I am planning to get an auxiliary outboard motor (likely to be a Yamaha
High Thrust T9.9), and mount it on the transom of a 18-ft center
console. I have a couple questions related to exactly where to
position it:

1. I have a 115hp main outboard motor already mounted at the center of
the transom. Should I mount the small auxiliary motor in the left of
the main motor or in the right? Does this really matter? I prefer to
mount it left of the main motor if I can do that.

2. What is the minimum distance between the main outboard and the
auxiliary outboard? I guess the auxiliary outboard is supposed to be
mounted as much at the center of the transom as possible in order to
push the boat properly, right? But the main outboard already takes the
center place. Therefore, the auxiliary outboard must be off to the
side. I am trying to figure out how close I should place the auxiliary
outboard to the main outboard. Does this really matter anyway? I have
a feeling that the rod that links the main outboard and the auxiliary
outboard together may dictate how close I can put them together.

3. I would like to know how deep I should position the auxiliary
outboard into the water. I have found two rules in the downloaded
owner manual of Yamaha outboard. The first rule says that we should
keep the cavitation plate at least 1 inch below the bottom of a boat if
the outboard is being used as a main motor of the boat. The second
rule says that we should keep the cavitation plate several inches below
the water surface if the outboard is being used as an auxiliary motor
in a sail boat (something to do with the sailboat tends to roll
around). How do these fit into my case? Because my boat has a semi-V
bottom, its sides are higher than the center. If I follow the first
rule, I assume I should position the cavitation plate of the auxiliary
outboard one inch below the bottom of the boat that is slightly higher
than the lowest bottom of the boat because the auxiliary outboard is
not centered in the transom. Is this right? If I follow the second
rule, I will position the cavitation plate in a different place than if
I had followed the first rule. Which one is correct?

4. I will mount the auxiliary motor on a motor bracket that can lift
the motor up or down vertically. But that motor bracket seems to be
designed for being mounted on a flat transom. But the transom in my
boat is slightly curved. How should I mount the motor bracket onto my
transom? Do I need to use some shims? How do people normally handle
this situation?

Thanks in advance for any info.

Jay Chan

Hi Jay,

My boat is not exactly a fit to yours, but I may provide some limited info for
you.
I have a 22 foot sailboat which is fitted with the T9.9 Hi Thrust as the sole
power
source. It is offset half way between the center line and edge of the rear
transom
on the port side. The offset does not seem to effect performance, but the
intent of
the manufacturer was to get the engine out of the way of the backstay (I
believe).
I have a large Garelick adjustable motor mount, which is positioned so that the
next
to lowest setting keeps the engine a bit lower than Yamaha recommends. I find
that
there is less chance for the prop to come out of the water in most conditions.
I keep
the very bottom setting for very wavy conditions in a following sea. There are
two
more positions, but only the second from the top can be used for running, but as
I
mentioned before, the propellor seems to cavitate less when lower in the water.
The
nice thing about this Garelick is that it has a high range of lift distance,
which allows me
to lift the long shaft high enough so that the prop clears the water when tilted
back in
the non running (sail only) position.

Hope this helps,

Sherwin D.

wrote:

I am planning to get an auxiliary outboard motor (likely to be a Yamaha
High Thrust T9.9), and mount it on the transom of a 18-ft center
console. I have a couple questions related to exactly where to
position it:

1. I have a 115hp main outboard motor already mounted at the center of
the transom. Should I mount the small auxiliary motor in the left of
the main motor or in the right? Does this really matter? I prefer to
mount it left of the main motor if I can do that.

2. What is the minimum distance between the main outboard and the
auxiliary outboard? I guess the auxiliary outboard is supposed to be
mounted as much at the center of the transom as possible in order to
push the boat properly, right? But the main outboard already takes the
center place. Therefore, the auxiliary outboard must be off to the
side. I am trying to figure out how close I should place the auxiliary
outboard to the main outboard. Does this really matter anyway? I have
a feeling that the rod that links the main outboard and the auxiliary
outboard together may dictate how close I can put them together.

3. I would like to know how deep I should position the auxiliary
outboard into the water. I have found two rules in the downloaded
owner manual of Yamaha outboard. The first rule says that we should
keep the cavitation plate at least 1 inch below the bottom of a boat if
the outboard is being used as a main motor of the boat. The second
rule says that we should keep the cavitation plate several inches below
the water surface if the outboard is being used as an auxiliary motor
in a sail boat (something to do with the sailboat tends to roll
around). How do these fit into my case? Because my boat has a semi-V
bottom, its sides are higher than the center. If I follow the first
rule, I assume I should position the cavitation plate of the auxiliary
outboard one inch below the bottom of the boat that is slightly higher
than the lowest bottom of the boat because the auxiliary outboard is
not centered in the transom. Is this right? If I follow the second
rule, I will position the cavitation plate in a different place than if
I had followed the first rule. Which one is correct?

4. I will mount the auxiliary motor on a motor bracket that can lift
the motor up or down vertically. But that motor bracket seems to be
designed for being mounted on a flat transom. But the transom in my
boat is slightly curved. How should I mount the motor bracket onto my
transom? Do I need to use some shims? How do people normally handle
this situation?

