Lindsay Lord Hybrid

[B_Wurts]

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.

[B_Wurts]

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.

[B_Wurts]

Bottom Chamfer Blank

[B_Wurts]

For those not familiar with Lindsay Lord, he was a professor of Naval Architecture prior to WWI. He did his graduate studies at MIT. He held a supervisory role with the US Navy. He researched planing hulls.
Lord’s information about planing hull Aspect Ratios is found on pages 11-19.

https://etchellsfleet27.com/wp-content/ ... -Hulls.pdf

Ryan Burch’s “Lord Board” is an application of Lindsay Lord’s research.
If you read the deck, Burch has written “Lindsay Lord Planing Hull.”
Photo of the Burch Lord Board from this link;
https://laundrysurfer.files.wordpress.c ... -board.jpg

[matt23]

Is the length 48 and width 22. Ie the 0.4 ratio

[matt23]

I'm trying to get my head around the 0.4 thing. If the length is 48. Would the width not be 19.2 ?
This isn't a criticism. Just want to work it out

[rodndtube]

Yes, that is correct, 19.2 inches. But, I wouldn't get too bent out of shape going up to 19.5 inches or down to 19.0 inches... but, going to 22 inches or down to 16 inches begin to reveal changes in the pure science of it. Most likely one will introduce curve into the form and maybe some level of rocker, nose kick or tail kick. All the other aspects of the design can affect the pure science and engineering of it if taken to a facility like the Naval Surface Warfare Center (NSWC) Carderock's David Taylor facility with its myriad water basin testing capabilities.

[nomastomas]

I'll add another grain of salt to what Rod has aptly pointed out... all of Lord's experiments were conducted by pulling what amounted to a sled across flat water. The only time my G5 prone board is on "flat" water is when I'm paddling, and then I never paddle at planing speed. So, while I would describe myself as a proponent of Lord's work on planing hulls, and while his theories have greatly influence my own designs, his theories cannot be directly applied to surfcraft operatining in the continuously variable environment we refer to as a "wave". In fact, Lord's work pales in comparision to the advances being made with Computational Fluid Dynamics (CFD) mentioned elsewhere by Wurts. Check this out...https://blogs.sw.siemens.com/simcenter/ ... ital-wave/ From the article "In conclusion, even though a perfectly flat water surface does not represent real wave breaking conditions, CFD results matched well with field research to predict relevant trends. In a first pilot project the engineers proved how simulation truly helps to confirm what surfers feel – and even understand why they feel it from an engineering perspective. " Cool stuff...

[rodndtube]

Nomas, Lord did mention testing that sled in various surface conditions and how the aspect ratio could affect the planning characteristics. He also addressed to some degree a V-hull in the forward nose area of the plank. That V-hull is something I speculated about in a post a long, long time ago on the forums as an approach to dealing with surface chop chatter in under-6 ft waves and with open ocean cross swell in 7 to 14 ft waves. As you addressed in these pages as well.

Some form of tri-hull may address some of those wave surface conditions which brings to mind some of Gus Acosta's designs. I am thinking a greater tri-hull than we normally see in some existing paipo boards where the hulls are simply too shallow to address these conditions. But, I also think that a form of more radical V in the nose area could also be a solution.

My curiosity, and need, will probably never be satiated as I most likely will not be engaging in that kind of wave at this stage of my surfing life. And it is also hard to justify a one-trick pony on my surf trips as the board would not be used in my normal range of surf conditions.
The wave pictured below is around 12+ ft, about 800 yds out, the offshores are blowing good and when zooming in on the wave face the surface condition can be observed.

[nomastomas]

Not exactly well-groomed...That wave looks like a wave I surfed in Nica back in 2006. Deep water reef way off shore. I was surfing a HP LB back then and we surfed off a panga, so easy paddle over to the peak.. Howling offshores made it really hard to get in. It would have been a pretty wild ride on a prone board!

[rodndtube]

Yes, very nice wave but a little bumpy at times. I usually let my mates catch the first one or two of the waves in the set pass through so my wave would be smoother But hitting one of those cross chops could have me airborne for 10 yards. The wind rushing up the wave meant keeping a very low profile during the drop and hoping the "rain" would clear clickly so I could see without losing my contacts.

[B_Wurts]

matt23,
I have not been ignoring you. Just finished a marathon write-up (Fri-Tues) of a non-surf design I had to submit by Tues. afternoon. I encourage you to read Lord's Chapter 2 about Aspect Ratio (pp. 11-19). When a watercraft is planing, only the bottom surface is in contact with the water (Figure/photo below).

