Another breakage over the weekend, this time the rear beam.

Wind was gusty and strong but died in the afternoon. While sailing back in the crew noticed a large crack just inboard of the inside bolt, still under the washer. Completely through and clean, typical looking brittle failure. Does anyone have any wisdom/experiences to share on this. I'm fairly convinced it is related to fatigue. I had been contemplating replacing them as they are old and corroding around the fittings, but now my hand has been forced.

It was interesting to note that the boat didn't fall apart, even with me sitting above the crack getting the rudder up. The tramps seemed to be holding it all together. If it was the final race of a regatta with a win needed, I could've still sailed it hard in anything upto 15 knots and I think it would've held together. It was bizarre!

Nick

I haven't broken a beam yet.... touch wood. Coming from the aircraft industry I was quite amazed at how thin the walls are on these beams.. I don't know the loads and haven't had time to work them out but I am sure they are quite significant. Also the issue of bolting the hulls on with SS bolts through Ali is bound to cause corrosion issues which inevitably leads to failure with such loads. WIth the SS and Ali combo its a matter of 'when' not 'if' it happens. Darryn Kopp has done a fine repair on his beams which I will leave up to him to discuss if wishes to do so.

Cheers

Anyone know where to get monel bolts? Otherwise I will just have to use duralac in key locations.

I'm intending to replace the beam entirely rather than repair with a sleeve. I may reinforce with a sleeve at some stage, if it's legal, although crevice corrosion would be an issue where water puddles inside the beam.

I have checked the onesteel and smorgon catalogues in search of a 3.5 - 4mm wall thickness with no success.

Grease the bolts mate. Stops corrosion and makes them easy to remove when needed.

Most Catamaran owners manuals recomend using grease on the beam bolts.

Hi Nick

Apparently we get our beams from Capral. Fortunately for you their head office is in QLD (at least it's the right state)

71 Ashburn Road, Bundamba QLD 4304
PO Box 768, Booval BC QLD 4304
Tel 61 7 3816 7000 Fax 61 7 3816 7111

They will probably only sell a full 6m length but they may have a local distributor who can cut you a length.

The guys in VIC have been rounding the corners (2mm radius) and getting them anodised. But that's all optional. Anodising seems to be cheap these days though.

Luckily my crew and I work in the boating industry and he has already had the material delivered. He's cutting it this arvo. I do want it anodised, it is well priced atm, but I also want to race in a regatta this weekend. We will repair, race this weekend, then get it anodised next week, or keep it as a spare and replace with an anodised one.

Hopefully it doesn't blow too hard this weekend, but it's not looking promising.

Nick,

Strange that it was the rear beam and not the front beam. It's usually the front beam that cracks due to corrosion around the inboard bolt followed by fatigue due to mast loading forces.

I had my front beam let go at the 2004 Vic state titles on Port Phillip Bay and resulted in tearing out the chainplate with part of the hull followed by the deck parting from the hull. <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

If you think that the front and rear beams are of the same vintage replace them both. I used plenty of Duralac between the SS striker plate strap and the Aluminium beam.

Regards,

Peter

p.s. How did you go in the rest of the regatta ?

Yeah, we'll be replacing the forward beam too. I assumed there would be significant carnage, as you described, if the forward beam failed.

I haven't got the boat operational yet so couldn't attend the regatta last weekend. I haven't heard anything about it except that there were apparently large seas and high winds off the gold coast. Anyone got any other news?

(The word is that it was cancelled with only 1 entry.)

Any suggestions for attaching the mainsheet track to the rear beam. It was bolted along the entire length with the nuts inside the beam.

This seems like a potentially annoying way to do it. Only reasonable way I can think of doing it is to get a long bit of timber, drill holes in timber with track holes as guide, hot-glue-gun the nuts and washers to the timber at the drill holes then insert timber into the beam at the right position and start turning the bolts until they all grab tightly then remove timber. If they don't tighten enough, gaffer-tape a wrench to the end of the timber and try to line it up with the nut on the inside and tighten the bolt.

Am I on the right track? (excuse the pun...)

Nick.

I think that my Nacra 5.2 had holes drilled on the underside of the beam that were big enough to pass a socket thru.

Nick,
Flat ring spanner taped to a batten.
A small bit of tape in the ring so the nut won't fall thru.
An assistant with electric screw driver.
I also put a washer on the top of the nut with some Duralac which helps keep the washer in place and also minimises reaction between the stainless and aluminium.
Start with the centre holes and work out from each end of the beam.
May take about 30 mins with a good assistant and you will never have to do it to that beam again.
You can also connect the traveller with long pop rivets but will have to put in bolts sooner or later when the rivets corrode the aluminium and let go.

Regards,
Phill

Nick,

Phill has the answer. The only issue is access to inner rear beam bolts if you need to separate the hulls again for any future work. An alternative design is to buy a flat section traveller track that you can drill a hole small enough for an allen key and use cap screws instead of bolts. Then you can remove the track and beam together and never have to go through the process of fumbling around blindly for the inner bolt heads. <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" /> The inboard bolt holes in the beam needs to be just big enough for cap screw head and the hole in the track just big enough for the allen key.

I've seen this design used on a number of newer Mozzies and it looks great and works well. You can also regularly check bolt tension without any fuss.

The alternative is to keep persevering with long ring spanners and a torch for accessing the rear beam inner bolts.

Regards,

Peter

My track is too short to reach the inner hull connection bolts so don't need to worry about that. I will do the ring spanner method, only option for me I think. 30 mins isn't too long.

Thanks for the help, I'll let you know how it goes.

Hi Nick,

I just tapped the holes in the beam and used countersunk bolts. No need for nuts, plenty of Duralac in tapped holes and check them for tension occasionaly. I think some Mossies are done this way also <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />. Some Mossies seem to work OK with rivets, with low profile tracks, again plenty of Duralac (dissimilar metals jointing compound).

Regards Gary. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Finally got the boat put back together and sailing again on the weekend at Lake Cootharaba's season opening regatta.

For anyone that is interested, the key to bolting the mainsheet track on is to have a spanner that keeps the nut level. First side took about 2 hours to do until we figured that out, second side took about 20 mins (We bent the end of cheap spanner to get the head level). We kept the washers on the nuts with super glue and put duralac on the washers. All held together well.

Regatta was well attended by cats, dinghies and trailer sailers. We seemed to do alright in the last two races (missed the first race because of putting boat back together). Not sure if it was changed after I checked but the provisional results had me as 3rd and 1st on handicap in those races. Will try to get the race times because I wasn't convinced we did that well in the first race. Second race wasn't a surprise because we had a blinder first lap.

As some of you may be aware, I have a square head main on my boat. We noted this on the entry form as required but handicap wasn't modified on provisional results. Will probably get it dropped a minute or so in future regattas so ppl don't get their panties in a bunch. Will consider running off pure F16 handicap as soon as I get a kite, shouldn't be too far off the pace with practice.

At this point in time, with preliminary results, the square head main seems to be quicker, as probably expected by most ppl. Would love to have some other mozzies to race against now.

PS. Speaking of panties in a bunch, what trapeze harnesses are ppl using, I cannot find one that's comfortable. I even forked out for a good magic marine one but it would cut circulation off to my legs when I sat down, left some fairly serious bruising after a days sailing. Probably just need to spend more time sorting out the straps.

Nick,

Great result. Well worth persevering with the track despite missing the 1st race. I think I may have made up a small block to hold the spanner and nut and work from the centre outwards but that is all history now.

Regards,

Peter