Centerboards

[Gordy Hill]

With my boat I sailed in very shallow water with bottoms of mud, weeds, sand, oyster shells, or old chevy engine blocks.

I like the uphaul - downhaul system Graham designed, but I changed it a bit.

In my first Great Race , my friend was continually 'searching' for the bottom using the horn of the centerboard. We would pull it up in shallow water and then not know when it was deep enough to put it down a bit. In light wind, or during a lull the board would float in a position leaving 4-6 inches exposed out the bottom.

I used a hole cutter to cut two 3" holes on the board and, after taping off one side I filled them with epoxy and bird shot. This left the board floating about a foot lower. In this position it was still at quite an angle and basically 'weightless'. When it touched the bottom it pretty much took care of itself and returned to it's position when the water got deeper.

For me, the uphaul-downhaul with the addition of weight worked quite well.

I also changed the shape of the leading edge of the centerboard.

If there's only about 6" under your hull only a small triangle of board will be exposed. If you let the board out a foot and then cut off 6" on a line parallel to the bottom, what's left is a board with much more showing when there's only 6" of water. I didn't actually use an exact number of inches, but that was my thinking and I ended up with a board with a sweeping curve to the leading edge. It helped measurably in very shallow water and I really don't think I gave away anything in deeper water.

[Travis Votaw]

An interesting treatment for sure.  On my Princess 22, Pilgrim, the long shallow keel pretty well allows windward performance with the board up.  The problem , though, is the kick up rudder.  While the kick up and downhaul features work very well, I've noticed that pressure on the blade when immersed about a foot is very strong.  And if you are sailing in deeper water and don't lower the rudder all the way, it will let you know about it real quick ;D

I realise that the old fashioned shallow draft balanced rudders designed for sharpies would not be nearly as efficient as the one designed by Graham. but it might be fun to try one out just to see how it works.

Bottom line, I suppose it depends on how much REALLY shallow water I would sail in.  Most of the Texas bays are very shallow around the edges

Question for Graham:  How hard would it be to design a shallow, balanced rudder blade that would have about the same draft as the keel to use in the existing rudder head?

[dstgean]

You could try one of the sharpie rudder deisgns that is semi-ballanced and add an endplate for a bit more bite.  Try looking at Chapelle's New Haven sharpie or Parker's redrawing of the same craft.  Looking foreward to hanging out with you again at the T200!

Dan

[Gordy Hill]

Travis,

I also added one 3" circle of weight to the rudder blade. I considered adding more it worked so well. It just made the blade want to float a bit lower and tend itself when in shallow water. It always seemed that when the blade kicked up because of the botttom I was always pretty busy and not really able to adjust it right away.

[Howard]

Comments on this thread, along with Tom and Graham's recent experience with the CB being damaged in shallow water bring to mind this sketch I made of CB designs:

The "historic" CB design is the low profile version, common to shallow water boats of 100 years ago. In reading up on these boats, you find comments such as, "like it or not, a centerboard in shallow water is going to act as a depth finder", meaning the board is going to be in constant contact with the bottom. Going further, you find they even used them as parking brakes....nosing the bow up on a beach, then lowering the board to dig into the bottom to "park the boat".  When you look at the leverage forces under those conditions, you marvel that they could ever build anything that strong. Certainly, the low profile board in a hell for stout case would be required. They must have worked, as they got around with them. Simple and very strong.

The high profile board is designed for performance....as long as the water is deep enough to allow it. Same with the rudders. I don't remember seeing any kick up rudders of the modern style in Chapelle. Perhaps they tried them and they didn't work, but more likely, they didn't think of them. Once you get it in our head there is only one way to do things, people are slow to change. That and most of them had high sterns and a shallow keel that allowed them to use a low aspect, barn door rudder. From what I've read, they didn't work all that hot......requiring a lot of room to turn, and required some skill to use. Turn them too fast and they went from a steering device to a brake of pure drag. But they were simple. Protected by a skeg and no moving parts.

So it looks to me like both designs have something going for them. One is simple and very strong......the other works better. Perhaps a reasonable solution is a hell for stout board of the modern, high profile design in a hell for stout case? Lowered only halfway looks like a reasonable solution to the shallow water problem. Halfway down, it looks the same to me. If there is lee helm, balance it with a reefed or double reefed main.

A possible solution to the rudder problem is to lower the pivot point of the rudder, such that when in the "up" position, a lot of rudder head rotates down and forward to balance the rudder. Hard to do with a transom mounted rudder, as there isn't enough clearance to let it down.

[Designer]

Howard, it is always good to explore all of the options.

If I did not have a lee helm issue when reefed all of the way down in heavy air with the board half down I would just repair the board and leave it as designed because I liked the way it worked. 

That board has really been abused in three Everglades Challenges and a Texas 200 as well as local racing and cruising and held up well, there is no damage to the trunk. The board could not have over rotated had it not been all of the way down and the wind blowing us backwards with the tip stuck in the bottom. My redesign is the only way I can get the board further forward without messing up the foot well area in the cabin and the least amount of work modifying the trunk. I plan to use the same board.

Why does the boat have lee helm? I underestimated the effect that the windage forward would have in strong winds when the boat is over pressed and the sails are feathered and lacking power. I did attempt to to compensate for lee helm by taking much more area proportionately out of the main than the mizzen. I could cut down the mainsail but I would have to take out more sail area than I want because it is just right in normal winds. Another option would be to put a third reef in the main which I might do after I mull it over for a while.

[Howard]

Graham's comments remind me of why some of us shouldn't be armchair boat designers. We know just about enough to be dangerous. To get these right requires the coordination of a lot of moving parts......lot's more to it than we realize. 

Fun to think about, but best to leave this to somebody who knows what he is doing!

[paul_stewart]

Regarding a third reef in the main:

   Graham, I'm curious what you think of putting away the main sail and hoisting a small 'storm sail' on the main mast.  Not sure 'storm sail' is appropriate name for it,  but it would be the same size as a 3-reefed main and would probably have better shape.   Being small, it wouldn't need much storage space and might even be affordable.  The full-size main could rest in the cabin.

If we're going to heave to and adjust for a few hours of beating into high wind (e.g., Bay River to Harker's Island),   that switching of sails seems reasonable.

--Paul (not somebody who knows what he is doing)

[Peter HK]

Not sure 'storm sail' is appropriate name for it,  but it would be the same size as a 3-reefed main and would probably have better shape.

Trysail

Cheers

Peter HK

[Designer]

Paul,

The last thing that I want do do is strip a sail off off the mast and stow it away and bend on another one. Take a look at the reefed photo, the set looks pretty good and I expect that a third reef would also look pretty good.

I did not observe any cloth distortion under load when double reefed, in fact for the same wind and pounds per square feet, there will be less square feet and hence less load on the sail.

We are not talking big boat offshore sailing.