Spreader Tube

[Scott Galloway]

A "Spreader Tube" inside the mast: Should there be one?

Please find a photo of my mast in the spreader area with the spreaders removed bbelow. There are three holes in the mast in a vertical line. The top and bottom holes are for the bolts that through bolt the spreader bases together. The twisted wires ran out of the middle hole into the spreaders protected by a snug fitting heavy short plastic sheath (perhaps heat shrink tubing).

There was no spreader tube inside the mast.

I have searched this site and found the following. In the "Alll Those Wires Inside my mast gotta Go" thread, Ebb wrote, "The spreader tube is there of course to keep the thrubolt from squeezing the mast where all the work is concentrated, spreader sockets and the four lower shroud tabs. It is installed from outside into holes that just fit the tube."

On the "Spreader Socket Broken" Thread, Bogel wrote, "Spreader bases are through bolted with no bushings inside the mast. Original upper bolt was a 1/2" x 4.5" and the lower bolt was 1/2" x 5". Lower bolt also holds the lower shroud tangs."

I have reviewed the manual and find no mention of a spreader tube or spreader bolt bushings in the text, in the specifications, in the drawings or in the sample Ariel equipment inventory. On the other hand, no spreader detail drawing is provided.

So my question is: Was a spreader tube provided inside the mast during construction by Pearson on the Ariel. My Ariel is #330. If not, have owners added such a tube?

[ebb]

If somebody can explain why there doesn't need to be 'anti-compression tubes' in way of the two bolts thru the spreader fitting - I would like to know.

To hold the spreader fittings & those four pieces of s.s on that the shrouds connect to, you need two s.s. bolts through the mast. There would be IMCO no way to cinch up the nut on a bolt, even if you used two jam nuts (running two thinner nuts against each other) the nuts wouldn't be safely 'locked.' Any cinching on the bolt would distort the wall of the mast. The two 3/8" bolts on my mast have/had nylon lock nuts. It is possible, if the bolt is exactly the correct length to cinch these crown-like nuts to a refusal point, considered locked. And therefore NOT bending in the mast. It's possible that the nylon insert could deteriorate, I guess - so the rig is depending on some nylon to hold it together. Think I would like a compression tube in there and a 100% mechanical lock. We're tightening against the compressionm tubes.

Because of the spreaders also being there, I would think that this is a bending point, or at least a bending opportunity for the mast under sailing conditions. Of course the spreaders are there to keep the mast from bending too much.

The compression tubes are there to make sure the mast tube cannot change shape. Also the c. tube acts as a liner and spreads the point load of the bolt in the hole in the mast I'm thinking how a thin metal conduit flattens at the point of stress when bending - and how that compares to the 30' tube that is the mast on 338. A former owner worked on the spreader fittings and included compression tubes for the two bolts.

Also, the leeward side loosens, the windward tightens, leading to mast bending stress at thoise upper shroud terminals. I can't see how it can be any other way than to have that simple keeper tube in place between the port and starboard tabs.

338 will have airfoil spreaders iunstalled. There is a socket piece that fits a shaped hole thru the mast, but the spreaders sit on shoulders of that insert therefor bearing against each other. The shroud tabs will have their own bolt and a neutralizing compression tube to insure that the mast cannot change shape at the fittings. I may go with a single 1/2", and thicker walled aluminum pipe if I can find it, rather than conduit.*

It would be VERY interesting if The A/Cs left the factory without this little bit of (necessary, I believe) sophistication, and lasted all these years without a single mast break!

And it may have been that the spreader fitting/shroud plate combo were deemed wide enough to spread any bending point loads that compression tubes were unnecessary. Yet the forces on the mast there aren't changed by the two aluminum castings.
I don't know, but given that the mast is old, and, who knows, does aluminum get stronger or more crystalized as it ages, I like the idea of that little bit extra in those little bitty tubes.

I believe, also, that a search will reveal that the spreader castings have given up the ghost for some owners. What did they do, and how did they install the refit?


*Rather than goop the hell out of those s.s. bolts going thru aluminum tubes, thru aluminum mast, thru aluminum fittings, why can't we use fiberglass pipe? [Or fiberglass TUBE - see later Garolite post]

[Scott Galloway]

I do understand the theory Ebb. Your explanation makes me feel even more that an internal spreader tube or bushings on the two thru bolts that tie the two spreader sockets and mast together would both be good ideas. However, I am not terribly interested in building something that might be not be compatible for some engineering reason with the design of the Ariel/Commander spreader system.

