Some Wind

[higgs]

Last Tuesday we had gusts up to 54 kts. I went to check on Trav'ler and found two damaged stanchions. The boat is shrink wrapped and was sitting broadside to the wind. These stanchions are pretty substantial - 1 inch tubing with eighth inch walls. They are tall, which means more leverage at the base. One stanchion broke at the base while the other just pulled base and all. I posted a photo to show how they are mounted as it is a little unusual. They mount to a built up area that should have nuts imbedded in the glass. The one that pulled out must have been repaired as only self tapping screws were used - but the screws were long and big. I am stunned by what happened. The force of the shrink wrap pinned against those stanchions must have been considerable and it is making me rethink using shrink wrap again.It is repairable and I have a spare stanchion to replace the broken one so this is not a terrible tragedy.

 

[Paul Akers]

Don't Know How It Would Happen By Wind

Was the wind strong enough to cause the damage? Was it wrapped by you or the boat yard? Maybe they noticed it before the wrapping occurred. It sounds like the hauler caused the damage. I had similar damage one time when my boat was hauled by a crane and they use the "X" frame to lift it. The "X" frame didn't extend out beyond the beam (12'10") of the boat so the straps were drawn in against the lifelines. The lifelines were pulled and something had to give - two stanchions. The marina took the responsibility, but only after I questioned it! They happened to be on opposite sides of the boat from one another. Look for wear or chafe on your lifelines, first.

 

[Dave Groshong]

There's no way

That 54 knots of wind bent that tubing! Even with shrink wrap for sail area, unless the tubing is really substandard stuff???

 

[higgs]

Whatever

While I did not drive the Travel lift, I was in charge of the haulout. There were no problems - I have done haulouts literally dozens of times and am positive no damage was done at that time. I cannot say there may have been prior damage to that tube, but I had never noticed anything. I used last years wrap to cover the boat, which I did myself, so I know all the stanchions were solid as I tied lines off to them to help support the framework for the cover. Like I said - I am stunned by this. I have stored boats in mid west winters for 30 years and never seen anything like this.

 

[Jim]

I agree

the boat next to you hit you!

 

[David10790]

Not just the Wind

No way the wind could bend or break a stanchion. At 50 knots the wind pressure is 6.2 lbs per sq ft. Even if the stanchion was supporting say 10 sq ft of shrink wrap, that's only a 62 lb force. Here is some good data for calculating wind loads:The Generic FormulaFor using the actual sustained wind speed expected (were we to actually determine it) :Force, F = A x P x CdA = The projected area of the itemP , Wind pressure (Psf), = .00256 x V^2 (V= wind speed in Mph)Cd , Drag coefficient, = 2.0 for flat plates. For a long cylinder (like most antenna tubes), Cd = 1.2.Note the relationship between them is 1.2/2 = .6, not quite 2/3.This is the force on a discreet constant section. I.E. A length of tubing or some other such member that is part of a structure. The Force per unit area would be found by setting the area to 1.This is the simplest form of all that stuff in the textbooks, at standard temp and atmospheric pressure, for the range of wind speeds we see and the general size of the members on our toys.

 

[jimq26]

Too much shrink on your shrink wrap job.

I was involved with shrink wrapping film used for packaging (Union Carbide) during my long sales career. Do you have any idea of the incredible amount of force created when the film is heated and shrunk? Be it a boat, a dog bone, a toy etc. when you overshrink the film, you can almost crush the contents. They should have left more slack in the film (less heat) in any area that you had something like stantions or pulpit / pushpit standing and open to bending pressures from the wrap.Good luck with the repairs Higgs.All the best,

 

[Ross]

David, you didn't follow your own formula

1st V= MPH not knots2nd you didn't apply Cd50knts = 57.5 mph squared =3300 about times .00256 equals 8.4 times Cd (1.2 up to 2.0) for clyinders and flat plates normal to the wind. Noy that it would bend a stanchion.

 

[caguy]

Ross and David it's going to be a long winter.

 

[Ross]

Let's see if we can start a fire and keep

ourselves warm. ;D

 

[caguy]

I found the shaft on my wind indicator vane bent

to about a 60* angle. We don't generally get winds blowing that hard at MDR. The shaft is made of 1/8" aluminum and it took a good force to straighten it out. I fianlly cut off the bent part and shortened it as much as possible. I can't believe the wind would cause it to bend like that. Only other answer is a drunk seagull.

 

[CalebD]

My I hate shrink wrapping rant.

