Boom lengths

Don´t overdo it! A F18 boom of 240cm will be to short. You only need an aluminium 40x2mm tube of ca 250cm length, cut it to length after testing. Use a Dyneema loop from the clew around the boom and to the upper mainsheet blocks.

Edited by revintage on Jan 05, 2022 - 03:14 PM.

Kevin219 wrote: I'm looking to retro fit a boom to my Nacra 6.0 NA. Ever since having a square top main made, the "boomlet" doesn't provide the leech tension I need. So the foot of my main is 7'10". Can anyone provide to me the length of a Nacra F18 boom or a Nacra 20 Carbon boom? Both of these booms I can get from Murrays but I can't find the lengths of either. I also might have a lead on a Nacra inter 20 boom. Might someone be able to give me a length on it?

Thanks in advance
Kevin

Hi Kevin, you might want to re-think this. If you're not getting leech tension it can probably be corrected with mast pre-bend and rig rake. You know this but it is worth mentioning, you want the traveler car on the sail moved forward to increase leech tension.

If you add the boom, you will need to modify the rotation arm (aft and up) and reinforce the main with straps and a cringle. If you have the over-rotator it will not work. A boomless main is just not the same as a rig designed with a boom. You will likely also have a problem with downhaul, or will need to modify the sail here also.

The 6.0 NA is a monster and fast as shit when tuned correctly. Modifying it to a boom rig will open up several new issues.

Hey Kevin, add the boom and find out by yourself, about the new possibilities about sail adjustment, it gives you. Boomless is suboptimal but easy to deal with, especially for your head 😉 . About rotation, move the rotator to the back of the mast and add trim fittings. I have done this mod on both my 5.5 and 5.8. If unsure, check with your sailmaker about the opinion, about the sail ha made for you.

Edited by revintage on Jan 05, 2022 - 04:26 PM.

Leech tension isn't a good way to describe my issue. This picture is worth a thousand words... you can see the sail folds over when the "outhaul" is brought on. Look at the W shape of the batten at the first reef point. It really is a grotesque sight, much worse in real life.

So I need a boom. Revintage, is 240cm the F18 standard boom length?? that would be JUST shy of what I require I think.

As for the mast rotation, I hate the mast rotation on this 6.0 due to the boomless design. With a boom it will become self tacking. Another bonus.

Last by not least, the boom will allow me to use the reef point I had made.

Kevin

i'm not familiar with boomlets, so I hope the collective will correct me if wrong. My conventional battens are longer and allow me to stretch the sail from the leech to the luff by using a batten-end and cord. To this old-time beach cat pilot, it just looks like these battens are too short.

Kevin, please add an image of the whole sail, the one you show does not look so nice.

About boom, just buy std tubing and the gooseneck fitting. Note, your foot is 7ft 10"=239cm, you need ca 10cm for the outhaul.

To this old-time beach cat pilot, it just looks like these battens are too short.

The battens are full length. Luff to Leech.

Revintage, I will resort to buying a stick of alum if it comes to that. Below another picture. clear to see the bottom half of the sail has 2 distinct concave sections to it.

The factory boom on my 2000 I20 is 104.75 inches not including the gooseneck. Add 2 inches for the gooseneck.

Kevin, the image tells it all, you need an outhaul(if the battens are correctly tensioned. So begin with to follow tominpa´s suggestion about the two lowest battens. Maybe you could also choose a stiffer bottom batten?

If going for boom you will need to recut the main and remove the forward flap under the lowest batten. No big operation. As you now have a square top with higher CoE than the original, it will probably be a good solution to loose the few cutaway square inches.

Pete, the Inter boom is absolutely a good option. On my new rebuild of the 5.8 I have a Inter20 main on an alu Tornado mast together with a self tacking Tornado jib. Though I will not use the rather heavy rectangular section, Tornado style, Inter20 boom and instead use 40x2mm round with the system shown above, but without the blocks, only a single sling with a clamcleat.

Edited by revintage on Jan 06, 2022 - 05:24 AM.

Pete, the Inter boom is absolutely a good option. On my new rebuild of the 5.8 I have a Inter20 main on an alu Tornado mast together with a self tacking Tornado jib. Though I will not use the rather heavy rectangular section, Tornado style, Inter20 boom and instead use 40x2mm round with the system shown above, but without the blocks, only a single sling with a clamcleat.

I recently built a lightweight boom out of a sunfish spar to replace the heavy rectangular boom on the 20.
Only had it out once so far but seemed to work well

Thanks for that dimension, Pete. So F18 boom is out. Nacra I20 Boom will work.
I am quite weight conscious however and I may hold out for the dimensions of the Nacra 20 Carbon boom. The stiffer bottom batten is a thought, but its an otherwise good looking sail. I think the boom is my best bet.

Thanks

Something just came to mind. Are you having this issue in heavy air? Nacra offers a stiffer bottom batten for the 6.0 in heavy air to reduce what they call the sail hula. I had it on my 6.0 and it did reduce the inversion but
did not completely do away with it. Seems to be a common thing with the 6.0. I got the batten from Rick Bliss at New England Catamarans.

Pete

Kevin, don´t waste ridiculous 475$ on a carbon boom for an old 6.0, the weight difference compared to aluminium is insignificant.

I have an N20C and normally I'd just go measure the boom for you, but..... It's 900 miles away right now.

First, I agree, add a boom! Boomless sucks; notice how a-cats went that direction, but now all run booms. That simply reinforced what I already believed to be true.... Booms are better and give more control over the sail.

There's a big problem that nobody has mentioned though, the 6.0 and other similar Nacras have sails that extend further down the mast the a conventional boomed rig. Unless you are going to cut the bottom of the sail off, you need a curved/deck sweeper boom.

The Tack of the sail is plenty far from the tramp. I was simply going to mount the boom at an angle. Plenty of room to pass beneath.

Good for you, wlrottge. Sweet ride.

Kevin219 wrote:

To this old-time beach cat pilot, it just looks like these battens are too short.

The battens are full length. Luff to Leech.

Revintage, I will resort to buying a stick of alum if it comes to that. Below another picture. clear to see the bottom half of the sail has 2 distinct concave sections to it.

I don't think this is a boomless issue, from a previous sailmaker POV, it's a sail design issue. Building a boomless main had challenges. I had raced a 6.0NA with a square top and it took me a couple of rounds to get the shape correct. I would suggest take pictures up the sail at about mid draft in every 5 knots of wind. Watch when the sail "flips inside out". My guess, it is about 8-10 knots of wind.

But, it would be worth trying a boom and see if you like it. On my modified 18-2, I am using a section of aluminum hand rail for decking. It's about 3"x1". And 10' sections are easily to get. I wouldn't invest a lot into it until you are satisfied with the result.