How To Build A Spoon

[MTBarrels]

Just a note pointing out that an (approximate) reconstruction of the comments I intended to make in my earlier post now appears there (replacing my whining about IE crashing).

mtb

[AM_Glass]

Thank you MTB for the very valuable post clearing up my confusion on what cloth re-enforcment to use. A few questions, what "ounce" glass were you giving values for? Second, where did you get those numbers (ref)?

And another question about the rails. The outer edge rail shape question has been asked, which I was wondering myself. Another question is in regards to the inner edge rail shape. What is the transition from foam rail to pure glass deck? Is it a wedge shape? rounded? abrupt? At some point the foam will be too thin and no longer give any strength, yet if the transition is too abrupt I imagine a large amount of stress during flex to be located in that area. Is the transition for the torsion bar the same?

[Man O' War]

MTB -- No wonder you were tearing your hair. What a post! God bless you. You just saved us a bundle of money and gave us peace of mind too.

DR & GLASS -- Doc is talking shaper-talk and I don't quite get the numbers, but just for fun here's a comment on rail shape based on common sense.

You're on your brand new spoon hitting a hard bottom-turn to the right, banked over about 60 degrees. Freeze that image. From about your knees back, the inside rail, the right one, is lifting. The lift is more pronounced as you go back. So the rail at your knees is 60 degrees but as you go back it's trying to level out. Maybe half-way back it's 50. Maybe all the way back, it's 30... if you follow me. The rail is flexing upward and the back of the board is twisting counterclockwise, trying to flatten out and get away from the pressure.

Now, since you have that picture on pause, what about rail strength? If the rail could, it would fold in on itself. It has the water bending it inward from one side and the deck bending it inward from the other. It's caught in the middle. You give the rail some strength to fight back by giving it some arch, right? Where will you put the arch? Just somewhere in the middle? The rail is a couple of inches wide. You have some choices to make. You put the arch at whatever point the rail is feeling the most stressed out--where it would buckle, if it could.

In my non-engineering opinion, you locate that by going to the edge of the rail buried there under the water and drawing a perpendicular line up through the rail. Where it passes through the rail, that's your pressure point. So where the bank is the steepest, by your knees, 60 degrees, and the board is cocked way over, the line passes through a point closer to the deck and away from the edge. Where the bank is the shallowest, the line passes through the rail out farther toward the edge.

If this is true--and it makes sense to me, but I stand corrected if MTB or Dale or someone comes along who knows better--if this is true, then the implication for your rail design is clear. The apex of your arch must move with the pressure point; i.e., closer and closer to the edge of the rails as you approach the tail.

Now look at the pictures of the Paul Gross Velo as posted by Flexman. viewtopic.php?t=1259 The high point of the arch or ridge moves slowly out toward the edge as you approach the tail, because (I think) that's where the pressure point is going too. I shaped my rails the same way but less skillfully.

I don't know if this answer fits your questions. If nothing else, it might help you come up with some answers of your own.

[flexspoon]

Rail shape transition.
Maybe this will give some clues?

http://flexspoon.com/pics/rails/railzz1.htm

[Marky V]

OK mtb
I was probably getting a bit over excited, I know that epoxy and carbon are not New materials, neither is balsa. What I am thinking of is extending the flexible eps core, balsa sandwich skin concept to its natural conclusion as a spoon!
As for hotwiring eps, you can cut any shape as long as you have the time to make the different shaped wires necessary. For our application, as you well know a sanding block with some 60 grit paper is quicker and easier.
I have been put in my place
sorry

[DrStrange]

eyeing Flexman's rail photos looks to me like there is in the tail, as move laterally, a bit of upward curve to bottom of hull i.e.normal low tail rail shape like solid board, but with the solid part of the rail removed and only the bottom glass remaining. Am I correct?

My orig question about rail shape above (50/50, 60/40 etc) was partly about this issue (though not clear in what I wrote), i.e. is the top 1/2 of the rail's shape present in the finished board or does the hull bottom come up to the widest outline of the rail and then just kind of round over and down to the deck? Dang, is that a clear question? Wish I could post sketches but alas, no scanner.

[MTBarrels]

MTB -- No wonder you were tearing your hair. What a post! God bless you. You just saved us a bundle of money and gave us peace of mind too.

Just keep in mind that everything I said is based on how my boards function (and the degrees of flex that occur during their usage). One also needs to be careful when discussing the strength of materials when under compressive loadings--especially thin laminates or sandwich construction (where buckling may be the primary cause of compressive failure). If the laminate is thin, or the core of the sandwich has a low compressive strength, then the stiffness of carbon fiber can be an important factor in inhibiting the onset of buckling.

mtb

[MTBarrels]

Thank you MTB for the very valuable post clearing up my confusion on what cloth re-enforcment to use. A few questions, what "ounce" glass were you giving values for? Second, where did you get those numbers (ref)?

