David Tyler wrote:

Which begs the question - why are you posting on a topic you know nothing about, but not asking pertinent questions? Please read our forum guidelines.

Well, use your intelligence. Is the topic "masts", or "metals, materials and engineering"?

As someone else was polite and enlightened enough to state above, interesting things come out of the cross fertilization of different disciplines.

The original poster discarded a potential cheap and quality component because it did not have enough clearance ... when the obvious thing to do from an engineering point of view was stick it in a lathe and make more clearance.

Then, from an engineering point of view, I suggested potential ways of improving on it.

Someone who is limited to only fitting available items will see the world differently from someone who fabricates, or take stuff and modifies it. And has 

a) knowledge of which tools can do what to what materials, 

b) inspiration from work done in other fields.

For example, I would not expect a wooden mast builder to know about the qualities of Delrin. Or even that it existed.

At the end of the day, "masts" is a sub-section of engineering and, trust me, ship builders regularly call on the expertise of engineers to calculate and resolve problems.

But the most important question that rose for me, is why use a butt-welded (top hat shaped) piece ... why not just use a longer section of tube passing through and welded to a collar - and with closer tolerances - as it would give more support to the mast?

Especially if you are thinking of leaning it forward at an angle. The more contact area, the more you can spread the load (force). 

I'd be interested to know where, in worse case scenarios, junk rig masts snapped or did damage to the boat?

Some people instead fill the annular gap between a metal mast and a metal collar with a hard polyurethane rubber which can be poured and cast in place, a detail which has been the subject of other threads.

Links?

Yes, I was thinking of something like Delrin (Acetal), which you can cast and precision machine (or even laser cut). It is "slippy" (high lubricity), and has excellent non-compression, non-corrosion (insulating) and vibration absorbing characteristics; and is unaffected by solvents, fuels, etc. Unlike polyurethane, it also has good "rebound" qualities and does not deform so quickly

They use it for suspension bushings on big semi/articulated trucks and it comes in up to 24" diameters. Compressed, it would probably even work as a water seal.

So imagine something like that collar, with the extrusion threaded on the outside, and a Delrin bushing/seal on the inside and an O ring to seal it. Then an threaded ring around it, that once screwed down tightens it all together (like on the chuck of a drill, or a plumbing compression joint). Sure, some wooden chocks, a mallet and a gaiter has worked for 100s of years, but it would look and act more elegantly.

Or take that bolt compression idea someone else suggested (which was a bad idea as all the forces would be concentrated on the tips of the bolts) and instead ... machine a broad groove on the inside of the collar and use a compression ring in there to spread the load. 

(See attachment below for inspiration - a perfect example of inspiration from another field).

Yes, galvanic corrosion occurs when two different metals are in contact, worse where salt water is acting as an electrolyte. Think bicycle seat post becoming siezed in the seat tube on a big scale ... but there are all sort of lubricants and surface coatings to use.

The problem with galvanic corrosion, an electrochemical process, is that one of the metals experiences an accelerated corrosion rate, which is going to be aluminium mast if placed in a steel ring. I'm guessing the forces are not great and so aluminium to aluminium would be the way to go. However, if the decision is a financial one bear in mind that when you mention stainless steel, there are different grades and alloys of stainless steel to check, some are corrosion resistant, others not so much.

And lastly, just as a heads up, if anyone lives near an aircraft salvage yard, or a military surplus supplier, keep an eye out on what they have, as those industries scrap the most amazing items and materials. Where you tax dollars got spent!

I'd also be looking to learn from aerospace, e.g. Boeing developed some great anti-corrosion treatments for aluminium.

Branwen's mast steps consist of 5 rings of 1" plywood. Sandwiched between them are 2  O rings of 1 1/4" silicone rubber. Tightening 8 bolts to draw the plywood rings together squeezes these O rings on to the heel of the mast, gripping it tightly. It is completely silent. Loosening the bolts will allow the masts to be withdrawn. It is not necessary to have the O rings made; I simply cut the silicone rubber rod to length so that the two ends meet.

My article "Converting Branwen to Junk Rig"  in issue 70 of the JRA Magazinr has a photo to clarify  the method. I'm about to leave the Bahamas for the Azores, so won't be able to respond to any questions until I get there.

The tricky thing about a perfectly snug fit for the step is if anything changes later on, say when the mast has been pulled for the winter, and you go to put it back in, and it doesn't want to fit. This can be discouraging at the boat ramp… she said, speaking from experience. If the step is oversized and has wedges, then you trade that perfect-fit problem for fussing with wedges that work loose. I am watching this discussion with interest.

As far as the anonymous issue, if it makes you feel more comfortable, anonymous individual, perhaps you could choose a "JRA name" to use while you are here. You'll note, that if you look at the JRA fora without signing in, everybody will be shown as anonymous – which is what people who are nonmembers see. Boat theft has not to my knowledge ever been an issue for members, and if it were, the international reach, and community, of the organization would be likely to be an asset for recovery– besides that junk rig makes a boat distinctive enough to not be a particularly good target for organized theft.

We have typically been an organization of individuals who choose to actually know one another, and enjoy that aspect of the group. If you prefer not to make those connections, a JRA alias would be helpful just for keeping conversations straight, particularly when somebody would like to refer to any contributions you have made to the discussion, or to speak to you directly.

Thanks!

Shemaya

Anonymous Member.  If you go to your profile, you can edit your privacy settings so that your name can only be seen by other members.  Indeed, this is how it is set up by default.  If you are particularly uncomfortable at having members see your name, then you can just allow us to see your first name.  You can even use a false name if that's what floats your boat, but personally, I find it rather discourteous for members to be anonymous.

I went with belt and suspenders. I was lucky and found a section of plastic drain pipe that matched my mast.  I also built and installed the step the way that Arne describes with 2 screws to initially hold the step in place until I was sure it was plumb.  I didn't epoxy the two sections.  The upper plywood part of the step is held in place with with eight rugged screws, similar to lag screws. I wanted the option add a little rake if needed. I don't see how the screws could all break or rip out. But then the dry weight of my boat is only 2000 lbs.

If available PVC / plastic pipe is a little undersized you may be able to use pipe couplings at the step and partners.