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Between the two trips I made to the Sand Patch grade in 1974, there was a derailment on the hill. Some empty cars jack-knifed on this curve. As I mentioned earlier, the Southern Pacific did not allow more than 4,000 horsepower to be couple behind the caboose or empty cars. The best placement for a helper set was for the helpers to shove one-third of their tonnage and to pull two thirds. To figure out this exact spot in the train you had to do some math. First total all of the horsepower, the road power and the helper set. Then divide the total horsepower into the total tonnage for the train. This gives a ratio of tons per horsepower. Now multiply the ratio by the total horsepower in the helper set. This gives the tonnage that the helper set will handle. Two thirds of this tonnage should be behind the helper set. There are two other numbers that are important and that is the trailing tonnage. Couplers and drawbars can only take so much strain. We have just computed the trailing tonnage for the helper set. We need to subtract all the tonnage handled by the helper set from the total tonnage to see how much tonnage the road power is pulling. For a one percent grade the trailing tonnage for the road power should not be over 9,000 tons and trailing tonnage for a helper set should not be over 7,500 tons. For a two percent grade the trailing tonnage for the road power should not be over 4,250 tons and trailing tonnage for a helper set should not be over 3,815 tons. Another rule was that there should be no empties in the block of cars (one third) that the helper is shoving. The best practice was to place all empties at the rear of the train. Disk 119