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Author Topic:   1961 13 STANDARD Engine Shaft Length

19snooky63 posted 01-15-2015 05:24 AM ET (US)
[Some dimension of the] transom [of a 1961 Boston Whaler 13-foot STANDARD boat] is 17-inch. The anti-ventilation plate of the recommended short shaft or 15-inch shaft outboard will be 2-inch above keel. Will this affect performance? I am getting a 25-HP. Thanks.
macfam posted 01-15-2015 06:35 AM ET (US)
That's about right. You want the anti-ventilation plate ABOVE the keel, never equal to, or below. The best performance and control, and least porpoising occurs when plate is 1-inch to 2-inch above the keel.
jimh posted 01-15-2015 09:48 AM ET (US)
The transom of the older Boston Whaler boats is designed for outboard engines with a short shaft or 15-inch shaft. There really is not any particular dimension on the transom that is supposed to be precisely 15-inches.
Having an outboard engine with the wrong shaft length affects performance.
dg22 posted 01-15-2015 10:45 AM ET (US)
When measuring the transom, you need to take a vertical measurement. It should be closer to 15 inch.
jimh posted 01-15-2015 11:38 AM ET (US)
The vertical height will be shorter, but it won't be 15-inches on a transom of 17-inch height with the usual transom angle of around 13-degrees. It will be more like 16.5.
The trigonometry will be
vertical height = COS(transomAngle) x (transom height)
vertical height = COS(13) x 17
vertical height = 16.56
dg22 posted 01-15-2015 03:29 PM ET (US)

I read a post here that the actual transom angle of the 13-footer is 20-degrees. I borrowed my daughter's calculator and this works out to a vertical height of 16 inches using the formula Jimh provided. If I remember correctly that is close to what I measured a few years back.
http://continuouswave.com/ubb/Forum4/HTML/005272.html

19snooky63 posted 01-15-2015 05:39 PM ET (US)
thanx a lot folks you were realy helpful,i,m doing a total redo outside is buffed out,inside is blocked to 220,shold buff it out this weekend,came with orig brass and stainless,will post pics if I can fig it out,thanx again.

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Author	Topic: 1961 13 STANDARD Engine Shaft Length
19snooky63	posted 01-15-2015 05:24 AM ET (US) [Some dimension of the] transom [of a 1961 Boston Whaler 13-foot STANDARD boat] is 17-inch. The anti-ventilation plate of the recommended short shaft or 15-inch shaft outboard will be 2-inch above keel. Will this affect performance? I am getting a 25-HP. Thanks.
macfam	posted 01-15-2015 06:35 AM ET (US) That's about right. You want the anti-ventilation plate ABOVE the keel, never equal to, or below. The best performance and control, and least porpoising occurs when plate is 1-inch to 2-inch above the keel.
jimh	posted 01-15-2015 09:48 AM ET (US) The transom of the older Boston Whaler boats is designed for outboard engines with a short shaft or 15-inch shaft. There really is not any particular dimension on the transom that is supposed to be precisely 15-inches. Having an outboard engine with the wrong shaft length affects performance.
dg22	posted 01-15-2015 10:45 AM ET (US) When measuring the transom, you need to take a vertical measurement. It should be closer to 15 inch.
jimh	posted 01-15-2015 11:38 AM ET (US) The vertical height will be shorter, but it won't be 15-inches on a transom of 17-inch height with the usual transom angle of around 13-degrees. It will be more like 16.5. The trigonometry will be vertical height = COS(transomAngle) x (transom height) vertical height = COS(13) x 17 vertical height = 16.56
dg22	posted 01-15-2015 03:29 PM ET (US) I read a post here that the actual transom angle of the 13-footer is 20-degrees. I borrowed my daughter's calculator and this works out to a vertical height of 16 inches using the formula Jimh provided. If I remember correctly that is close to what I measured a few years back. http://continuouswave.com/ubb/Forum4/HTML/005272.html
19snooky63	posted 01-15-2015 05:39 PM ET (US) thanx a lot folks you were realy helpful,i,m doing a total redo outside is buffed out,inside is blocked to 220,shold buff it out this weekend,came with orig brass and stainless,will post pics if I can fig it out,thanx again.