Need help to size on asym spinnaker?

Hey guys. This is my boat. Spin halyard comes in just above forestay.

http://sailboatdata.com/viewrecord.asp?class_id=4350

I take it a main consideration is the forestay length compared to the luff length.

Forestay is 52.04' / 15.86m
I: 50.33' / 15.34m
J: 13.25' / 4.04m
P: 52.00' / 15.85m
E: 16.42' / 5.00m

Here are some very cheap asym spins. It looks like some will be pretty close. Do you think any will suit? I am thinking the "momentum 08, or 10 might do? This is for cruising not racing.

http://www.china-sail-factory.com/stocksails.aspx

 

Depends on length of the prod, and if the prod is going to articulate. If you do not use a extendable spinnaker pole/sprit, either of the above will probably work.

Also depends on whether or not you intend to tight reach - downwind sails tend to be fuller and longer in the foot. A articulating prod allows a longer luff, and a longer foot as it can be tweaked to windward and expose more sail to the wind when downwind - it doesn't stay in the wind shadow of the main.

Often people just jury rig a spinnaker pole to become a bowsprit for a asym on cruising boats - makes gybing a treat and sail handling much simpler.

--
CutOnce

 

The asymetric is a beatiful tool. I have two. Big Boy and Little fellow

The aloft mass of a big spinaker becomes unstable in a seaway...thats why they call them Blisters. If you get blisters trying to keep the sail under the boat, your autopilot will get a headache.

A smaller sail is more versitile. You cant reef an asymetric. My BIG BOY rapidly becomes overpowered and I must bear off or shift down.

The additional sail area.. mass..of my BIG BOY makes it unstable in a light winds and difficult to steer deep angles.

The BIG BOY is difficult to take down and hoist because so much sailcloth must be controlled by the snuffer.

Visabilty is poor under my BIG BOY.

I love my Little Fella....use it all the time. When in doubt go smaller.

 

Yes I have been told to go smaller and this will be used to help cover distance as I will be sailing across the pacific. So it might be faster over all if it is smaller and used a lot than too large and left in its bad the whole time?

The smaller sail has these specs. Would you say it is OK for my boat?

Momentum-SP.SET-AR-08 Assymetric Spinnaker W/Medium Blue Launch bag. Area 93.8M Luff 14.55 Leach 13.65 Foot 7.66

Larger unit.

Momentum-SP.SET-AR-10 Assymetric Spinnaker W/Mediu Blue Launch bag Area 118 Luff 16.3 Leach 15.32 Foot 8.65


Like most cruisers it will not be used from a pole or sprit. It will be connected to the end of the anchor roller.

 

Im not a numbers man...Id say use your intuition on size... luff length and LP.

I fly the asymetric off a stem roller. Works fine. I use a downhaul led aft to a winch for tack height and luff tension.

A spi pole is a very valuable tool...poled out headsail or occasionally poled out asymetric.

 

I have an extendable whisker pole. But no real spin pole. I am not a numbers man either, but I do not know enough to just pick a spinnaker from a brochure and was hoping someone on here would know more. I think the one with the 14.5M luff should be on the smaller side of OK for my forestay length of 15.8m. But then again the rig is fractional and maybe the one with the 16.3m luff might be OK. But I worry that I will not be able to get it tight enough in some conditions. I have ZERO experience with these asym sails. Only some limited experience with symmetric used with poles. My experience tells me I will not use a symmetric much on an offshore trip with only my girlfriend on board so I want something manageable.

Nice boat and nice setup Michael.

 

I think I have Momentum 08 (came with the boat not sure it is AR-08 it has SLU=14.4m, SLE=13.29m, AMG=7.01m and 7.63m). It is surprisingly well made and works very well at least at tighter angles (I have symmertic spinnakers as well). Certainly excellent value for money at that price!

My boat has I=14.7m and J=3.97m, thus not that far from yours. Since your forestay is clearly shorter than SLU of Momentum 10, I don't think you can use it porperly without a rather long pole. You need to be able to strech the luff. I run mine with 4.3 m long spinnaker pole just above pulpit with normal spinnaker sheets. My forestay is about 15.2 m and spinnaker halyard is a few cm above the stay.

 

As when buying any sail, even a used one for downwind sailing, ALWAYS measure your actual boat.
That foresay measurement specifically is just a calculation that assumes an average sheer and average mast rake. (I know. It's my site. I'm questioning myself as to how useful this number really is. There are so many variables that can affect the foresail hoist.) And boat builders often change the size of the standard rig over time.
You can use these numbers to get an idea idea for pricing etc. But you never know what you really have until you measure.
Randy Browning
Norwalk, CT USA

 

Of course Randy...you need to know the hoist. But then what ? After max size comes usability.... The unknown factor. Only the end user can decide .
For instance ....will you hoist the sail inside of the bow pulpit ?

How much do you deduct from max hoist to allow the asymmetric bag to stand clear of the masthead genoa roller furling swivel ?

How important is visibility under the foot of the sail ?

What apparent wind angle range do you need ?

Personal preference , plus the way you will actually use the sail become critical

 

Thanks Randy. I will have to get someone in California for measure my boat. I am in Australia and will sail it home in Feb so sails need to be ordered before I get there. Nice site BTW.

 

measuring for downwind sails

Yes. You could be right. Deciding the dimensions for a downwind sail could have more pitfalls than just 'luff-leech-foot' for an upwind sail. Under ideal circumstances you would have a sailmaker help you decide. But I'm more than sympatheric to those who look into the used sail market in order to economize. I should add that downwind sails can usually be reduced and shortened at a fairly modest expense. So purchasing a used sail that is a bit too big shouldn't be a fatal error.

 

The most critical measurement for an assymetric is the length of the luff verses the length between the end of the prod (or where the assy tack is attached) and the halyard point.
A big cruising boat will commonly have an assymetric luff that is 106 - 108% of this length depending on the other dimensions of the sail. This will provide a good beam/broad reaching assy sail, if you want to sail tighter angles with it (80-95AWA) the luff needs to be straighter (down to about 102% or less and the sail needs to be flatter, more of a multihull thing.

 

used asym

Makes perfect sense to me.
I was simply emphasizing the importance of having an accurate measurement to start with. If you are purchasing a used sail, it will be hard to know, ahead of time, how full or flat the cut is. If it needs to modified, it's always easier, and less expensive with a sail that is too big, rather than too small.
In the end, the amount you actually save may be just in the luck of the draw.