how many horses

JAC: I have done a fair amount of work measuring draft forces with various tools and implements. First I have to say I have a few concerns about the Peace Corps articles mentioned by Sabine. There are some real misinterpretations in that document. The most serious is that it takes a force of 30 kg to move a 30 kg load. Perhaps 30+ to lift it but not drag it. Dragging a load on a sled or stoneboat on firm ground like pasture or hay ground will take a force of 30% to 40% of the gross weight of the load. So it will take about 30 kg force to move a 75 kg load. Some of the other tabled draft estimates are suspect as well but its not important now.

Sled and stoneboat draft is very predictable and that is one reason they are nice training and conditioning implements. I often encourage folks to think in terms of equivalent loads when preparing a young farm team to plow. Draft in the range of 600 to 800 lbs is pretty typical for a 12 inch bottom 6 inches deep around here. If you use the general rule-of-thumb that 40% of the gross weight will go to force in the chain and you want your team to be prepared to plow you can create a equivalent plow load by loading the sled to a gross weight of 1500 to 2000 lbs (600/.4 = 1500, 800/.4 = 2000). If they pull that confidently they will have an easy transition to the plow. If they are not prepared and are faced with a plow load they will start jumping the furrow and causing problems to avoid the load.

Some of these draft issues have been on my mind because of some of the recent discussions. Just the other day I summarized some of the work I did with a sled and a 1900 lb log under a range of conditions. It is in the Sustainable Forestry section under the ground skidding thread. It considers uphill and downhill draft as well.

If you are interested in round baler draft that too is predictable. On firm, level hay ground with pneumatic tires the pulling force needed will be 5% to 10% of the gross weight of the baler. So if the loaded baler weighs 3000 lbs the average pulling force will be 150 to 300 lbs, not a big deal for a conditioned team of drafts. There is a summary of some of our work with logging draft that also included wagon draft in a technical guide linked to Jason Rutledge’s Healing Harvest Forest Foundation web site. http://healingharvestforestfoundation.org/ You can download a copy from there. Things you drag, things that roll, of course the pull will vary based on the surface and slope but the pull is pretty predictable. Wagons and balers that weigh the same will not be much different unless it is a ground driven baler.

The Peace Corps document takes a standard tractor-based approach to sizing a team and implement. That is you start with your high draft task, say the moldboard plow, and size it to accomplish the plowing in the days available before mud sets in or planting time, whatever works in your area. Then select your tractor hp and base the other tillage tools on the power available. That can be difficult to apply to animals because they are not a tractor. Tractors can go all day an only lose the time it takes to turn on the headlands. Horses abilities will be influenced by age, temperature, relative humidity, conditioning, tool adjustment and many other factors. We usually have excess power with a tractor so little thought is given to how tillage depth affects tillage draft.

Here are a couple of tillage draft maps that we made with horse drawn tillage tools, a 23 tooth spring tooth harrow for seedbed tillage and a 6 ft, single gang disc harrow. The pulling forces were measured with a pull meter and linked to location with a GPS. Then geographic information software was used to create the surface map. In each case we split the field in half to evaluate tillage depth or disc weight. The low draft half of the disked field was with the standard disk, the higher draft half was with 160 lbs additional weight added to the disk to increase depth. The low draft half of the spring tooth harrow field was with a 2 inch tillage depth, the higher draft was with a 3 inch depth. If you look in the northeast corner of that field you can see where we started with a 4 inch harrow depth, drafts in the 800-900 lb range. We went about 100 ft and I called it off, I did not think it was reasonable to ask the team to work a that level of effort throughout the day that early in the season.

I have noticed that folks really like to sink those springtooth harrows in the ground. Huge increase in draft with little or no improvement in seedbed quality.:eek:

Good discussion.

I actually did make a new forum to focus on discussion like this. I may move some other threads here also.

Knowing the pure pulling power can definitely have merit in making initial considerations, but animals are not machines, and there has to be some understanding about how they can become accustom to certain types of work, based not only on size and conditioning, but on the way they are directed to accomplish the task, the way they are harnessed or yoked, and other elements that only a teamster can bring to the equation.

Carl

John: It was actually a 23 tine harrow so probably for ease of recall think of 20 lbs per tooth at 2 inches, 30 lbs at 3 inches and 40 lbs per tooth at 4 inches. That is in disked soil.

I was looking back at some of my records of what others have reported with some of these tools. In 1917, Ohio State University professor Harry Ramsower published Farm Equipment and How to Use It. While not listing specific draft values, he described these spring-tooth harrows in common use: 2-horse harrow, 15-tooth, 4½ ft; 2- or 3-horse harrow, 17-tooth, 5½ ft; 3-horse harrow, 23-tooth, 7½ ft; 4-horse harrow, 25-tooth, 8½ ft. He did not indicate a depth of operation for the harrow. Although two horses handled our 23-tooth harrow at the shallow settings, three horses would have worked hard to pull it throughout the day at the deepest setting which averaged nearly 1000 lbs draft, quite a bit more that we would expect with a moldboard plow.

In 1931, Iowa State University professor J. Brownlee Davidson published tillage draft estimates for animal-drawn implements in a book titled Agricultural Machinery. A normal draft for a single-gang disk harrow was listed as 70 lbf per foot of width, but likely drafts ranged 50 lbf to 150 lbf per foot of width. The normal draft of 70 lbf per foot listed by Davidson was a good predictor of our disk harrow draft (72 lbf per foot). Our disk draft was 90 lb per foot with the added 160 lbs to increase depth of operations. The high-end draft of 150 lbf per foot seems quite high, but a heavy disk in soft soil could sink in and pull extremely hard.

Davidson listed a normal spring-tooth harrow draft of 75 lbf per foot of width, but likely drafts ranged from 25 lbf to 150 lbf. The normal draft of 75 lbf per foot is close to the draft we measured (83 lbf per foot) with the middle depth setting (notch 4, about three inches deep). The low-end draft of 25 lbf per foot is similar to what we measured (29 lbf per foot) when pulling the harrow without any tines in the ground. The high-end draft of 150 lbf per foot is greater than we measured in using notch 2 (4 inches, 131 lbf per foot), but it is probably pretty accurate since we could have increased tillage depth and draft by one more notch in the lever.

If you put something together let me know how it works. I have been doing some pasture and hayground renovation with a rolling aerator, not with animal power though. A disk tool in pasture ground have a lesser gang angle so would pull easier, but would need more weight for penetration. Might end up being about the same as our disk in tilled ground.

John: Can you explain what you are doing and trying to accomplish with your pasture work?