Yep I hope that's how my post reads throw away the old rear beam, weld some patches on the front beam if it's straight then use that as the new rear beam and buy a new front beam. I wouldn't drill the holes under the old beam I would put the bolts through the traveller then put a spanner on a long thin pole to tighten the nuts inside the beam

Pete still frequents the "thebeachcats.com" forum under the username pbegel

I purchased some battens from him earlier this year. Nice guy - easy to work with.

I have his email address if you have trouble making contact.

Edit - I see you're already engaged with those guys on that forum. I'm sure you can make contact with him.

Check your privet messages.... I just sent you his email

First, if you have a way to get it to you, I think I have have a rear 5.5 crossbeam with a dent in it. It is in Houston. I may have some other cross beams that you can have. There are probably people like me near you. We held onto damaged hardware first, thinking we might need it and later because the snakes living in it had gotten BIG.

A couple of comments:

The front beam does not look like the one on my 5.5 uni. The tramp track on your is separate, mine was internal to the beam, like the 6.0. It may be a homebuilt replacement. I would not order anything based on the dimensions of that beam. Also, I do not remember factory beams corroding like that

I have replaced at least 3 NACRA crossbeams. Online companies normally only stock 8 foot beams and shipping an 8.5 foot tube is over half the cost. Your best bet is to find one locally.

A used 6.0 beam with no corrosion would be ideal. Check other catamarans for beams that have the same dimensions, F18's for example.

Did the Inter 20 use the same extrusion?

If you buy a tube from a metal dealer, tell them this is is for structural use. No reputable supplier will sell you anything they have questions about. I had an industrial supplier search the stack for a tube that had 6061-T6 printed on it and the paperwork taped to it. Try to avoid surplus companies, they do not always know what they have or you may be buying a reject.

Good luck

All F18 and "Inter" (20, 18, 17, etc) beams are not round - they're all sqround and wouldn't work on these hulls (without significant modification, anyway).

that's a new one...

Jake is referring to the beam mounts for beam tubes (old style) versus the flat - sided design currently employed. Modernization via the newer beams will require hull mods to the attachment molding/laminating.

Too bad Jim Bauman has retreated to the CA mountainside...that used to be an F 18 HT debacle for awhile... maybe A cats, as well. Jim did a bunch of beam mods for the F 18 HT guys and the Tybee teams back in the day.

Interesting, I'm starting to wonder what crazy combination I have here. When we dry fitted the front beam on the hulls, the couple of holes to choose from to go over the stud in the beam moulding in the hull (my boat has a threaded stud coming out of the hull, not a threaded hole like most nacras) didn't make much sense. Either the beam seemed to extend slightly out over the edge of the hull, or sit inboard slightly so that the outside strap barely grabs the end of the beam. I hope that made sense.



Can anyone with a 5.5 in one piece and original parts give me some exact measurements for their beams (length, OD, ID, and distance inboard from each end for the anti-rotation bolt? Or point me to a document on the inter webs with such info.

Huh...that's not supposed to be a stud if I remember correctly...and, is that black material carbon fiber in the beam socket? I don't remember any 5.5's having carbon either (did the Uni version have some perhaps?). I'm pretty sure my 5.2 had a bolt that went down through a has spherical spacer through the beam into the hull. It was necessary to loosen that up and move the hull inward to get a new trampoline on. I can't imagine how you would do that with a stud there.

You might find these links useful to 5.5 manulas over at thebeachcats.com. I see that it had a side laced trampoline which would have meant that you could use a stud in that position on the beam...but they still show a bolt.

Nacra 5.5 assembly manual

More nacra assembly manuals.

OK, so I'm starting to realize my current beams don't add up. I think perhaps they didn't come from/with these hulls, even if the intention was for them to fit when they were rebuilt. They are 8ft 5in long (is this spec for the 5.5?). The front beam has the tramp track riveted on, as people have pointed out isn't normal. The studs coming out of the hull need corresponding holes in the beams. As I said, the rear beam has holes that don't line up in a way that makes sense, and the front beam it turns out doesn't have holes at all! The beams have a lot of weird holes and stains from previous fittings, add if they were set on a different boat. The Nacra manual shows the traveller track running the full length of the rear beam. Mine has a stain in the beam where it looks like one used to run full length, but now finishes short, on the inside of each hull. The plot thickens.

My 5.8 has a bolt through the top of the beam and beam strap about where that stud is. I highly recommend you contact the closest Nacra dealer to you and get the original specs of the beam. Don't be shy about contacting them even though you don't want a beam from them now they know that if they look after you properly now you will buy something from them one day. Sometimes the beam isn't the widest part of the boat when you are beaming up a boat to it's maximum width you need to find the widest part on the sides of the boat and measure from there. You may not have a standard tramp so will need to be conscious of installing the tramp you have the way it is installed now or you will be up for money to modify the tramp. An original Nacra 5.8 front beam will have a track built into it to slide the tramp into don't know about your boat

Nacra made two versions of the legacy rear beams. The earlier version used a bolt-on traveler track that ended short (inside of each hull). The newer rear beam included the traveler as part of the extrusion, so naturally it would be the full length. There was a slot machined into the track to allow the beam straps to pass through. Sounds like you have the earlier version.

