How to properly attach fittings to mast?

[Terra Nova]

Commonly used for isolating mast hardware is a thick, heavy duty, self adhesive, plastic (PVC?) tape that can be found at builders supply houses and hardware stores. You really want to avoid slippery plastics that will allow the fitting to move under extremely heavy loads.

[AZ-Oldguy]

I think it is going to be "drill and tap". I can get the parts and tools easily locally, don't know where I would get Monel rivets without having them shipped.
For those who suggested the one piece drill and tap. I don't know how you would protect the stuff inside the mast while using one. I plan to use a drill stop, and will penetrate the mast only as far as the wall is thick.
I was swayed away from the thought of aluminum pop rivets, because they still have a stainless "nail" inside, and I don't know how you would isolate that. Thanks for all the help. This forum is the best! I will report back later on the week.

Glenn

[Aqualibrium]

Before drilling make sure you understand the diameter of the tapping drill required and use accordingly.
You must drill an undersized hole to enable you to cut the thread with the Tap
Adequate thickness of mast wall is essential for heavily loaded components.
Tensile strength of aluminium is low and with thin mast sections it is very easy to overtighten screw and strip the thread

[ausnp84]

Originally Posted by Aqualibrium

Before drilling make sure you understand the diameter of the tapping drill required and use accordingly.
You must drill an undersized hole to enable you to cut the thread with the Tap
Adequate thickness of mast wall is essential for heavily loaded components.
Tensile strength of aluminium is low and with thin mast sections it is very easy to overtighten screw and strip the thread

That's a great point! Ie. if your mast wall is only 4mm thick, you shouldn't try and drill an 8mm tap into it. Also, For an ie. 8mm tap, I believe it's a 6.5mm hole.

What size machine screws / bolts are needed for the job? And how thick is your mast wall?

n

[HappyMdRSailor]

I love how passionate people are about this subject!!!

None of it very debatable with the exception of NF v NC... The rest is personal preference...

Amazon or McMaster Carr will have the stuff in your mailbox in a day or two, and likely to actually save you money ...

Good luck Glenn, and let us know how you make out !

[Martkimwat]

For attaching items to my masts (Tradewind 33 and Parker 27) I used flush stainless steel rivnuts of the correct size for the bolt I wished to use and used Tef-Gel as the isolating medium which was originally developed for the aviation industry but is now sold (in UK) in most chandleries. A small tube lasts forever because you use so little of it. Rivnuts come in various types some with raised heads but in general you want the flush mount type. They can be attached by using a hand type riveter that has additional Rivnut mandrels. Just make sure to read and follow the instructions - you are NOT trying to break a rivet mandrel, merely squeeze up the Rivnut inside the mast, otherwise you can snap the mandrel and damage the Rivnut (done that, been there!) Also, to ensure the Rivnut does not turn when tightening the bolt, they have a ribbing along the outside that grips the hole, therefore it's important to use the correct size drill so that the Rivnut should be a reasonably tight fit BEFORE it is pulled up. (Again, been there, done that!) Note that Tef-Gel is great for all mixed metal fixings, it comes with a small applicator brush (bit like an eye-liner brush) and as I said, lasts forever.

[Joyful Noise]

I keep a truck inner tube on the boat with my tools and used it for, among other things, for reinstalling a modified winch mount on my mast when it became necessary to replace an old Barient winch with a Lewmar 40 I had laying around

[Bluebeard]

Another vote for coarse threads, it's not opinion, it's engineering!
As for the type of fastening, if the loads are serious then some engineering thought is worthwhile.
If the loading is primarily shear (ie the load is trying to slide the fitting along the mast) then a bolt will be strongest and failure will be crushing of the mast wall in bearing. If you are using rivets or rivnuts then failure could be crushing of the rivet against the mast wall. What will happen isn't intuitive but knowing the materials a rough engineering analysis (Roark) can be done. My guess is that the rivet will fail before the mast wall.
BUT even for a mainly shear load there will be tension on some of the fastenings. (the load is not only trying to slide the fitting, but also topple it). Personally I would be very wary of drilling and taping into a thin wall mast - anything less than 6mm / 1/4".
The pullout capacity of a threaded fitting is fairly easy to calculate - area that must be sheared times shear strength of the alloy divided by a fudge factor as it will shear from one side first. As for the pull out strength of a rivet, they are used seriously and the manufacturer should be able to advise a strength in a known substrate.

For an instant answer I would have a good look at what the mast builder used in a similar application - if they used rivets, use rivets etc.
Duralac is an industry (offshore and aviation) accepted anti corrosion paste, TefGel I don't know.

[Jesse]

Rivnuts might offer a few solutions to mounting problems. They come in an array of materials(conductive & nonconductive) and nearly all have mounting flanges. They do require a larger hole for installation, which can be problematic in some cases. It's a goofy sounding name but it's a excellent product that does exactly what you want to do.

[Tessellate]

Originally Posted by Dave22q

Gasket material from an auto supply store will work as well as the very expensive bedding compounds from a marine supply store. Cut to size and glue to the fitting using any adhesive or even vasoline. Drill, tap and screw.

Good tip on the automotive gasket sheets. I didn't know about such things. Just what I was looking for. About $5.50 on Amazon for a 10"x26" sheet, Fel-Pro makes them. A few different kinds, but the Fel-Pro 3157 (rubber+fiber) looks better than the cork ones. I have some other uses this sheet will come in handy for too.

Another idea I thought of is silicone repair tape (non-sticky but stretchy, used for things like water hoses), which I already have on hand.

Funny how many different materials people use for this. An employee in my local marine store said he uses paper bags. I said I thought that'd just dissolve away eventually.

[JPA Cate]

Here's what we have used over the years that has worked well"
Silver greasy anti-seize (comes in a plastic bottle with a spreading brush in the lid)
Plain lanolin
Duralac

Not isolating things does make a mess. I usually find the inner tube pieces alongside the road, but any old inner tube makes a good isolater for the cheek blocks. You can also, if you prefer, glue it to the cheek, but you still need to liberally slather the threaded holes in the mast with your product of choice.

Depending on their size, you might want to made timber pads for between the block and the mast. Tape sandpaper to the mast and rub the timber on it till it takes the curve of the mast, while still being flat on the other side.

Ann

[ScottMeilicke]

Taping sandpaper to the mast is brilliant. Thanks Ann.


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[sartorst]

Personally I would not put any thing under the fitting because it would not be isolated after the fastener is installed and would allow movement which would loosen and cause more problems and would use blue thread lock which seals off water and oxygen that would cause corrosion and you dont have to worry about them coming loose

[Steve Bean]

I've salvaged a large blue cylindrical vinyl fender that was discarded after it leaked. I think the material is too thick to use for mast hardware, but so far I've used it for mounting the engine controls in the cockpit. I also have some white fenders that I'm planning to cut up to make winch-handle pockets. Very tough resilient material, for free.

[Sandero]

Drill and tap and set on scribed. as Ann Cate described mounting block. Cut the mounting block ti the precise shape of the "thing" you want to attach to a mast... block, winch or grandmother...clearance holes the the block. You can use several plastics of even teak for the block.