I’ll use my last Discord post to give this place a test run.
My most recent builds/experiments create a rectangular planing surface for the bottom (parallel edges). Bottom chamfers allow me to use traditional curved rail outline templates.
The rectangular shape uses an Aspect Ratio in the Lindsay Lord 0.4 range.
I call them Lindsay Lord Hybrids.
The chamfered hull is simple to make. Start with a rectangular blank with the desired dimensions. Shape the long edges on the bottom of the rectangular blank first to create the angled chamfers. Flip the chamfered side down and draw the desired planshape outline on the top (deck) side. Cut the planshape outline from the deck side.
Two simple steps. Then shape the rest.
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Deleted post combined with original post.
Looks good! Great to have a more linear format again, start to finish.
I notice the “deleted” post is still up, just the message thats gone. So seems like we can use edit to erase words, but the post itself remains.
Also, are you having to click link in email every time you log in? I am, and i’m thinking I must be missing something.
Thanks. Definitely prefer the forum style format.
Yeah. I have to sign in from an email message every time.
Wonder what’s up with that.
Is this a reference to Greenough edge boards or more of a validation of the yard possum Hydrodynamica design?
Who is Lindsay Lord?
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Thanks Mike. Nice Segue LOL
CoolDad,
The Yard Possum is Ryan Burch’s Lord Board, a validation of Lindsay Lord’s research.
If you read the deck of the Yard Possom, Burch has written “Lindsay Lord Planing Hull.”
Pages 11-19.
Lindsay Lord was a professor of Naval Architecture prior to WWI. He did his graduate studies at MIT. He researched planing hulls. He held a supervisory role with the US Navy.
The Greenough Edge does not have a planing surface with parallel edges.
Photo of the Ryan Burch “Yard Possum” at this link.
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Somebody made the observation that the aspect ratio would not be 0.4 for the board figures I posted.
Yes. If you assume a 48" long, rectangular planing surface; width would have to be 19.2" to get a 0.4 Lord aspect ratio (AR).
However, if you do a little calculating from my diagrams, my tail width is 18". I used chamfers to create a rectangular planing surface that is 18" wide. If I assumed the entire 48" length was part of the planing surface, my AR would be 0.375. But that would not take into consideration the acute slope of nose kick/rocker which takes up 3"-4" of board length. My assumption is/was the actual rectangular planing surface is 18" x 45" (AR = 0.4). (If you look at the pictures of Lord’s foam test planes, there is only the slightest curved chamfer at the front of his test planes.)
The benefits of the Lord 0.4 Aspect Ratio are decreased resistance, increased load capacity and reduced percent wetted surface.
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Have you taken it out and surfed it yet? How does it do? Could you put tail rocker and a narrower tail to give you better turning? So make it a midlength, which goes super fast in the middle but still turns well with weight back on the tail?
Also, what did you do with the rails after the steps you posted?
And sorry last couple questions, in the book Lord references planing angles that correspond to the aspect ratios, did you take that into account when designing yours? Presumably a higher planing angle would also affect the aspect ratio?
Very last one: with the right nose to tail curve, do you think you could make a board that preserved this aspect ratio as the nose lifts out of the water? I’m thinking that would lead to even higher speeds
Teek
I have seen your questions. And they are not simple to answer.
So I will think about how to give you concise, summarized responses without writing an essay.
More later (math ellipsis)…
The design in the figures above is the control (no tail channel), for comparison with the tail-channel model I built (figure below). I made all of the chamfered bottom-rail prototypes from 6-pcf XLPE.
https://mypaipoboards.org/forum3/viewtopic.php?t=981&sid=9675c0b77154a90ecfaa73846f3f2c1c
I’ve had the Control model out on the NC coast one time and the tail-channel model out on the NC coast 3X.
https://mypaipoboards.org/forum3/viewtopic.php?t=981&start=20#p9828
The shorter the board, the less tail rocker is needed. Lord’s foam test planes had no rocker. Adding rocker will change the hydrodynamics (likely slower). Also, my tail channel requires that there be no tail rocker to function properly — flat from the nose kick to the tail end.
However, I have considered designing longer boards with more traditional SB shapes with a chamfered-bottom flat section (AR 0.4) somewhere in the mid-section of the SB. Tail and nose sections with rocker — should maintain turning performance and improve speed.
The 6-pcf XLPE is tedious and slow hand shaping, making it difficult to incorporate detailed rail shape. So I rounded the top rails to around 42% of board thickness. Also rounded top and bottom edges of the nose section in front of the chamfers. If I had a 2- to 3-pcf EPS or PU blank, I would probably shape “down-rails” that extend to the edges of the chamfers, maintaining the chamfer and parallel bottom edges. Would give it more of a space-age look.
No. I did not consider planing angle when designing. Tail channel and flat planing surface with parallel edges were my main objectives. The 0.4 AR was a fortunate coincidence on the first go round.
Traditional 42” bodyboards have no rocker (for speed) and only have nose kick.
These 48" models I built are more of a kneeboard/bodyboard hybrid.
The bottom surface inside my tail channel provides indirect rocker in the tail and the channel functions as a low-drag, finless fin.
how did it go , Bill ?
cheers
Ben chipper
Ben,
Chad Sickney riding the 42” Lord Hybrid (with Coanda Channel).
2nd Wave — Under the Fluid Awning
Entering the Liquid Tunnel
Bill
looks like it works great ,
THANKS for the footage mate .
is that a wave pool , somewhere ?
cheers
Ben
Wave pool, yes. “Waco Surf” in Waco, TX.