Mast thickness

[Jack Long]

I want to know the thickness of the mast material so I can get the right size rivets for the steps. Will measuring the wall inside where a halyard comes out give me the right number or does the thickness vary along the mast?

Thanks,
J

[Cheechako]

the thickness may vary going around the mast. I have seen some extrusions like that. Most masts are extruded so they are similar thickness in the longitudinal direction. generally, they should be pretty close all around except near "tracks" etc

[Squeaks]

Jack:
Others will hopefully back me up but drilling and tapping with SST (stainless steel) machine screws would be much stronger. But SST rivets, not alluminum, at a minimum.

[Jack Long]

Planning on SST rivets. 6 per step.

My instinct was to go with screws but I was really leery about trying to tap 70ish holes. Then I noticed most of the boats around mine were riveted and I rejoiced.

[delmarrey]

Originally Posted by Squeaks

Jack:
Others will hopefully back me up but drilling and tapping with SST (stainless steel) machine screws would be much stronger. But SST rivets, not alluminum, at a minimum.

Most masts the wall thickness is less then 1/8" thick unless you get into the very large yachts. If one were to drill and tap for a #10-32 screw there would only be 4 threads in a 1/8" thickness and even less in smaller masts.

It's a general rule to have at least a depth of thread 1-1/2 times the diameter of the screw/bolt for true holding power, even more so in aluminum.

Rivets are stronger in this case only because they would never pull out without distorting the metal into and external *******. Where as the threads would strip out just by over tightening.

Although I did drill and tap my mast for some cheek blocks for the lazy jacks which have a side-ways pull, but everything else like the gooseneck, steps, pole track, boom-vang, spreaders and thru blocks are all riveted. I still may end up pulling the screws and installing rivets if they show signs of coming loose.

The other thing about screws is they leave a shape protrusion sticking out the inside of the mast for lines to snag on. A selection of short screws was important in my case. Whereas, rivets leave a rounded knob on the inside.



http://www.answers.com/topic/rivet

[Alan Wheeler]

If you can find, use Monel rivits. These will not cause the corrosion issues SST will. If you do use SST, then coat in lanacote before placing them in the hole. If the step is SST as well, then you need to use a urathane adhesive sealant like 3M5200 or Sikaflex or any similar, as a bedding compound. A small amount will squeez out. Just wipe clean with some turps on a rag.
If you did go for a thread, you always want to use a corse thread like UNC etc. on any threads under 8mm(5/16). From 8mm up you can use the finer metric threads. Coat threads in lanacote. For speeding up tapping the thread, you can use a battery drill on a slow speed and a good starting tapping. Just spin the tap all the way through. It's quick and works well.
Be very cautious of using Aluminium rivets. They are soft and can shear without you ever knowing they have. Monel is strong and corrosion resistant.
Most mast sections are similar in thickness all the way around. But watch for twin section extrusions. These will have a seam down the sides and the mast is twice the thickness along that seem. A rivet slightly longer than needed will still take up.

[Cheechako]

+1 on Lanocote at any SS alum interface. I used a jar of anhydrous lanolin for year for everything from the threads on anchor clevis' to screws in the mast, to tapered seacock lubricant and even on my turnbuckles etc. It's the only thing that will keep those ss screws from becoming a permanent part of the mast! I believe Lanocote is mostly just Anhydrous lanolin.

[Stevens 47]

The thickness depends on your ali section. I have attached pics of my old and new mast section. The new section is much thicker at the side walls due to how it is constructed. If you mast is oval chances are that the thickness is consistent. I would try to talk you out of mast steps, they are such a pain and a place for your lines to get hung up on. In my opinion they also ruin the lines of the boat.

Jack

[David M]

If I could add a little, boatyards are going with Tefgel in place of lanolin as a way of stopping electrolysis caused by dissimilar metals. I have used both, I agree that the Tefgel is the better stuff.

[imagine2frolic]

At the base of the mast should be a whole for the wiring to exit

[Jack Long]

I don't think the steps ruin the lines. Certainly not any more than solar panels, wind gens, dinghies, and/or male crew.

I will be solo most of my time after the Ha-Ha and that makes the steps pretty compelling. There are other ways to get up by yourself but nothing that isn't a big hassle. In another post somebody made the point that with the steps he is very diligent with various maintenance, repairs, spot checks, etc...

[Taipe]

Beware of using Lanakote or any other anti-corrosive metallic paste on turnbuckle studs! They have enough lubricant effect to cause the turnbuckle to swivel under load, particularly on forestays and backstays. In addition to a cotter pin, I am not sure if the use of two nuts on each stud, one above & one below each end of the turnbuckle, could prevent this from occurring.

[Bowdrie]

Originally Posted by Taipe

I am not sure if the use of two nuts on each stud, one above & one below each end of the turnbuckle, could prevent this from occurring.

From an engineering standpoint, the use of "Jam nuts", as it were, to prevent a turnbuckle from loosening is counterproductive and only increases the load on the threads.
Cotter pins, or using a length of bronze welding rod that is bent into an elongated Z shape, capturing both cotter pin holes is the way to go.
As an aside, those stainless "closed body" turnbuckles that were commonly found on the older Taiwan built boats can be a disaster.
The same, to a lessor degree can be said of the T-bolt style, and those in which the wire is swedged directly into the upper threaded turnbuckle stud.
I know,, many like them, they were designed to save a few bucks and save a few ounces, but they are a poor second, (or third,) choice compared to a real forged bronze jaw/jaw turnbuckle.