The performance numbers refer to the fiber strands that are ultimately wolven into cloth (or wound around a form as a yarn). Hence in the real world, the type of weave would also be a factor (but not included in table numbers). The numbers in the table would be most representative of a "unidirectional" cloth with almost all (say 90% of the glass content) in straight lines with the cross-weave (remaining 10%) going over and under the straight strands.

As far as the data, I got the basic numbers (density, Young's modulus, Yield strength) off the internet from a short course on fibers:

http://web.ew.usna.edu/~pjoyce/composit ... Fibers.pdf

The other two parameters (e.g. "twang", "max flex") I calculated from these basic three.

And another question about the rails. The outer edge rail shape question has been asked, which I was wondering myself. Another question is in regards to the inner edge rail shape. What is the transition from foam rail to pure glass deck? Is it a wedge shape? rounded? abrupt? At some point the foam will be too thin and no longer give any strength, yet if the transition is too abrupt I imagine a large amount of stress during flex to be located in that area. Is the transition for the torsion bar the same?

I can only answer for my boards, which generally have quite different rails from GG's (see detail pic of Isurus on p.7 of the 3 g's thread). The outside rails are typically low and the chines are usually round with a radius of 1/8" in the areas where foam joins to the bottom. The inside rail to bottom junction is usually moderately rounded to very rounded as it is the lower part of my thumb grip in the rails. Same thing for the torsion bar on my older boards (replaced by the raised kneewell area in the later boards). The only place I have had a stress problem is at the aft termination of the torsion bar where it joins to the bottom, or the equivalent area on boards with the kneewell pad. However, the failure occurred not where there is thin foam, but rather just a little bit farther aft where the pad/bar laminate bonds to the bottom. A few more layers of selectively oriented unidirectional cloth in that area seems to have eliminated the problem.

mtb

[Man O' War]

"A fire in the master's house is set"

http://www.swaylocks.com/forum/gforum.c ... age#210853

[flexspoon]

Found some pics of spoons including a standup spoon:




Many more fabulous spoons here:
http://www.worth1000.com/cache/gallery/ ... st_id=1675

[Man O' War]

If he hits the pier, he's forked.

[DrStrange]

question for MOW (or anyone else w/ insight) after the quote

Now strengthen the deck in the knee area by adding 8 partial layers rail to rail but not over the edge onto the hull. The length of the first layer is 2 ft. Each of the next 7 layers is 2” shorter than the one before it. Use 33” from the tail as your center point. Glass the first 4 layers; cure 24 hrs. Glass the last 4 and cure. You can glass all of these very dry.

Next, add strength to each rail deck-side by cutting 10 strips of cloth a little narrower than the rail at the 33” point. The first strip is 4” long and each succeeding strip is 1” longer than the one before it. Do a set of these for each rail. Using the 33” point as your center on each rail and starting with the shortest strip on the bottom, glass both sets down (dry).

Am I correct that on the flat deck the longest piece goes on first while on the rails the shortest goes on first? Why? And why do this two part process instead of layered pieces going all the way edge to edge on the top of the board stopping just short of wrapping over the rail line?

[Man O' War]

Dr S -- We're getting to be old friends.

Right, for the reinforcement in the knee area on the deck, I started with the longer sheet first, the normal way. (And I did go rail to rail there.) I did it this way because if I mentally cross-section the deck lengthwise, I want to see a torsion bar, thickest under my knees and tapering out both ways.

That extra rail reinforcement I did the opposite way. The reason I did it in the first place was that when I flexed the board hard downward on the horses, I could see where the weak point might be on a free fall. Even though I had already gone up onto the rails with the deck pieces, I wanted a little more insurance against breakage. Remembering the words of my mentor that it's better to overbuild than underbuild, I did it. I applied this stack of patches upside down, shortest piece on the bottom, because the rails are curved slightly inward, concave, and I wanted a reverse curve on the patch.

A lot of it was just instinct and might not be effective or necessary.

Hope this helps.

[flexspoon]

He envisioned riding deeper in the bowls of the long and continuously peeling waves which characterized the region in which he lived. being somewhat detached from the mainstream methods of riding waves, he invented a new technique.
His method rejected the accepted attachments to boyancy and floatation. It rejected the accepted paradigms dictating the size and shape of wavesliding craft. it was its own thing. a little shell to ride in at high speeds. a neutral-boyancy disk allowing him submarine under large sets. the spoon.

This spoon shows the tapered foam rails - the classic "toilet seat" look.
And the flatter, less-bellied nose.

http://mjmiller.typepad.com/milladro/2005/04/spoon.html

[DrStrange]

Flexspoon--is that a "small wave" spoon w/ the lower rocker etc?

MOW thanks for the response. Makes sense to me. On consideration, thinking (would love feedback from anyone on this) that glass rope bar lam'd down center of board would serve for added strength and possibly less weigth added. Sort of like the stringer in conventional board. With as much glass as already on there, not likely knees will cause damage directly, the concern is compression failure from flexing. A central bar or two a couple inches apart, would eliminate this????