Glen-L.com

I was born and raised in Annapolis and I'm currently living in Seattle. ( rather be in Annapolis) I've tried two times previous to get answers at this site. I'm really getting frustrated, so for the last time, here goes.. I'm curious to know what the benifit is in angling the daggerboard aft and is it necessary on a small skiff. Also, and more important, I would like to know the method for determining the distance from the mast to the daggerboard and once built would adding a small jib adversly affect the handling?????? Thank you.

Not sure of the answer to your question...hopefully one of the experienced sail people will chime in.

Which design are you referring to?

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Bill

I told my wife we needed a three-car garage for my projects...she told me to ask her for permission next time before I buy a house.
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I sincerely apologize if you have asked questions previously with no response. I have family in Annapolis and Seattle, two of my favorite cities to visit.

The questions above are more about the designing of boats than the building of boats. In fact most of us here on the forum are merely builders of boats from Glen-L plans and most of us are not educated enough in Naval Architecture to answer your questions with any certainty.

If you have a specific Glen-L boat you are referring to let us know what it is and someone with a more in depth knowledge of that particular design may be able to answer your questions. You could also try contacting our hosts to see if they could answer your question about a design if nobody here knows.

If I were to attempt a guess at the question of why the daggerboard would be angled I could think if two possibilities. 1. Angled daggerboards may produce less intersection drag much like a swept back aircraft wing. 2. A angled daggerboard may allow for a more shallow draft than the same area of daggerboard that extends straight down.

As for mast/daggerboard positioning. A brief internet search on a boat design forum turned up this response from Petros: "You want the centroid of the area of the centerboard to match the centroid of the area of the sail. That is how you place the mast relative to the centerboard. And than you fine tune it in the water by adjusting the forward or aft rake of the mast so you have minimal side pressure on the tiller when on a reach."

Hope that helps.

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Wow Chris that was good. I am always pleased with the answers that come out of this forum. I know angling the mast makes a big difference but didnt know why.

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John Amundsen
Monte Carlo
Winter Haven, FL

Maybe it will be done by G6 and maybe not.

To make it simpler for those who visualize the concept like me (and possibly more muddy for those who don't):

The goal of the placement of the daggerboard is to balance the helm. The center of lateral resistance (CLR) of the hull is primarily determined by the location of the daggerboard, centerboard, or keel, since the hull itself is designed to have as little resistance as possible. This means that as the boat is pushed sideways by the wind (or anything else), the CLR is the point around which it pivots because it's the point that least wants to move through the water sideways.

The Center of Effort (CE) of the sails is the mathematical point around which the sideways force of the wind is applied through the fuctional levers of the sails to the hull.

The reason why this is simple and important is that if these two points are very far apart fore and aft, then an excessive amount of helm will be required to counteract the effect of the lever (CE) pushing against the pivot (CLR), and lots of helm makes the rudder act as a brake. If the CE is aft of the CLR, then you get weather helm, meaning that the boat want to point up into the wind where it can't do anything except flog the sails into lifelessness. If the CE is forward of the CLR, then you get lee helm, meaning that the boat wants to constantly fall off from the wind, leading to unintentional gybes and all of the damage and danger that that entails.


There are a couple of reasons why this is not simple, though. First is that determining the actual CE and CLR is a tricky task, since one needs to take all of the various effects of wind and water into account. That's why it's best left to a certified marine architect who understands all of thew math. The other reason is that these are sailboats operating in changing conditions, so the CVE will move forward or aft depending upon popint of sail, sail selection, rake of mast, balance of ballast (you in a dinghy), etc.

So, you see that once the sail plan and hull are balanced, one needs to constantly adjust that balance by sail handling and adjusting the ballast (you in a dinghy) to move these points around for good balance.

If you're trying to do the plan yourself, remember that the traditional approach is to place the CE slightly aft of the CLR so that, under a nominal position, a very slight weather helm is induced, since that's safer than a lee helm.

I hope that's at least as clear as mud.

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I gather then that if he adds a jib he would need to locate the centerboard farther forward and possibly move or adjust the mast slightly aft?

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"Nothing screams poor craftsmanship like wrinkles in your duct tape."

Two years ago I was in Japan where I had intended to build a sailing skiff and chase the tuna around. Fuel prices over there are usually double what they are here hence the need for a little creativity. Call it sail-trolling if you like. I had shipped nearly everything required to build. (Insert very long story here) Shipped it all back and now I'm more determined than ever to accomplish my goal. I didn't mean to step on anyones toes at Glen L. I was just looking for a little help because the design I paid for doesn't totally suit my tuna fishing purpose and I will have to modify nearly every aspect of the design. While not a builder and certainly not a designer, like VU I'm a pilot and I'm up to the task. I'm familiar with CLR (generally at the beam) and CE (generally at the ctr. of the sails) but not the formular for determining the distance between them. Another "wonderment" is how this relationship changes every time another sail is added. Thanks to all who responded.

vupilot and bikermouse said it very well.

For instance if you have ever watched a windsurfer, they know the balance between the center of lateral resistance CLR and center of effort CE of the sailplan instinctively, because thats how they steer. When the sail is raked aft the boat turns into the wind because the CE is pushing the aft end of the boat off the wind which is turning the bow into the wind. The reverse is visa versa.

When you heel the CE typically moves aft which increases weather helm. This is a good thing because in a well designed boat the vessel will "round up" into the wind before capsizing.

Perhaps the board raked aft was to move the CLR aft to offset something done to the sailplan. You will sometimes see planing sailboats with raked boards to help keep the boat balanced when the bow comes up and out of the water on plane.

$ 0.02 Steve

Hey gang,, I finally got it through my thick Irish noggin. I was looking around the web for plans of other small sailboats and discovered that evidently the CLR and CE are supposed to be directly over/under each other. Why I thought differently is beyond me (maybe it's a genetic defect) Thanks again.

As they told the old indian you must endeavor to persevere. I purchased the book Thirty Wooden Boats from the Wooden Boat Store. It's touted as a study guide but the print is so small as to make it useless for that purpose there-by making it a rip-off in my opinion. However, I did find a difinitive explaination regarding the relationship between the CLR and CE. "The relationship between the CE and CLR - that is, the horizontal distance between them expressed as a percentage of the waterline length - is termed the "lead." (This is what I've been looking for all along.) "It has been found by trail and error that, as a general rule, the CE should lie forward of the CLR by 10-20% of the waterline length to produce a well-ballanced vessel". Good Luck and good sailing.

I'll be curious to see what you come up with in your own design. I know this is (obviously) a site for Glen-L boats, but surely you could get away with a photo or two and a review once she's in the water.

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