Mac25 Spinnaker dimensions?

[StinkBug]

I've been wanting to get a spinnaker for my little boat for all those light wind days when going downwind is such a bore that I usually end up starting the motor. my mast has a tang a couple feet above the forestay with a block hanging on it for a halyard, and the boat came with a pole. I just need some lines a sail and some various other rigging. The biggest question is what size sail should I be looking for? Also what is the difference between a radial head, tri-radial, cross cut, etc?

I've found one with a 22' luff and 16' foot, which sounds about right, but I wanna be sure before spending money.

Thanks!

 

[Jackdaw]

The types of sails describe how the panels are constructed. Tri-radial best, then radial head, then crosscut. But for starting out all are OK.

That 22x16 spin is about a foot smaller in each dimension than it should be for your boat, but that will be OK. If it's in good shape, buy it and get it flying!

 

[THECUSCUS]

That one will work, but be a tad on the small side ( won't be much bigger than a 150 genny). If you have an un-modified fractional rig, your "I" measurement for your headsail is around 21.5', so your spinnaker "I" will be that plus the distance above your spinnaker block is. Your "J" is the distance from the forestay attach point on the chainplate to the front edge of your mast (there seems to be afew different posted dimensions for this, I suggest you measure yours for accuracy). The foot size divided by the "J" is ROUGHLY the % of the genny (its actually the LP of the sail that is used, but the foot size is close enough). So, if your "J" is 10', then this sail is roughly a 160. A good sized spinnaker would be more in the 180 range.
My spinnaker has a 22.75 luff and a 17.75 foot, and its pretty anemic! Plus I now have an almost mast head rig and its really too small now.
You need a spinnaker pole for a symmetrical sail and don't for the assymetrical (cruising, gennaker) type.

 

[StinkBug]

I've flown symmetrical spinnakers quite a bit on other peoples boats, but never on my own so I've never had to worry about sizes and such. Even at that size I'm sure this one would be a hell of a lot better than my little 100% jib. Hell my buddy and I hoisted the spinnaker from his little 505 and even that was a big improvement.

 

[Freedom77]

I suggest going oversize symmetrical tri radial on the chute. Your "I" dimension is actually closer to 23 ft due to the fact that the mast sits above the deck on the raised cabin. I x J x 180% = I 23 x J 10 x 180 = 414 sq ft. +/-. This is for the standard Mac fractional rig. I had Freedom mast head rigged, So I am carrying 525 sq. ft. Then you and the committee have to decide on the colors for the panels:cussing: Your chute will identify you from a long way off and you will strike fear in the hearts of mere mortals. Luckily there is no shortage of sailmakers in the SD area. Ask them about the dimensions on the sail you mentioned and see if it's a fit. Good Luck and keep us posted.

 

[MrBill_FLL]

asymmetrical:


http://s64.photobucket.com/user/ftldiver2/media/MACGREGOR/sail4.jpg.html?sort=3&o=182

also have the jib, genoa and main are but no symmetrical dimensions.

 

[StinkBug]

Thanks for posting that, I'd prefer a symmetrical sail though.

 

[THECUSCUS]

Here's a picture taken this weekend of my puny spinnaker (22.75 luff, 17.75 foot). Now granted my rig has been modified ( to use J24 headsails), but the thing was still too small before the mods. But it matches my motor, so I can't get rid of it.....lol

 

[StinkBug]

That does look a tad small. So what dimensions do you think would be optimal?

 

[THECUSCUS]

Here's the same sail with the factory rig setup, sailing closer to the wind. The luff looks about right here. How high up is your spinnaker block?

 

[StinkBug]

Is the spinnaker hoisted to the top of the forestay in that pic? Same spot as the jib?

I have a tang that's basically at the mast head for the spinnaker.

 

[THECUSCUS]

It goes to a block about a foot above the forestay tangs. I wouldn't go more than 18" above where your upper shrouds attach to the mast. Any higher and the mast is unsupported, and you could bend the mast sideways.