Best way to fasten something to a Sailboat Mast

[44'cruisingcat]

When I put my rig together I used monel rivets on anything with serious load on it. Except the gooseneck, which has 8 drilled and tapped screws.


A pneumatic rivet gun makes life much easier.

[four winds]

Here's what the blind side of a sealed high strength aluminum rivet looks like after installation. Not a typical rivet. To me this would be the best material and design to be smashed up against the inside of an aluminum mast.

Edit to add,...... 44, this post wasn't in response to your mention of monel. Love that material in my 40 year old trouble free fuel tank.

Probably look at my gooseneck tomorrow. Recall it's bolted and curious how thick is the mast. I've been assuming this thread was about mast steps only for some reason.

[Terra Nova]

What do think would shear quicker, a stainless machine screw or an aluminum rivet?

[four winds]

Originally Posted by Terra Nova

What do think would shear quicker, a stainless machine screw or an aluminum rivet?

Depends on how long it takes crevice corrosion and dissimilar metals to weaken the bolt.

[leftbrainstuff]

Originally Posted by ZipTie

What is the best way to fasten something to a Sailboat Mast like mast steps, goose neck or cleats?

A boat mast is usually 1/8 inch thick and painted or anodized. Is very easy to drill and tap as it’s very soft.

Most mast makers like Z Spars, Selden and Sparcraft use Aluminum Blind Rivets because they work well.

1) All Aluminum Blind Rivets are the 1st choice
· * No galvanic corrosion issues – aluminum mast/ all aluminum rivets
· * Very easy and fast to install
· * Tool and rivets are cheap
· * No real accuracy is needed
· * Rivets are self-tightening and conforms to a sloppy hand drilled holes

2) Drill & Tap would be a 2nd choice as it takes more tools and skills
· * Using Stainless Steel screws and bolts can have galvanic Corrosion issues
· * Very detailed and slow process
· * Need special and sometimes expensive tools
· * Hand drills and hand taps are not very accurate and prone to angled or oval holes

3) Fine or Course threads for taped holes on a mast?
· * Fine thread are preferred as they are 10% stronger and cover more surface area
· * Fine threads do not tear the soft aluminum that boat masts are made of
· * Fine threads give you more threads to hold onto the 1/8 inch thickness of a mast
· * You will want to use Tef-Gel or Loctite Blue 242 on the threads

Monel rivets. You also need to isolate using tefgel or mylar.

Always use coarse threads on non ferrous material. You need a minimum of one diameter thread depth. Anyrhing less use rivets.

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[delmarrey]

Originally Posted by four winds

Depends on how long it takes crevice corrosion and dissimilar metals to weaken the bolt.

Agreed! I've seen masts with rivets and screws both, pulled out.
What's really bad is when a rivet is pulled out and leaves an ******* and cracks. At least if a screw pulls out it can be replaced with a rivet.

Being a Machinest for 45 years I've learned there are options. Screws, usually being SS, I recommend using if you know you're going to be removing on occasion, and that you use a sealer (Tef-Gel). Fine thread or course, it doesn't matter. The fine thread one can just get tighter but will also strip out easier when tightening.

But for any fitting that is going to have a lot of vibration like an eyelet or track I'd recommend rivets. They will not work loose with stress, if installed properly. The nice thing about rivets is that they crimp themselves to the mating metals much like a wire crimp but with more tightness then a screw.

So, it really comes down to the application. As well, be sure to use the Tef-gel behind SS fittings.

What would be ideal would be self-clinching nuts but getting them inside the mast is a big ordeal.

[Zai]

I've used these rivet nuts with good results in aluminum.

[ZULU40]

Originally Posted by Terra Nova

What do think would shear quicker, a stainless machine screw or an aluminum rivet?

Obviously the aluminium rivet. Less obviously it goes to the number of fasteners you use.

What do think would shear quicker, a stainless machine screw or 20 aluminium rivets?

[Sdwcheney]

I have a Nonsuch 30 with a free-standing mast. You do not drill into a Nonsuch mast. The preferred method is to use stainless steel bands with rubber or plastic under the band. This is the strongest way to attach to any mast.