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.)

Regarding the realistic application of Lord's research to modern surfcraft, the simplest Paipos have flat bottoms and parallel rails. I suspect Lord's comments about open ocean performance relate to large boats, traveling at relative high speeds in short period, large swells -- not surface chop.

His foam test planes are very much like "finless" Paipos and modern body boards. The benefits of the Lord 0.4 Aspect Ratio are decreased resistance, increased load capacity and reduce percent wetted surface. One primary benefit is speed. While riding surfcraft, you are planing -- using the entire planing surface -- when you have reached take-off velocity and have just caught the wave, when dropping straight down the face, and when you have hit the trough to outrun whitewater to get to open face. These are times when you are accelerating and want to achieve maximum velocity as fast as you can.

Most surfers agree, flat bottom boards are fastest (but significant surface chop, can make for a bumpy ride). However, design variables for surfcraft change significantly as board length increases. One of the biggest variables that changes is rocker -- the shorter the board, the less rocker needed. Many other variables come into play also, depending on board length, rail length and curve, rail profile, number of fins (finless, single, twin, thruster, quad, etc.), width and hull contours.

While CFD can do magic, often, because of the immense number of variables involved, it is often only a step or two beyond SWAG (Scientific Wild Ass Guess).

[rodndtube]

Lord was commissioned by the Navy to research large boat/small ship designs for interdicting smuggling aka in the "cigarette boat" to PT or PC (patrol coastal) size category. The Coast Guard and Navy needed boats/ships that could patrol large areas of the Caribbean (and similar littoral waters) and also interdict suspect smugglers. Mostly rum runners back at the time of his book and way before airborne surveillance using drones, helicopters, fast cutter ships embarking fast boats and double-hulled/tri-hulled. So those large boats/small ships potentially could have a large, flat wetted area in addition for a relatively short bow as most of the need-for-speed were in favorable sea conditions (less that Sea State 5).

[B_Wurts]

Lord was commissioned by the Navy to research large boat/small ship designs for interdicting smuggling aka in the "cigarette boat" to PT or PC (patrol coastal) size category. The Coast Guard and Navy needed boats/ships that could patrol large areas of the Caribbean (and similar littoral waters) and also interdict suspect smugglers. Mostly rum runners back at the time of his book and way before airborne surveillance using drones, helicopters, fast cutter ships embarking fast boats and double-hulled/tri-hulled. So those large boats/small ships potentially could have a large, flat wetted area in addition for a relatively short bow as most of the need-for-speed were in favorable sea conditions (less that Sea State 5).

I am aware.
The PT boat was one of the smallest naval watercraft at 80’ length (max speed 41 knots).
PCs were a bit longer at around 180’ (max speed 35 knots).
Those lengths could have open ocean problems in shorter period (higher frequency) swells — which would impact Lord Aspect Ratios.

For most riders, surfing speeds are significantly slower.
https://bgsurfphysics.blogspot.com/2018 ... peeds.html

[matt23]

Sorry for the late reply. You two our obviously are a ot more scientific than myself.
So as a rule of thumb you tend to stick around this AR. I don't want to digress away from the topic but what is Greenoughs AR?

[nomastomas]

Greenough's Velo is a "displacement hull" design. Lord worked with "planing hulls", so his theory on AR would not apply to the Velo.

[B_Wurts]

Sorry for the late reply. You two our obviously are a ot more scientific than myself.
So as a rule of thumb you tend to stick around this AR. I don't want to digress away from the topic but what is Greenoughs AR?

As a retired scientist, my perspective is influenced by science. While I was building my “first 42-inch,” foam and glass board, it occurred to me that I could use chamfers to create a rectangular planing surface with a curved rail planshape — so I did.

I really wanted to build a 48” model with a modified Lis Fish planshape (nose and tail removed with “very slightly” narrower width at the nose). I added rail chamfers for a rectangular planing surface. My 48” AR of 0.4 was a fortunate “coincidence,” that I discovered after the fact.

A guy named John Mellor on Swaylocks would mention Ryan Burch’s Lord Board from time to time. That got me curious enough to make chamfered rails. I learned more after. So now, my flat-bottom designs around 60” and under are influenced by Lord’s 0.4 AR and rectangular planing surfaces.

As NM Tomas said, the Greenough Velo is a displacement hull.