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Nacra 18 Square

Posted By: Minnesota

Nacra 18 Square - 07/24/18 03:40 AM

Hi Everyone! I have a 1987 Nacra 18SQ that I was looking to do some modifications to and would appreciate some input.

I'm planning to add a jib for additional speed & to make this beast of a boat tack better. It'll require a new forestay at the minimum since the current one parts about 1 meter down form the mast attachment. Would it be a good idea to fabricate a bridal foil to better distribute the load onto the hulls? Has anyone here ever done this before?

I'd like to upgrade the hulls to something a little larger than the 5.5 hulls it currently has so it can better handle 2-3 people on it during a lazy afternoon. Is there any harm in using some 1986 foam core 5.8 or 6.0 hulls in its place?

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Posted By: JeffS

Re: Nacra 18 Square - 07/25/18 05:37 AM

Gday there is a guy in Sweden putting 5.8 hulls on wider beams and putting a Tornado mast on with Tornado self tacking jib, which is sort of what your considering, if you want I will private message his facebook link to you, he's quite outgoing with his info, he currently has a widened 5.5. I'm guessing your looking at keeping your mast and maybe a F16 self tacking jib or Taipan 4.9 jib. Craig in Qld has put a new square top sail and infusion rudders on his 18 square and he says that has sorted the tacking issue. I haven't sailed my 18 square yet but hope to next month once I have the mast bits sorted, mines got a carbon 32ft mast and big square top sail and I'm hoping that will sort out the tacking. There is also a thread on catsailor.com which I revived a while ago and it has great info on spinnaker conversion etc. Good luck with your project as there are a couple more being revived at the moment and I have a mate looking for one to do up
Posted By: reVintage

Re: Nacra 18 Square - 07/28/18 02:51 PM

Hi,

The Swedish guy here ;-) . If you want to add a jib it will work with a self-tacking Infusion or another F18 ditto. I have done this to our 10" wide 5.5 . See image below where a Hobie Tiger mast is used.

As I see it, it would be easiest to share the forestay load with a third centered Dyneema forestay and a low Dyneema bridle(Liros Static 4 or 5mm) at ca 1´ 2" heigth. You might have to lengthen the side forestays and shorten the top snout, as the jib luff is 19´ 7". If you are lucky, it will fit without altering the side fore stays, as the 18SQ mast is almost 2´ higher than the F18 mast.

If we assume 220lbs total static forestay tension, let the center stay take max 80lbs and the side forestays split the rest. Tricky, but it will work, if you have a Loos to check tensions. Don´t know how much sag you will get in the jib luff, though.

For next years 5.8 Frankencat build, that Jeff refers to, I bought a pair of 18SQ beams, but had to return them as I found them all to weak to use for 2 persons. Designed and built new 10.5" inch wide ones. First opted for a pair of 6.0 hulls, but changed to the 5.8s from the same source, as they where in much better shape. Also bought a Tornado self tacking jib instead of the 49er mentioned in the link below.

https://www.catsailor.com/forum/ubbthreads.php/topics/288287/re-taipan#Post288287

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Posted By: JeffS

Re: Nacra 18 Square - 07/29/18 10:34 AM

Thanks for jumping in Lars, I didn't want to just chuck your name out there, I'm just waiting on my new sidestays for my project
Posted By: reVintage

Re: Nacra 18 Square - 07/29/18 02:19 PM

Hey Jeff,

Looking forward to more info about your new project.
Posted By: Minnesota

Re: Nacra 18 Square - 07/30/18 11:57 AM

Jeff - Thank you for the pointers. I have a ~10-15 year old 5.8 jib I am planning to use for the first iteration. The mast I am using is a 32 ft aluminum mast, pretty sure it is the original that came with the boat - It is identical to the one from the 5.8 I have been sailing on.

Lars - Thanks for the pointers on the Jib attachment. I'll give that a shot when I set it up in the spring. Can you share more details on your concerns on the original 18 square beams being too weak? I was hoping I wouldn't have to fabricate new re-enforced ones. Did you just add the reinforcing at the hull attachment points or through the whole tube?
Posted By: reVintage

Re: Nacra 18 Square - 07/30/18 09:11 PM

First of all remove the striker band and rod and check for corrosion. Images of the rotten ones I got below.

The 18SQ beams I bought had no inserts what so ever. If so, try to find a pair of Australian 5.8 beam inserts. Think JeffS knows a guy who has a pair. Also add a 4" long 0.120" tube in the center.

My 5.5 front beam had tube inserts of something like 0.08". If you have them, change them for 16" inch long 0.120" and also add a 4" long center insert.



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Posted By: JeffS

Re: Nacra 18 Square - 07/31/18 03:48 AM

wow that is corroded and would be a sloppy boat, the inserts for the beam ends are called I beams enable you to really tighten your beams without compressing the tube and are supplied by Brisbane Catamaran Centre. I'm assuming your welding a patch on those beams Lars or did you replace them? Definitely need the beam centre post. From what I hear the 18 square goes upwind brilliantly, outpointing most big cats but is slow off the wind, so I'm considering a spinnaker for mine but I do know they are a bit tender in the bows as far as pitchpoling so I'm reluctant to add the weight of a bowfoil up front.
Posted By: reVintage

Re: Nacra 18 Square - 07/31/18 07:39 AM

No worries Jeff, couldn´t accept that crap. The seller in the Netherlands didn´t mind and gave me the nice 5.8 hulls instead. Had to pay the shipping though. One of the guys in the 5.8 FB group said he had a pair of inserts. I made the new beam of 2x100mm tubing and the center and inserts of 3x100mm that I slotted 15mm for a tight fit. Then a M8 bolt through the beam end, like the new 5.8, with spacers from top to bottom. Used stainless 40x3mm for the beam strap and M16 for the striker rod.
Posted By: JeffS

Re: Nacra 18 Square - 07/31/18 11:17 AM

Yep my mate Dazz has some I beams, are there many 5 8s over your way, I'm going off on a tangent here but I'm wondering about sending one of mine over for Texel so I can do it next year or wether I try and hire or buy one there but bring my sails and foils
Posted By: reVintage

Re: Nacra 18 Square - 07/31/18 05:16 PM

I have no figures about how many 5.8s are left in Europe. For what I understand, the last 5.8 for the European market was produced in the US 1999. So no high hopes of finding a raceready boat over here. Anyway I guess, the Netherlands is where you have the best chance to find one.
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