[Terra Nova]

I once had to haul someone up the mast on a Tayana 55, using the main halyard winch. On the way down he used the winch as a final step before then stepping onto the deck. Once his weight came off the halyard, and onto the winch, the winch fell on the deck. Corroded pop rivets had barely held the winch base bracket to the mast.

[Moody46CC]

A lot of somewhat conflicting advice here. I did see the first posting which advocated in priority some things with rivets first. But then came conflicting opinions, but the trend seems to be monel rivets or big aluminum, heavy duty rivets with some sort of sealer against galvanic corrosion.

The fellow with the Nonsuch has an interesting idea, but I'm looking to install an eye for a whisker pole and the location will be above the gooseneck. A steel band would wreak havoc with in-mast furling--or hanks for that matter.

But all good stuff. Thanks all.

[chasmains]

Hi, new member here. I just wanted to add that threads are evaluated for strength in the shear capability at the bottom of the loaded portion of the thread, either inside or outside thread. That said, the engagement surface area of the other threaded component's threads determines this shear surface. Explained: if a thread is engaged to the bottom of its root, then the shear surface is the width of the root of the thread (or the distance from one revolution root to the next root, which would equal the pitch of the thread). For example, 1/4-20 threads have a pitch of 20 threads per inch, so the shear surface width would be 1/20" or .050", and the shear area is .050" x the number of threads engaged x pi x diameter of the hole or bolt at the root of the thread. And to find shear strength, the shear area is then multiplied by 1/2 the tensile strength of the base material.
But, threads are never fully engaged with each other. Therefore, the looser the fit, the less thread engagement surface, the smaller the thread base in width, the smaller the shear area, and the weaker the threaded connection. You have to measure each part to determine thread engagement. Make sense? You can extract fine and coarse thread maximum shear areas from the Machinery's Handbook, and it may be on line somewhere.
I really wanted to point out that there is another way of attaching stuff to your mast. I don't know, but I'm guessing that the mast material is not really strong for threading since it needs to be soft so it is easy to extrude into a mast. A great alternative attachment method is the threaded rivet nuts sold by, for example, McMaster-Carr. Aluminum rivet nuts size 1/4-20 for 1/8" thickness are shown here: McMaster-Carr . You need the correct drill bit and a rivet set tool to install, but the threads are probably much stronger and hardened, and would require anti-corrosives anyway, inside and out. There are no SS rivet nuts listed, but they may be available somewhere else. Have a look. CW

[Rockyscience]

Hi All, I have been using one of these for years to pop threads into thin metals.
It works great and the blind nuts can be aluminum, just put any size you wish in like a rivet.

[Capt_Flrp]

When I stumbled onto this forum, I was thrilled with the amount of knowledge shared and the lack of opinions stated as facts argued ad nausea. I do have to pipe up on this particular thread however. I would first agree with all preferring the rivet solution vs. threads of any sort. I do, however, have to point out the error in the fine/course thread argument going on. Assuming sufficient length of engagement, proper tap drill size, lubrication on taps, etc. etc., the fine thread is stronger than the course thread for the following reasons:
1) In tension (pulling against the threads) the stress area of the fine thread is larger, and in shear (pulling the fastened object along the adjacent surface) the minor diameter is also larger.
2) Fine threads have less tendency to loosen since the side of the thread incline is smaller and hence so is the off torque.
Other advantages include finer adjustment when needed (irrelevant in this ap), more easily tapped in hard materials and thin walls, and lesser torque required for equivalent bolt preloads.
On the other hand:
1) Fine threads are more susceptible to galling
2) Generally require longer thread engagements
3) Are more susceptible to damage and fouling
4) Metric versions are generally more difficult to obtain.
On the neg

[Bulawayo]

When I attached mast steps Spar Craft advised me to use Monel rivets. I didnt even realise there were high strength rivets available, so thanks. That also means ordering some now!!

Originally Posted by four winds

There are structural aluminum rivets. They can be identified by having a domed head. Have set quite a few over the years but not on a sailboat.

High-Strength (HS) Rivets | Stanley Engineered Fastening