Spreader problem

[Sir Rondo Normal]

Originally Posted by LH44 Anne

Combining the tang and spreader base gives a single point of failure for both.

Yes I understand that but you're judging the engineering of the rig by two pictures. As one poster pointed out there may very well be more fasteners that we can not see.
Now I don't know what the lateral load placed on those screws is but obviously the designers/engineers who built the mast did know and also knew what the boat design was intended for, off shore cruising.
Like I said in a previous post, this boat will go off shore again but only after a total refit, including the standing rigging.

Originally Posted by LH44 Anne

Getting away with it probably isn't what your wife has in mind, I suspect, whether at the masthead or back on deck.

THAT, I take exception to... Judging and condemning a rig from two pictures tells me something about you and that statement (apparent judgement of me) backs it solidly.

[chala]

Originally Posted by edsailing

I would NEVER put a clamp on the shroud under the spreader. The reason is simple - clamping the shroud stops the strands moving and can cause metal fatigue as the flexing is stopped by the clamp. How do I know? I've had a shroud fail for this reason in mid-Atlantic - I learned my lesson!

May be the clamp did it. I have no doubt that the spreader can accommodate the few mm if any movement of the shroud.
In regard to the OP if you draw a continuing line from the shroud to intersect the mast the intersection point looks like to be just under the spreader socket. If you where to draw a line from the bottom of the machine screws to the chain plate it will leave a gap under the spreader sockets. By first feeling if there is a possible movement of the sockets an if, by removing one of the spreader it would be then easy to check if that connection is sound.

[SkiprJohn]

My last rig had seizing wire figure 8s several times around the upper shroud holding it to the outboard end of the spreader through small holes drilled in the spreader ends. I thought this was good in that it did not squeeze the dickens out of shroud but held it in place quite nicely.
kind regards,

[LH44 Anne]

Originally Posted by Capt Wraun

Yes I understand that but you're judging the engineering of the rig by two pictures. As one poster pointed out there may very well be more fasteners that we can not see.
Now I don't know what the lateral load placed on those screws is but obviously the designers/engineers who built the mast did know and also knew what the boat design was intended for, off shore cruising.
Like I said in a previous post, this boat will go off shore again but only after a total refit, including the standing rigging.

THAT, I take exception to... Judging and condemning a rig from two pictures tells me something about you and that statement (apparent judgement of me) backs it solidly.

If you don't want other views than your own, why are you asking here? I'm out.

[Sir Rondo Normal]

Lol, to learn of course. There are a number of members on this forum who have demonstrated their knowledge time and time again. Their opinions are valuable and I accept them with gratitude. I'm not looking for a free online inspection of my rigging but it's always good to "pick the brains" of people with experience/knowledge.
Like I said before, I will be enlisting the services of a rigger anyway but when that rigger shows up at my boat, I would like to not only know what he's talking about but be able to ask questions of him to judge his level of competence as well.
You come along with 46 posts to your credit, a blank profile and snippety attitude and get offended because I don't accept your judgement?

See ya!

[LH44 Anne]

Originally Posted by Capt Wraun

[snip]
You come along with 46 posts to your credit, a blank profile and snippety attitude and get offended because I don't accept your judgement?

See ya!

I wasn't aware that the number of posts and profile details are a measure of competence and experience. I didn't get offended in the least; I didn't ask you to accept my judgement. You asked for views, I gave you mine.

I guess I'll just have to post more so my opinions will have merit.

[Wotname]

Originally Posted by LH44 Anne

I ......
I guess I'll just have to post more so my opinions will have merit.

Nah, it works the other way

[osirissail]

Before this gets out of hand - remember, everybody's posts are merely their opinion based on their experiences. And there are a lot of different experiences out there.

Just because something didn't fail previously doesn't mean it is a good design, just that the materials absorbed the abuse over the years and now may or may not fail. Fatigue cracks take a lot of time to show up.

The spreader base combined with lower shroud tang system on your boat is "out of the ordinary" for large boats but for "small boats" where cost is a major factor in the manufacture they can save some dollars by "combining" things and over the expected life of the boat get away with it.

Engineering-wise, every time you heel under sail your windward lower shroud exerts a restraining force on the spreader base/tang, that force will be in a straight line from chain plate to the lower row of machine screws above the spreader. This will, if the angle of the bend in the lower portion of the spreader base/tank is not correct exert an outward force to the spreader. However at the same time the main shroud will tighten and exert an inward force on the spreader. And they, most probably, will cancel each other out in the design.