I am interested in knowing if anyone out there with an Ariel or Commander has removed their spreaders and looked to see if they have an internal spreader tube. Bogel did look and found no bushings apparently. He didn't mention a spreader tube. Do all Ariels / Commanders even have the third (middle) hole pictured above. Since someone decided to run spreader wires inside the spreader arms in my boat, it is conceivable that that same someone might have removed the internal spreader tube if there was one.

Although it is hard to see this in the above photo, the middle hole is slightly larger than the two end (bolt) holes, and the middle hole has a rough hand-filed camfer on the outside. The hole was completely filled with the electrical wires and their plastic sheath, but alas no spreader tube inside. It does not appear that there ever was one. I suppose one could add such a tube, but since the spreader arms are hollow and the spreader socket has hole in it also, I am not sure how I would design such a thing, without modifying the sockets. Has anyone out there actually added a spreader tube or spreader bolt bushings?

Did Pearson originally install a spreader tube? Does anyone out there know? I'd like to put my mast back together soon. My has already spent too long on the asphalt beach.

[mrgnstrn]

I am replacing my spreader bases, and when I took it apart, there was no compression tube in the mast.

and when I think about it, I don't think it's needed. You really don't need to crank down on the bolts, since they are loaded in shear, not tension.

all those bolts do is (a) locate the spreader base on the mast and keep it from sliding up or down or sideways (loaded in shear) and (b) give you a place to hang the lower shrouds, which also loads the bolt in shear.

the spreader tubes are in compression, and the bases act to spread out that load along the mast. since there isn't any point loading on the mast, compression tubes don't seem to matter to me. the spreading out of the compression load avoids the need for it. yes, there is slight compression of the mast when the bases squeeze against it, but its spread out over a lenght of ~8 inches or more. so it's not like the mast is going to buckle there.

and I also think time-in-service lends to the opinion that the existing design is adequate. If you were starting over from scratch with a clean piece of paper would you do it differently? maybe.

but if it ain't broke, why try to fix it.

[Scott Galloway]

mrgnstrn,

I think Ebb has some important things to say about spreader tubes, but I am with you. I figure that if my mast was designed without an internal tube and it survived for 39+ years, I need not invent the wheel.

However, since my mast was rewired and stuffed with foam by a previous owner, probably when it was tabernacled, I decided it might be wise to ask other owners whether they do or do not have internal spreader tubes. I needed to rule out the possibility that an internal spreader tube was an original feature, but that someone removed the internal tube on my boat's mast to run wires into the spreaders.

Since the comments made on this thread by you and on another thread by Bogle seem to point to the conclusion that "there never were internal spreader tubes in the Ariel mast", I reattached my spreaders today.

It feels good to have the mast back together.

[ebb]

That's what it is. (sorry for the recapitulation!)
Some of us should find this beastie under the old spreader brackets on the mast.
The original spreader brackets as I remember them did not fit the radius of the mast very well.
If they did they could have spread the load of the spreaders pressing against the side of the mast. And perhaps have spread the compression load of the bolts thru the mast.
It was another area of the mast begging for a fixing.

You know my attitude: Just because there were no compression tubes there does not make the omission correct.

Two 1/2" bolts were used to mount the original spreader brackets.
The top bolt was very rusty, the one with the tangs was in good shape but threads were bearing on the hole in one side of the mast.
In lit'lgull's mast the bolt hole was egg shaped. There definitely had been a lot of pressure from the shrouds dragging on the bolt.

Lit'l gull is going to another type of spreader.
But the lower shrouds will still be separately mounted with a 1/2" 316 hexhead bolt.
RIGHT, four shrouds on one bolt.
Scott, and others found no compression tubes in the mast when they took their spreader system apart. Just the bolt alone going through the 1/8" thick mast wall.

The reason the "compression sleeve" or tube is usually put in a mast is to prevent the mast walls from being deformed with tightening of the bolts.
The usual way this is done is when the exact position for the shroud tangs bolt is known
the hole for the compression tube is drilled thru the mast.. It's a BIGGER hole than the bolt.
The compression tube is inserted and cut square (90 dgrees)* to the mast OD, or a scosh longer. About 3 1/2" long.
Then the bolt washers and tangs and nut is threaded on.
Then the bolt is tightened to refusal onto the ends of the compression tube. That is a second good reason for the tube.
AND the larger hole makes for more bearing surface on the edge of the thin mast wall. That's the theory.

