|Topic Review (Newest First)|
|01-19-2010 07:33 AM|
I want to touch on a couple pounts raised in the posts above. Olson34's post is somewhat outdated regarding boats that are balanced fore and aft and his comment about IOR boats going to weather.
In the late 1970's and into the 1980's designers began moving towards boats with finer entries and more powerful sterns. At first these boats tended to develop a tendancy to jack the stern out of the water and force the bow down causing the boat to develop increased weather helm, which forced the helmsman to use more helm which in turn meant greater drag and so poorer windward performance in a breeze. But by the late 1980's and into the 1990's designers learned to model the hull shape so that there was not a large shift in fore and aft trim with heel. They also determined that a fine bow helped with tracking and leeway, and that more powerful stern sections permitted greater stability without the inherent motion comfort and limit of positive stability liabilities of an over dependance on form stability.
When it came to rising up on one of their fat stern quarters and try to round up, there was nothing worse than the later IOR era boats. But also while it is true that the IOR boats generally make their best VMG pointing slightly closer to the wind than more modern designs, they tend to make a lot more leeway and do not have the upwind speed, and so the are not especially good up wind compared to a more modern design. And as a broad generality IOR boats do not handle a chop as well as modern designs.
Next worse and not all that close would be boats with moderate beam and a clean run aft in the hull form like all the descendants of the Cal 40, the Cascades, the Niagara's, and others. These boats have a lot of drag generated by their large amounts of wetted surface and their inefficient keels and rudders.
It is also a mistake to say, narrow fins with bulbs tend to generate more leeway than wider fin sections. At very slow speeds in moderate winds, as would occur immediately after a tack, a deep, narrow fin will make slightly more leeway than a larger surface are, lower aspect ratio fin, but the deep aspect ratio fin has way less drag and so accellerates more quickly, and almost immediately generates enormous lift as compared to older style keels. That said, these more efficient keels take a little more skill to sail well, since they do not tolerate pinching as much as older keel types. But while it takes a little more skill to sail with these modern high aspect ratio keels, they make way less leeway than earlier lower aspect ratio keels.
The other thing about a bulb is that it acts as an end plate, tricking the keel into acting like a higher aspect ratio than it is, delaying stalling and reducing drag due to the tip vortex albeit a partial trade off since a bulb adds small amounts of drag due to more wetted surface and frontal area.
I also disagee that most racing hulls are optimized for downwind sailing. These days there are still designs optimized for particular venues, but the majority of modern race boats are optimized for all around performance, meaning the have their performance optimized for all points of sail, but especially upwind and deep reaching. The fine bow, eliptical hull sections and moderately full stern sections that were popularized on IMS typeforms and carried over into the newer IRC boats, go upwind with a more comfortable motion, minimizing disturbance of the flows over thier sails, keel and rudder, pointing higher, making less leeway, and exceeding hull speed and with boatspeeds that sometimes exceed true wind speeds producing tremendous VMG's with smaller crews than earlier designs. And while ULDB's (ultra light displacement boats- typically L/D under 115) are still popular for Pacific downwind racing, but for the rest of the world, ULDB's are an outdated design concept that neither makes sense for cruising or racing since they are one trick ponies and modern racing requires boats that go upwind and can reach well.
Both the Compact 16 and the Westerly 25 are classic cases of boats with a lot of wetted surface and inefficient sails and underwater foils. That said, I have always liked the Compact 16 for messing about in shoal draft waters.
|01-19-2010 04:20 AM|
Narrow fins with bulbs tend to generate more leeway than wider fin sections; although they carry more ballast deeper which helps them stand up and carry more sail area. The trade off is efficient in moderate winds when the boat can use the ballast weight as righting moment; but in heavy air this type of keel does not track as well as a wider fin section. (canting keels are outside the scope of this discussion)
A smaller headsail that can be sheeted closer to the centerline of the boat; sheets run inside the shrouds is better for pointing ability than a large headsail; but at the cost of reduced area. It would depend on the boat and the windspeeds that you would expect to normally sail or race in to determine if a close sheeted smaller headsail is better than a larger headsail and lower pointing angle.
If you are looking for a boat that points high and sails fast to windward you might research the PHRF ratings for upwind performance; there might be some variation in the numbers from the 'base' rating. A lower PHRF equates to a faster hull.
Nowadays most racing hulls are optimized for downwind sailing (Spinnaker) with a hull form that will plane while sailing downwind (ULDB); while still providing adequate upwind performance (with plenty of railmeat). That's not to say the VMG upwind is poor; it just is not optimal.
When a boat sails upwind at it's hull speed the apparent wind angle does move forward. It's how well the sails can produce lift (and how easily the hull is driven) at that shallower wind angle that determines how well the boat points. Heavier wider beam boats with full keels will not point as well as a lighter, narrow beam hull with a fin keel and close sheeted low stretch sails. But; the heavier built boat may be more comfortable in rough conditions and more able to withstand heavy conditions without any failure of the hull.
|01-19-2010 01:14 AM|
|puddinlegs||To the OP, you might want to pick up a copy of Bob Perry's recent book... say what you want, but it's a pretty darn good current overview of sailboat design.|
|01-18-2010 07:40 PM|
I would second most of Jeff's excellent post.
Personally, If I had to pick one feature in boat design that can enhance speed and ease of trim to weather, I would suggest a boat with more symmetrical waterlines, fore 'n' aft.
I have always found that the one saving grace of the IOR hulls (the best designed ones, anyway) was driving them to weather. Next best and very close would be boats with moderate beam and a clean run aft in the hull form like all the descendants of the Cal 40, the Cascades, the Niagara's, and others.
Worst are the fat-and-flat stern boats that bury the bow in a puff and then rise up on one of their fat stern quarters and try to round up.
That design allows room for king sized beds aft, though, and are quite popular for "gracious dockside living."
Happy boat shopping, and fear not -- there's a perfect boat out there for you, somewhere.
|01-18-2010 07:15 PM|
Thank you all for your input. Thank you Jeff for simplifying the topic for me. I saw reviews of two boats, a Compac 16, and Westerly 26 twin keel, and read that they both perform poorly going into the wind. I looking to buy my first boat, and wondered if their was a particular hull design to look for.
I am so new that I had to google iron genny. Thanks again.
|01-18-2010 03:37 PM|
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
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.
|01-18-2010 12:37 PM|
to all the items listed
i would add new sails or sails in very good condition.
narrow entry is very important.
|01-18-2010 09:13 AM|
|FishSticks||I've heard no mention yet of the schooner rig, but mine goes like blazes and is downright comfortable when I abide by the rule stated below. I'm 74-1/2.|
|01-18-2010 08:17 AM|
|trantor12020||I think the best sail for going head into wind would be the iron genny. no tacking requires.|
|01-17-2010 03:11 PM|
In addition to sheeting angles for the headsail, the ability to maintain or adjust tension on the headstay is also important, typically done with some sort of adjuster on the backstay -- i.e. tightening the backstay will in turn tighten the headstay, reducing wind-induced sag and maintaining sail shape and pointing ability.
Generating hydrodynamic lift from the keel is also really really important. Deeper fin keels with appropriate foil shape are best. If the boat stalls, you want to fall off to get flow going over the keel to start generating that lift.
Obviously righting moment will be important, too -- thus the heavy bulbs on the ends of long keels, and the row of heavy people hanging by their butt cheeks from the weather rail. Generally, the more upright the sails are, the more effective they are at moving the boat forward rather than sideways.
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