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Core Sound 17 hull #357


Dnjost

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If the foil section is continuous the length of the board blank, you can make two foil shaped templates, which compensate for the height of a router or my preferred tool a laminate trimmer, with a flat bottom router bit. You set the bit depth and plow out along the chord's length (front to back), then move the templates down the length of the blade as you cut.

 

If the sectional shapes changes, you can use the same technique, though there will be transition zones, where say a 009 section transitions to a 0010 (for example). I use the fatter section to the transition line, then belt sand the difference after plowing with the router.

 

The last 1/4 of the blade should taper down a bit, which can be an eyeball thing or you could develop templates for the router too. Leave an 1/8" to a 1/4" wide flat (squared off), on the trailing edge. It's easier to maintain this edge and will not hurt performance.

 

Hand planes will do a good job, but asymmetric shapes are a likely outcome. Templates can help in this regard. There are a number of ways to do this, but I've found the best make repeatability easy. It's nice to be able to do one side and get the exact same results on the other. The template or guide for the router or laminate trimmer is basically a larger version of the foil section, allowing for the thickness of the template/guide. Lightly tack the template/guides to the blank and plow out between them. When done , move down the blade and plow out some more. I've seen some that make a sliding shoe type of thing, but I've always suspected it would flex in the middle and create hollow sections. I like a fairly narrow spacing for the template/guides so the base of the router or trimmer doesn't apply much down force. Yeah, I have to move the guides, but at least it's accurate.

 

post-304-0-97596400-1366120901_thumb.jpg

 

This quick sketch should give you an idea. The gray area is the template/guide for the router/trimmer.

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OCD? Perhaps common enthusiasm? Some are only interested in the destination. Others enjoy the journey too.

 

I once built a 6 foot rudder using the router slide technique. It was a vain attempt at duplicating a CNC type device. (CNC being what the high end custom foil builders use). It didn't work well for me. I was left with long divots that never faired out well.

 

(edited......PAR's post appeared while I was typing mine. I got the hollowed out sections......divots........he was referring to. I had never considered the fore and aft version).

 

I think you will find the patterns to be a better solution than my up and down router slide technique. Since the board tapers, you will need more than one pattern. Key to making the pattern is to go beyond the half shape of the foil. You need the full thickness of the board marked, such that the bottom edge of your template will rest on the same flat surface the thickest part that board blank rests on. You shape until the square bottom edge of the template touches down and no more. Slide that up and down and you will find the high spots.......hopefully no low spots.

 

I like the way Graham suggests doing these and that is to mark out leading and trailing edges and margin of the thickest sections, and connect those with lines, then hog off everything outside the lines and with only 4 cuts, pretty much have the board shape defined. You can then go at it with your plane and sanders, guided by the templates, to finish the foil shape with a pretty good level of accuracy. The complicating factor being the tapered foils.

 

As for your leading edge, technically, the shape would be a 90 degree quadrant of a circle, the radius of which is a function of the foil shape and chord length. For a 9% foil, that is .89% (.0089) of the chord length. For a 10% foil, it is 1.15% and for a 12% foil, it's 1.58%. Too much fun? To form the shape, you could try the rope trick, or at this scale, perhaps glue a piece of brass or stainless rod of appropriate diameter to the leading edge? Since you have a router, you could use a box core bit and rout out a groove to leave the leading edge of the epoxy saturated rope or metal rod flush to the surface. Sand......don't plane......to it and you have a durable and well shaped leading edge. Or, if you want to avoid that OCD label, simply round it. :P

 

As for the trailing edge, the chord calculation of the foil assumes the trailing edge meets at a single point. Build it that way and you have a knife edge, which you don't want. So if you want a 12 inch board when completed, better to calculate it as something like 13 inches and lop off the last 5% or so to leave you a thin, but square trailing edge. Somewhere in the 1/8th" to 1/4"is right for most boards of this size. On the board in the photograph, cutting at the next to last mark on the foil template would seem to be about right.

post-303-0-52600800-1366119972_thumb.jpg

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Video shows how a commercial foil maker does it. Their CNC machine is working fore and aft, just as Paul's template method uses. After that, process is pretty much the same.

 

If polystyrene would work as a rudder/CB core, a person could easily do the same thing with a hot wire foam cutter:

 

 

If only it were that easy.

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the airfoils plotter actually has a halo feature that would allow exactly what Paul describes.  After tacking the templates to the blank, I am less than confident of my initial north south approach,  perhaps East - West with a couple of halo type templates.  worth a look anyways, doesn't cost anything...yet. 

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  Easier and more reliable than the router set up.  Pretty simple. 

Definitely easier, can't think of any reason why it is more reliable.

 

When shaping something that is expensive in materials, and continues to get more expensive with labor it becomes more important not to make mistakes.  Everyone has to find techniques they are comfortable with and can have faith in to be accurate.  Using either a router or a circular saw scares me more than the hand plane as in one quick motion based on a simple error in calculation you can make a mistake from which there is no recovery.  It is just not possible to do with a hand plane, not in one stroke any way.

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Scott - 

If one sails, it is all about the journey.  For if you wanted the final destination you would have taken a powerboat, ferry, or visited via Google Earth.  It's ALL about the voyage. 

 

Leading edge is straight.  Trailing edge has the taper.  Plans show simple fairing with removal of material between prescribed lines. 

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I was referring to the fairing process it takes to build. I love to build just hate the fairing process, whether it be boats or drywall. I love the sailing journey to a destination. When I finally say enough is enough on my 28 and turn her over I will be in high gear again mentally and physically. :)  :)  :)

 

Sorry I'm not adding anything to this thread.

 

Scott

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My comments had nothing to do with the journey.  It was my theory on making sure I got to the destination without an accident.  I don't use hand planes for a Zen experience.  I use them for the control.  And with practice, they work very fast.

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  • 1 month later...

It is a good thing the Okoume comes 2.5 inches longer than 4X8.  Will mark off end of 6mm panel for scarfing, Then use that edge to rough cut the forward panel.  From that will then scarf the rest of the bottom panel and then loft.  It will be a little longer than needed, But easier to work with.  

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  • 2 weeks later...

Momentus day.  bottom panels finally cut to shape.  I gave up on the plywood scarfing as I was not happy with the quality of my craftsmanship when producing the 8:1 scarf.  So, I finished by using the 3"tape method with the two strips overlapped each side by and inch. I experimented with using heavy duty plastic as a release film, packing tape, and waxed paper.  The winner was clearly waxed paper.  It was very easy to remove, and left the smoothest joint.  It will be easy to blend these joints in with the rest of the hull.  

 

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