Mast pumping and running backstays

[Ded reckoner]

Have you ever experienced mast pumping? Is the phenomenon of mast pumping, for which running backstays are the solution, only caused by use of a fractional rig? Are running backstays always an effective remedy? Can mast pumping be quiesced, or the onset of mast pumping be delayed, by reefing the main more?

[four winds]

Have experienced it on my standard masthead rig. Have standard single backstay.

Tuning my rig specifies the lower forward shrouds to have more tension than the lower aft shrouds. Did that and the problem went away.

[Moody46CC]

I have a masthead rig but it has jumper stays. They are supposed to do away with the necessity of running backstays.

[UNCIVILIZED]

About the only kind of mast you wont see it on/it can't be induced in is a rotating CF wing spar... and if you do see it on one of those, dive for a hatch - like Right Now! As it's about to rain CF, sails & rigging.

Basically what I'm saying is that given the right conditions, it's possible for such to occur in pretty much any rig. With the caveat being that the stouter the rig, the less likely you are to see/have/encounter it. And that generally, runners in their plain form, are used opposite a Staysail stay, so that you can get sufficient stay tension to carry heavier weather sails.

But Runners, with & without Checkstays (or a multiplicity of them), Babystays, & a few other types of moveable "standing" rigging, are used to stabilize or plain old, hold up, a whole multiplicity of rig designs.

PS: If a sailmaker or rig designer goofs, he/she may actually inadvertently induce rig pumping, by placing the heads of sails or stays in the wrong spot(s). Including the headboard of reefed mains. For there's a good bit of aft pull on the headboard of a reefed main when going to weather, & thus said spot on the mast.

[Snowpetrel]

a combination of mainsheet tension and backstay tension can reduce pumping. On an old wet noodle masthead rigged IOR boat we had to be pretty on the ball, due to no runners, and inline spreaders. Things got scary when we dumped the main in a puff, or reefed, with the mast dancing about until the main stabilised things as it was sheeted back in. The babystay tension was also critical, as was vang tension. The theory is that the backstay and babystay bend the mast forward and the main stops it going too far forward.

[caradow]

It would be important to know exactly what kind of mast you have. I assume it is a frac rig with swept back spreaders? Please confirm.
Agree with all that has been said however sounds like your mast just needs to be tuned appropriately.
No need to add runners to a conventional cruising rig. It should be able to be "dialed in". Also runners are a pain in the @ss. However boats that have runners enable you to control mast bend and thus mainsail twist independent of forstay tension.
One potential problem that has not been mentioned is that your mast may not be stabilized at the partners appropriately. Very important to also check that out.
Good luck and let us know what you find.

[sailcrazy]

Our mast has straight (not backswept) spreaders. We are a sloop masthead rig, and have a babystay with a S/S rigged to it. As was explained to me, the backstay counters the headstay. And it you put a load on the babystay (ie, a staysail), there is nothing to support it backwards-except the running backs. and if you do not support that point of the mast in a backwards direction, as when running the S/S and rig the running backs....you will get pumping. Works that way for us every time! Advise given to us is that the forward angle between the babystay and the mast should equal the backward angle between the mast and the running backs. And if your spreaders are backswept...they provide that backward support, and running backs are not required. At least that's what we were told.

[meirriba]

Originally Posted by caradow

It would be important to know exactly what kind of mast you have. I assume it is a frac rig with swept back spreaders? Please confirm.

I believe that swept back spreaders usually allow/cause prebend in the mast and subsequently less pumping. Or am I missing something?

[roverhi]

The Westsail 32 mast came with the provision to add running backs at the staysail stay but they were not supplied. Thinking was the mast section was strong enough to take the pull of the staysail stay. One of the very early Westsails made a circumnavigation of SoPac. On the final run down the Oregon Coast on his return he got in some stinky weather. He had dropped the main and was running just under staysail. He went forward and just happened to look up the mast and got a bit of a surprize. Without the mainsail leech providing support the mast was going so far out of column he feared that he was going to lose the rig. Fortunately, the rig held but he became a firm believer in running backstays for a double headsail rigged boat.