Housing a stainless steel bolt inside an aluminum compression tube inside the mast has to be asking for trouble.
Maybe that's why the aluminum tubes are often conveniently forgotten.
Do everything we can to isolate the s.s. from aluminum. Could Lanocote the bolt in the aluminum tube. And slip on thin polyethylene washers between metal pieces on the bolt.

GAROLITE G-10
Recently Garolite #10 plate has appeared (again) on the scene. Used as an alternative for the cast mastheel fitting that goes bad on A/C and Triton boats. Garolite won't cause galvanic corrosion (or conduct electricity)
or weld to aluminum, like one piece will to another.

Garolite G-10 tubing is also available. This strong impact/tension exterior grade makes it fairly expensive.
Now suppose I ran the 316 tang bolt through a 1/8" or 3/16" wall tube of this material (there'd be a 3/4 or 7/8" hole thru the mast), instead of aluminum....is that cool?
The tube in this ap is easily replacable and won't corrode.
As for the clamping action of the 1/2" bolt:
The exterior of the tube can be seen to be itself 'supported' by the hole it is in -
and the ID of the tube is supported against deforming by the bolt that goes thru it.

Can we assume the phelolic/glass tube can take the tightening pressure of the bolt and the stresses on it? Any ideas???

This material doesn't show any signs of peeling or delaminating that I can see.
Have a collection of pieces of plate.
Maybe somebody has an ap that has caused concern????
__________________________________________________ __________________________________________________ _______________________
*see post #8 below.
Post #7 - Also use RICO'S blueline to get to his spreader pipe installation

[Rico]

I believe that the material's compressive strength would be enough to deal with the regular use loads on it... And all but the most severe overtightening...
As the garolite tubes would be prone to wear and a reduced lifetime expectancy, I would replace them every now & then...

I would go with stainless and gobs of lanocote!

My take on this issue; as well as the 'how to' is here:
http://www.pearsonariel.org/discussion/showthread.php?1552-Commander-155-Mephisto-Cat
Post #87

[ebb]

Rico, there it is - in fantastic close up!
How could I have forgotten? My cobwebbed brain is getting unreliable.
But I'm glad this method is revealed so well.
When we go abroad on the newww google it seems that most people don't know what a compression sleeve/tube/pipe is. Now we have the goods.

Can't disagree with your choice of pipe.
Can't say it's pipe because pipe has its own peculiar diameters that will never conform to normal fractions of inches. So even that 1/8" wall stainless must be classed as tube - in case somebody wants to find a piece.

Also, it's perhaps obvious, that my "squared off" cut of the insert is not for a beautiful arched bracket that's mounted on top - but for a standalone single bolt instal that creates a convenient flat for the first washer. Certainly would grind the pipe to the radius of the mast when a curved bracket is going on top.

It was great going back to the beginning of your thread to see what you've done and ache at your adventures.

Lanocote OR more tech non setting Tefgel (teflon paste). There's not an atom of space there around that bolt in the pipe.

onlinemetals.com
0.75 OD X 0.12 Wall X .51 ID T-316/316L Tube ----- One foot $18.18 plus S&H.
That's a lot cheaper than what you have to get from McMasterCarr for Garolite tube.

Even a 1/2" 316 bolt shank in a .51 hole in 316 tube has to be isolated.
Don't forget to butter the 3/4" holes in the mast.
Grease the brackets and the mast and lay in a piece of polyethylene film (or UHMW tape) for isolation insurance.
Check the shank diameter of the bolt you intend to use with calipers befor ordering.

Of course with that toterance you'll HAVE to use Lanocote to get it in to the pipe (and OUT again in the future.:eek:)

Thanks for the nod on the Garolite tube, Rico.
But cotton and plastic ain't stainless!

POSSIBLE STAINLESS ALTERNATIVE
Acetal bushing stock is available from usplastics (ID 1/2"- OD 3/4" - $7.70FT).
Also stock 5/8" and 1" OD.
This is the same or similar (delrin) material that our new rudder shaft sleeve bearing is machined from.
This is possibly the only plastic that can be considered a metal alternative!

And of course, what the mast makers use: Aluminum Tube.