I am in the process of replacing a bent mast support rod and sleeve on a recently purchased 2000 Nacra 450. I just discovered that the stainless steel bolts on one side of the dolphin striker strap are loose due to corrosion of the mating threads. I believe there is a backing plate (likely aluminum) inside the cross beam. Unfortunately, it is difficult to access because there is a stiffener around one the outboard hull attachment bolts. I don't want to mess with the hull attachment bolts on this 20+ year old boat. Any advice on how to reattach the dolphin striker strap? I was actually thinking about dropping bolts down from the top but that would require making small access holes in the top of the cross beam and later plugging them. any suggestions would be greatly appreciated.

All Nacra dolphin strikers have a compression sleeve that prevents collapse of the crossbar and stands up to the compression loads from adjusting the pre-bend and mast loads. https://www.murrays.com/product/56-2506/ I have replaced my DS in the past and had to find a way to hold the compression sleeve in place during assembly. I think this is what you're referring to as a backing plate. It's a very fiddly part, and I used a piece of 1x2 board with a half-circle in the end to cradle the compression sleeve, and a piece of bungee cord to secure it while passing the dolphin striker through the compression sleeve and securing the bolts. No easy way to get it right, but with help you can thread and secure the system before releasing the bungee cord. If the compression sleeve is already in place, you can use a 3/8 bolt to secure it in place as you withdraw the dolphin striker from the bottom, then use that to help align the compression sleeve as you replace the DS. The trick is to keep something in the hole to maintain alignment as you replace the bent DS.



Edited by tominpa on Apr 21, 2024 - 09:45 PM.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Tom, I think he is talking about the V-bar bolts. Mark the SS bolts should be welded to a SS plate. There is also a sleeve added outboard inside the beam for reinforcement. They need to be fixed. You've got galvanic corrosion from the dissimilar metals.

Do a search here. This has been discussed in detail many times. Pictures would help. There are instructions and how to add pictures to a thread.

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Philip
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I just wanted to add that Nacra recommends withdrawing the crossbar attachment bolts at least every year and using a teflon lubricant when re-tightening. It just keeps things from seizing up. BTW, the bolt to follow your DS is 3/8" x 5" and just holds the compression sleeve in-place during replacement.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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I am repeating this message as I'm not sure it went through.

Hey Guys,
Sorry for the confusion; my terminology is off. I have actually removed the bent mast support rod and associated compression sleeve (no choice as it was frozen to the rod due to corrosion). What I am referring to are the bolts holding the dolphin striker bar to the front crossbar. I checked the manual that Tom provided a link to above and found the following:

The bolts that connect the striker bar to the front crossbar should be loosened occasionally to check for cracks in the crossbar. If cracks are apparent, the crossbar should be replaced. There is a back-up plate inside the crossbar so these bolts can be tightened easily from the outside. Again, do not overtighten, since the bolts could snap.

My problem is I cannot get to or even see the back-up plate inside the crossbar. The holes in this back-up plate are likely corroded as the bolts simply pulled right out. When I removed the plastic end cap from the cross bar, there appears to be a stiffening component surrounding the inboard crossbar attachment bolt. This makes it impossible to access the backing plate. I haven't yet tried to loosen the crossbar attachment bolts but I'm afraid they'll be corroded as well. I am located in SW FL where there's lots of salt laden air and warm temps year round.

Just wondering if anyone has ever replaced this back-up plate or if there is an alternate way to reattach the striker bar bolts to the crossbar.

Mark

The repair to the crossbar hold-down bolts usually requires drilling or removal of the old backing plate, and laminating an new threaded stainless backing plate. These have to be fabricated from stainless plate, threaded, then laminated in place. Before doing this, you should try tapping the backing plate for a slightly larger bolt. Tapping new threads involves drilling out the corroded threads and chasing a tap into the new metal. This would be a much easier repair if the backing plate is still securely in place but only has damaged threads. Other solutions were tried in this thread. https://www.thebeachcats.…ms/viewtopic/topic/16831 Also here https://www.thebeachcats.…topic/topic/1853/start/0 With pictures: https://www.thebeachcats.…forums/print/topic/16831

Since the last software update, I have to login every time I visit the forum or posts are under the Guest name. These are being routinely deleted due to spammers posting as Guests. I'll continue to follow to see if this helps.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Hey Tom,
Thanks for the valuable info. I will try to tap new threads into the backing plate one size up as my first attempt. If that doesn't work, the helicoil or some other insert sounds good. I will keep you advised.

Mark

Hello Tom,
Just wanted to let you know that I was able to retap the three port-side holes in the backing plate, originally 5/16" diameter, to 3/8". All three bolts holding the dolphin striker strap are securely in place and the new mast support rod and sleeve are installed. Thanks for your help.

Mark

That's great! Thanks for checking back in to report.

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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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