Lifting Hull Form To Weather
Kevin,Yes, I have examined the two articles that you sent. As you suggested... they didn't cover the theory that I was suggesting exactly... but they did cover some of the thought about the hull form at various degrees of heel. And that some boats of course are designed in a way to allow heeling without the hull form becoming a lifting foil to leeward.I also really enjoyed an IOM (International One Meter) site in UK. As an RC aircraft modeler, I have a great respect for the insights that modelers often enjoy. Their latitude to play often yields a great variety of results, many of them quite interesting. In some short dialog with the owner of the web site, he lamented a problem on one of the designs he owns that he labeled snap weather helm. A gust of wind simply causing a round up before adjustment control can be made.One of the points of that discussion is that it occurs only when the boat is moving well and a puff suddenly heels it. If boat speed is slower, the effect is much less or non existent though the induced heel angle may be as great. Again, this seems to support my thinking that asymmetrical lift is the primary force at work.He also shared that one of the new designs uses a hull shape that actually provides lift to weather and that this hull experiences no problems with weather helm even though it has a broad section aft. It makes great sense. Instead of a wide mid section... a general widening toward the wide stern yields a heeled and immersed leeward hull that doesn't present as great of a curved foil into the water. The bottom has liberal rocker, so that when heeled, the bottom now becoming the windward water line foil, has a good amount of curvature.Such a shape then would see the asymmetrical foil caused by heeling to have the greater curvature windward which would generate lift to weather and the boat would enjoy heeling and not suffer the effects of weather helm caused by a lifting foil to leeward. Of course, it might suffer lee helm if the center of the windward lift was positioned too far aft. The great advantage however is that a little lee helm generation would be a good thing to counter the inherent weather helm during heeling caused by the couple of the CE extended leeward of the center line and the drag of the hull appendages now windward. That couple is a given as well as the desirability of a slight bit of weather helm. What is now possible is the calculated injection of enough lee helm to tweak. This would be done by choosing the apex position of the rocker foil. Slightly aft of the CLR would induce a slight bit of lee helm when heeling.Fascinating stuff. I'm not sure what the trade offs for such a hull would be. We know that more rocker contributes to hobby horsing in a seaway but with less pounding. It probably adds a little whetted surface and drag. It however may reduce rudder requirements for two reasons. 1. The rudder wouldn't need to be as large to counteract weather helm and 2. The rocker would enhance turning abilities. So, the trade off to a reduced rudder for more rocker may be a wash as far as drag is concerned.I think the day may be coming when a boat will be evaluated as much for its heeled footprint as its SD numbers. What would be interesting is a computer analysis of the lifting forces of a hulls footprint at varying degrees of heel. Probably most monohulls would show leeward lift... but that may change with new designs.Here is url for the UK site...enjoyArlyn