Rivets or Machine Screws When Splicing a Mast?

[Baby tug]

Originally Posted by s/v Jedi

There’s these wires attached to masts… we call them shrouds and stays, and they take the (side) load, not the bottom of the mast

Isn’t that what I said if you’re worried about the mask breaking where it was welded , I suppose you could put install another stay or two , Shroud Whatever , like i said Neanderthal works for me what can i say Just my opinion

[Chotu]

Originally Posted by s/v Jedi

Take a little more care and time in these buying decisions Chotu, it saves significant amounts of money. The link I posted is for 500 bolts, certified top quality as well. Boltdepot is a box pusher just like Newport Fasteners.

I write this because I was in the same situation and decided to change that after learning how big the savings can be. If I buy something over $100 now, I put it in the shopping basket but don’t check out until at least a day has passed. During that time I try to find alternatives a couple times, think if it’s really the right product to get and sometimes I even change design to be able to use another, much more affordable product. In almost 50% of the cases I end up buying something else or from another place

I know, I know. You should see how carefully I shopped for most things. I mean look. I’m about $45,000 less than a new Mast would have cost me. And I have temporary sails for free. You don’t even want to understand what price I got pallets of Corecell for. Bought directly from Gurit in Canada And epoxy in 55 gallon drums from the manufacturer. And pallets of fiberglass. I’m frugal. Trust me. Lol

And for most of the stuff I have shopped well. But this is such crunch time that one got past me. However, I showed them the link that you sent me. And they are looking at adjusting the price for me. I have been a long time customer. And they realize something is out of whack.

[Chotu]

Originally Posted by RaymondR

The point I'm making is that sail boat masts in use are subjected to a number of forces which may work together to create stresses which a simple analysis does not identify. I used the example of running back stays to illustrate where this might apply on a sail boat.

The combined stresses created are known as bi-axial or tri-axial stresses and now that we have computers the primary technique used to identify them is known as "finite element analysis". This technique breaks the structure down into small volumes each of which is analysed to identify the stresses on an x,y, z axis basis which stresses are then translated into the adjoining volumes as starting points for their stress analysis.

I'm not an engineer so would not swear to any of that in a court of law but during my oilfield career bent and broke a lot of stuff and had quiet a few of the engineers who investigated the incidents explain to me how I had screwed up.

In laymen's terms, the analysis of masts is complicated **** bro.

Do you know who is good with this stuff? Eric Sponberg. He’s retired. But he was a master with this stuff.

Also, I’m proud to say my entire boat was designed using finite element analysis to determine the laminate schedule and all the various places. It’s as light and as strong as it can possibly be. It doesn’t fall into the design spiral where you add extra material because you think it doesn’t look strong enough. But it actually is. And when you add that extra material, you have to straighten up another location to carry that weight. And then after adding that wait, you have to straighten up another place to carry that. And you end up with a piece of junk.

Finite element analysis keeps the negative design spiral from happening.

[malbert73]

Originally Posted by boatpoker

Glad to hear you are making progress

Meanwhile DIRT FREE has been stuck in Great Bridge VA with a blown engine. We were Bahamas bound

It cost us $6k and 6 weeks to get it out and dismantled only to find that Westerbeke does not have the parts we need and won't tell us the OEM so we can get them elsewhere.

We just ordered a new Beta for $18k with a four to six month delivery
(best we could find). So another 6 months of dock fees plus the cost of installation.

On top of that, Canadians are allowed only 6 months in the US and we just applied for an extension at a cost of $1100 for biometrics exams (digital photos, fingerprints, retinal scan). That stuff goes to the FBI and they might let us stay a few months if we come up clean.

So here we sit in VA with nowhere to go. Wanna trade places ?
Still love the cruisin' life

Oof- that really sucks I am sorry. Though you could be in the Bahamas engineless.

Do you have a thread about the repower process? Curious which Beta- we love our 50 (V2203)

Sorry for thread sidebar Chotu- glad to hear mast is going well now

[Dave_S]

Originally Posted by Chotu

316 socket flat heads. 1/2” dia x 3/4” long. Coarse thread

It takes 130 of them to do the job. Well, I think it was 112 but a few extra in case.

Where are those “you get what you pay for” guys???

I want them to get on here and congratulate me on getting the finest screws money can buy. Ha ha

These are just my opinions but I'm sure it's better than the advice you have been listening to.

