Rerig Part 4: Stuck Navtec U-Bolt Chainplates

It’s been a long road to finishing our rerig. Going on 5 weeks now with the mast out, I’ve started to get very antsy to go sailing. Being patient is always the hardest part of any project that takes the boat out of commission (ex, haulouts). After 2 weeks, most projects had been finished and it was just a matter of waiting for BSI to produce the rod.

The downside to rod, as mentioned in Part 1, is it generally can’t be made locally / onsite and therefore takes longer to get. That downside is apparent now in the delays with BSI producing the rod – even though we gave them the end fittings order 5 weeks ago, and final measurements 3 weeks ago, they still haven’t started producing the rigging.

In contrast, a couple weeks ago two new Selden masts arrived in the yard for brand new boats going to the Seattle Boat Show, with wire rigging ready to go, and those masts were fully rigged and stepped in a week.

I wouldn’t change my decision to go to rod – it’s worth it for keeping the mast tang system the same – but if we were buying a new boat someday, I would probably try to avoid rod or would consider it negative points for a boat being considered. It’s a wonderful material, but for a cruiser, availability and ease of access are more important.

Navtec U-Bolt Chainplates

The hardest part of the rerig however (other than the waiting) has definitely been pulling the chainplates for inspection. More specifically, pulling the Navtec U-Bolts above the chainplates.

C&C’s with rod have a somewhat uncommon chainplate system (O’Day’s and Ericsons also have a similar system). At the deck there are six big ½” U-Bolts (one for each shroud) that go through the deck to a thick aluminum backing block. That backing block has a recessed cup on the upper side which is used to capture the head of a stainless steel tie rod. The tie rod then goes down to connect with traditional chainplates inside the boat, attached to a fiberglass bulkhead inside some cabinetry.



Totally inadequate lever arm for pulling 1/2″ U-Bolts

It’s actually a pretty great design, because the chainplates are completely dry and pristine – I have no concerns about those since they never see water. And the U-Bolts likely do a better job of sealing out water at the deck level than traditional chainplates do. This is because they have a cover plate which fits tightly with the deck, and then the legs of the U-Bolts are flanged (they have a “lip”) so that they are wider than the holes in the cover plate – they overlap it and fit quite snugly.

The downside is they’re really hard to get out. The SS U-Bolt legs interact galvanically with the aluminum backing block, producing pasty white powder which basically locked the U-Bolt into the aluminum block.

Attempt #1

I worked for about 6 to 8 hours on the starboard aft U-Bolt, spanning about a 2 week time period, without any success in budging it.


Aluminum backing block for the U-Bolt

Things I tried:

  • Vinegar (supposed to help dissolve aluminum corrosion)
  • PB Blaster
  • Hitting the bolts and block with a hammer
  • Heat (via a heat gun). I didn’t want to try a torch, because the bolts are inside cabinetry, and there would be some risk of setting things on fire.
  • BoatLife Release (used to release adhesives like 5200).
  • Hammering in a paint scraper between the backing block and deck.
  • Hammering in a cold chisel (bought this 3 piece set off Amazon for $13).
  • Above deck, prying upwards with a long screwdriver.

Advice from the Internet

I always Google for blogs or forums where others have solved the same problem already, but I found very few people who have pulled Navtec U-Bolts and lived to tell about it – err, bothered to write about it. Wally Bryant did it, but he didn’t write much about how he got them out. He has the same model boat, but an older year, and his chainplates were bedded in silicone (mine were bedded with butyl I later found out).

An Ericson owner pulled Navtec U-Bolts destructively, by cutting them apart. I really didn’t want to do that though because they cost $300 – each! – from RigRite. Or you can try to have Garhaeuer or a machine shop make them – for a more reasonable cost – but I don’t know if it’s the same design and strength as the original.

I found an O’Day owner who pulled his using shroud tension plus heat. I was tempted to do this – wait for the new rig to come, and then just go sailing, with the backing block ⅛” loose. Or just tension at the dock and see if that worked.

Attempt #2 – Success! (Aka “We’re gonna need a bigger wrench”)

Since I was having no luck on the stbd aft U-Bolt, I started on the port mid (main shroud) U-Bolt to see if that one might be easier. After about an hour, it wasn’t any easier, so I gave up for the day. Later that week I came back with a 24” wrecking bar (afaik, a wrecking bar is just a big prybar) I bought from Tacoma Screw for $10.

I heated the U-Bolt legs and aluminum block from the underside for a full 2-3 minutes with the heatgun on high, and then tried the prybar up on deck. No luck at stbd aft, so I switched to the port mid one. No luck… wait – I got movement! Once one leg was unstuck, the other was simpler to get moving, and I got the U-Bolt out. You can’t imagine how happy this moment was – after 8 hours working on one thing with zero progress, getting something apart is a really big win.



