If I understand the Brit's summary of the Finn's analysis, there is a net force pushing down on the bows from a spinnaker, but it is substantially less than if the same sail area was on a high aspect rig with the fore to aft CofE at the same distance from one end of the boat? Experience seems to contradict the interepretation of the numbers. Even rereading the article seems to say the same thing, that bows are flying and the boat feels steadier, but the numbers don't lie, so there is more pressure on the bows. In an effort to make sense of both I wonder if the explanation is that while some additional pressure is put on the bows the additional foward speed.... (does something causing the leeward bow to actually ride or float higher?) As I think about this more, I'm still having trouble with a net down force. If you observe the end of the spin pole properly preloaded or otherwise, it bends up as the loads increase. Although part of that is how it is supported and how the loads are applied, if there is a net down force it has to be applied at one of the 3 corners and its not happening at the clew or the tack. (loosen them under some load and see which way they go) Looking forward to some logical, factual input.

Wouter, I'm unable to find link to Bethwaite's article on your site. Is it there and I'm just not finding it?

Also, Wouter, my recent experience and Randy Smyth's article in White's book on spinnaker's indicates that although you can sail deeper with a spin, and you feel like you are going fast and you have flow over all sails, you are sailing too low. Under a spin you need to be sailing higher than what feels right, about the same as non spin boats, but going 'way' faster.

Todd, just because you can pitch pole with the spin up doesn't mean there isn't more force lifting the bows with a spin than without. There is a potential for considerable pitching moment if the boat is not trimmed properly

The direct forces at the clew, head, and tack of the chute are pulling forward, forward/leeward, forward/up/leeward (respectively) from the boat, thus not pushing the bows down. However, the force on the rig as a whole is acting 15, 20, maybe 25ft up the mast. This induces quite a moment in the system which is reacted by a couple that pushes the bows down and pulls the sterns up. The boat is in "pitching equilibrium" (for lack of a better description) when the force of the chute pulling up on the tack equals the force pushing the bows down. This is also helped along by the skipper and crew moving aft in the boat. The force of the skip and crew weight counteracts the upward force of the sterns.

Ultimately there must be a net down force for the system, otherwise the FAA might get involved.

You both gave some great explantions.

I KNOW that there is also upward force applied to the bows, most of the time actually. And yes, of course, my spin pole wants and does bend upward with the sail load of the chute.

I was just interjecting because earlier, the posts acted as if ALL the force was ONLY lifting the bows!

I too have some mast rake which is more than I ran without running the chute. Of course this helps also.

As Shannon stated, all the load, whichever direction, pulling on the mast somewhere above the base, will essentially also 'lever' the bows down some at times.

This has been a great discussion.

Todd Bouton
N6.0na +
#111

I would refer you to Frank Bethwaite's book page 401 in which he describes how 18 ft. skiff sailors use the lift from the spinnaker to control the height of the bow when sailing through waves. Just thought I would throw that in. I don't have a spin.