Installing boom extensions

General
21

Agree!

Mike Quill sent me another alternative approach that I’m also considering:

Mike Quill, NS26 wishbone extension
Mike Quill, NS26 wishbone extension1728×2304 954 KB

All I have is the picture. It appears that it involves adding tubes that match the current boom tubes, held on to the current tubes with an inner sleeve, and room for the casting to be inserted into the aft end of those additions. What I need to know for this alternative is the ID and OD for the tubes and insert sleeves.

– Bob

22

It will be two weeks until I get to the boat. But I may have a photo.

My casting is different I believe. It has two holes in it that lead into the tubes. It was made in 1981.

It was too heavy. The end of my boom went on a diet a few years ago and became much lighter. It’s still heavy but noticably easier to work with now.

Tom

23

Hi Bob,

That’s an interesting problem made worse by salt water I think. A reply to 3. using Google AI proposes the following:

Installing a boom extension on the aluminum wishbone boom of a Nonsuch 26 is a highly effective way to move the mainsheet blocks back, but it creates a high-load, high-vibration environment where stainless steel and aluminum must be meticulously isolated. Because this fitting bears heavy loads from the mainsheet and topping lift, standard plastic washers alone will eventually crush or deform under pressure. [1, 2, 3]

To ensure structural integrity while completely stopping galvanic corrosion, use a heavy-duty, multi-layered isolation method:

1. Insert structural sleeves (for internal extension inserts)

  • If your Nonsuch 26 uses an internal sleeve or a cast aluminum extension piece that inserts into the existing boom tubes:
  • Wrap the hidden sleeve section in heavy-duty vinyl wrap or wide, high-tensile plastic electrical tape before sliding it into the main boom.
  • Coat the inside of the boom tube and the outside of the sleeve with a thick layer of Lanocote or Tef-Gel to block out trapped moisture. [2, 4, 5]

2. Isolate external stainless fastners (rivets vs. through-bolts)

  • If through-bolting (Recommended for high loads): Use Delrin or heavy-duty nylon shoulder washers (also called top-hat washers). The sleeve of the “hat” goes inside the drilled hole of the aluminum boom, keeping the stainless bolt shaft from physically chewing into or touching the aluminum walls. [4]
  • If using rivets: Ensure you use monel rivets rather than standard stainless steel rivets. Monel is a nickel-copper alloy that has a much closer galvanic compatibility with aluminum than stainless steel, greatly reducing the risk of corrosion.

3. Use heavy-duty backing plates

  • Do not rely on thin plastic washers under the mainsheet blocks or eye straps.
  • Cut a custom, rigid isolation gasket from 1/16-inch thick G10 fiberglass sheet or heavy-duty polyethylene (HDPE). Sandwiched between the stainless steel hardware and the aluminum boom, this solid plastic spacer distributes the heavy compression load across the aluminum without compressing or cracking. [2, 4]

4. Apply a chemical barrier compound

  • Liberally paint Duralac (barium chromate paste) or Tef-Gel onto all fastener threads, under the bolt heads, and directly into the drilled aluminum holes. [2, 6, 7]
  • Unlike standard lubricants, these marine-grade pastes do not wash away in saltwater, permanently blocking electron transfer between the metals. [2, 6]

Are you working with a custom internal aluminum sleeve that slides into the boom tubes, or are you mounting an external stainless steel bracket/pad eye over the end casting? Knowing the exact style of your extension kit will help specify the right fasteners. [5]

24

Thanks, Jim.

I still think that what’s marketed as AI really should be called, “automated generation of statistically-based plausible text” if we had better truth-in-advertising laws.

That said, the state of the art’s improving a lot. It’s summarized a lot of good suggestions consistent with the best advice I’ve received. I have to say I’m impressed.

It’s also made a few suggestions that I’d be less enthusiastic about adopting. In all fairness, even those are within the range of advice that people might produce (although I’d still reject it). FWIW, those I’d disagree with are:

  1. “Wrap the hidden sleeve section in heavy-duty vinyl wrap or wide, high-tensile plastic electrical tape before sliding it into the main boom.”
    Too much friction when inserting, with risk of damaging the barrier and defeating the purpose. Not likely to hold up.
  2. “through-bolting (Recommended for high loads)”
    Overkill, more complicated, makes removal more difficult when corrosion protection fails
  3. “If using rivets: Ensure you use monel”
    Monel is good advice. Using rivets at all is more iffy, IMHO. Once you’re dealing with thicknesses big enough to hold threads, screws provide greater strength and ease of removal. Screws also keep future maintenance accessible to owners with less equipment and skills.

Again, though, the Google “AI” result had more good points than not overall.

Depending on whether your post and my reply trigger more discussion, we might want to break follow-up into separate topics: “what AI can and can’t do for us sailors,” vs. “installing boom extensions”.

-- Bob

P.S. Status of my boom extension process is that I’m working on removing the boom end casting. With it off, it’ll be easier to determine the trade-offs. As I see it, I’ve got three alternatives. I could pay for machining to make the stainless extension fit. I could bolt in aluminum tube extensions with an internal reinforcing sleeve. I have in hand what’s needed for either solution. The third choice would be to give up on the project and put the stuff up on the INA Marketplace for someone else to try.