Mast & Sails

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Alm

Post by Alm »

Does the protruding inner tube extending out 1 1/2 feet seem about right?
It's about 6" inside and outside.

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gbellware
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Post by gbellware »

John,

The key here is not the length, but the wall thickness. There is a complicated formula that I would be happy to share, but in a nutshell...the inner tube could be a scant 1" in length if it were a solid core. The "modulus" is the critical factor, it relates to the strength of the tube relative to it's diameter. The smaller the diameter the thicker the tube wall needs to be in order to achieve the same strength, measured in psi and deflection, for your mast. OK, enough mumbo jumbo, you just need to get a tube with a thicker wall than the mast and you will be good to go with a short insert. And 6061 t6 would be preferable if you can find it.

g

John Monroe

Post by John Monroe »

Hi Alex & gbellware,


Good information from both of you. I believe it was you Alex that originally told me the wall thickness looked to be about 1/16 of an inch in the outside 1 1/2" o.d. aluminum tubing. I have found out that you must use sliding tubing that fits inside one another. I found this very hard to find tubing at http://www.texastowers.com/aluminum.htm It is 6063-t832 with a yield strength of 40,000 psi. Both the 1 1/2" and the 1 3/8" inner tubing have a wall thickness of .058. Texas Towers sells in 6' and 12' length but by buying in the shorter length makes the shipping is much lower. The picture is the way I have finally decided to make the mast with the inner insertion tubes butting up against each other to make a solid inner section of tubes for extra strength but not that much extra weight. Thanks for the help and understanding. As the project comes along I will keep posting,
John

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gbellware
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Post by gbellware »

John,

I don't mean to complicate things, the design you have looks fine, at least it has exhausted my limited knowledge of metals. The reason I suggested the schedule 6061 (extruded) tubing is because as I recall, even though the yield strength is identical to the drawn tubing you have selected it is actually stronger and stiffer (up to its yield point). But it looks like it is not available in the right sizes.

Just be aware that with your design the mast will only be as strong as the INNER tube, given that the wall thickness is the same for both.

I look forward to hearing how this works out.

g

Alm

Post by Alm »

I don't uderstand, why 18" length of the insert (outside). Like I said, with walls approximately 1/16 (i.e. 0.0625", but may be it's 0.05" or so), BSD inserts extend only 6" otside and 6" inside. Also, you may check these guys: http://www.mcmaster.com/ (dial Aluminum Tube in search). They have this one (below) for the mast. Slightly thinner walls than the one you mention, i.e. slightly larger ID, but okay for 1.3/8" OD inserts, considering some glue. The maximum pressure seems to be MUCH lower than yours, and makes me think that your guys meant something different - it can't be 100 times difference.

Also, considering that BSD longest mast (for 36 sf sail) costs only $180, including all the inserts, mast-top, bottom-plug, foam inserts, anodized, rounded edges, etc, etc - may be you should just buy it. If you phone and email him every week (after placing the order by phone and waiting for, say, 6 weeks), you'll get it before the end of the spring. May be even without a dozen of phone calls, if you get lucky :-)

Tube from McMaster:

Material- Aluminum Alloy 6061
Shape- Single Line
System of Measurement- Inch
Outside Dia. 1-1/2" (1.5")
Inside Dia. 1.402" (VS 1.384" in your tube)
Wall Thickness .049" (VS 0.058" in your tube)
Maximum Pressure Range, psi 501-750 (VS 40,000 psi in your tube???)


Btw, I've got those egg-shaped plastic fittings for BSD hardshell kayak rig (to attach the struts to the hull), with pins/locks thingies. They can be yours for shipping (probably with struts too). I understand, you have a sail rig on a wooden hardshell kayak. I've dismantled BSD rig from hardshell kayak and won't be using it ever again - local wind and temperature pattern is more suitable for downwind kayak sailing than full-size upwind rigs. I'm still using the big rig with folders in remote trips, though (different fittings).

John Monroe

Post by John Monroe »

Hi guys,

That's a very kind offer Alex. If the struts are the reinforcements for the pontoon cross bar I already have them built and on. Mine look like Balogh's but are heavier duty. But thanks.

I had just about given up on finding 1 3/8" od 6061-T6 aluminum tubing and was going to buy a Balogh mast when I come across the telescoping tubing. I have also found 6061 much cheaper then at McMasters, Speedy Metals is one. Below is a rundown on the tubes that are too sloppy or too tight.

