Tapping bolt holes for reef track in old aluminum boom

[patrickkidd]

The old bolt holes for the 1” boom reef track on my 1981 J/30 are stripped out so I need to tap new ones right next to the old ones. Any advise on tapping 1) an aluminum boom and 2) an old aluminum boom like this. I only get one shot at it. Is it just like tapping steel? See attached photos

thanks!

 

[capta]

I would drill and tap the original holes one size larger and not add any more holes than necessary.

 

[patrickkidd]

I would drill and tap the original holes one size larger and not add any more holes than necessary.

Why one size larger?

 

[DrJudyB]

I would guess that stripping the aluminum isn’t the immediate cause of failure. More than likely the problem is primarily due to galvanic corrosion between the aluminum boom and the steel fasteners. I’ve done lots of Re rigging on old masts and booms and I speak from experience.

Personally, I’d rethink the old reefing hardware... I’d get rid of the track entirely and install a cheek block 4-6 inches aft of the location of the reef in the leech. You don’t need adjustable track - when was the last time anybody adjusted it!?! Nobody ever adjusts them once they are in

Track on the boom is extra weight with no advantage for reefing compared to a fixed cheek block.

Drill and tap new holes for the cheek block. Assemble with Tufgel to prevent galvanic corrosion. Remove and inspect periodically for corrosion, or during annual rig maintenance.

judy B
Semi-Retired sailmaker

 

[capta]

Why one size larger?

I doubt you'd have the "meat" left to get good threads on the old holes. It will be a lot of work if the holes in the track also need to be drilled out to fit the new machine screws, but IMO, it is the right way to make the repair.
I suppose you could go with Judy's suggestion as well, but it is possible that the track was for different mains and racing?

 

[DrJudyB]

Looks like a brand new sail (It's unusual to have foot slides on a J30 though).

Your sail maker should have installed the reef on the leech of the sail so that it is at least 4 - 6" in front of the reef block on the boom . It doesn't need to be precise, as long as the vector pull downs and aft.

Tie a reef line around the boom, reeve the line up through the reef on the leech, and then down and back to anywhere aft of the reef hardware on the leech, and you're good to go.

 

[DrJudyB]

but it is possible that the track was for different mains and racing?

That's probably the reason for installing the track, but it is a very old fashioned (circa1970's) and clunky-heavy way to rig a boom. There's really no practical advantage, especially since we stopped building mainsails with have a bolt ropes on the foot.

 

[capta]

That's probably true, but it is still a very old fashioned (circa1970's) and clunky-heavy way to rig a boom. There's really no practical advantage, especially since we stopped building mainsails with have a bolt ropes on the foot.

Am I to take it that you mean all mains now made (obviously except for classic boats) have tape and go into a slot? How does one tie the reef points? Around the boom? That's just nuts.

 

[DrJudyB]

Am I to take it that you mean all mains now made (obviously except for classic boats) have tape and go into a slot? How does one tie the reef points? Around the boom? That's just nuts.

Um.... no. That's not at all what I meant.

Sorry there was a typo. Maybe that's what sounds nuts to you.
I meant to write
" There's really no practical advantage, especially since we stopped building mainsails with bolt ropes on the foot."

To clarify: 99.9% of all mainsails sold today are built with a loose foot.

To clarify further: With a loose footed main, the aft line for slab reefing can be tied directly to the boom, rather than to a cheek block on a track that's fastened to the boom.
That is separate and distinct from the lines in the intermediate reef points (aka nettles) which are tied around the slab, between the intermediate reef point and the foot of the sail. Intermediate reef point lines should never be tied around the boom.

Hope that clarifies.

Judy

 

[thinwater]

I would drill and tap the original holes one size larger and not add any more holes than necessary.

a. A larger hole will weaken the boom more than a row of smaller holes in the same plane (weakest link principle).

b. The traveler track would be weakened by the larger hole, which looks like a problem.

And everything Judy said. You really don't need it. But I can see the desire to put it back like it was.

Tapping aluminum is easy. Google it and practice on a scrap first. (It's not that easy until you've done a few.) Use coarse threads.

 

[capta]

a. A larger hole will weaken the boom more than a row of smaller holes in the same plane (weakest link principle).

b. The traveler track would be weakened by the larger hole, which looks like a problem.

And everything Judy said. You really don't need it. But I can see the desire to put it back like it was.

Tapping aluminum is easy. Google it and practice on a scrap first. (It's not that easy until you've done a few.) Use coarse threads.

So you really think doubling a string of holes in a line would be stronger than opening the existing holes a 1/16 of an inch? I don't.

 

[jssailem]

I would suggest you contact a good aluminum welder and have him/her fill the old holes then grind them smooth.

I am of the Loose foot Main crowd. So I would do the cheek block thing near the end of the boom. Then follow the previous thread style of tied Reef line on the boom, run line up to the reef clew and down to the cheek block. Then forward towards the mast. Easy technique.

 

[Sailor Sue]

If you really want to use the track again check out Rivnuts or Rivet Nuts. You use a larger hole to install a threaded insert that will take the original fastener. The insert is installed similar to how a pop rivet works. Google Rivnut or Rivet nuts.

 

[justsomeguy]

Google Rivnut or Rivet nuts.

And they come in aluminium too.

 

[thinwater]

So you really think doubling a string of holes in a line would be stronger than opening the existing holes a 1/16 of an inch? I don't.

That's OK. I'm sure. I've run into this engineering challenge many times. A common inspection issue.

a. The holes are on the neutral axis (center plain). The boom would fail by buckling, not sheer through the neutral plain.
b. The weakest point will be the largest hole. Two holes some distance apart will have little cumulative effect. This is why you can rivet plates together, for example. The holes should be at least 4 diameters apart (aircraft and industrial spec).

Either would be fine. The concern is weakening the track by drilling larger holes. It can break.

The answer would be different for a different hole location, but this is a low-stress area. This is why boom attachments are on the central plain. Drilling holes top or bottom, near mid-span, is much more troubling.

 

[BigEasy]

Apparently you have already purchased the new track as seen in the first photo.
I wouldn’t want to remove the old track and leave six open holes in the boom. I would redrill & tap as necessary. Use tefgel as Judy recommended on the new screws.