The Moretti stock has been replenished, so the engineering committee can get to work.
Keel Envy
- Thread starter Sailavie1
- Start date
I watched that cool video again, and was really struck by how little draft the H25 has. I can understand the desire to improve that, whatever the means! It really must effect performance.
A few years back I co-owed a shoal draft S2 with a similar keel. I learned that year why owners of like boats said that S2 stood for 'Slowly Sideways'.
A few years back I co-owed a shoal draft S2 with a similar keel. I learned that year why owners of like boats said that S2 stood for 'Slowly Sideways'.
That is precisely the appeal to projects like this. Thay spark little fires in all sorts of mental tinder.
- Will (Dragonfly)
Love to see boaters trying to improve performance? I think overall we have lost too much of this. Way to go!!! History: The far forward rudder was used by Chris Smith (Chris-Craft) on some of his race boats with huge positive results.
There's a reason it's called "theoretical hull speed" it's simply a tool... more applicable to matching the most efficient powered propulsion to full displacement hull limitations. Adding a foil to a hull will alter this limitation. So the "theory" becomes a much less important consideration.
Joe, I appreciate what you are saying. I agree that hull speed is a tool but, as it is used to express the concept of the the point when a boat's wake begins to interfere with further acceleration of a hull moving through the water, not limit it, just become an additional force to over-come, it isn't theoretical. It is founded in both observable physical phenomena and Bernoulli's equation for fluid dynamics.
As it applies to modern high performance sailing? I don't know what math naval architects are doing to be sure their designs perform as expected.
I do know that hull speed is often referenced on sailing sites, like this one, when choosing or describing the performance of their auxillery, just as you said. But for most of us, we calculate it or look it up on a chart and use that to determine if we are getting the performance out of our rigs that we think we should be getting.
Someone, earlier in the thread asked what Sailavie's bow - board would do to hull speed. I answered that it shouldn't effect it. Someone else responded that the bow - board most certainly would. However, I think we were talking about different things. When someone talks to me about hull speed, I think of that attribute given to any vessel moving through the water at displacement speeds. I understand that is not a limit to the speed a boat can go, it is just a value that is used in some boating applications. What the person meant when they asked their original question was probably more like, "what do you think it will do to the boat speed?" Of course that is a great question that is interesting to speculate on but I don't think even today's mathematical models can answer that question as well as experimentation.
I don't mean to be rude by stating this but, I can't believe that the concept of hull speed has no place in modern sailing. It still seems like an important hurtle to consider when designing a boat, even a planing racer. The wake that has to be over-come and is still generated until planing is achieved. How fast is it? How much wind (sail) is needed to over-come it and how quickly can it be passed to get an advantage over another boat that is trying to do the same thing? Also, at what heel angles will the boat be at when it reaches that plane? You can't determine that until you know what hull speed is because until you exceed that speed, you won't plane.
If I were to design a racing boat, I would disregard most of that, however, because I would simply build the lightest boat with the flattest bottom that had the straightest lines in the rocker, hard chines, waist and bow that I could. She'd be wide, around 2 to 1, with a deep narrow CB weighted at the bottom but not too much. Her freeboard would be canted inward at the stern (maybe a fantail) , her V-bow would be full and plumb. She'd look as much like a log cut in half with the flat face being the bottom as I could get away with and still be able to work the deck and get the bow shape. I'd likely put a narrow Marconi main with full battens for plenty of roach. Step the mast just aft of center and fly big head sails. In fact, I would toy with the idea of putting a delta rig on her instead. The only calculations I'd be concerned about would be lateral resistance to driving force so I could balance the helm. I'd consider a CB that moved fore and aft but, I'd rather save the weight and use the swing of the CB to fine tune balance instead.
That's about it. No calculations because I would be going for what I thought of as the farthest I could go in the fast direction. Then I'd see how well I did. If I were designing for someone else, I'd do the math.
If course, that's not what I want out of a sailboat. I want a boat that goes anywhere there's water to get there by, is as self-sustaining and independent of civilization as possible, and is comfortable to live aboard. Sailing well is just a bonus.
Good thread rant. I feel purged. I hope someone else chimes in with a critique of my perfect racer or adds their ideas, while we wait to see how Sailavie1's experiments are going.
- Will (Dragonfly)
Andres boat points better. We have both fundamentally modified the fore-aft balance with the appendages that have been crafted and the additional fabrics being flown. The engineering department has never entertained boat speed measurements but maybe with the imminent arrival of coated black laminates there may have to be some.
Nah.
Nah.
Sailavie1,
As a professional wood worker, I am interested in hearing a little about your shaping and fairing techniques. What tools did you use to shape the convex surface and how did you match up the concave surface to the bow shape?
Thanks for asking Will. Wood working is a hobby of mine and building things is as much fun as enjoying the final product afterwards.
To build the centreboard/bow joint, I first taped multiple layers of masking tape on the bow and marked 4 evenly spaced horizontal reference lines. The layers of tape made up the thickness of the fiberglass and neoprene which were to be added later to the plywood joint. The four horizontal reference lines were used to trace the bow profiles along the joint area. A Profile Copy Gauge was used to trace along each unique bow contour and make copies out of wood.
The four wood copies were then used to measure the amount of material needing removal along each half of the centerboard joint. Once the correct amount of material was removed from each reference line (by hand chisel), the segments in-between were sanded down using a disk sander and a Makita 9031 Belt Sander. This process was repeated on the other matching side prior to lamination with thickened epoxy.
I selected the NACA 0014 foil profile only because it looked about right for the job. I simply downloaded the profile and made various sized paper copies suitable for the width and depth of the final blade. I used a similar process to the joint work to get the final foil profile by removing material at each reference line then sanding away in-between with the belt sander. A router, resting on the foil shaped wooden guides, was used to remove the majority of the reference area as shown above.
Hope this sheds some light as to how it was shaped. The fit turned out better than I expected with near zero lateral movement once the unit is tightened in place. Key was taping the layers and taking my time so as not to remove too much material.
For me, there is almost no feeling like having a join like that, work out. It is like magic happened because it is so hard to conceive that my work could be that perfect. You must be flying pretty high every time you look at it. I'd just spend all day gazing at and touching it if I had done it. Great work.
-Will (Dragonfly)
I modified the keels on my PDQ 32/34 a few years ago to solve a helm problem and to address a tragically blunt trailing edge. The result was very effective with no downside. The rig had also been enlarged just a little, so additional lateral plane was welcome.
In this case I would have played with adding considerable rake to the rig first, a full roach sail second, and then resculpting the keel a bit to add a little area and move the COE forward. Still a bit of work, but with less chance of unintended consequence and a slicker look.
In this case I would have played with adding considerable rake to the rig first, a full roach sail second, and then resculpting the keel a bit to add a little area and move the COE forward. Still a bit of work, but with less chance of unintended consequence and a slicker look.