Attaching whisker pole mast-track: rivet nuts?

[N.A.]

In my slow attempts to get my boat set up (greatly aided by folks on this forum), I am slowly arriving at readiness for a mast-track to attach a whisker-pole to (my sailmaker said I would need a track to handle shifts in proper pole height at mast as genoa is furled and/or drifter used).

The mast-track part I understand, but attaching it... very expensive per the boatyard (multiple $k). I have a friend skilled at tapping, so I asked him about installing one together, and he asked, "why not use rivet-nuts?"... apparently these might be easier/better for working from only one side of a surface, and be easier than tapping a bunch of holes (without unstepping the mast, which I do not want to do -- more $k). Anyway, for those (like me) that have never heard of these:

Rivet nut - Wikipedia

en.wikipedia.org

Does anyone have an opinion about securing a track with rivet-nuts instead of tapping the mast directly and using screws? My understanding (per my sailmaker) is that only a couple of screws (e.g. for a D ring) are simply not enough to handle the loads (E34, standard rig), so a track with many screws is the right way to go. But rivet nuts sound easier, assuming I can figure a way to lanolin-coat them to prevent mast electrolysis. Or maybe that's the reason people don't use them?

Any advice appreciated!

PS: I am imagining not rigging blocks to raise/lower pole with a line(s), but just positioning the pole manually... easier to install. Opinions re: that welcome too.

PPS: Considering Garhauer for the track/car. Yet again, opinions welcome.

 

[ConchyDug]

I'd check what material the riv-nuts are. If you are in saltwater they'll corrode fast. The steel riv-nuts are a bitch to install but won't corrode as fast and you'll need the right tool not a harbor freight special. Brown Tool sells them or The Yard Store both aviation tooling companies. I'd coat the riv-nuts in some kind of zinc phosphate primer or tefgel. The real pain is removing one when they start to spin. You have to sand the head off and they will fall into your mast. I can send links for the tools and where to buy good riv-nuts if you want. Aluminum ones might work but are very susceptible to over torquing and and will strip easily.

 

[southofvictor]

I’d tap the mast for screws. It should have enough thickness for a good connection. As far as I know rivet nuts are made for situations where material is too thin to get enough threads for a good connection. I used them to attach our wheel pilot pedestal bracket to the pedestal after the original sheet metal screws stripped out. So far so good on that front.

I’ve also heard they can be a pain to deal with if they strip / fail in their bond to the substrate, because they just spin and spin. You can’t get the screw out or a drill bit to bite to drill them out. Since the pedestal thickness didn’t look like it would allow for adequate threads I thought I’d give rivet nuts a shot.

 

[G Kiba]

I would be worried about the protrusion of the rivet-nut inside the mast if you have halyards running through. Not to mention the wiring and possible conduit already in place. Definitely tap the holes and use proper length fasteners. You may want to use a fine thread pitch if you are worried about strength. Typical mechanical design rule is 3 threads minimum. You can multiply the thickness you are taping by the pitch to get the number of threads. Be sure to put Tefgel or Lanicote on the threads if you ever plan to remove the track.

 

[Loren Beach]

I would be worried about the protrusion of the rivet-nut inside the mast if you have halyards running through. Not to mention the wiring and possible conduit already in place. Definitely tap the holes and use proper length fasteners. You may want to use a fine thread pitch if you are worried about strength. Typical mechanical design rule is 3 threads minimum. You can multiply the thickness you are taping by the pitch to get the number of threads. Be sure to put Tefgel or Lanicote on the threads if you ever plan to remove the track.

This is the normal accepted method. Same on all three of the boats we have owned over the decades. I did have to install a new track on our one-design Ranger 20, for racing -- both for a spin pole and whisker pole for white sails class. Later two boats came with tracks secured by screws tapped into the spar. Do size the screws so that they penetrate only an eighth inside the spar to avoid wiring/halyards.

 

[G Kiba]

I’d tap the mast for screws. It should have enough thickness for a good connection. As far as I know rivet nuts are made for situations where material is too thin to get enough threads for a good connection. I used them to attach our wheel pilot pedestal bracket to the pedestal after the original sheet metal screws stripped out. So far so good on that front.

I’ve also heard they can be a pain to deal with if they strip / fail in their bond to the substrate, because they just spin and spin. You can’t get the screw out or a drill bit to bite to drill them out. Since the pedestal thickness didn’t look like it would allow for adequate threads I thought I’d give rivet nuts a shot.

Striped threads. What a pain! I have used Helicoils to repair striped threads on my mast to boom connection. You can get them in stainless steel. Anything that flies (jets, missiles, etc) and is made of aluminum has Helicoils or threaded inserts or rivet-nuts. They work great!

 

[Christian Williams]

Tap for me. If using only one Genoa no need for track at all fixed point fine since clew height does not change.

 

[N.A.]

Many thanks, folks -- very much appreciated!

Based on your comments, I'll probably drill & tap* just to avoid stuff sticking inside the mast and risking abrading coax/wiring/halyards. Had not been thinking of keeping the screws short enough not to protrude into the mast, but now will.

* PS: Is there a trick for drilling/tapping such that one does not damage stuff inside the mast? The taps I have seen are tapered, so would need to go a ways into the mast to get the full thread in the drilled hole. I'm also a little unsure about how to deburr the inside of the drilled hole without enlarging the thing such that the tap no longer fits closely enough... is there a trick for that?

@G Kiba -- I am slightly confused; are you recommending rivet nuts/helicoils for this or not? Your first post makes the case for tapping, your second for rivet-nuts.

Thanks for the reminder re: # threads for holding strength. I think my mast is a LeFeil (boat made by Pacific Seacraft after they bought molds from Ericson); I believe (LeFeil no longer making masts, so not completely sure) that wall thickness is 0.156" (5/32")... that would give me just about 3 threads for a 1/4-20 screw.

On that note, I am unsure going to a much finer thread would solve a pull-out force issue; finer thread pitches surely come with shallower thread depths, which I would think might tie to some requirement for more threads to get decent holding strength. I have heard (and used) the 3-thread rule of thumb, but also heard "one screw radius" as a rule of thumb... I suspect that for standard mid-range threads (like 1/4-20 etc) these rules are about equivalent, but for finer thread pitch it may be that the 'radius' rule suggests more than 3 threads are advisable. My friend is a ME, so he can probably tell me or find out... I'll ask.

 

[Prairie Schooner]

. . . . * PS: Is there a trick for drilling/tapping such that one does not damage stuff inside the mast? The taps I have seen are tapered, so would need to go a ways into the mast to get the full thread in the drilled hole. I'm also a little unsure about how to deburr the inside of the drilled hole without enlarging the thing such that the tap no longer fits closely enough... is there a trick for that?
. . . .

You could use a drill stop collar on your drill bits. For tapping you can start with a tapered tap, then switch to a bottoming out tap. For deburring, you might be okay if the final screw sticks out (in) a little bit and if you're really concerned you could sand smooth the end of the screws.

 

[HerbertFriedman]

I have drilled/tapped holes in my mast and boom, use fine thread bolts, 10/32 works well, that usually gives 4 threads for the mast thickness.

 

[G Kiba]

Don't use rivet-nuts for this applications or Helicoils. Helicoils can be bought in lengths and are not the same as rivet nuts. They replace the threads in a tapped hole. I use them in cases when a thread is striped. Helicoil is a brand name. Beware there are many knock-offs from China of lesser quality. Don't go to Harbor Freight for them and watch out online.

 

[N.A.]

Many thanks, folks! Drill stop collar and regular bolts it is

Really appreciate the help!