I tried to refrain from commenting but it's worrying me, and better it worries you than me.... Sorry 🙂

The size and type of screw seems to me to be an unsuitable choice for this purpose.

If you are fitting these countersunk fixings flush on a radius section. A 1/2" X 13 screw through 3/16" and into 1/4" material will have less than 0.150" (3.8mm or not quite 2 turns) of thread. It will not locate well with poor axial support in the threaded material and nothing to speak of in the outer skin.

If you are going to continue with them, my advice.
Do not let the countersink of the screw bottom out on the inner material section, it must only contact the countersink in the outer material otherwise the fixing applies ZERO clamping force between the two pieces of material. There will be no stretch across the two materials and therefore no load... Pointless having the screws.

You should do some testing on some scrap to get the right torque settings for these. Drill, tap, and countersink a few holes exactly as the job will be done with both sections and profiles used. Then assemble it exactly the same way, including whatever Loctite or wax or anti-corrosion on the screws. Then tighten them untill the threads start to fail (torque decreases) record the maximum torque for each one. Take the lowest torque setting and use 80% of that torque as your setting for all the actual mast screws you fit.

It will be a low % of the specified settings for those screws and you will not get the tensile or shear strength you might be expecting but it will be your best setting.

[Chotu]

Hi Dave.

Actually I had no idea you could do it any other way. I didn’t realize you could counter sink all the way to the second material inside the mast. That definitely would not be a good idea no matter what project you are working on. So I’m with you there.

These were 82° heads. The only thing available. And what I was thinking is they would counter sink into the outer mast only. And then they grab the inner piece with the threads.

I have also done plenty of reading that says do you want the screw to be twice as big of a radius as the material is thick. This is for aluminum. This is what I read somewhere. It would stand to reason that this is correct because that’s what I see on my crossbeam also.

I also read that course threads are preferable to fine threads for this application. The idea is there may be less threads going through the material, but the depth of the threads into the material is superior.

I also just came up with 3.25 threads in the 1/4 inch material.

What do you make of all of that?

I like the torque to destruction testing idea.

[s/v Jedi]

Originally Posted by Chotu

Hi Dave.

Actually I had no idea you could do it any other way. I didn’t realize you could counter sink all the way to the second material inside the mast. That definitely would not be a good idea no matter what project you are working on. So I’m with you there.

These were 82° heads. The only thing available. And what I was thinking is they would counter sink into the outer mast only. And then they grab the inner piece with the threads.

I have also done plenty of reading that says do you want the screw to be twice as big of a radius as the material is thick. This is for aluminum. This is what I read somewhere. It would stand to reason that this is correct because that’s what I see on my crossbeam also.

I also read that course threads are preferable to fine threads for this application. The idea is there may be less threads going through the material, but the depth of the threads into the material is superior.

I also just came up with 3.25 threads in the 1/4 inch material.

What do you make of all of that?

I like the torque to destruction testing idea.

Well, I posted my research earlier in the thread that indicated that a M8 or 5/16” bolt was good and a 3/8” at the upper limit and the M10 too big. You went for 1/2” which is not 10mm but 12.7mm so way too big.

The documentation will show you how deep the countersink head goes.

[s/v Jedi]

I did the math: your mast is 3/16” which is 0.1875” a 1/2” flathead bolt has a head height of 0.223” so it’s way too big.

Edit: socket head height is even more… over 1/4”. Even at 5/16” it is more than 3/16”.

1/4” head height for a socket machine screw is 0.127” so will fit.

[Chotu]

Originally Posted by s/v Jedi

I did the math: your mast is 3/16” which is 0.1875” a 1/2” flathead bolt has a head height of 0.223” so it’s way too big.

Sh*t.

More data though. Data to decide if I want to continue this or not. Because this stuff sucks.

It also sucked wasting $900 today on a MFD I didn’t even want.

So I need to return these machine screws anyway after all that.

5/16” it is

Thanks for catching this. Have I mentioned how much I hate building boats yet? Lol

[s/v Jedi]

Originally Posted by Chotu

Sh*t.

More data though. Data to decide if I want to continue this or not. Because this stuff sucks.

It also sucked wasting $900 today on a MFD I didn’t even want.

So I need to return these machine screws anyway after all that.

