i'm talking about purely running down wind or close enough too that course. the sail wants to fly when I take it up on deck to look at it, so Idon't think Ill have trouble setting the thing and seem to have seen yachts pictured with nothing but a bloody big spinnaker set ..no pole no nothi'n so whats the go?
If you look at the photos of yachts apparently "running off" with the spinnakers a'blow with no pole, you will generally find two things. That said spinnakers are, in fact, assymetric; and, that the mainsails are not squared away (with respect to the yacht or the course steared) but are trimmed in. If so, the yachts are not running dead down wind. In fact, I'd wager that for the most part you are seeing photo's of yachts sailing no lower than about 160 to 165.
Poles are used with symetric spinnakers for a couple of reasons. To get the tack and luff of the sail into clear air (i.e. away from the turbulance caused by mast
et al and the blanketing effect of the main); to give the luff of the sail an angle of attack on the apparent wind (Hauled to the side of the yacht, the sail is seeing a "reaching wind"); and, to spread the foot of the sail (i.e. to separate the tack and the clue--in the same manner a whisker pole does with at standard jib
when running off), which shapes the sail to generate lift
. It is when reaching (i.e. at roughly 55º to 120º apparent) that one does not necessarily need a pole with a symetrical. The further off, however the more the pole becomes necessary. That holds even with assymetrical spinnakers for the most part.
It is interesting to note that sailing "dead down wind" most often does not give one the best VMG. Heading up by 15º or so from DDW will increase ones distance sailed by about 7%; but, can increase one's VMG by as much as 25% for a reasonable advantage. Moreover, most monohull
yachts roll a good deal when sailed DDW as the stabilizing influence of the wind on the rig is foresaken. Prolonged rolling is exhausting at best and dangerous at worst.
In the final analysis, you will really have to just take the yacht out and give it a go to understand the foregoing. Doing so in reasonably light air can't hurt and will help. If the sail gets out of control just let the sheet run and the sail stream out in front of the yacht. You can recover by pulling it down by gathering in the foot from the tack while easing the halyard
. In no case "blow the halyard" or you'll end up "shrimping"--i.e. running over the sail and dragging it through the water
(which has been the ruin of many sails) nor let both the sheet and the tack line get away from you, in which case you'll really learn why the sail is often referred to as a kite! Frankly, none of this is rocket science. Just give it a go,