spinnaker dimensions

[Slinky Spring]

How do you know how big a spinnaker should be? I have a Jaguar 25 mastead rig. The mainsail luff is about 24 ft. The j measurement is 10ft 5. What size spinny should I be looking for? I have just bought one from an advert on this site but it is far too big. Look out for it on e bay soon!

 

[Abigail]

We have just ordered a cruising chute and found that all the suppliers, if you knew the vessel and the I & J could tell you their dimensions for a spinnaker. They do vary slightly but not signficantly.

So talk to your local friendly sailmaker and they can tell you! Also C&J Marine run a good used sail agency (we have an old spinny for sale through them as it's too big four our 40 footer) so both might help you with the one you have, and have something else you might be interested in.

No connection with them at all, but have found them helpful. HTH

 

[William_H]

How big should the spinnacker be is like asking how big a jib should be. Provided it fits in the dimensions of the boat then anything smaller will be just perfect in some wind ie too big sometimes and too small other times. We get quite consistant 20 knot afternoon winds which for most new comers is far too much for a normal ie class maximum sized spinnacker. People get put off spinnackers forever as the boat becomes totally uncontrollable. (Rounding up and on it's beam ends) Small is good.
I think a small spinnacker off a smaller boat can be bad if it is not tall enough. You don't want it too high when fully hoisted ie pole too high, and certainly don't try to fly it not fully hoisted. It wiill swing around madly. The spin need s to be about 10% less in length (height) than the forestay is long. (assuming the spin halyard comes out just above the forestay to mast attachment. The width can be perhaps half the length of the boat for a ghoster (limited by class rules) and a tiny spin can be barely as wide as the pole is long but full height. Small spins can also be quite narrow at the shoulders to reduce area and make them better for reaching.
I would strongly recommend you start with a tiny spinnacker and in light winds, they really are the devils invention but you can get a real buzz when the boat is trying to plane at way over its hull speed.
Now if the spin you have is too tall then perhaps sell if you can get a good price but a sailmaker can always cut it down to suit. If it is too wide it is easy (perhaps not pretty)to cut down the spin yourself. You fold the spin in half and run a sewing machine down a line from a point eg one metre in at the bottom up to the top tapering to the folded edge near the top. This makes a big pleat which can be cut on the scrap side of the sewing line. You can then do another paralel stitch line folding in the cut edges. SWMBO will be good at that. Use ordinary sewing machine and the thickest thread you can get from a haberdashery. (In other word you make the spin narrower by cutting out the middle. If you curve your sewing line out toward the folded scrap edge near the top you will get broader shoulders while if you go straight or curve in you get narrower shoulders. The trick is to sew and cut a little then hang it up horozontal at home to check the size and the camber and if you don't like it you can take more out.
I race a lot and with my fractional rig in a blow the jib is quite tiny so that in a run a spin can really improve performance (and scare the wits out of me) so give it a go regards will