I'm getting ready to attach some things to the mast of my Hunter 336, specifically a couple of rope clutches and a couple of cleats. Is the aluminum thick enough for a tap? I would prefer tapping over rivets for several reasons, but it seems to me that tapping might not work as well as rivets for thin material. Thanks for any knowledgable advice, Paul
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Use Anti-Seze with Threaded Fasteners
Can't answer your basic question but should you choose to go the threaded fastener route I'd recommend using an anti-sieze material if stainless fasteners are used. A couple materials on the market: Anti-Seze sold by West Marine or Lanocote marketed by Forespar, http://www.forespar.com/catalog/misc/lanocote.htm. When drilling holes try to miss the conduits in the mast. Recommend contacting the mast manufacturer for their cross-section. If the holes are on the side there should be no problem as any conduit is typically near the forward portion of the sidewall. When I installed the jamb cleats and a couple pad eyes on the mast for the topping lift I used both sheet metal screws as well as machine screws and they've held up fine. Might want to grind the points off the sheet metal screws to avoid them snaging the internal lines.
Can't answer your basic question but should you choose to go the threaded fastener route I'd recommend using an anti-sieze material if stainless fasteners are used. A couple materials on the market: Anti-Seze sold by West Marine or Lanocote marketed by Forespar, http://www.forespar.com/catalog/misc/lanocote.htm. When drilling holes try to miss the conduits in the mast. Recommend contacting the mast manufacturer for their cross-section. If the holes are on the side there should be no problem as any conduit is typically near the forward portion of the sidewall. When I installed the jamb cleats and a couple pad eyes on the mast for the topping lift I used both sheet metal screws as well as machine screws and they've held up fine. Might want to grind the points off the sheet metal screws to avoid them snaging the internal lines.
I recently tapped
my mast to install a whisker pole track and associated uphaul/downhaul blocks and cams. I can't say what the mast wall thickness was, but I believe that it was sufficient for at least 3 threads. I did check first with the mast manufacturer regarding thickness and location of internal lines, and was told it would be all right.
my mast to install a whisker pole track and associated uphaul/downhaul blocks and cams. I can't say what the mast wall thickness was, but I believe that it was sufficient for at least 3 threads. I did check first with the mast manufacturer regarding thickness and location of internal lines, and was told it would be all right.
Nutserts
For threads to hold there should be at least three complete threads in the material. Aluminum being soft, maybe more. I have used "Nutserts" in place of threads in thin materials. There are other names for them; threaded inserts, Pop threads, etc. They are threaded inserts installed with a Pop rivet type gun. They come in aluminum and steel although I haven't yet seen them in stainless. They work good, are fairly easy to install, and are pretty strong. Check out your local hardware store.
For threads to hold there should be at least three complete threads in the material. Aluminum being soft, maybe more. I have used "Nutserts" in place of threads in thin materials. There are other names for them; threaded inserts, Pop threads, etc. They are threaded inserts installed with a Pop rivet type gun. They come in aluminum and steel although I haven't yet seen them in stainless. They work good, are fairly easy to install, and are pretty strong. Check out your local hardware store.
Ideally throughbolt on flat sides
If you are installing items onto the flat sides of your mast, the best proceedure is to through-bolt them. This can be done not only with nuts on the opposing side but with barrel nuts as well. To use barrel nuts, you will need to cut down the bolts to the point where they just reach the other side of the mast. Then you should be able to insert the barrel nut and have it catch the end of the bolt. I have done this with mast up and the boat in the water. Besides strength, through bolting will allow you to remove devices for maintenance or to attach small items to the devices, such as the eye of a snap shackle to a mast mounted eyestrap. The problem with tapping is that you may only get to screw into the aluminum once or twice before the stainless screws destroy the threads in the soft aluminum.
If you are installing items onto the flat sides of your mast, the best proceedure is to through-bolt them. This can be done not only with nuts on the opposing side but with barrel nuts as well. To use barrel nuts, you will need to cut down the bolts to the point where they just reach the other side of the mast. Then you should be able to insert the barrel nut and have it catch the end of the bolt. I have done this with mast up and the boat in the water. Besides strength, through bolting will allow you to remove devices for maintenance or to attach small items to the devices, such as the eye of a snap shackle to a mast mounted eyestrap. The problem with tapping is that you may only get to screw into the aluminum once or twice before the stainless screws destroy the threads in the soft aluminum.
Pop rivets when possible
I prefer to use stainless steel pop rivets. There is usually not enough material on a mast to get three threads of a metal screw to hold in the aluminum of the mast. If there is vibration, the screw could back out until corrosion builds up between the screw and the mast, then you can't get the screw out, no matter what. Since the pop rivets flare inside the mast, they have better holding power than a screw and you can drill them out if you need to remove the attachment. I also like to put a pop rivet in old holes to make it look better, if you remove something and the hole is visible.
