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Helen Gone asks, What is the maximum green slope you should have at a cup?
Over time, it became design convention to reward golfers who have hit a green in regulation and putted within 3 feet of the hole by giving them a putt with little break. While no one knows how golfers proclaimed this their right it's not the 11th Commandment (either mine or the Lord's), after all golfers expect it, and course managers responsible for speed of play (and revenue) demand it. Such "rights" spawn design R.O.B.O.T.s from architects, including yours truly.
It's frustrating for the golfer, his partners, and following golfers to have to line up a putt no matter how short. And, no one argues that it should be unusual for putts to "de-green" themselves, as summed up by Golden Age architect Harry Colt:
"In no case should a green be contoured so that a ball runs away from a putter like a swine possessed by the devil."
Given today's increasing green speeds, that's getting harder to do for architects. Older greens had a steeper, more natural appearance, and still achieved reasonable putting quality because they were slower, had higher, bumpier grass cuts, and "grain," where today's grass varieties don't.
The Stimpmeter (a greens speedometer, empirically measuring how fast they are and, more importantly, how they compare to tournament greens and the faster and smoother sand-based USGA greens) changed all that. With green speeds increasing gradually, the "basic slope" of greens has gradually been reduced to maintain "fairness" and "reward skill" a precision putting stroke as follows:
1920-30s up to an 8-degree slope.
1940-50s 4-6 degree was typical.
1960-70s 3-4 degree was typical.
1980-90s 2-3 degree slope (3 degrees being the maximum recommended by the USGA)
2000 Architects, clubs and the PGA Tour prefer greens slopes of 1.5-2.25 degrees.
That leaves architects a narrow range of slope for design!
Creating 3-degree slopes requires designing swales of 2 degrees, since most greens have both front-to-back and cross slopes. If both slope components are 2 degrees, then, as geometry students know, the hypotenuse (which is the actual maximum grade) is 1.414 times the legs of a triangle, or about 2.8 degrees, under the USGA-recommended maximum, and allowing for construction error.
Greens still need at least 1.5-degree slope for good surface drainage. Slow drainage leads to disease, compaction and, in cold climates, freeze damage.
To allow for construction error, I design minimum slopes of 1.75 degrees (requiring minimum swale slopes of 1.25 degrees).
Even within that narrow range, I adapt slopes to anticipated maintenance, turf type, and resulting anticipated average and maximum green speed.*
We have been asked to design more green slope specifically to allow higher, less-stressful mowing heights, assuming that will prevent higher green speed, but it doesn't work for long. Eventually, golfers want faster greens for "one event," which turns into demand for fast greens as daily conditions as sure as the sun rises and as sure as "I missed my crucial putt" complaints follow.
PGA Tour players prefer the flattest greens because, 1) they like low scores, and 2) they play the course once a year. Learning intricate green contours quickly and scoring well don't mix.
Hmm. Pros hate steeper contours, but everyday "course regulars" often prefer them to make every round different!
Is there any better reason to design some challenging contours? No, but there are additional reasons, like flat greens looking artificial in rolling topography.
* I anticipate green speeds will continue to increase, at all types of courses, so, while I have pushed the design limits, like old football coaches I get more conservative over time.
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