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.

[img:left]http://www.thebeachcats.com/gallery...p;g2_itemId=112991&g2_serialNumber=3[/img]

[img:left]http://www.thebeachcats.com/gallery...p;g2_itemId=113033&g2_serialNumber=3[/img]

[img:left]http://www.thebeachcats.com/gallery...p;g2_itemId=113034&g2_serialNumber=3[/img]

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!