We had Odalisque 'professionally' shrink wrapped one season. I was not happy about it for many reasons but mostly because it seemed to hold the moisture in the boat rather than out. Sure it kept the snow and ice off but it held in the moist air and I remember seeing my old 1967 Atomic 4 engine sweating in condensation not to mention the mildew in the cabin. I believe that the 'professional' did not leave enough ventilation. Having said that it sounds as if Higgs tried to re-use the previous years shrink wrapping which is an laudable idea; trying to keep the dumpsters free of this product come springtime. Shrink wrapping is so wasteful as most everyone throws out the film (and frame) from year to year.We now use some electrical conduit to make a frame and tie 2 tarps over it and use lots of duct tape and carpet remnants (per shrink wrap job on our boat). The stuff needed to do this is re-usable (to a point) and there is plenty of ventilation (as there should be) and a lot less goes into the dumpster each year and it is cheaper. Of course, you do have to check up on your boat around any severe weather event. My worst fear is that either of our tarps blow off during a wind event and get spread out between some neighbors masts or other gear.In any event Higgs, I am sorry to hear about the damage to your boat whatever caused it. Locally strong winds (read: near tornado event) can pick up debris and whatnot and blow that into whatever it wants to. I refuse to join the scientific pissing match as to whether the wind could have caused the damage as my observations of weather indicate that almost anything is possible.

 

[Jim]

Higgs, I do like your boat

what kind is it? Hans?

 

[higgs]

Some additional thoughts

Jim - thanks - the boat is a Nassau 34 which looks a bit like a HC, but no where near as much $.I was reusing the shrink wrap. No problem at haulout, as I was ground crew and saw it all. The boat next to me is 12 feet away and was in place when I put up my tarp. All stanchions were upright.i am no engineer, but there is, I suspect, more to the forces than earlier stated. First, the framework - fiberglass tape - is tied to the stanchion from the center beam - putting stress on the stanchion. Secondly, stress on the stanchion will not only come from the side, but also from the "roof" section of cover, which will be stressed at the same time as the side of the cover. Thirdly, it would seem to me that stress would not be distributed evenly upon the tube because of leverage. With the tarp turned over the stanchion's top, much more stress would be transfered to the base. I also check the boat at least once a week and all was fine before the wind storm. I question the figures further when I think about the warning not to tie tarps to jack stands. One would wonder how, if stands were chained, wind could cause one to get pulled out if the figures given were all there is to the stresses present.I do think that there is a good possibility that the stanchions had been previously damaged- especially since the one that pulled out was attached with different screws than others, indicating a repair in the past. If this is the case, and I suspect it was, I am grateful to the wind for pointing out a weakness aboard my boat. None the less, in 3 seasons with this boat, I never had any reason to suspect weak stanchions. The one that pulled out was at the gate where swimmers would use it to help one's self back on board, certainly putting strain on it in a direction that would have made it more vulnerable than pressure from outboard. Just some thought - I appreciate comments and condolences

 

[Jeff]

Remove life lines

I'm not a shrink wrapper (in So Cal) however I would guess that the pressure is coming from the wrap on the life lines.Remove the life lines prior to wrap. Even let the stanchions poke through?I am also somewhat interested in how a life line system can collapse from wind but is expected to support a 250lb sailor being thrown into it like a Tyson clobbered boxer.

 

[RichH]

I can speel einginear

"am no engineer, but there is, I suspect, more to the forces than earlier stated. First, the framework - fiberglass tape - is tied to the stanchion from the center beam - putting stress on the stanchion. Secondly, stress on the stanchion will not only come from the side, but also from the "roof" section of cover, which will be stressed at the same time as the side of the cover. Thirdly, it would seem to me that stress would not be distributed evenly upon the tube because of leverage. With the tarp turned over the stanchion's top, much more stress would be transfered to the base. "I can speal ingineer ..and load that is transmitted to the top of the stancheon (as you describe in the above paragraph) can impart infinite loads to the base of the stancheon base. All you have to do is press perpendicularly into the roof (especially if the 'roof' is tight) and by the magic of trigonometry you can multiply by ten or more times load the transmitted into those stancheon bases. if you dont want the stancheon bases bent you will have to arrange a 'rafter' that is able to SLIDE freely across the the top of the stancheon so it doesnt impart any side loads to the top of the stancheon. Looks like a GRAND DEER stancheon. Was the boat built in Taiwan?

 

[higgs]

Can't remove lifelines

In the usual shrink wrap operation lifelines are an important part of the cover's structure.Your point about the 250 lb sailor is well taken. I often wonder how may stanchions can actually take a shock load of a guy that size. I would suggest that most boats could not take the impact of a guy that weight falling hard against the life lines, particularly if the stress in the fall focused on the top of the stanchion.

 

[higgs]

Rich

rich, you support my thinking. Are you an engineer?Yes, the boat was built in Taiwan. I realize that some of the stainless from this part of the world is not up to our standards here in the US. On this boat, i have not seen any evidence of inferior stainless - at least until now.

 

[Ross]

Higgs think of your stanchions as large

crow bars or wreaking bars if you prefer. The leverage can be figured bu the width of the base and the length of the stanchion. Then you add the pull on the lifelines to the force in the stanchion directly and you add up the load very quickly.

 

[higgs]

Ross

That is the point I was trying to make in an earlier post. If the force against the stanchion was 62 lbs per square inch, it seems to me the base of the stanchion would have to support that force exponentially to the height of the stanchion. I may be using the wrong term,but bottom line is the base of the stanchion is subjected to a hell of lot more load than 62 lbs due to the fact that all the stress along the length of the tube is transfered to the base.