When we built ours, installed running backs and used them anytime the winds were strong enough to necessitate going down to the 2nd of 3 reefs. Setting the running backs was no big thing. Would set up the future windward backstay with the four part tackle when it was on the lee side and then tack. That was all there was to it. The mast sections on most cruising boats will take the load of a staysail with just the support of the mainsail in most conditions. For nasty weather, we felt way way better having the running backs added that little bit of support to the mast, however.

[leftbrainstuff]

In engineering terms an overconstrained rig can be tensioned so that mast pumping (column bending) is not visible. Overconstrained is an engineering term that reflects more constraint than is mathematically necessary to carry static loads. In practice we're dealing with dynamic loads so overconstraint is necessary.

The engineering issue is less about mast flexing, which if it remains within the elastic range of the material, does not pose a structural issue. It may ultimately pose a fatigue issue but that's a propellor hat discussion.

What you want to avoid is unloading of the standing rigging. This can quickly lead to mast failure because you are doing the equivalent of removing that standing rigging element. If this results in under constraint then the mast may fail.

Ideally your static rig tensioning should be the minimum tension at which that stay will never reach a zero tensile load.

Any tension more than the above simply increases the compressive forces in the mast which correlates linearly with the buckling failure mode.

In practice we dont know all the vector loads in the system so we apply rules of thumb. As an engineer I visualize the vectors and preload the rig accordingly. Then with the mast under load you can 'feel' many of the standing rigging loads at deck level. I'm mainly looking for loss of tension in my stays.


Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[sirkus]

You really need to be more precise to describe what is going on.
A good thing is, when sailing, film the hole mast, and specially the upper part and the mast foot/deck.
There is usually only a tuning of the rigg thats needed. Sometimes there is a weak support on deck.
I have had to deal on a few issues of mast pump. The one that took the most time, turned out to be a too big a slack in the forestay. There on a video you could see the top of the mast go back and forth when sailing.
Just to mention a few issues that goes under the term of mast pump.

[neilpride]

Originally Posted by meirriba

I believe that swept back spreaders usually allow/cause prebend in the mast and subsequently less pumping. Or am I missing something?

No, you right , sweep back spreaders rigs are more stable, some short of mast pumping with in line spreaders and no doublé set of lowers is quite normal, babystays help a bit and if you have a second inner forestay to fly a staysail or storm jib and if is placed far from the main forestay , a set of running backs are a must, the other way is called solent rig, 2 furlers placed really close from each other, runing backs with checks stays are normally see it in race boats or boats with hig streesed rigs, also i see some masthead sloops with a bad rig tuning inducing even more serious mast pumping , to much backstay tensión, rake put more mast pumping in place , thats why you see in hig tech racing boats lots of checkstays .....

Make a good tune of the rigging by a reputable rigger and you see some diference....

[caradow]

merriba you are correct however it sounded like the original post was questioning the validity to adding runners to a frac with swept spreaders. I am still unsure exactly what he is asking.
I have owned many race boats with runners in the past and I also own an older 50 foot ketch with a telephone sized mast with runners. Despite the size of the mast I have seen slight pumping in the Gulf Stream which necessitates some tension on the windward checkstay to counteract this movement. However I have always thought it a design flaw to have to add runners/checkstays to a cruising rig. I guess that is why I love the rig on my cat which is a triple spreader with diamond stays and a baby stay. Not to get political but take a look at the rig on Voyage Cats. On the other end of the spectrum I own and have raced a Starboat that will let you know quite quickly if you miss a runner in a heavy wind gybe.
Anyway sounds like neilpride may be a rigger and I would just follow his suggestions.

[CLady]

Add runners when possible. A baby stay would be another good addition--this is not the same as a staysail stay. On my boat, the baby stay has it's own track to adjust tension--the line runs aft to the cockpit so it can easily be adjusted when conditions change. Between the running backs and the baby stay along with the hydraulic backstay adjuster, my tall rig, (and not fractional), can be tensioned nicely for changing conditions--wind and seas.
The inner stay, which is attached to the mast at the same level as the running backs, also helps to stabilize the mast in heavier wind and seas conditions. the baby stay is what helps to bend the center of the mast as well as stabilize it.

Proper attachment of the mast to the deck where it enters through the deck is also important and stabilizing the attachment of the mast to the mast step and maintaining the proper distance from mast step to deck is necessary so pumping in disturbed seas--when the boat is bobbing up and down a lot, is very important.

I hope this is helpful in some way.