(I re-post this message here because I cannot get any reply when I
posted it elsewhere. Sorry about the re-post)

I am planning to get a 9.9hp outboard motor as an auxiliary motor. But
I don't know how long the shaft should I get. Should this be 15", 20",
or 25"? I have a feeling that the shaft length is depending on the
height of the transom. The transom height is 21" as measured from the
top edge of the transom (where the main motor is mounted on) to the
bottom of the transom as shown in this picture of my transom:
http://www.geocities.com/jaykchan/Ma...o_Transom.html

Just in case the transom height is not the right info for determining
the shaft length, I also provide the following info. Hopefully,
between the picture and the following info, we will be able to
determine the right shaft length:
Main Outboard Shaft Length: 20"
Boat Draft with Main Outboard is Up: 26"
Boat Draft with Main Outboard is Down: 12"

To complicate thing a bit, I likely need to mount the auxiliary motor
on an motor bracket, such as this "Offshore Auxiliary Outboard
Brackets" from Garelick:
http://www.westmarine.com/webapp/wcs...ducte/10001/-1...
This is supposed to lift the motor vertically by 15 1/2''.

Or this "Lift & Lower OB Bracket (for less than 20hp motor)" from
Garelick:
http://www.westmarine.com/webapp/wcs...ducte/10001/-1...
This is supposed to lift the motor vertically by 11-1/4".

I want to use a motor bracket. The reason is that there is a 6" tall
object on the spot where I am supposed to mount the auxiliary motor
(please see the picture in the link above). This means I cannot simply
mount the auxiliary motor over the edge of the transom.

Will the use of motor bracket affects the shaft length that I should
get?

Thanks in advance for any help.

Jay Chan

On 31 May 2006 11:09:17 -0700, wrote:

I am planning to get a 9.9hp outboard motor as an auxiliary motor. But
I don't know how long the shaft should I get.

As I understand it, the cavitation plate (horizontal surface above the
propellor) should be at least several inches below the bottom of the
boat when the motor is fully lowered. This is to prevent turbulent
water and air from being sucked into the prop, which causes over
reving and excessive slip (cavitation). Obviously your choice of
mounting location for the motor bracket plays into this decision.

Wayne.B wrote:
On 31 May 2006 11:09:17 -0700, wrote:

I am planning to get a 9.9hp outboard motor as an auxiliary motor. But
I don't know how long the shaft should I get.

As I understand it, the cavitation plate (horizontal surface above the
propellor) should be at least several inches below the bottom of the
boat when the motor is fully lowered. This is to prevent turbulent
water and air from being sucked into the prop, which causes over
reving and excessive slip (cavitation). Obviously your choice of
mounting location for the motor bracket plays into this decision.

Thanks for the info. If I understand you correctly, you are saying
that the propellor of the auxiliary motor should be several inches
below the bottom of the boat (just like what the propeller of my main
motor current is). Here, the transom of the boat is a semi-V; the
auxiliary motor will be mounted on the side of the main motor where the
bottom of the transom is higher than the true bottom of the boat. I
assume that I need to positon the propeller of the auxiliary motor
slightly above the propeller of the main motor in order to keep the
propeller several inches above the bottom of the transom (instead of
several inches above the true bottom of the boat). Is my understanding
correct?

One thing that I would like to know is:
What's the definition of the length of the shaft of a motor? How
is this being measured? Is this measured from the axis of the
propeller to the bottom edge of the solid mass of the large motor head
(that occupies the upper half of an outboard motor)?

Thanks for any following-up info in advance.

Jay Chan

wrote:
snip..
One thing that I would like to know is:
What's the definition of the length of the shaft of a motor? How
is this being measured? Is this measured from the axis of the
propeller to the bottom edge of the solid mass of the large motor head
(that occupies the upper half of an outboard motor)?

Thanks for any following-up info in advance.

Jay Chan


As I understand it...you measure from the edge of the bracket that
clamps onto your transom to the top of the cavitation plate.
(or if the motor is mounted...from the top of the transom where the
outboard clamp sits to the top of the cavitation plate)
Approx 15" is considered 'short shaft'....
20" would be 'long shaft'.

Don White wrote:
wrote:
snip..
One thing that I would like to know is:
What's the definition of the length of the shaft of a motor? How
is this being measured? Is this measured from the axis of the
propeller to the bottom edge of the solid mass of the large motor head
(that occupies the upper half of an outboard motor)?

Thanks for any following-up info in advance.

Jay Chan


As I understand it...you measure from the edge of the bracket that
clamps onto your transom to the top of the cavitation plate.
(or if the motor is mounted...from the top of the transom where the
outboard clamp sits to the top of the cavitation plate)
Approx 15" is considered 'short shaft'....
20" would be 'long shaft'.

Thanks for the explanation of how a shaft is being measured. This
should help me in selecting the correct shaft for an auxiliary motor.

Jay Chan