Ordering a new in-mast furling mainsail - correct boom angle?

DrJudyB · Oct 21, 2018

Wanderwind said:
I am preparing to order a new furling mainsail. It's my first time ordering a furling mainsail and it has been a problem since we bought the boat, so I don't really trust any of the measurements of the existing sail. I'm looking for advice/info on the correct angle of the boom when measuring.

I've attached a pic of where I set it when I measured. Can anyone with an in-mast furled mainsail let me know how this position looks?

Thanks,
Daniel

Every manufacturer of furling masts, Zspar in your case, publishes sailmakers’ instructions. Every competent sailmaker consults the specs. Once you identify the model number of your mast and boom, your sailmaker can look it up.

https://www.usspars.com/wp-content/uploads/2011/03/sailmkr.pdf

Your sail loft sail salesperson should know this. If s/he doesn’t know how to guide you, find another place to buy your new sail.

Judy Blumhorst
Retired sail loft owner

Ward H · Oct 21, 2018

@DrJudyB
Saw your tag line and immediately jumped over to the Hyde Sails Direct website. Enjoy your cruising.

DrJudyB · Oct 21, 2018

Wanderwind said:
Hi Judy,
This is great information but I have no idea what I'm looking at. Is the 6% number on the second page indicating the boom angle?
Thanks,
Daniel

Daniel (@Wanderwind )

Yes, if your mast and boom match the model numbers on the page, the 6 degree indicates the boom angle. Have you confirmed the model number of your mast and boom?

Joe · Oct 21, 2018

Let the sailmaker guide you, he/she should come to the boat for consult, measuring and fitting.... it then becomes his responsibility to get it right. If you're trying to save a few bucks and going the mail order route.. it's all on you. This sounds like the perfect time to call in an expert.

DrJudyB · Oct 21, 2018

Wanderwind said:
Joe, is it typical for a sailmaker to drive 4 hours for a consult?

Not for free.

One way or the other, you will pay for their time. You're buying the experts time., not cloth and battens.

Seriously, a reputable, experienced sailmaker can give you a quote without the measurements. All the name brand lofts can do it. To get the ball rolling, and to give you a quote, all the loft needs is the luff, and foot measurements, your choice of cloth and vertical battens or not. Then you can decide if you want to pay them to come measure for you or measure yourself. In this day and age, there are many good sailmakers can build you a sail if you follow their instructions measuring.

If you select an online loft, be sure to google their reputation. And be very careful if somebody gives you a quote that's 30-50% cheaper than the name brand lofts who will accept long-distance jobs.

Judy
Loft Owner on a sailing sabbatical.

SG · Oct 21, 2018

I've nothing to add on Judy's advice about listening to your sail maker.

However, Daniel's picture has the boom so close the "arch" with the main sheet tight.

Question?: I wonder how he's going to get that angle right when the wind and waves require that the boom have some "play" to move around. In that case, I don't think you want to "load-up" the rig by having the optimum boom "angle" like that. Now if he has a hydraulic vang which he uses to set the boom at that angle...
??? I've only used these in the mast furlers on "other peoples boats". We've always had conventional main sails on our boats.

DrJudyB · Oct 21, 2018

Wanderwind said:
Hi Judy,
I'm planning on going with Mack based on recommendation of several dock neighbors and what seems to be a decent reputation online. They're about a 4 hour drive away in Stuart FL. I don't know what you'd consider an "online loft".

I already got a quote and then watched their video on measuring (

) and the guy just says to position the boom 'as if you were sailing'. Given that this sail has never worked right since I've owner the boat, I was hoping to get info from a fellow Passage 42 owner...

So, based on the doc you linked, it said 6% for the boom, which translates to 3.43 degrees. Using SAS trig with my foot and luff measurements, I ended up inch shorter on the leech than I'd measured with the tape. So, I guess I did pretty good estimating...?

I'd really rather pay someone to come measure and install the sail but options around here are kind of limited. I'm going to call them tomorrow and see what they say...

Thanks!

It’s 6 degrees, not rise over run. The percent sign is a typo. All furling mains have to be designed with 4 to 6degrees at the boom, depending on the mechanism, to allow the foot to roll up compactly without becoming too bulky to fit inside the mast.

Mack Sails will know what to do for your in mast furling mainsail. Follow the instructions they gave you. Be sure to tell them what boom and mast you have, and supply the Zspar documentation. Tell them you have had difficulty with furling in the past and they will help you solve the problem.Send photos if requested. Mack Sails will take it from there.

Joe · Oct 22, 2018

Wanderwind said:
Joe, is it typical for a sailmaker to drive 4 hours for a consult?

To answer your mysterious question... I don't have any idea. However, your tag says "Jacksonville" and there are certainly a couple of lofts in the area... uh... here's one that will definitely come to the boat .. North Sails, Jacksonville In-mast furling They make good sails, too, I'm sure you've heard of them.

jeff356 · Oct 22, 2018

Had the same questions as you as I had pushed out my Boom Vang to lower the boom. Contemplated going with mail order sails but had the local North Sails rep come out and climb all over the boat and take all kinds of measurements. I will have sails that will fit my setup like a glove and worry about if I screwed up in providing the specs or if they could be better set up.
Good luck.
Jeff

Valerio · Oct 22, 2018

AS DRJUDYB said, you need a little less than 90 degrees so the foot is not going to make a bulk when you are rolling in. I strong advise against battens. If you are not racing ask no battens and a reduced luff, there is a rope at the end of the sail that you can pull if the main is luffing. Whit my new main rolling in and out now is very easy job, even in strong winds.

uncledom · Oct 23, 2018

I'd just like to mention that Dacron stretches and to that end what ever degree of margin you pick will decrease over time. I went with Tri-Radial Pentex which doesn't stretch and is thinner although stronger than Dacron. My furling main never worked so well. Still very happy 5 years later. I used a small sail house in Stamford so your results may vary.

dakno · Nov 13, 2018

I second everything Ive read hear. I had many issues with my oe furling main and most were operator error. Most people seem to think that after 8 or more years a furling main is due for a recut or replacement, true that. My new 2017 main came from North Sails, very happy with it. I went from full length battens from Doyle (oe), to no battens and a reduced leach. I lost about 50 sq ft of sa on the main but its a dream to furl, it's what life is supposed to be like. 3 things...1) know where your vang should be, mark it, when furling; 2) lubricate upper and lower rollers , outhaul car as frequently as you can; 3) furling should be done dead to the wind..yes you can get some help from the wind by falling off to port with a Selden because of the offset sail slot but I think the energy you gain there is offset by extra pressure on the outhaul car.

Ordering a new in-mast furling mainsail - correct boom angle?

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