McMaster Products

Material Aluminum Alloy 6061
Shape Single Line
System of Measurement Inch
Outside Dia. 1-1/2" (1.5")
Inside Dia. 1.402"
Wall Thickness .049"

1.402”- 1.375 = .027 slop space between inner and outer tube. Too much.


Material Aluminum Alloy 6061
Shape Single Line
System of Measurement Inch
Outside Dia. 1-1/2" (1.5")
Inside Dia. 1.37"
Wall Thickness .062

1.370”- 1.375 = +.005 so the inner tube won’t fit inside the outer tube.

This is what I keep finding when researching 6061 aluminum tubing. But the thing is I have never found 1.375 in 6061-T6 anywhere on the net. However using

Texas Towers
6063-T832 aluminum
3 - 6'x1.500"x.058" Alum Tubing.$ 40.50 -------3 pcs-6’ of 6061, .062 wall thickness from McMaster $199
2 - 6'x1.375"x.058" Alum Tubing.$ 24.60
This is really cheap.

But using telescoping aluminum the inner tubing space slop is only .009 which is just about right for epoxying the tubes together with a thickened epoxy.

Alex I'm sure the 6 inch protrusion is just fine but I will feel better with my longer protrusions and the added weight won't be that much.

Here is a picture of what I think you are calling a strut.

John



Image

Alm

Post by Alm »

Yes, I meant these struts (and black mounts on the hull).

0.09" is a much smaller slop than 0.027". This is good for permanent joints (i.e. inside part of the insert), but I am not sure this is good for the outside part, which is supposed to slide in and out easily. May be you should ask somebody in metal shops who deal with this more often. When the clearance is barely enough to shove it in, any grit, corrosion, salt deposits or dents will make it very difficult. Again, - I'm not a mechanic, and don't know the exact thickness of walls in BSD mast, but I had such a problem when making a kayak cart - too little clearance. May be Tom Yost here knows better (ask in Homemade Kayaks or PM him).

Besides, too long outside section of the insert (18") will aggravate the above problem. The slightest bend in either tube, impossible to detect visually, will result in tremendous efforts needed to assemble or dissemble the mast, adding scratches and abrasions every time. Consider that once in a while you might have to do this on water, in inclement weather.

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gbellware
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Post by gbellware »

OK, so you got me intrigued enough to ask my favorite metalurgist (my 85 year old father, who has been in the business of metal rail fabrication for 50 years, still working every day and flying his own airplane!) and here is what he wrote:

Re: folding mast...

"As I was saying about section modulus - its merely a tool for
determining the bending strength of a given shape of material.
Unfortunately this keyboard won't let me type out the formula but
maybe I can say it in plain English. Usually it is expressed by the
letter S or Z. To find the section modulus of a tube, start with the
outside diameter raised to the 4th power. Subtract from that the
inside diameter raised to the 4th power. Now multiply that sum by pi,
and divide the whole thing by 32 and divide again by the outside
diameter. If the mast is 2" OD with 1/8" wall (making the ID = 1.75"),
I think you'll find the section modulus is .325 (the units will be in
inches cubed). Then if you have an insert with an OD of 1.75", and
if I've done the math right, the wall thickness will have to be 3/16"
in order to have the same section modulus, i.e. the same bending
strength. (All this assumes, of course, that the insert is made of
the same strength material as the mast).

Intuitively, I'd say that any reasonable length of insert will provide
adequate strength. But if one uses off-the-shelf materials I fear the
whole mast will be wobbly. Off hand I don't know what the tolerances
are for commercial tubing but I'm sure they're great enough to cause
great frustration. Not only will the diameter and wall thickness
vary, but tubes are slightly oval shaped. Because of these
tolerances, the inserts should be as long as possible. But the longer
the inserts, the more difficulty you'll have assembling and
disassembling.

I'm sorry if I sound too negative here. But I guess I've built too
many wobbly rails in my lifetime. Actually, if we were building a
rocket ship, or even just an airplane, maybe you could afford to
custom turn all the components to tolerances that are close enough to
make it more acceptable. But if we're talking commercial materials,
the best bet might be to work on a method of using some sort of
threaded fastener to firmly hold each connection."


Probably more information than you were looking for, but just thought I would share it anyway.

