SailNet Community - View Single Post - Good boat designs for sails windward
View Single Post
  #9  
Old 01-18-2010
Jeff_H's Avatar
Jeff_H Jeff_H is offline
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,564
Thanks: 5
Thanked 92 Times in 69 Posts
Rep Power: 10
Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about
I am not precisely sure what the original poster is asking. Normally, when I think of a boat that sails well to windward I think of that as the boat offers the best VMG (velocity made good) and not necessarily the one that points closest to the wind. There are three main factors which control how well a boat goes to windward, the ability of the sails to maintain flow at a particular angle to the wind, speed through the water, and the ability of the boat to resist leeway.

Upwind speed is a matter of minimizing drag, since drive is limited. Anything that adds drag will reduce VMG, so efficient sails and efficient underwater foils (keel and rudders) are important windward performance. I think that the posters above have hit the high points, but there are a number of items that I respectfully suggest could be a little misleading.

* Sloop rig with high-aspect, powerhead mainsail and/or full battens.
I agree with the sloop rig as being the most weatherly of the modern rigs. As noted tongue in cheek, schooners for all of their virtues do not point well because of their high drag and downdraft issues. Powerhead mainsails while good for reaching, are not so hot upwind where they offer more drag for the lift. It is also harder to control twist in the leech of a powerhead mainsail which also hurts upwind performance.

* Large overlapping headsail, either fractional or masthead. A good high points, but I disagree with several points that have been mentioned as follows:

*
Genoa supplies much of your drive to windward. Ability to sheet headsail in tightly, or at least control the slot.

Actually, large overlapping headsails are far less efficient upwind than non-overlapping sails because of greater drag per drive of the low aspect genoa and the interference between the trailing edge of the genoa and the mainsail. Overlapping genoas also tend to have wider sheeting angles than non-overlapping headsails. Overlapping headsails are a left over design feature from antiquated racing rules.

* Long waterline, narrow beam. Some people subscribe to a v-shaped keel for added lateral resistance, others prefer some kind of hard chine.

I agree with a long waterline as that tends to stabilize motion and reduce drag due to wave collisions. Fine bows tend to track well and offer some lateral resistance as well. But, Vee shaped hull sections tend to have more wetted surface and have more induced drag and so are not good for windward performance. There was a time when much of the resistance to leeway derived from the hull. For the past quarter century there has been a general consensus that the best windward performance is obtained when the hull is designed to minimize drag and leeway is addressed with the highly efficient foils.



Narrow beam is helpful up to a point, but reasonably larger amounts of stability are more critical to upwind ability and so a boat with a moderate beam rather than a narrow beam will often offer a lot better windward performance.

* High ballast ratios to keep the boat somewhat upright and reduce leeway.
I agree that keeping the boat upright is important for upwind performance, but again, its all about how its done. High stability allows a boat to stand up to a taller rig and therefore get by with higher aspect ratio sails resulting in a higher efficiency sail plan. Simply adding ballast is not necessarily a cure-all since greater ballast means greater displacement and greater displacement results in greater drag.



The best windward performance is achieved by keeping when a conscientious effort is made to minimize the weight of the boat and her gear and concentrate the weight as low as possible which is why bulb keels have become the norm. Bulb keels allow a lower ballast ratio to offer a lot more stability. Again its all in the execution. Big, poorly modeled bulbs can offer a whole lot of drag as well.

* Fin keel with NACA foil profile: the deeper and narrower the better. Deep narrow fins w/ bulbs is the trend.

* Spade rudder, likewise a lifting foil. Possibly dual rudders to keep the foil vertical when heeled.
Dual canted rudders that work at larger heel angles are great for reaching, but are not so great upwind where sailing flat is critical and the added drag of a second rudder can really hurt rather than help performance.



Jeff
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies

Last edited by Jeff_H; 01-18-2010 at 03:42 PM.
Reply With Quote Share with Facebook