I prefer to use stainless steel pop rivets. There is usually not enough material on a mast to get three threads of a metal screw to hold in the aluminum of the mast. If there is vibration, the screw could back out until corrosion builds up between the screw and the mast, then you can't get the screw out, no matter what. Since the pop rivets flare inside the mast, they have better holding power than a screw and you can drill them out if you need to remove the attachment. I also like to put a pop rivet in old holes to make it look better, if you remove something and the hole is visible.
Tapping, but if you rivet....
make sure you use the insert. I don't remember what they are called but it is a sleeve with a head on it that you insert the pop rivet in. This doubles the thickness of the rivet for the most strength. Almost all Hobie parts are connected with these. I think they are called a furrel. I prefer tapping. If you tap or use stainless rivets, use an anti-cease compound to stop electrolisis(spelling). Most fitting for the mast have enough fasteners to hold very well. I would definitely inspect all connections every year and make sure that the salt water has not corroded the connections. Winches, Cleats I would tap without question. r.w.landau
make sure you use the insert. I don't remember what they are called but it is a sleeve with a head on it that you insert the pop rivet in. This doubles the thickness of the rivet for the most strength. Almost all Hobie parts are connected with these. I think they are called a furrel. I prefer tapping. If you tap or use stainless rivets, use an anti-cease compound to stop electrolisis(spelling). Most fitting for the mast have enough fasteners to hold very well. I would definitely inspect all connections every year and make sure that the salt water has not corroded the connections. Winches, Cleats I would tap without question. r.w.landau
P.S. Taping Into Aluminum
Forgot to mention something useful. If you tap into aluminum you'll need aluminum cutting fluid or the tap will quickly gall up and possibly break. *cry While there are other brands on the market this is a link to the one I'm using: http://www.relton.com/ It is also useful on drill bits when drilling. Oh, and drilling through thin-sheet metal - that's always fun.:{ Select "Cutting Fluids" and then select "A-9".
Forgot to mention something useful. If you tap into aluminum you'll need aluminum cutting fluid or the tap will quickly gall up and possibly break. *cry While there are other brands on the market this is a link to the one I'm using: http://www.relton.com/ It is also useful on drill bits when drilling. Oh, and drilling through thin-sheet metal - that's always fun.:{ Select "Cutting Fluids" and then select "A-9".
Mast Fasteners In Aluminum
I originally drilled and tapped 1/4-20 screws into the forward face of the mast to hold a whisker pole track. Also used 1/4-20 machine screws to hold a spinnaker halyard cleat and used WD-40 to lubricate the thread tap, then sealant on the threads when I installed the screws. However the boom is much thinner aluminum and I've only used 3/16" diam aluminum pop rivets to hold a jamb cleat and the 4 hole eye straps to dead end my flattening reef, 1st and 2nd reef lines. The 1/4-20 screws and the pop rivets are all loaded in shear, not direct pull-out. I would typically not thru-drill my mast or boom (completely thru to the other side) since I have internal halyards in the mast and moving out-haul hardware and reef lines in the boom. I don't like self tapping screws for the same reason as they would leave a jaged point inside the mast or boom to catch on internal lines. For high loaded or shock loaded installations, such an after market attachment for a bail on the mast or boom for a boom vang you may have to use a stainless steel bolt with an internal sleeve and aircraft type nuts. Give some thought to how many fasteners are holding a piece of hardware, typically at least two, and four on those reef point eye straps. Compare that to how large a line and what kind of load is being applied (Look at West Marine's Rigging Section in their Catalog). Typically there may already be a similar installation by the boat or mast manufacturer to guide you.
I originally drilled and tapped 1/4-20 screws into the forward face of the mast to hold a whisker pole track. Also used 1/4-20 machine screws to hold a spinnaker halyard cleat and used WD-40 to lubricate the thread tap, then sealant on the threads when I installed the screws. However the boom is much thinner aluminum and I've only used 3/16" diam aluminum pop rivets to hold a jamb cleat and the 4 hole eye straps to dead end my flattening reef, 1st and 2nd reef lines. The 1/4-20 screws and the pop rivets are all loaded in shear, not direct pull-out. I would typically not thru-drill my mast or boom (completely thru to the other side) since I have internal halyards in the mast and moving out-haul hardware and reef lines in the boom. I don't like self tapping screws for the same reason as they would leave a jaged point inside the mast or boom to catch on internal lines. For high loaded or shock loaded installations, such an after market attachment for a bail on the mast or boom for a boom vang you may have to use a stainless steel bolt with an internal sleeve and aircraft type nuts. Give some thought to how many fasteners are holding a piece of hardware, typically at least two, and four on those reef point eye straps. Compare that to how large a line and what kind of load is being applied (Look at West Marine's Rigging Section in their Catalog). Typically there may already be a similar installation by the boat or mast manufacturer to guide you.
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