For the Weekender.... how much of the keel gets rounded? To be specific, does the keel get rounded all the way to the back and then how far up the front stem? I'll look at some finished photos too to try to figure it out.
Really excited. Boat has been sitting in garage for ever! 5 years! I have recently done a lot of work and will be fiberglassing in a week or so! Very excited.
From a performance stand point, you don't want much rounding on the bottom edge at all, just enough to permit paint to stick well. The forward and trailing edges can receive considerable rounding, even "streamlining" but it will have marginal impact, on the abilities of such a low aspect appendage. So, a 1/2" to 3/4" round over on the leading and trailing edges and a light "easing" on the bottom edge, is all you need. An easing is just to "break" the edge or to soften it up a touch. Paint and varnish don't like to bend around crisp edges, they'll just crack and chip easily if they are. I ease an edge by gently swiping a piece of 100 grit over the edge a few times. This breaks the edge and leaves it very slightly rounded, which paint will adhere to fine.
I rounded the entry point completely, to just about 2 - 3 feet past the stem, then gradually reduced the rounding to a 3/4" radius. Works well.
To continue this thought a bit,
Paul: I plan on having a fairly hard break from the sides to the bottom of the keel and the same at the chines. Around 1/8" radius or so. This may be too small a radius, but I don't know. I have a powerboat that we decided wanted larger radius curves at the chines, but a sailboat is cutting through the water and might want really hard corners below the water to resist slippage.
Enlighten me O Sage?
Dale
Crisp edges are used on vessels that can routinely achieve speed/length ratios over 1.5. Weekender and Vacationer can't reach these S/L ratios, though a very lightly built one may, if briefly, as it surfs down the face of a wave.
A crisp edge permits the water to "release" on a boat in plane mode. This decreases parasitic drag which allows the boat to go faster. On a displacement mode craft, like many sailboats including Weekender and Vacationer, this crisp edge thingie isn't necessary nor welcome. With a S/L lower then 1.5 (Weekender and Vacationer will be below 1.4) you want the water to be as undisturbed as possible. This means soft edges and gentle radiuses on all underwater surfaces.
The only exception to this general guide is the bottom flat of the deadwood assembly. This is a place you want the water flow to "release" it's grip on the keel, so it can "bite" fresh flow, as she makes way. The crisp edge should begin just aft of the big curve on the forefoot and continue to the very stern.
A healthy radius can be used on the leading edge of the deadwood (the bulbous curve area in the forefoot) as this will "soften" up the keel's entry into the on coming flow.
The same logic applies to chines. Though they do help the boat bite to windward, it's a very small amount and only certain areas, of the immersed chine actually provide any real grip (around midship and aft). If the boat was able to get beyond S/L's of 1.48, then a crisp chine would be beneficial, especially from the back of the cabin and aft. On a race boat, this would be an area of concern, but on a these well burdened little cruisers, there's little measurable gain.
Technically, the crisp leading edge will make a lot of eddies on the leeward side of the keel. This piles up slower moving water near the forefoot, which then "bleeds" over to the windward side, which decreases efficiency. The idea is to get good "penetration" into the flow, keep it attached to the keel (so it can generate lift) and release it crisply at the trailing edge.
Practically, the Weekender/Vacationer keel is quite inefficient. This is a combination of it's unusual plan form (profile), lack of streamlining (blunt leading and trailing edges) and very low aspect ratio (depth). So, improvements, such as streamlined edges and healthy radiuses will be marginal. If these things, as well as other appendage upgrades are employed, much bigger improvements in windward ability and leeward skid (which is considerable on both Weekender and Vacationer) can be enjoyed.
Powerboats want crisp edges, because the S/L is quite high for most (I have a powerboat that has a S/L of 7.2, which equals 35 knots at WOT). You'll want the water to "release" from this edge, otherwise you'll be dragging this still attached water, along with you, decreasing speed potential.