In the past years we've done quite a bit of repairs and adjustments to our cat. However this time we realy do not have a clue how to fix this.

The connection of the dolphin striker to the beam is made by two bolts(?) One of them is broken or pulled back in the beam. We can still see it, as the top of it is still in the hole. It doesn't look recently broken, or the cut is really flat. From the side entrance of the beam to the connection spot seems very far, and not realistic to reach??

As we have the feling that we're sailing already some time with this, my questions would be:

- What would happen if the other connection would fail?
- Is there a manner to fix this?

Below you'll find some pictures, One from the side which still is ok, and two from the described side. I must admit that on photograph it looks worse than in reality.

I would definately fix this. If the other bolt fails, your mainbeam will break, the mast come down and you are left floating with two partially connected hulls. The weather will probably be foul as well as this puts the largest load on the boat. Your call, but I would want this corrected on any boat I sailed.

To fix this, you will need access to the inside of the beam. You will probably have to disassemble the boat and remove the compression pads inside the beam to get access to the inside reinforcments and the bolts. Have a look at how the dolphin striker is tensioned. There is probably some mechanisme (nut/bolt) where you can take some of the pre-tension in the beam off.
The compression pads might be glued in place, or have a layer of corrosion blocking material on them. A 2x4 and a slegdehammer might be neccesary to remove them. Once removed, a spanner taped to a batten is the proper tool for holding the bolt head while the nut is removed.

When you disassemble the boat, you will probably find that the strap is secured with additional flathead bolts. Take them out and inspect the whole load, or replace them with new bolts of the same hardness.

Half the job is starting, as Marcus Aurelius said. Begin by having a look inside the beam with a flashlight.

Hi Rolf,

Thanks for your reply! As we are heading towards a race on sea coming weekend (more forces on the boat with the waves coming in), it might be smart to fix this. So I think we'll start in a few hours from now.

To completely understand your story I was wondering what you mean by "compression pads"? Are those the plates inside the beam? (I want to be sure I'm hitting the right part!)

And by a 2 x 4 you mean a peace of wood? (still trying to learn English)

And if yes, after hitting them out, how to replace them again? (just glue?)

After doing some research I found a picture from the beam and a drawing from The Infusion (We have an Inter 18) which looks kinda similar. After taking of the beam cap, and taking out the bolts, we still face the "bolts housing" Or is this the part to remove?

Hi,



The drawing shows the internal structure the broken bolt for the beam strap is screwed into. If the drawing is correct, all you have to do is to unscrew the broken bolt (bolt removal kit from a hardware store and a drill is needed. If you are unlucky and the bolt is seized you might have to drill it out and tap new threads) and replace the bolt.

A kit like this might be all you need if the bolt is not stuck too hard: [img]http://images.biltema.com/PAXToImageService.svc/product/large/2000016851[/img]

From the drawing it also looks as if the tension on the strap can be relieved by turning the nut at the bottom of the dolphin striker. Check how much tension you have on the beam today by measuring deflection at the ends with a straight egde lying along the length of the beam.
Make sure you loose up the dolphin striker before trying to remove the bolts. There is a lot of tension on that strap.


When assembling again, I would use blue locktite on both bolts for the strap and the nut on the dolphin striker to insure against something working loose and breaking the boat. This is a critical structure after all.



On compression pads:


The compression pads are the part the beam bolts passes through inside the beam. Without these, when you tighten the beam bolts, the beam itself would compress and break.

On the drawing the second part from the left is the first compression pad, and the third part is the other one.

The pads differ in design. On the picture you see a different style (a not as rigid design) with the beam bolt passing through it.

The 2x4 (yes, it is a piece of wood ) was what I had to use to remove the compression pads on an Marstrøm Tornado. Hopefully you will not have to resort to the same level of force (or violence).

When you reassemble the beam, the pads should be isolated galvanically from the beam as the metal might see galvanic corrosion if not. There are special compounds for this like duralac. This might be enough to also fix the beams in place depending on how tight the fit is.



If you wait a couple of hours, I bet Jake comes online with a better way to do it




I sympathize with you on the english language. It would be so much better if the rest of the western world could agree on speaking norwegian or another proper germanic language instead of the english variant of germanic. (that should get some interesting replies )

If the bolt broke then that may be a side effect of another problem. Check the dolphion rod and its bolt and make sure you have it adjusted correctly. If it is too loose and the mast is compressing the rod down too far it could cause the bolts to fail.
We had this on our N20 and we noticed it because the sound of the threads scraping across the beam was a little frightening. it looks like the medial bolts are the ones that failed so that may be indicative of this problem with or without the awful sound of threads scraping across the beam.

"Sie verrückt Deutschen!"

Looks like the part that's broken is 30044 on the diagram. I think your going to find that those bolts are welded to the small plate. Your going to need a new part or get the old one out and grind the welds to get the bolt out. Hopefully it's just tack welded. Have a new bolt welded in. I would suggest you replace both sides with new parts. If you decide to fix just the broken side and replace the broken bolt, do your self a favor and replace both bolts not just the broken one. Also find and use some form of corrosion preventative when you reassemble like Tefgel or lanacote.

I blame our public school system (which still rarely teaches the metric system) and my stellar IQ of 76.

But 'mericans did bomb the snot out of most of the world (at some point from 1776 to present), so I guess that makes it okay.

Flame-suit on

(And for non-English speakers, this is all a joke)

In the immortal words of Jack Churchill:

"If it wasn't for those damn Yanks, we could have kept the war going another 10 years."

