Actual Shaft length 1987 70hp Merc 20"? - Moderated Discussion Areas

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Author Topic:   Actual Shaft length 1987 70hp Merc 20"?

number9 posted 12-20-2008 09:09 PM ET (US)
Can anyone provide the true dimension from cavitation plate to top of mounting bracket lower surface? Went to the Worldwide/European Merc site and their drawing don't go back that far. Will appreciate any help on this.
Also searched the forums and found some positive comments on these motors. Any more info appreciated also. Found three of these NIB.
Thanks and ya'll take care,
Bill
Tohsgib posted 12-22-2008 12:41 PM ET (US)
All 70's of that era are 20"
Tom W Clark posted 12-30-2008 01:08 PM ET (US)
One poorly understood aspect of the "shaft length" dimension is that it is merely an indication of the height of the transom the motor is designed to best fit.
"Shaft length" is NOT a measurement from the cavitation plate to the motor mounting bracket. It is also not consistent between manufactures or even between different models within one manufacturer's line of outboard motors.
number9 posted 12-31-2008 07:28 PM ET (US)
Tom,
You said, "One poorly understood aspect of the "shaft length..." Have read more than a few of your knowledgeable replies and just wonder why you replied as if the topic question was dumb or author was ignorant of what your reply stated. Obviously if one were in the market for a new or used outboard, a question as asked would be a good one and possibly indicate the author knew of the variations you mentioned.
Wouldn't it be better to tell us why the lengths do vary, where to find the actual dimensions and why the heck the industry doesn't make this information widely known to individual consumers.
Bill
lizard posted 01-01-2009 11:52 AM ET (US)
http://www.smalloutboards.com/shaft.htm
The above link is a good reference for this question.
Tohsgib posted 01-02-2009 10:48 AM ET (US)
I thought Tom's explanation was fine and not condescending at all.
Tom W Clark posted 01-02-2009 06:28 PM ET (US)
Bill,
I think you are reading things that are not there.
As an aside, a very common misconception about the typical online question and answer here is that a reply is simply an answer to the question posed, and if the person asking the question gets the information they are looking for, then that is the end of it, as if the dialogue were only between the participants.
The reality is that there are hundreds or maybe thousands of other folks reading the thread and there will continue to be for years to come as Google and other search engines yield search results for different inquiries.
Knowing that this is the case, we can all be helpful by being mindful of this and include information that may be of use to such folks.
In this case I know there will be others reading this thread trying to figure out what "shaft length" really means.
Because it so commonly misunderstood, a simple explanation may help others understand what it really is.
By the same token, it is good if we try to avoid all but the very most common acronyms and not reply to questions presuming readers already know all the background.
It is also nice when folks asking for advice for a problem report back after the problem is solved to finish up a thread with a conclusion, even though their own needs may have already been met.
L H G posted 01-09-2009 10:20 PM ET (US)
This may help out: Lots of good information directly from Merc, particularly on recommended engine mounting heights based on boat speed potential. (see written text and examples)
http://www.marinepartsman.com/installing-an-outboard-on-your-boat.html
L H G posted 01-09-2009 10:24 PM ET (US)
Further to the above, note that the "notch in transom" that Mercury refers to, allowing a higher engine mount, is a similar condition to a Whaler Drive.
number9 posted 01-10-2009 03:40 AM ET (US)
Picked up my three Mercs last night, will report back on actual shaft length/transom height when one is removed from the shipping crate.
Tohsgib posted 01-12-2009 12:23 PM ET (US)
Again...all 70's come in 20" shaft only. Would be cool droppiing all 3 on my 19 revenge which is designed for a single 20" or twin 20's so why not triples?

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Author	Topic: Actual Shaft length 1987 70hp Merc 20"?
number9	posted 12-20-2008 09:09 PM ET (US) Can anyone provide the true dimension from cavitation plate to top of mounting bracket lower surface? Went to the Worldwide/European Merc site and their drawing don't go back that far. Will appreciate any help on this. Also searched the forums and found some positive comments on these motors. Any more info appreciated also. Found three of these NIB. Thanks and ya'll take care, Bill
Tohsgib	posted 12-22-2008 12:41 PM ET (US) All 70's of that era are 20"
Tom W Clark	posted 12-30-2008 01:08 PM ET (US) One poorly understood aspect of the "shaft length" dimension is that it is merely an indication of the height of the transom the motor is designed to best fit. "Shaft length" is NOT a measurement from the cavitation plate to the motor mounting bracket. It is also not consistent between manufactures or even between different models within one manufacturer's line of outboard motors.
number9	posted 12-31-2008 07:28 PM ET (US) Tom, You said, "One poorly understood aspect of the "shaft length..." Have read more than a few of your knowledgeable replies and just wonder why you replied as if the topic question was dumb or author was ignorant of what your reply stated. Obviously if one were in the market for a new or used outboard, a question as asked would be a good one and possibly indicate the author knew of the variations you mentioned. Wouldn't it be better to tell us why the lengths do vary, where to find the actual dimensions and why the heck the industry doesn't make this information widely known to individual consumers. Bill
lizard	posted 01-01-2009 11:52 AM ET (US) http://www.smalloutboards.com/shaft.htm The above link is a good reference for this question.
Tohsgib	posted 01-02-2009 10:48 AM ET (US) I thought Tom's explanation was fine and not condescending at all.
Tom W Clark	posted 01-02-2009 06:28 PM ET (US) Bill, I think you are reading things that are not there. As an aside, a very common misconception about the typical online question and answer here is that a reply is simply an answer to the question posed, and if the person asking the question gets the information they are looking for, then that is the end of it, as if the dialogue were only between the participants. The reality is that there are hundreds or maybe thousands of other folks reading the thread and there will continue to be for years to come as Google and other search engines yield search results for different inquiries. Knowing that this is the case, we can all be helpful by being mindful of this and include information that may be of use to such folks. In this case I know there will be others reading this thread trying to figure out what "shaft length" really means. Because it so commonly misunderstood, a simple explanation may help others understand what it really is. By the same token, it is good if we try to avoid all but the very most common acronyms and not reply to questions presuming readers already know all the background. It is also nice when folks asking for advice for a problem report back after the problem is solved to finish up a thread with a conclusion, even though their own needs may have already been met.
L H G	posted 01-09-2009 10:20 PM ET (US) This may help out: Lots of good information directly from Merc, particularly on recommended engine mounting heights based on boat speed potential. (see written text and examples) http://www.marinepartsman.com/installing-an-outboard-on-your-boat.html
L H G	posted 01-09-2009 10:24 PM ET (US) Further to the above, note that the "notch in transom" that Mercury refers to, allowing a higher engine mount, is a similar condition to a Whaler Drive.
number9	posted 01-10-2009 03:40 AM ET (US) Picked up my three Mercs last night, will report back on actual shaft length/transom height when one is removed from the shipping crate.
Tohsgib	posted 01-12-2009 12:23 PM ET (US) Again...all 70's come in 20" shaft only. Would be cool droppiing all 3 on my 19 revenge which is designed for a single 20" or twin 20's so why not triples?