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