Interesting findings:

  • The U-Bolt was bedded with butyl, not silicone like Wally Bryant’s earlier C&C (or maybe this was a factory difference – there was a Canadian and a US factory making C&Cs).
  • The deck is not cored with wood here! I expected marine plywood, like other hardware reinforced areas of the deck, but instead it was some hard composite. Not quite as hard as epoxy, and light orange (peachy) in color. I’m not sure if this is just a local potting, with wood core a ¼” or so away, but as far as I know these hadn’t been pulled before, so a potting seems unlikely.
  • The U-Bolt was in perfect condition. After cleaning off the aluminum corrosion, the stainless steel was spotless.

The one mystery I haven’t figure out is – if the U-Bolts weren’t leaking (I’ve never observed any leaks from them inside the cabin), how did so much aluminum corrosion happen?  I can only guess that either cabin moisture, or very small amounts leaking from above deck while under sail, provided enough galvanic medium for some very gradual galvanic activity.


A Kinked Rod is Not a Happy Rod

A rerig is preventative maintenance – if we found any serious breakages it’d mean we waited too long. Yet we can’t help but hope to find some kind of horrific part-about-to-break issue, because it makes us feel the rerig was truly needed. Like the cracked tang we found last year. For the most part we’ve been finding nothing but boring spotless rod and connections. No corrosion, no pitting, no telltale cracks, nada.

We have had one small bright spot though – kinks in the rod forestay inside the furler! When we pulled the forestay out of the nasty sludge that accumulates inside a furler after 33 years, I found 3 or 4 bends in the rod. They were small (5-10 degrees), but rod rigging isn’t supposed to have any bends at all, unless they’re intentional (at a spreader). Rod can be bent once or twice, but if it’s repeatedly bent, it work hardens and gets stressed at that point, possibly leading to a rig failure in a place where I feared it the most (inside the furler, the forestay is uninspectable).


I’m not sure how the rod became bent like this. Most likely the forestay was under-tensioned for years and the foils had been pressing on the rod at awkward angles while sailing in higher winds. I noticed the mistune about a year after we got the boat, so some of the damage could’ve been done by us, but I suspect it was going on years before that too. Nevertheless I’m glad we’ve switched to wire for the forestay.

Repainting the Mast Step

After our success repainting the mast collar (thanks to Natalie’s painting skills), it made sense to also do the mast step, which was looking pretty gross.

As with the mast collar, we sanded, sprayed on one layer of zinc chromate primer, followed by one layer of Rust-oleum paint in satin brown. Before and after pictures below. 






The new sheaves are here! Very nicely done, and produced super fast (received I think 2 days from ordering!). I’d recommend Zepyhrwerks again if you have any need for sheaves.



6 thoughts on “Rerig Part 4: Stuck Navtec U-Bolt Chainplates

  1. Steve Bean

    How about switching to a non-aluminum backing plate? For prying the U bolts up, maybe a pair of small steel wedges to drive between the U bolt and the cover plate.

    1. Patrick

      That’s an interesting idea. I’d probably need a 6 inch wedge. Not sure there’s enough room for that though. The cabin top is about 6-8″ away on one side, and the toerail 8-10″ on the other. Not much room to swing a hammer. Might be worth trying though. I got 3 out with the prybar but the last 3 are extra tenacious.

      1. Steve Bean

        I’m thinking custom shaped wedges, used as a pair, one from each side, greased. Use a C-clamp to pull them together. This way you don’t need the hammer. Apply some pressure and let it sit while you apply heat, penetrating oil, carefully chosen incantations… I don’t know what would be best to use to attack the white aluminum corrosion stuff. Using any liquid from below is working against gravity. Use heat from a tiny torch directed only to the aluminum, and quickly, to expand the aluminum and not the stainless U-bolt. The heat conductivity of aluminum is much greater than that of SS. Theoretically this discrepancy, however slight, is in your favor. Trying to chill the bolt with dry ice would be a bit extreme, I think. But, since the bolt is accessible from above, your assistant could hit the bolt with the dry ice from above, occasionally tightening the screw, and you heat the backing plate.

  2. Fer Skipper

    Thanks for sharing this!! I own a Cal 28-2 (1986) with the Navtec U-Bolt Chainplates type, which I didn’t even know the precise name, and have the same questions you posted here. But I have one more if you don’t mind. So once the u-blot is set apart, and the thick aluminum backing block is free; how to get it away from the rod? Like, does it have to go all the way down the rod? Cos, in my case, it’s inside a locker, meaning I have to cut things out.
    Also I have this corrosion you mentioned, which I though would be caused by water by the u-bolt, but it was always dry!

    Thank You

    1. Patrick

      Is your backing block inaccessible or you mean you can’t access the bottom of the rod? In my case I just unscrewed the tie rod from a threaded coupler above the chain plates (after removing a cotter pin). If you can’t access that part you could clean the block in place.

      Regarding why the corrosion shows up even with no obvious water leaks, I’m not sure… Perhaps just because it’s aluminum, which forms a white powder in reaction with oxygen I believe. And there’s always cabin moisture.

      If you have pictures of the access issue feel free to email me from the Contact link.

  3. Fer Skipper

    Thank for for your answer! I was taking some pictures this weekend in the boat. I’ll send you a picture. Thanks


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