mind, eliminated all rig pumping even in extreme conditions, and gave me some chance the whole lot would stay up in a rollover or if any one wire or tang broke.



You can see the red runners tied forward and the babystay/inner forestay. In this photo.
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Old 11-06-2017, 17:13   #9
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Re: Checks, Runs and Baby = more strength?

Quote:
Originally Posted by barnakiel View Post
If you are talking any normal alloy spar then look at your wires as two different functions: some add stiffness to otherwise extremely flexible spar while others carry sails or counterbalance SIDE loads induced by such sails.

Runners balance the side load from sails flown on inner forestays. A sudden pull from an inner forestay could otherwise pull the stick out of column. Once too far out of column, the spar collapses.

At the dock in stable conditions the spar is in balanced conditions. In waves and with some sails hoisted, you may (or may not) need extra support. Hence the runners and any other semi-standing rigging. There are ways to have runner-less inner forestays too (e.g. with some swept spreaders)

Give or take. If the wire is there, there is a reason. Other than that any extra wires are only weight aloft and drag. There is no benefit in excess.

Cheers,
b.
Correction: Runners balance fore & aft loads. As to the purpose of added wires to spars, sometimes there's no need for them from a structual standpoint, but they can aid greatly in terms of sail shaping. Be the boat a masthead rig, or fractional, doesn't matter.

My 2-tonner had a pretty strong, & stable 3-spreader rig. But much of the stability came from the dynamic tension induced by the wiring. For example, it had 2' of prebend over it's 56' length. And with the hydraulic backstay I could add a LOT more bend, especially if I also cranked up the babystay. She had runners & check's too, which were there primarily for shaping the main, but when things got lumpy they were nice for stabilizing the spar in terms of peace of mind. As it didn't pump much, regardless.
Masthead rig BTW.

While I've crewed on & looked after other boats where on paper the rigs were hell for stout. But in the real world, unless they were perfectly tuned, I was always nervous, & checked the rig's alignment & bend underway a lot.

Pick up copies of some of Brion Toss's stuff. It's a good place to start. And I created a thread perhaps a month ago in a quest for furtherance of rigging knowledge, to which a lot of folks contributed links to & titles of a lot of great references on the subject. It's worth digging up, & following it "down the rabbit hole" if rigging really interests you.

Also, get involved with racing. Especially befriending the; sailmakers, riggers, & boat maint. guys. It'll be a bits & pieces learning thing, but the basics will come real fast. And with a little time, interest, & questions, you'll know as much or more than most riggers out there.
Read the Dashew's books too www.setsail.com/free-books
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