Good thing that we are now able to joke about those horrors

Tad just had a thread a few months ago where he repaired the same problem on an older Nacra 20. The bolts are welded to a plate and it's probably not reasonable to repair the plate - you should order a new one.

Once replaced, tension the dolphin striker as per the Nacra instructions. They usually have a measurement on the mast post where you put everything together, measure where the top of the beam is on the mast post, then start tensioning the big nut on the bottom of the beam until the beam raises so far on the post.

That said, that is a major problem. I would not sail it until that is repaired as it will be a catastrophic failure if that remaining bolt lets go.

Last evening we have opened the beam, and came to the joyful conclusion that the compression plate is in our case a sort of compression tube of about 30 cm in length. It was made out of aluminum, so no galvanic corrosion, and rather easy to get out. After some serieus hits with a heavy hammer and a peace of wood, it was "movable". We made a hook out of an iron tube, and hit it out. The bold was indeed welded and broken. Due to the fact it was spot welded, we were able to replace it on the same plate. (however it's not very necessary to replace such a plate with an original if you would break it, as it realy is nothing special at all)

The biggest trouble we had was getting one of the beam bolds back in as it needed a very high torque. However with a bit of grease it finally went in there.

For now we tensioned the nut on the dolphin striker to the point which it had before. Howeverwhen looking at all of you're posts, I try to understand how to measure this, as we do not know if it was on the right spot before. I've studied the Inter 18 Manual, but without any result. (nothing mentioned there)

At the moment we have the cat on our trailer, as we're intending to go to a race this weekend (but it seems the weather is not cooperating)so the mast is off. Should we set the dolphin striker with the mast up or down?

What is exactly the mast POST? Is this the threaded end with the ball on top? In that case no measurement there.

With the mast off, we discovered yesterday that there was almost no tension on it. We also tried to figure out what is th working principle of the dolphin striker, and to be honest were not able to figure it out 100%. Can anybody explain?

Well Arjan it's very simple.

The dolphinstriker is the backbone of your cat and it takes all the compression load of the mast (and sails!).

So, regular maintenance on this item is very important. The aluminium bars (de strippen) should be snug (strak) at all times. Measured with the mast off!!!!!!!!!!!!!.

Grab a bar just in the middle between the side and the rod (rod=het verticale stangetje vanaf de bal naar beneden) and feel the tension. It should have no more play then a few mil. (Max.5 mm)

Before giving the bars more tension you should loosen the ball on top of the mast step (maststep=de aluminium plaat plus verhoging die op de beam is gepopt waar de rod met schroefdraad doorheen loopt). It's also called a mastpost.

So you can screw the rod unlimited down incase the ball was completly down to the post.

Because you are spi-ing also, a good tensioned and well maintained dolphin striker is a life saver!

The dolphin stricker creates a counterforce to the mast pushing down on the beam. Without it your beam will collapse the first time you sheet in hard. It should definitely have some tension without the mast on.

There is a procedure by Nacra to set the dolphin stricker tension. I had it on a piece of paper somewhere for my 5.2, but it probably was in the file I gave the buyer when I sold it. The tension was set to induce a curve on the round mainbeam. But the inter series have a different beam, that are not just circular, so the procedure might be different.

I'd suggest you give a call to your nearest Nacra dealer.

Great thread, guys.

Hope you get this sorted before you sail. Maybe you can find another boat to compare against on the beach? The info from Nacra would be the best, of course.

Good luck, let us know what you find out.

Mike

3/8" pre-bend. You don't need any elaborate measure technique. Adjust lower nut on dolphin striker snug then turn lower nut 3/8" up to tension and prebend. Finish by tighening the upper nut.

upward prebend to counteract the downward force of the mast compression

Okay, yes,yes, you could call the nacra office, that's the most carefull solution.

But, having suffered from the design errors from Nacra, I've learned to use my own common sense:

Take any traffic-bridge; they are always prebend in their structure . This pre-tensioning is quite logical because when loaded,you don't want to charge the construction directly with a bended sag (and its belonging tensile load on the construction parts)

So, prebend is the solution for all this misery! (Then the load will automatically be led to the side with pushback forces on the bolts ;as you have experienced just now)

Prebend with no load on (mast off) is only possible with sufficient tension on the dolpin striker. Tensioning the rod, feeling the bars of the dolphin-striker at the same time and looking at the frontbeam will give you a pretty good idea of what is needed.

So, my suggestion is look for a small centimer prebend!

I bet with you that all comes together with a few mil play in the bars.

Regardless of what the factory spec is, I would set it up and take it for a short sail through some wave action to weather with the main hard on. Go back to the beach and check the setting and check the bolts. Most likely you will need to re-adjust as it may settle in a bit. Lacking any info on set up I would make sure there is about 3-4 mm upward bend with the mast up and the main sheeted hard on the beach.

It's an interesting thought from catman to aim for a prebend of the frontbeam of some mils under load.

But I really don't know if that will help with the right adjustment.
Because there is the matter of real heavy dynamic loads during the sailing. You can imagine that by meeting waves, jumping and/or sudden windblows, the front beam (via the mast) has to cope with short dynamic overloads.

When the frontbeam is bended down the horizon shortly by overload, the load on the bolts on the sides will reverse from pushing to pulling sideways. Also very shortly, so giving a real shockload.

I think the bending beam itself can survive this swings easily. But if this happens often it may explain bolt-damage (other than supposed corrosion).

This may mean that you have to give so much prebend that this never happens, or atleast as less as possible.

+1 lots of people had to sacrifice to get us where we are today

I had to do this on my boat before I sold it. Once you get the beam bolts out and stick a flashlight in there, its rather easy to resolve.