The bolt-strip looks indeed similar to the one I know from prindle.

For repair you could consider the easy quick way: the strip is there only for mounting ease, because the enforcement-box will take over the washing-ring-function of the strip.

Then just replace the bolts with 316SS bolts, with the nearest bigger size (and okay, add a washer too). Try to pick bolts with an unthreaded shaft just below the head, so they won't eat the alu.

It looks from the picture as if the bolt-holes in the box are a bit worn out, hence also the bigger boltsize.
But it all depends on the condition of this boxholes and the holes in the beam and the dolphinstriker itself, if this is a reasonable solution.

I propose this solution because I think that here the used material of the bolts is indeed a higher grade SS, tougher and stronger, but more vulnerable for galvanic corrosion.

In my experience all the prindles, nacras and inters in a salty sea environment are predestinated to have these dolphinstriker problem. It's just a matter of time; in fact you should check this regularly and change bolts every 5 year.

could you flip that over, and re-tap/drill new holes?

While you're at it could you cut larger holes along the sides to reduce weight without changing strength too much?

Jay,

Adding larger holes along the side of the beam box, i.e lightening holes, is a huge no-no. The shear loads are carried through the side of the box and you are compromising the structures ability to handle the compression loads applied from the bolts when the beam is mated to the hull.

I will add one caveat; outboard of the beam bolts, i.e where the dolphin striker attaches, you may be able to reduce the shear capacity some. I would not risk it on my boat, especially seeing as the original box has already corroded a fair amount.

The bolt heads are welded to the little plate.

Yes but this serves only mounting ease. If you use a wrench taped to a stick, you can also hold the bolts in non/turning position.

And lightening holes in the vertical sites of the enforcement box are theoretically not a problem. The box only keeps the upperside and the lowerside of the beam separated on the same distance. It only needs to withstand their compression towards each other. That´s common mechanical theory.

But , what weight do win by this

Well looks like I need to make my own. Just heard from my Nacra dealer and nobody in the US has this part - he has to order it from Nacra EU for the reasonable price of ... $41.50!

I'll be hitting up Skycraft later to get the aluminum strip.

Think I might be able to JB Weld the bolts into the backing strip?

As northsea pointed out, the fact that they are welded is just for ease of installation. There's no benefit to welding it. Make a stainless plate with holes and bolt the bolts through it.

It would be easy to weld bolts to a stainless strip, send me your dimensions and I will see what I can do.

I'll go ahead and take care of the fabrication - thats my mission for the week.

Neighbor says he can weld SS for me.

THe part about the bolts being welded for ease of installation I think is only half correct. I think its also to make sure that the bolts don't try to loosen themselves.

I have only experience with the old Prindles where I used several times separate bolts on the dolphin striker. With a lock-nut they never came loose.

But that was in the time that there were no inserted enforcement boxes in the beams. So maybe you'r right today.

I can theoretically image that there could be micro-movements between the enforment box and the inside of the beam; because of swing load on the beam. This might then lead to micro-turning the bolt head.
Don't know; but I agree with you to be sure of this risk.

I'm also not oblivious to the fact that the nut can still loosen, however tightening these will be a lot easier the bolts are welded.

I like to add a remarkable fact which I discovered this weekend with regard to galvanic corrosion on a cat.

I've used already some time for the axes in my rudder release system (Prindle like) a special high grade SS because the normal 316SS bolts bended too much and too soon.

So, I ordered in the US a rod of 6mm highgrade 630 Stainless Steel and made clevispins of that by myself. This type of SS is socalled ferritic steel and can also be magnetized.

This weekend I finally had a bended one again.

At my surprise is was not only bended but also rusted near the head where the spring attaches. So galvanic corrosion despite the grade or thanks to the high grade!

I think that this is why this high grade bolts for the dolphin-striker connection are more prone to corrosion. And the necessary welding probably makes it worse.

The end of a galvanic corrosion process can lead to a broken bolt.
The cat-manufacturer starts searching for a stronger more high grade bolt, but ends up with a solution which in fact is even more vulnerable for corrosion.

How old is the nacra in question? You can't inspect what you can't see. This could be a wake up call for some of the owners of older nacras. Pull the end cap, put a flash light in the end, and maybe you can prevent a major failure.

I'm willing to bet these are standard 316 hardware. To go to an exotic stainless (and weld it with a matching material) is very un-nacra like. It's more likely that the one that broke was not welded perpendicular or on-center and carried most of the strain from the dolphin striker....something that NOT welding these will help to prevent. Just a thought.

It's the first time I've seen this kind of failure on these boats...so Occam's Razor would point more to something being inconsistent with this particular boat rather than a systematic problem.

It's possible you could safety wire them to have a looser but captive part.

Jake, but 316 SS isn't magnetic, isn't it?

Undecided said that the bolts were magnetic.

316 stainless is "barely" not magnetic to begin with and only if it is properly annealed. Even if it is a good quality 316, it can start to become magnetic after being cold worked...i.e. put under a lot of repetitive force without heat....which it certainly has been in this case. How they were welded may have also affected the magnetism of the material unless they were annealed after welding. It is possible that these bolts are 316 even though a magnet is attracted to it after the life they have been through.

As for the warning to other "older" nacra owners (although I don't consider Undecided "old" ... she's "experienced")

Please bear in mind that this boat has done, at last count, more than 7000 ocean miles under her if you count just the worrell's and tybee's shes done.

Some of that was with my fatass hanging off the rear corner.

how old is it?
I am pretty amazed at how well our boats actually hold up to years of use and salt water

mine is a 94, and it on the beach 150+ days a year.

so far I have had to replace a dolphin striker, shroud tang, helicoiled ALL beam bolts, and am close to getting all my extrusions in a shop to address corrosion issues (around beam bolts, rotator pivot bolt, etc).

just normal wear from use.
Much better than watching it rust away, or become part of a garden in a backyard.

its a 2001.