NACRA 5.5 uni - project boat - damaged main beam

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?

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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.

I'm pretty sure that Nacra once marketed a widened 5.5 as a factory available 18 square if I remember that correctly. You may have some sort of combination of the two.

But, yes, if you intend to use that sail, you are definitely going to need a boom. Note that if you can put a strop around the boom to the mainsail so that the mainsheet loads are directly transferred to the sail, and only use the boom to support an outhaul adjustment, you can go with a much smaller (and cheaper) material for a boom (like most of the catamarans available today do).

Thanks Jake,

Hoping some others chime in on this, but what were you thinking regarding boom specs? Build my own (like the beams) rather than try and source a nacra original? Perhaps 2" 6061 Aluminum tube, maybe 0.0625 wall thickness? How about a gooseneck assembly? The old main beam had a rudder gudgen fitting attached facing aft, I suspect this was how the boom was attached when this was an 18sq. My sail doesn't come all the way down to the tramp at the tack, so I would need something a little higher on the mast. Maybe getting ahead of myself here, but throwing some ideas around.

Nothing says that the sail has to meet the boom at the goosneck...they could be three feet away and the boom angled upward if need-be...but, that takes up a good bit of real estate to get across the boat and having the boom up higher on the mast is definitely desirable.

BTW, sunfish masts will make an operable boom (or spin pole) and they're typically cheaper from a sunfish dealer than you can get the same extrusion from a metal wholesaler.

2" .0625 is plenty stout, that's what my i20 had.

Some downhaul will probably pull that sail close to the bottom on the track.

yeah, I figured that will help a bit. Didn't have the downhaul rigged up for the test.

What sort of gooseneck fitting do the older boom Nacras e.g. 5.2 use. I believe they were rectangular booms, so what could I make work? I've google searched and pulled up some pics of hardware (not installed, just the item) and I can't visualize the connection.

I like this idea a lot. Would I have just one loop/strop and pick one of the 3 holes in the clew plate, or have multiplier strops, one in each hole, to maintain the option of pull point? Or will the outhaul take the place of a clew traveller type arrangement, by adjusting foot tension and sail shape ?

I remember that the 5.2 used a short piece of 3/4

(roughly) square stainless tubing as a trunion. It had a pin through the top and a pin through the side that attached to stainless yoke fittings in the boom and the mast.

The boom fitting was a

U

shaped bent piece of stainless (15 gauge?) that had a large hole in the middle with a bolt (5/16

? maybe 1/4

?) that went through a plastic end cap in the end of the boom. That

U" shaped yoke could swivel on the bolt and swivel on the pin.

The mast had a fitting that riveted to it and made a yoke with the pin oriented in the vertical axis.

Really, though, gooseneck fittings are a dime a dozen...you could probably adapt just about anything from any sailboat.

The boom fitting attachment and the tiller crossbar arm fittings were the same from what I remember from my 5.2

Just one strop. The out haul will determine the foot tension. It is important to note that the mainsheet should either pull straight down, or preferable slightly forward to induce rotation and to not pull the foot of the main flat.

As in, my strop will probably go through the furthest aft of the three holes on the clew plate, pulling the boom towards the mast somewhat?

Yes a slight inducing of forward pull to help promote mast rotation is a good thing. Too much however will bend a boom, even a two inch diameter one. If the bottom attachment point of the main sheet is between 1-2 inches forward of the hole in the main that should be about right. I know from experience that three inches will bend the boom.. When I say bend I don't mean catastrophic destruction, but rather a permanent bow.

Are you talking about a sail that is pinned to the boom at the clew separately from the mainsheet? If you put a strop around the boom and use that connect the mainsheet directly to the sail and only use the boom for outhaul, you shouldn't be able to bend the boom (I wouldn't think).

On the Nacra 20s I've owned, it was amazing how much we could bend that rectangular boom when sheeted hard (because the sail and the sheets were pinned at different places).

I am talking the main attached to a strop which is attached to the clew. The boom simply runs through the strop. The out haul however does attach the boom to the sail and that connection is what allows forced rotation and bent/bowed booms.
One could argue the out haul needs to be eased a bit but I would disagree. When I noticed the first boom I assumed one of us had landed on it during a capsize. The second one had not been in a capsize before I noticed it was bowed.
In both cases the boom was/is still serviceable, it just bothered me that it wasn't straight.

A Sunfish mast is a 2 1/4

section. Fairly heavy section. The booms are 1 1/2

and are used for spin poles and booms.

I made a boom using a 2

section. I found a aluminum cap that fit. It might have been from a Holder 14 boom. If you have access to a lathe you can make one easy enough. I got a shroud anchor bolt from a Hobie 18 or 16 and installed that in the cap. I had what is called a super goose which was for a Hobie 18 boom. This is an aluminum fitting that the eye of the shroud anchor bolt will fit perfectly. This same fitting attaches to the goose neck fitting on the mast. Simple and strong. I believe that fitting is still available from Murray's. Google

Hobie super goose

I will try to post a couple pic's if you like.

Hello while I am a newbie cat sailor. I do own an 18sq I think you are right in your assuming that you have a chopped down 18sq.

Mine was pretty much stock when I got her. Rectangular boom attached to bottom of 30' mast. Three pulleys attached inline on boom. Two torsion tubes running ontop of trampoline on either side.

I am curious if your booklets sail works though?

Also will you be adding a jib as the 18sq were unI'm because I would like to add one.

If you have any questions about the 18sq feel free to ask me.

Hiya all,

If you have been following this, then the latest is that the tramp has been restitched (fingers crossed) and installed on the boat. The trailer is finished, except for lights, and the front upright for the mast (the rear upright is finished, and pivots down for boat unloading). Still need to paint my welds. Also need to remove what's left of the ancient hiking straps and install new ones (line through eyelets, with pipe insulation foam wrapped around them). Also had the upholstery guy make a simple pocket on the front of the tramp (the white thing in the pic) with a velcro closure, for stashing the main halyard and the righting line.

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Next step is working on the rudders. Rudder thread is here

Hi there,

I plan to add a boom, and have committed to it now because of the able I chose rear beam/traveller and where the eyelets for the tramp lacing have been attached.

I will not be adding jib. I wish it had a jib, but the more I've read and learned, it seems it's a lot of modification to do it properly and it can put a lot of pressure on the bows (especially older boats like mine with the chainplates on the outside of the hull). Better off just finding a 5.5SL or another type of boat.

Have fun with your 18sq. Pics?

Finished! Maiden voyage last weekend was in very light winds, but enough to test everything out, and it went very well. Rigged quickly and without issue on the beach, and away we went. So happy to be done and looking forward to a great summer of sailing and exploring local lakes. Thanks everyone for you helpful input as I navigated this project.

Before: Dirty, damaged boat in pieces, as retrieved from a barn after sitting many years

After:

Nice!