5/16” it is

Thanks for catching this. Have I mentioned how much I hate building boats yet? Lol

Check my updated posts…. I think you need to go down to 1/4”. Dave caught this one, even though I posted about this before, it never registered anymore…

[Chotu]

Originally Posted by s/v Jedi

Check my updated posts…. I think you need to go down to 1/4”. Dave caught this one, even though I posted about this before, it never registered anymore…

Thanks.

I wish I could remember where I saw twice the thickness of the aluminum that you are putting the threads into. I thought it was in this thread. I guess not. I must’ve read that online somewhere.

Getting the new ones.

[Jim Cate]

Getting the new ones.

Should be a lot less expensive, too!

Jim

[Dave_S]

Originally Posted by Chotu

Thanks.

I wish I could remember where I saw twice the thickness of the aluminum that you are putting the threads into. I thought it was in this thread. I guess not. I must’ve read that online somewhere.

Getting the new ones.

I am not surprised that you can find this written up in what seem to be knowledgeable scripts but the rule of thumb that says for aluminium the threaded hole should be twice as deep as the thread diameter of the fixing. For some unknown reason 3/4's of the world believes, and are happy to spread as fact that this means if the material is 1/4" the bolt should be 1/2". That is backwards if you have 1/4" screw and you want a full strength threaded hole you should have 1/2" thick material in aluminium.

This is only related to thread strength in the material so that fixing will fail before the female thread. Which in your case would imply you want 1/8" screws which of course is ridiculous. The rule of thumb is only for thread strength not for shear loads or for maximum clamping loads per screw. You could always fit 15 times as many 1/8" screws 🙂 to get your loads back.

The rule of thumb that I would use is 1:1 - most rules are usually +/- a bit of 1:1, so approximately.

If you are 100% stuck on a countersunk screw be aware that because your outer skin material is thinner the countersink comes close to projecting through the inner face. Maybe consider 6mm, they will have a slightly wider 90° bevel and a little narrower so you will have a little more parallel section in the hole of the outer skin to give better axial support to the screw.

I know countersunk screws look schmick but you should only use them when you have to, pan head, or better for spec's, socket head cap screws (cap screws will catch on stuff, pan head less likely) You will get much better results from non countersunk screws.

My 0.02c
Cadmium plated 316 - 1/4"x20 button head cap screws.

[Dave_S]

Sorry I missed this...
Answers in blue.

Originally Posted by Chotu

Hi Dave.

Actually I had no idea you could do it any other way. I didn’t realize you could counter sink all the way to the second material inside the mast. That definitely would not be a good idea no matter what project you are working on. So I’m with you there.

These were 82° heads. The only thing available. And what I was thinking is they would counter sink into the outer mast only. And then they grab the inner piece with the threads.

The distance from the top of the head to the thread is greater than 3/16" so if you fit it flush it projects into the 1/4" material. Worse for fitting on a convex surface and worse for a clearance between bevel and inner skin material. If the countersink of the screw hits the inner material you are defeating the purpose of the screw

I have also done plenty of reading that says do you want the screw to be twice as big of a radius as the material is thick. This is for aluminum. This is what I read somewhere. It would stand to reason that this is correct because that’s what I see on my crossbeam also.

See my previous post.

I also read that course threads are preferable to fine threads for this application. The idea is there may be less threads going through the material, but the depth of the threads into the material is superior.

Course threads when the material you are taping in to is weaker that the screw. i.e. if it is aluminium and the material thickness is
less than twice as thick as the screw is in diameter. Or in steel if the material thickness is less than equal to the thread diameter.

Fine thread if the aluminium is greater than twice as thick as the screws diameter.

If the loading is not an issue, use a course thread.

I also just came up with 3.25 threads in the 1/4 inch material.

What do you make of all of that?

1/4" material less the countersink for flush mounted screws this leaves less than 0.150" of thread. Less than 2 threads.

I like the torque to destruction testing idea.

[Chotu]

Thank you very much, Dave. Thanks for these responses and for saving my bacon as they say.

I just want to point out that the inside plate is 1/4 inch. The regular mast is 3/16. That’s why I came up with 3.25 threads in the 1/4” threaded part. I have 7/16” inch of material total.

So it’s 7/16” minus the countersink, with 3/16” being the depth of material available for countersink with 1/4” of material available inside the mast for threads to grab into.

That should change things quite a bit because it’s almost twice as thick as what you are calculating with.

So doesn’t that bring me back to almost half an inch? I have 7/16” of aluminum in total.