But that leads to the problem of frequent bending stress on the actual spreader base/tang plate - if the bent portion where the lower shroud attaches it does exactly match the aforementioned line from chain plate to attachment machine screws. Also remember that the wall thickness of the mast tube is thin and using machine screws to attach the spreader base/tang might be adequate but not necessarily the best way.

So close examination of the surface of the spreader base/tang in the area of the lower row of machine screws is suggested to detect any wrinkles or stress cracks.

You or the rigger might even use a "dye-penetrant" kit to see if there are any fatigue cracks in that area. If there is no evidence of fatigue cracks, press on and enjoy sailing until the next time you do a general rigging inspection.

Just like "surveyors" - there are good "riggers" and bad "riggers" so whatever the rigger advises is worth about as much as the many different opinions expressed here on CF. In the final analysis, you and your wife are the ones to make a decision whether what you have is adequate or not. It is your collective butts riding in the boat, not the riggers nor those expressing their opinions here on CF.

[Sir Rondo Normal]

Originally Posted by Wotname

Nah, it works the other way

It's not really the number of posts but the quality of posts.

[Sir Rondo Normal]

Thanks Osirissail for the very thoughtful and "quality" post. We will be going up for closer look this weekend. I have also contacted the builder of the boat as I'm trying to track down the maker of the mast to see if I can find out if there are compression tubes behind those spreader mount/tangs. It would seem to me that if there are compression tubes and throughbolts (and there may very well be) behind the mount/tang combos then all should be good (other than wear & tear of course).
If there are not, then we'll have to explore our options.

Again, I am grateful to all for your time and thoughtful contributions.

[osirissail]

It is highly doubtful that your mast system has through-bolts and compression tubes. But never say never.

Here is a drawing of what some large boat masts use to attach shroud tang plates. The purpose of the special cut bolt or simple bolt inside a compression tube is to provide an attachment for the tang plates without exerting any squeezing force on the mast tube walls.

For instance, if you put a standard bolt through a mast section and tighten down the nuts on each end you would start to squeeze and deform the shape of the mast tube. Not good. So a special bolt or bolt and piece of tubing is used to prevent any squeezing of the mast walls towards each other.

[chala]

Originally Posted by osirissail

Here is a drawing

This is not a true compression tube. The tube or special bolt is introduced from one side of the mast by a 7/8 hole witch mean that the opposite side can still collapse under load. A true compression tube is placed internally and in such a drawing both holes would be 5/8.

[rognvald]

Capt. Wraun, unless it is an optical illusion, it appears that the mast ( in picture 3)under the spreader socket base is inwardly deformed. If so, this could have been caused by a previous trauma and would cause a multiplicity of problems in alignment, structural integrity and applied load forces. I once repaired a mast on a 25 foot sailboat that had a similar problem and was able to heat the surface of the mast and then use a dent puller to bring the surface to flush without sacrificing the stability/strength of the metal. I then installed a compression post inside the mast to reduce loads and strengthen the base. A true mast compression post is loaded in the mast internally and has a larger O.D. than the pre-drilled hole through which passes the bolt/shaft . The principle is that the larger O.D. of the internal post prevents compression of the surface of the mast where the spreader sockets are mounted. On a large vessel, this is a safety measure and one should be installed. You should look carefully at your spreader assembly and be certain what is causing the problem. Good luck and good sailing, Ron

[Sir Rondo Normal]

Thanks for the observation Ron. I hadn't noticed that before but I think that is likely an illusion due to the shape of the tang and how its curved toward the camera. We will however have a closer look to be sure. I have been searching for info on my masts construction but so far, to no avail. I have found other masts on much smaller boats though, that do use a compression tube between the spreaders and a spreader mount/tang combo similar to ours, so I am hopeful.

Thanks again,

Ron

[rognvald]

Originally Posted by Capt Wraun

Thanks for the observation Ron. I hadn't noticed that before but I think that is likely an illusion due to the shape of the tang and how its curved toward the camera. We will however have a closer look to be sure. I have been searching for info on my masts construction but so far, to no avail. I have found other masts on much smaller boats though, that do use a compression tube between the spreaders and a spreader mount/tang combo similar to ours, so I am hopeful.

Thanks again,

Ron

Capt. Wraun, if your mast is oval shaped, the spreader base is likely deformed. If, however, it is oval with flat sides it may be an optical illusion created from the camera angle. Let us know what you find next time you're on the boat. Good luck and good sailing, Ron