Best,
g

Alm

Post by Alm »

Not only will the diameter and wall thickness
vary, but tubes are slightly oval shaped. Because of these
tolerances, the inserts should be as long as possible. But the longer
the inserts, the more difficulty you'll have assembling and
disassembling.
Now I understand why my 7/8" OD tube was very difficult to shove into 1" OD tube when making a luggage/kayak convertible cart. Don't know the walls thickness - there was some little clearance, and one tube went in and out almost perfect, but another one was a nightmare every time. I couldn't see any bend, but if it was the oval in cross-section somewhere (i.e. reduced clearance at the "ends" of the oval of insert, or at the "sides" of the oval of outer tube), or variations in wall thickness (again reducing little clearance amost to zero on some spots) - makes sense.

John Monroe

Post by John Monroe »

Gbellware thank your dad for the explanation. When I was working as a patternmaker I worked with a metallurgist for a couple of years. I guess it boils down to the material strength used, wall thickness and length. Length would be like snapping a pencil, which is easy when holding the ends, but if held with fingers close together is much harder.

My mast with the center tubing running completely through the outer tube gives a wall thickness of .116 along the entire length of the 13’-2” mast. In the Balogh mast the elasticity of the mast sections is weaker in the sections of the mast that have the wall thickness of. .058 until the insertion tubes double the wall thickness in the ends of the 1.5” od tubes. The double wall thickness would seem to be about 1 foot for every 4 ‘ of single wall thickness. The 4’ lengths would then be part of the elasticity of the over all 13’-2” length equation I’m getting dizzy.

In the end, Balogh has this all figured out as I have never heard of his masts failing. Alex and you bring up a good point that sand and tube distortion is a potential problem and that would favor the short insertion tube. So if I have these problems I can always cut the longer insertion tubes off into shorter ones.

John

Alm

Post by Alm »

sand and tube distortion is a potential problem and that would favor the short insertion tube. So if I have these problems I can always cut the longer insertion tubes off into shorter ones.
... and/or sandpaper/machine the outside section of insert to smaller OD, if cutting it won't help.
in the Balogh mast the elasticity of the mast sections is weaker in the sections of the mast that have the wall thickness of. .058 until the insertion tubes double the wall thickness in the ends of the 1.5” od tubes.
The cases of breaking BSD mast are very rare, AFAIK. Looks like the strength of 0.058" wall is high enough (again, if his is 0.058, which I don't know for sure, but it looks close to 1/16", which is roughly 0.06").

John Monroe

Sail Rigging?

Post by John Monroe »

I have been looking at pictures of Balogh sail riggings and it looks like some of them use the setup in the picture as a boom vang combination sheet line to help hold the sail down. Is this right? Others I have seen look to have a regular boom vang using a pulley and an upside down V line like a traveler line it looks like. Any thoughts?

John
Image

Alm

Post by Alm »

No. This is striclty control sheet. For those occasions when you need to be under the sail (as oposed to sitting aft of the sail). Downhaul line is a separate line, normally attached around the pulley located next to the pulley shown on your picture in the "tack" corner of the sail (lower corner next to the mast).

John Monroe

Post by John Monroe »

Does anyone know the inside diameter of the Balogh sail mast rings? I am using the Sunfish sail rings, which are 1 9/16 inches when they are snapped shut. But it seems like they may be too small to slide properly. It’s too cold and snowy to test outside right now.

The take apart 4 section mast has worked out well. I used the longer inner tube inserts that make an inner wall that runs the entire length of the mast. I think the mast will be extra strong.

Any information appreciated.

John

Image

John Monroe

Making A Sail Project.

Post by John Monroe »

It's finished.

The winter project conversion of my kayak to sail is finished finally and the results were much more then I might have expected. It sailed just great up wind, and that had been a big worry for me. I would guess 40 degrees off the winds and I could have checked it with my compass but was having too much fun and never thought about it at the time. I put 1 ½” curve in the luff and foot of the poly sail which seem to give the sail the wing curve needed. The stackable 4-piece 13-foot aluminum mast is easy to put up and take down. The side tiller requires less then an inch forward or back movement with a feather touch to adjust the heading and I was surprised I could just lay the tiller down and the boat would hold its heading for quite awhile by itself which I would guess is good balance. The boat came about nicely as was gibing around ok also. I think I will raise the mast 6 or 8 inches so the boom clears my head.

Thanks for the help and suggestions along the way.

John


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