Measuring an asymmetric for a catamaran?

[Franziska]

Hi,

I need to measure the max dimensions for an asymmetric on my cat.
It's an older one-off with modified rig, so there are no dimensions to get of yard or designer.
As my preferred sailmaker is not local here I'd need to measure myself.

Now the question.

As all three edges of the sail are loose cut I wonder how to measure the sail.
The usual measure sheets are for monohulls and do not take the large beam of a cat into account.

Ideally I'd run my sheets outside of the leeward shrouds to a point way aft.

I have no bow pole but plan to mount the tack so that it can be pulled towards the windward bow with a bridle.
Bow pole is not an option.

Anyone around who has done this?
Has anyone a suitable measure sheet?

Thanks Franziska



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[Franziska]

70-120 Angle approx.

[barnakiel]

Depends on how you control the sail. Sails furled top to down can be longer in the luff than 100% (luff) measurement. Sails furled zero style must be shorter than 100% of the measurement, minus the distance for the hardware.

Other measurements up to what style of the sail you want.

b.

[Franziska]

Thanks B!

I'm leaning towards a sock and not a furler (budget).

Max windspeed about 20kn.

www.ladyrover.com

[barnakiel]

Then I would build a short (with luff that can be made bar tight) asymmetric sail for upwind and reaching work. Heavier cloth. Possibly dacron.

I would build a longer luff sail for broad reaching and running. Lighter cloth. Likely nylon.

For broad reaching and running ask for something that will float to windward. Have a quick look at N/S G2 for inspiration. Webb Chiles uses one and says it is a great sail. You can read his view on his blog.

North Sails: G-Series Gennakers

b.

[Franziska]

Guess the G2 looks about right.

Having read in Webb Chiles articles I guess I should perhaps wait and get a furler as well.
Still, could I shift this to windward?
I doubt it, as I would need the tension on the AT rope, no?

Thanks again, main question is open though, how to measure it...

www.ladyrover.com

[barnakiel]

You measure as they show you in the cheat sheets online.

Additionally, measure beam at the mast and then max beam.

Next measure spreaders length and how high they are from the base. Most cats have spreaders (much) shorter than max beam and this may be important for the sailmaker, depending on what sail you get.

Have a drawing of the rig for the sailmaker too - maybe there is one already for your boat somewhere online. If not, draw it yourself.

Take pictures, they help sailmakers.

My tip: consider having a sailmaker over to your boat for measuring. This is actually very common for custom and semi custom rigs.

If you want one sail to cover the scenario with the tack at the center as well as the tack at the windward hull, you measure for a kite that fits the central mounting point, not the beam bow point.

You measure 100% dimensions. The extra luff length of the G2 will be decided by te sailmaker.

(My own preference is for minimal extra length - as I get very upset sailing in light airs whenever our kites collapse and get caught on our bow rails).

Tip: some makers have G2 styled sails sold off the shelf ... these can be easily priced 2/3 of a custom one.

Big hug,
b.

[Tom and Maje]

Do you have a one off boat? I ask because most sailmakers I've dealt with will know the model of a production boat and be able to tell you what you need. You shouldn't have to measure the sail yourself.

Also, from personal experience, get one the is slightly smaller. That way you can keep it up in higher winds.

Maje

[Franziska]

Thks.

Yes, she's a one-off. I can get the sail for a very fair deal made by a friend who is a sail maker.
Unfortunately this guy is about 1800km from here, so I got to measure myself.

I measured the genoa and it worked.

I know in principle how monohull sails are measured, but have never measured an asymmetric with a moveable tack for a catamaran.

That's the tricky part. Barnakiel has thankfully given me an intro to this.

Still if anyone can evolve on it, even better.

www.ladyrover.com

[bruceb]

I am more used to tris, but the same principles apply. Get a tape measure long enough and pull it up with your halyard. Get a measurement from the center line "tack" position and also to the aprox point where your bridal would allow it to tack. On a cruising boat I would use the lesser of the two for your max luff length, less any planed furler drum/upper roller. Next, pull the tape aft (outside everything) to your most aft sheeting point where you would plan on mounting a block. Last, lower the tape and get a measurement from the center line tack back around to the same aft block.
Your sailmaker should be able to work from those dimensions.
Depending some on where you sail and the typical wind conditions, a drifter/reacher on a furler will probably get the most use, and be very easy to set and douse. It does not have to be a "max" size to still work very well.
B

[Franziska]

Thanks Bruce! I'll try that in the next few days.

www.ladyrover.com

[bruceb]

Three others while you have that tape out I should have added - Halyard while up to mast base/deck intersection (height total), and then on deck from the center line tack to the mast front (J spin) (should be in front of/greater than your forestay tack), and front of mast to the bridal tacks.
That should be plenty to work from and shouldn't take but half an hour to get all the dimensions.
Use a good tape that isn't likely to break, or run a small line up with it to help bring the halyard back down. I hate retrieving halyards.
B