Thanks in advance for any info.

Jay Chan

Hi again Jay,

Forgot to mention that my transom is not flat in the horizontal plane,
so I had
to put about a 1 inch shim on the outboard side to square it up. Works fine.

Sherwin D.

wrote:

I am planning to get an auxiliary outboard motor (likely to be a Yamaha
High Thrust T9.9), and mount it on the transom of a 18-ft center
console. I have a couple questions related to exactly where to
position it:

1. I have a 115hp main outboard motor already mounted at the center of
the transom. Should I mount the small auxiliary motor in the left of
the main motor or in the right? Does this really matter? I prefer to
mount it left of the main motor if I can do that.

2. What is the minimum distance between the main outboard and the
auxiliary outboard? I guess the auxiliary outboard is supposed to be
mounted as much at the center of the transom as possible in order to
push the boat properly, right? But the main outboard already takes the
center place. Therefore, the auxiliary outboard must be off to the
side. I am trying to figure out how close I should place the auxiliary
outboard to the main outboard. Does this really matter anyway? I have
a feeling that the rod that links the main outboard and the auxiliary
outboard together may dictate how close I can put them together.

3. I would like to know how deep I should position the auxiliary
outboard into the water. I have found two rules in the downloaded
owner manual of Yamaha outboard. The first rule says that we should
keep the cavitation plate at least 1 inch below the bottom of a boat if
the outboard is being used as a main motor of the boat. The second
rule says that we should keep the cavitation plate several inches below
the water surface if the outboard is being used as an auxiliary motor
in a sail boat (something to do with the sailboat tends to roll
around). How do these fit into my case? Because my boat has a semi-V
bottom, its sides are higher than the center. If I follow the first
rule, I assume I should position the cavitation plate of the auxiliary
outboard one inch below the bottom of the boat that is slightly higher
than the lowest bottom of the boat because the auxiliary outboard is
not centered in the transom. Is this right? If I follow the second
rule, I will position the cavitation plate in a different place than if
I had followed the first rule. Which one is correct?

4. I will mount the auxiliary motor on a motor bracket that can lift
the motor up or down vertically. But that motor bracket seems to be
designed for being mounted on a flat transom. But the transom in my
boat is slightly curved. How should I mount the motor bracket onto my
transom? Do I need to use some shims? How do people normally handle
this situation?

Thanks in advance for any info.

Jay Chan

Thanks for sharing the info about your auxiliary motor in your
sailboat.

Would you please tell me which motor bracket from Garelick that you are
using. Because your auxiliary outboard is exactly the same model as
the one that I plan to get, the motor bracket that you have selected
should be a very relevant info to me.

Glad to hear that the outboard can be mounted offset from the center
line without affecting the performance of the outboard. Also glad to
hear that you are mounting the outboard in the left side of the transom
where I intend to mount mine. Seem like those two things are really
not problem at all. Now, I just need to make sure the rod that connect
the main motor with the auxiliary motor can clear that area.

Because yours is a sailboat, I have a feeling that it must have a round
hull, right? How exactly do you position the auxiliary outboard? Do
you position it in relation to the true bottom of the hull or in
relation to the bottom edge of the transom?

In your second reply, you are saying that you need to put some shims
behind the motor bracket to make it to conform to the curve of the
transom. Which material do you use?

Jay Chan

sherwindu wrote:
Hi Jay,

My boat is not exactly a fit to yours, but I may provide some limited info for
you.
I have a 22 foot sailboat which is fitted with the T9.9 Hi Thrust as the sole
power
source. It is offset half way between the center line and edge of the rear
transom
on the port side. The offset does not seem to effect performance, but the
intent of
the manufacturer was to get the engine out of the way of the backstay (I
believe).
I have a large Garelick adjustable motor mount, which is positioned so that the
next
to lowest setting keeps the engine a bit lower than Yamaha recommends. I find
that
there is less chance for the prop to come out of the water in most conditions.
I keep
the very bottom setting for very wavy conditions in a following sea. There are
two
more positions, but only the second from the top can be used for running, but as
I
mentioned before, the propellor seems to cavitate less when lower in the water.
The
nice thing about this Garelick is that it has a high range of lift distance,
which allows me
to lift the long shaft high enough so that the prop clears the water when tilted
back in
the non running (sail only) position.

Hope this helps,

Sherwin D.

wrote:

I am planning to get an auxiliary outboard motor (likely to be a Yamaha
High Thrust T9.9), and mount it on the transom of a 18-ft center
console. I have a couple questions related to exactly where to
position it:

1. I have a 115hp main outboard motor already mounted at the center of
the transom. Should I mount the small auxiliary motor in the left of
the main motor or in the right? Does this really matter? I prefer to
mount it left of the main motor if I can do that.

2. What is the minimum distance between the main outboard and the
auxiliary outboard? I guess the auxiliary outboard is supposed to be
mounted as much at the center of the transom as possible in order to
push the boat properly, right? But the main outboard already takes the
center place. