Shaft Angle Table

The table below computes the distance between the aft end of the strut bore and the shaft entry point for strut drops between 6 to 10 inches and shaft angles between 6 to 16 degrees.

Definitions : Strut Drop and Shaft Angle

Photo courtesy of Glen-L Marine Designs

Drop is the distance from the strut base to the centerline of the shaft bore at the aft end of the strut.

Angle is the degree of the slope between the strut base and the shaft bore centerline.

The Algorithm

To find the length of the adjacent side of a right-angle triangle when the length of the opposite side and one angle are known, use the cotangent of the angle :

adjacent side = cotangent (angle) * opposite side

If your calculator doesn't have the cotangent function, use the following formula :

adjacent side = 1.0/tangent (angle) * opposite side

How to use the Table

To use the table, scan down the 'Drop' column until you locate your strut's specified drop.  Select the desired shaft angle from the second column.  The 'Length' column for your selection is the distance between the aft end of the strut bore and shaft entry point.

Sample application

For example, the distance between the aft end of the strut bore and shaft entry point for a strut with 7" drop at a shaft angle of 12 degree would be 32.9324 decimal inches (32.078 inches).  Installing the same strut at a shaft angle of 8 degrees would require 49.8076 decimal inches (49.067 inches). 

If we wanted to increase our boat's propeller efficiency (and speed potential) by decreasing the shaft angle from 12 degrees to 8 degrees, we would have to shift the shaft entry point 16.07 inches further forward than it's installed position at 12 degrees e.g. 49.8076 - 32.9324 = 16.8752 / 12 = 16.07 inches .

References and related links

Shaft angles and layouts Chapter 11, Inboard Motor Installations, Glen L. Witt and Ken Hankinson
Struts WebLetter 37, Glen-L Marine Designs
Inboard Motor Installations by Glen L. Witt and Ken Hankinson
Math to Build On by Margaret S. and Johny E. Hamilton


Strut Drop (inches) : 6    6.25    6.5    6.75    7    7.25    7.5    7.75    8    8.25    8.5    8.75    9    9.25    9.5    9.75    10    


Drop
(inches)
Angle
(Degrees)
Length
(Decimal inches)
Fraction
(16ths)
Length
(Inches - 16ths)
6.00 6.0 57.0862 1.3790 57 -  1/16
6.00 6.5 52.6613 10.5812 52 -  5/8
6.00 7.0 48.8661 13.8573 48 - 13/16
6.00 7.5 45.5745 9.1924 45 -  9/16
6.00 8.0 42.6922 11.0755 42 - 11/16
6.00 8.5 40.1469 2.3510 40 -  1/8
6.00 9.0 37.8825 14.1201 37 -  7/8
6.00 9.5 35.8546 13.6734 35 - 13/16
6.00 10.0 34.0277 0.4431 34
6.00 10.5 32.3731 5.9696 32 -  3/8
6.00 11.0 30.8673 13.8772 30 - 13/16
6.00 11.5 29.4909 7.8551 29 -  7/16
6.00 12.0 28.2278 3.6445 28 -  3/16
6.00 12.5 27.0643 1.0280 27 -  1/16
6.00 13.0 25.9889 15.8217 25 - 15/16
6.00 13.5 24.9918 15.8688 24 - 15/16
6.00 14.0 24.0647 1.0350 24 -  1/16
6.00 14.5 23.2003 3.2045 23 -  3/16
6.00 15.0 22.3923 6.2769 22 -  3/8
6.00 15.5 21.6353 10.1648 21 -  5/8
6.00 16.0 20.9245 14.7918 20 -  7/8
Index
6.25 6.0 59.4648 7.4364 59 -  7/16
6.25 6.5 54.8555 13.6887 54 - 13/16
6.25 7.0 50.9022 14.4346 50 -  7/8
6.25 7.5 47.4735 7.5754 47 -  7/16
6.25 8.0 44.4711 7.5370 44 -  7/16
6.25 8.5 41.8197 13.1156 41 - 13/16
6.25 9.0 39.4609 7.3752 39 -  7/16
6.25 9.5 37.3485 5.5764 37 -  5/16
6.25 10.0 35.4455 7.1282 35 -  7/16
6.25 10.5 33.7220 11.5517 33 - 11/16
6.25 11.0 32.1535 2.4554 32 -  1/8
6.25 11.5 30.7197 11.5157 30 - 11/16
6.25 12.0 29.4039 6.4630 29 -  3/8
6.25 12.5 28.1919 3.0709 28 -  3/16
6.25 13.0 27.0717 1.1476 27 -  1/16
6.25 13.5 26.0331 0.5300 26
6.25 14.0 25.0674 1.0781 25 -  1/16
6.25 14.5 24.1670 2.6713 24 -  1/8
6.25 15.0 23.3253 5.2051 23 -  5/16
6.25 15.5 22.5368 8.5884 22 -  1/2
6.25 16.0 21.7963 12.7414 21 -  3/4
Index
6.50 6.0 61.8434 13.4939 61 - 13/16
6.50 6.5 57.0498 0.7963 57
6.50 7.0 52.9383 15.0120 52 - 15/16
6.50 7.5 49.3724 5.9584 49 -  3/8
6.50 8.0 46.2499 3.9985 46 -  1/4
6.50 8.5 43.4925 7.8802 43 -  7/16
6.50 9.0 41.0394 0.6302 41
6.50 9.5 38.8425 13.4795 38 - 13/16
6.50 10.0 36.8633 13.8133 36 - 13/16
6.50 10.5 35.0709 1.1338 35 -  1/16
6.50 11.0 33.4396 7.0336 33 -  7/16
6.50 11.5 31.9485 15.1763 31 - 15/16
6.50 12.0 30.5801 9.2815 30 -  9/16
6.50 12.5 29.3196 5.1137 29 -  5/16
6.50 13.0 28.1546 2.4735 28 -  1/8
6.50 13.5 27.0744 1.1912 27 -  1/16
6.50 14.0 26.0701 1.1212 26 -  1/16
6.50 14.5 25.1336 2.1382 25 -  1/8
6.50 15.0 24.2583 4.1333 24 -  1/4
6.50 15.5 23.4382 7.0119 23 -  7/16
6.50 16.0 22.6682 10.6911 22 -  5/8
Index
6.75 6.0 64.2220 3.5514 64 -  3/16
6.75 6.5 59.2440 3.9038 59 -  3/16
6.75 7.0 54.9743 15.5894 54 - 15/16
6.75 7.5 51.2713 4.3414 51 -  1/4
6.75 8.0 48.0287 0.4599 48
6.75 8.5 45.1653 2.6449 45 -  1/8
6.75 9.0 42.6178 9.8852 42 -  9/16
6.75 9.5 40.3364 5.3826 40 -  5/16
6.75 10.0 38.2812 4.4984 38 -  1/4
6.75 10.5 36.4197 6.7159 36 -  3/8
6.75 11.0 34.7257 11.6118 34 - 11/16
6.75 11.5 33.1773 2.8370 33 -  1/8
6.75 12.0 31.7563 12.1001 31 -  3/4
6.75 12.5 30.4473 7.1565 30 -  7/16
6.75 13.0 29.2375 3.7994 29 -  3/16
6.75 13.5 28.1158 1.8524 28 -  1/16
6.75 14.0 27.0728 1.1643 27 -  1/16
6.75 14.5 26.1003 1.6050 26 -  1/16
6.75 15.0 25.1913 3.0615 25 -  3/16
6.75 15.5 24.3397 5.4354 24 -  5/16
6.75 16.0 23.5400 8.6408 23 -  1/2
Index
7.00 6.0 66.6006 9.6088 66 -  9/16
7.00 6.5 61.4382 7.0114 61 -  7/16
7.00 7.0 57.0104 0.1668 57
7.00 7.5 53.1703 2.7245 53 -  1/8
7.00 8.0 49.8076 12.9214 49 -  3/4
7.00 8.5 46.8381 13.4095 46 - 13/16
7.00 9.0 44.1963 3.1402 44 -  3/16
7.00 9.5 41.8304 13.2856 41 - 13/16
7.00 10.0 39.6990 11.1836 39 - 11/16
7.00 10.5 37.7686 12.2979 37 -  3/4
7.00 11.0 36.0119 0.1900 36
7.00 11.5 34.4061 6.4976 34 -  3/8
7.00 12.0 32.9324 14.9186 32 -  7/8
7.00 12.5 31.5750 9.1994 31 -  9/16
7.00 13.0 30.3203 5.1253 30 -  5/16
7.00 13.5 29.1571 2.5136 29 -  1/8
7.00 14.0 28.0755 1.2075 28 -  1/16
7.00 14.5 27.0670 1.0719 27 -  1/16
7.00 15.0 26.1244 1.9897 26 -  1/8
7.00 15.5 25.2412 3.8590 25 -  3/16
7.00 16.0 24.4119 6.5904 24 -  3/8
Index
7.25 6.0 68.9791 15.6663 68 - 15/16
7.25 6.5 63.6324 10.1189 63 -  5/8
7.25 7.0 59.0465 0.7442 59
7.25 7.5 55.0692 1.1075 55 -  1/16
7.25 8.0 51.5864 9.3829 51 -  9/16
7.25 8.5 48.5109 8.1741 48 -  1/2
7.25 9.0 45.7747 12.3952 45 -  3/4
7.25 9.5 43.3243 5.1887 43 -  5/16
7.25 10.0 41.1168 1.8687 41 -  1/16
7.25 10.5 39.1175 1.8800 39 -  1/16
7.25 11.0 37.2980 4.7683 37 -  1/4
7.25 11.5 35.6349 10.1582 35 -  5/8
7.25 12.0 34.1086 1.7371 34 -  1/16
7.25 12.5 32.7026 11.2422 32 - 11/16
7.25 13.0 31.4032 6.4512 31 -  3/8
7.25 13.5 30.1984 3.1748 30 -  3/16
7.25 14.0 29.0782 1.2506 29 -  1/16
7.25 14.5 28.0337 0.5387 28
7.25 15.0 27.0574 0.9179 27
7.25 15.5 26.1427 2.2825 26 -  1/8
7.25 16.0 25.2838 4.5401 25 -  1/4
Index
7.50 6.0 71.3577 5.7237 71 -  5/16
7.50 6.5 65.8267 13.2265 65 - 13/16
7.50 7.0 61.0826 1.3216 61 -  1/16
7.50 7.5 56.9682 15.4905 56 - 15/16
7.50 8.0 53.3653 5.8444 53 -  5/16
7.50 8.5 50.1837 2.9387 50 -  1/8
7.50 9.0 47.3531 5.6502 47 -  5/16
7.50 9.5 44.8182 13.0917 44 - 13/16
7.50 10.0 42.5346 8.5538 42 -  1/2
7.50 10.5 40.4664 7.4621 40 -  7/16
7.50 11.0 38.5842 9.3465 38 -  9/16
7.50 11.5 36.8637 13.8188 36 - 13/16
7.50 12.0 35.2847 4.5556 35 -  1/4
7.50 12.5 33.8303 13.2850 33 - 13/16
7.50 13.0 32.4861 7.7771 32 -  7/16
7.50 13.5 31.2397 3.8360 31 -  3/16
7.50 14.0 30.0809 1.2937 30 -  1/16
7.50 14.5 29.0003 0.0056 29
7.50 15.0 27.9904 15.8461 27 - 15/16
7.50 15.5 27.0441 0.7060 27
7.50 16.0 26.1556 2.4897 26 -  1/8
Index
7.75 6.0 73.7363 11.7812 73 - 11/16
7.75 6.5 68.0209 0.3340 68
7.75 7.0 63.1187 1.8990 63 -  1/16
7.75 7.5 58.8671 13.8735 58 - 13/16
7.75 8.0 55.1441 2.3058 55 -  1/8
7.75 8.5 51.8565 13.7034 51 - 13/16
7.75 9.0 48.9316 14.9052 48 -  7/8
7.75 9.5 46.3122 4.9948 46 -  5/16
7.75 10.0 43.9524 15.2389 43 - 15/16
7.75 10.5 41.8153 13.0441 41 - 13/16
7.75 11.0 39.8703 13.9247 39 - 13/16
7.75 11.5 38.0925 1.4795 38 -  1/16
7.75 12.0 36.4609 7.3741 36 -  7/16
7.75 12.5 34.9580 15.3279 34 - 15/16
7.75 13.0 33.5689 9.1030 33 -  9/16
7.75 13.5 32.2811 4.4972 32 -  1/4
7.75 14.0 31.0836 1.3368 31 -  1/16
7.75 14.5 29.9670 15.4724 29 - 15/16
7.75 15.0 28.9234 14.7743 28 -  7/8
7.75 15.5 27.9456 15.1296 27 - 15/16
7.75 16.0 27.0275 0.4394 27
Index
8.00 6.0 76.1149 1.8387 76 -  1/16
8.00 6.5 70.2151 3.4416 70 -  3/16
8.00 7.0 65.1548 2.4763 65 -  1/8
8.00 7.5 60.7660 12.2565 60 -  3/4
8.00 8.0 56.9230 14.7673 56 -  7/8
8.00 8.5 53.5292 8.4680 53 -  1/2
8.00 9.0 50.5100 8.1602 50 -  1/2
8.00 9.5 47.8061 12.8978 47 -  3/4
8.00 10.0 45.3703 5.9241 45 -  5/16
8.00 10.5 43.1641 2.6262 43 -  1/8
8.00 11.0 41.1564 2.5029 41 -  1/8
8.00 11.5 39.3213 5.1401 39 -  5/16
8.00 12.0 37.6370 10.1927 37 -  5/8
8.00 12.5 36.0857 1.3707 36 -  1/16
8.00 13.0 34.6518 10.4289 34 -  5/8
8.00 13.5 33.3224 5.1584 33 -  5/16
8.00 14.0 32.0862 1.3800 32 -  1/16
8.00 14.5 30.9337 14.9393 30 -  7/8
8.00 15.0 29.8564 13.7025 29 - 13/16
8.00 15.5 28.8471 13.5531 28 - 13/16
8.00 16.0 27.8993 14.3890 27 -  7/8
Index
8.25 6.0 78.4935 7.8961 78 -  7/16
8.25 6.5 72.4093 6.5491 72 -  3/8
8.25 7.0 67.1909 3.0537 67 -  3/16
8.25 7.5 62.6650 10.6395 62 -  5/8
8.25 8.0 58.7018 11.2288 58 - 11/16
8.25 8.5 55.2020 3.2326 55 -  3/16
8.25 9.0 52.0884 1.4152 52 -  1/16
8.25 9.5 49.3001 4.8009 49 -  1/4
8.25 10.0 46.7881 12.6092 46 -  3/4
8.25 10.5 44.5130 8.2083 44 -  1/2
8.25 11.0 42.4426 7.0811 42 -  7/16
8.25 11.5 40.5500 8.8007 40 -  1/2
8.25 12.0 38.8132 13.0112 38 - 13/16
8.25 12.5 37.2133 3.4135 37 -  3/16
8.25 13.0 35.7347 11.7548 35 - 11/16
8.25 13.5 34.3637 5.8196 34 -  5/16
8.25 14.0 33.0889 1.4231 33 -  1/16
8.25 14.5 31.9004 14.4061 31 -  7/8
8.25 15.0 30.7894 12.6307 30 -  3/4
8.25 15.5 29.7485 11.9766 29 -  3/4
8.25 16.0 28.7712 12.3387 28 -  3/4
Index
8.50 6.0 80.8721 13.9536 80 -  7/8
8.50 6.5 74.6035 9.6567 74 -  9/16
8.50 7.0 69.2269 3.6311 69 -  3/16
8.50 7.5 64.5639 9.0226 64 -  9/16
8.50 8.0 60.4806 7.6903 60 -  7/16
8.50 8.5 56.8748 13.9972 56 -  7/8
8.50 9.0 53.6669 10.6702 53 -  5/8
8.50 9.5 50.7940 12.7040 50 -  3/4
8.50 10.0 48.2059 3.2943 48 -  3/16
8.50 10.5 45.8619 13.7903 45 - 13/16
8.50 11.0 43.7287 11.6593 43 - 11/16
8.50 11.5 41.7788 12.4614 41 -  3/4
8.50 12.0 39.9894 15.8297 39 - 15/16
8.50 12.5 38.3410 5.4564 38 -  5/16
8.50 13.0 36.8175 13.0807 36 - 13/16
8.50 13.5 35.4050 6.4808 35 -  3/8
8.50 14.0 34.0916 1.4662 34 -  1/16
8.50 14.5 32.8671 13.8730 32 - 13/16
8.50 15.0 31.7224 11.5589 31 - 11/16
8.50 15.5 30.6500 10.4002 30 -  5/8
8.50 16.0 29.6430 10.2884 29 -  5/8
Index
8.75 6.0 83.2507 4.0110 83 -  1/4
8.75 6.5 76.7978 12.7642 76 -  3/4
8.75 7.0 71.2630 4.2085 71 -  1/4
8.75 7.5 66.4628 7.4056 66 -  7/16
8.75 8.0 62.2595 4.1518 62 -  1/4
8.75 8.5 58.5476 8.7619 58 -  1/2
8.75 9.0 55.2453 3.9252 55 -  3/16
8.75 9.5 52.2879 4.6070 52 -  1/4
8.75 10.0 49.6237 9.9795 49 -  5/8
8.75 10.5 47.2108 3.3724 47 -  3/16
8.75 11.0 45.0148 0.2376 45
8.75 11.5 43.0076 0.1220 43
8.75 12.0 41.1655 2.6482 41 -  1/8
8.75 12.5 39.4687 7.4992 39 -  7/16
8.75 13.0 37.9004 14.4066 37 -  7/8
8.75 13.5 36.4464 7.1420 36 -  7/16
8.75 14.0 35.0943 1.5093 35 -  1/16
8.75 14.5 33.8337 13.3398 33 - 13/16
8.75 15.0 32.6554 10.4871 32 -  5/8
8.75 15.5 31.5515 8.8237 31 -  1/2
8.75 16.0 30.5149 8.2380 30 -  1/2
Index
9.00 6.0 85.6293 10.0685 85 -  5/8
9.00 6.5 78.9920 15.8718 78 - 15/16
9.00 7.0 73.2991 4.7859 73 -  1/4
9.00 7.5 68.3618 5.7886 68 -  5/16
9.00 8.0 64.0383 0.6132 64
9.00 8.5 60.2204 3.5265 60 -  3/16
9.00 9.0 56.8238 13.1802 56 - 13/16
9.00 9.5 53.7819 12.5101 53 -  3/4
9.00 10.0 51.0415 0.6646 51
9.00 10.5 48.5597 8.9545 48 -  9/16
9.00 11.0 46.3010 4.8158 46 -  1/4
9.00 11.5 44.2364 3.7826 44 -  3/16
9.00 12.0 42.3417 5.4667 42 -  5/16
9.00 12.5 40.5964 9.5420 40 -  9/16
9.00 13.0 38.9833 15.7325 38 - 15/16
9.00 13.5 37.4877 7.8032 37 -  7/16
9.00 14.0 36.0970 1.5525 36 -  1/16
9.00 14.5 34.8004 12.8067 34 -  3/4
9.00 15.0 33.5885 9.4153 33 -  9/16
9.00 15.5 32.4530 7.2472 32 -  7/16
9.00 16.0 31.3867 6.1877 31 -  3/8
Index
9.25 6.0 88.0079 0.1259 88
9.25 6.5 81.1862 2.9793 81 -  3/16
9.25 7.0 75.3352 5.3633 75 -  5/16
9.25 7.5 70.2607 4.1716 70 -  1/4
9.25 8.0 65.8172 13.0747 65 - 13/16
9.25 8.5 61.8932 14.2911 61 -  7/8
9.25 9.0 58.4022 6.4352 58 -  3/8
9.25 9.5 55.2758 4.4131 55 -  1/4
9.25 10.0 52.4594 7.3497 52 -  7/16
9.25 10.5 49.9085 14.5365 49 -  7/8
9.25 11.0 47.5871 9.3940 47 -  9/16
9.25 11.5 45.4652 7.4432 45 -  7/16
9.25 12.0 43.5178 8.2853 43 -  1/2
9.25 12.5 41.7241 11.5849 41 - 11/16
9.25 13.0 40.0662 1.0584 40 -  1/16
9.25 13.5 38.5290 8.4644 38 -  1/2
9.25 14.0 37.0997 1.5956 37 -  1/16
9.25 14.5 35.7671 12.2735 35 -  3/4
9.25 15.0 34.5215 8.3435 34 -  1/2
9.25 15.5 33.3544 5.6708 33 -  5/16
9.25 16.0 32.2586 4.1373 32 -  1/4
Index
9.50 6.0 90.3865 6.1834 90 -  3/8
9.50 6.5 83.3804 6.0869 83 -  3/8
9.50 7.0 77.3713 5.9407 77 -  5/16
9.50 7.5 72.1597 2.5546 72 -  1/8
9.50 8.0 67.5960 9.5362 67 -  9/16
9.50 8.5 63.5660 9.0557 63 -  9/16
9.50 9.0 59.9806 15.6902 59 - 15/16
9.50 9.5 56.7698 12.3162 56 -  3/4
9.50 10.0 53.8772 14.0348 53 -  7/8
9.50 10.5 51.2574 4.1186 51 -  1/4
9.50 11.0 48.8733 13.9722 48 -  7/8
9.50 11.5 46.6940 11.1039 46 - 11/16
9.50 12.0 44.6940 11.1038 44 - 11/16
9.50 12.5 42.8517 13.6277 42 - 13/16
9.50 13.0 41.1490 2.3843 41 -  1/8
9.50 13.5 39.5703 9.1256 39 -  9/16
9.50 14.0 38.1024 1.6387 38 -  1/16
9.50 14.5 36.7338 11.7404 36 - 11/16
9.50 15.0 35.4545 7.2717 35 -  7/16
9.50 15.5 34.2559 4.0943 34 -  1/4
9.50 16.0 33.1304 2.0870 33 -  1/8
Index
9.75 6.0 92.7651 12.2409 92 -  3/4
9.75 6.5 85.5747 9.1944 85 -  9/16
9.75 7.0 79.4074 6.5180 79 -  3/8
9.75 7.5 74.0586 0.9376 74
9.75 8.0 69.3749 5.9977 69 -  3/8
9.75 8.5 65.2388 3.8204 65 -  3/16
9.75 9.0 61.5591 8.9452 61 -  1/2
9.75 9.5 58.2637 4.2192 58 -  1/4
9.75 10.0 55.2950 4.7200 55 -  1/4
9.75 10.5 52.6063 9.7007 52 -  9/16
9.75 11.0 50.1594 2.5504 50 -  1/8
9.75 11.5 47.9228 14.7645 47 -  7/8
9.75 12.0 45.8701 13.9223 45 - 13/16
9.75 12.5 43.9794 15.6705 43 - 15/16
9.75 13.0 42.2319 3.7102 42 -  3/16
9.75 13.5 40.6117 9.7868 40 -  9/16
9.75 14.0 39.1051 1.6818 39 -  1/16
9.75 14.5 37.7005 11.2072 37 - 11/16
9.75 15.0 36.3875 6.1999 36 -  3/8
9.75 15.5 35.1574 2.5178 35 -  1/8
9.75 16.0 34.0023 0.0367 34
Index
10.00 6.0 95.1436 2.2983 95 -  1/8
10.00 6.5 87.7689 12.3020 87 -  3/4
10.00 7.0 81.4435 7.0954 81 -  7/16
10.00 7.5 75.9575 15.3207 75 - 15/16
10.00 8.0 71.1537 2.4592 71 -  1/8
10.00 8.5 66.9116 14.5850 66 -  7/8
10.00 9.0 63.1375 2.2002 63 -  1/8
10.00 9.5 59.7576 12.1223 59 -  3/4
10.00 10.0 56.7128 11.4051 56 - 11/16
10.00 10.5 53.9552 15.2827 53 - 15/16
10.00 11.0 51.4455 7.1286 51 -  7/16
10.00 11.5 49.1516 2.4251 49 -  1/8
10.00 12.0 47.0463 0.7408 47
10.00 12.5 45.1071 1.7134 45 -  1/16
10.00 13.0 43.3148 5.0361 43 -  5/16
10.00 13.5 41.6530 10.4480 41 -  5/8
10.00 14.0 40.1078 1.7249 40 -  1/16
10.00 14.5 38.6671 10.6741 38 -  5/8
10.00 15.0 37.3205 5.1281 37 -  5/16
10.00 15.5 36.0588 0.9414 36
10.00 16.0 34.8741 13.9863 34 -  7/8
Index

           

PHP code written by Paul Kane, Chelsea, Quebec
Building the Glen-L Hot Rod : www.boats.chelseacoachworks.com

23-May-2022 19:45:42