So I have some new information! Apparently the beams I have now came from a Nacra 18sq, originally 11ft wide (?) and were cut down to 8'5" or 101in. I don't believe they have been installed with these hulls before, which explains why some things weren't adding up (hole locations for anti-rotation hull bolt, and stains where a full length traveller track used to be, along with a myriad of other old holes and stains). Not that this changes things much - I still need a replacement front beam, and ideally a rear one too. Would be nice to get original equipment, but if I do fabricate them myself, I'll be asking y'all for some hard numbers on the dimensions of various aspects of the factory beams.

I'm still open to purchasing some used beams, and a few of you have sent me contacts that I've replied to. Thanks for that.

Update: not a lot of used beams around. Looking at the blank tubing route. I can't measure wall thickness accurately, but it's a little more than 0.0625, and one source I have suggests 0.078 (5/64t) which apparently is an odd size. Thinking about going up to the common 0.125 (1/8in) and filing down the compression tube a hair to fit. Waiting on a quote for a stick of this stuff (4in OD) and I'm sure I'll almost fall over when I hear it.

Dolphin striker rod: trying to get around the $70 buying a new one, but custom making one mite be too expensive (I don't know any hobbyist machinists). Apparently 9/16th is an odd size for stainless rod, on top of the fine (18) thread. Damn sailboats!

V-strap: looking at either welding a brace over the corrosion at the centre of the V (isolating potential cracking and the mysterious drilled hole) while also acting as a dolphin striker rod casting. Or ordering the flat bar and bending a new one. Talking to a shop to figure out what alloy it is. He thinks 7 series (bendable, not very weld able) so may not be able to fix old one.

Oh, and to top off the weird sizing of all the materials (apparently this is deliberate by many manufacturers so that people have to buy original parts, not make them like I am) the trailer steel (channel) is an odd size, so I can't match it easily. Not that I care to much about that, since I'm not trying to fit anything to the old frame, just adding across the top of it.

That blank tubing shouldn't be too bad. I would guess about $140 for a 24' stick. The thinner material is actually more expensive....

If your going all home brew anyways, there is no reason you can use material sizes that are more available. Step the DS up to .625"

If I don't keep the ds rod to spec, the nylon ball won't fit atop the threads. Also I won't be able to reuse the compression tube, which appears undamaged.

Update: I've been busy! I built my new beams, and assembled the hulls, along with finishing the trailer. No tramp installed yet, and need to overhaul the rudder assemblies. First test today putting the mast and sail up, checking the stays were the right length and all my calculations add up (they did!). Very exciting to see it come this far!

One concern - with the sail up I noticed the old adhesive outline of a removed sail marking that reads '18s' (as in 18 square). You may be able to just make it out in the photo, below the Nacra logo and the red 5.5 numbers. So my 5.5 uni, made up of 18sq hulls, with previously chopped down 18sq beams, may now also have an 18sq sail?! I guess I don't really care what we should be calling it, but I would like to know if it truly is an 18sq sail, and if so, how that might affect the boat on the water. Bigger sail area comes to mind, with added power, but not sure if this will change the handling adversely (besides the extra healing moment). The mast is 29'6" long (excluding casting) and the sail seems to fit it well. I know early 18sq had a boom, then they went to boomless. This sail almost looks like it was made for a boom. Perhaps the silver colored clew plate could have been added later?. Even hooking my mainsheet to the most inboard hole of the clew plate, sheet tension isn't pulling outboard enough, and the foot of the sail won't tension properly. On the most outboard hole it looks just ridiculous - the foot of the sail has a giant flapping belly in it. I know the rear beam/traveller is meant to angle slightly forward on boom less, and slightly aft on boom rigs, but I don't think that will fix sail tension the way things stand. Any thoughts appreciated. Is it a 5.5 uni boomless sail, or 18sq boom/boomless sail? Issues?

[img]http://www.thebeachcats.com/gallery...p;g2_itemId=112746&g2_serialNumber=4[/img]

[img]http://www.thebeachcats.com/gallery...p;g2_itemId=112749&g2_serialNumber=4[/img]

You are correct in that this is not nearly enough angle on the mainsheet for a boomless rig to function properly.

Hmmmm. That's what I am thinking. *sigh*. So, does this frankenstein of a boat need a boom added to it now? The sail is quite nice. Do you think the mast is also from an 18sq, or were they the same as the 5.5 uni? (this mast is 29'6"). If I recall correctly, the 5.5SL mast is a little shorter than the Uni, but don't know the specs on the 18sq masts.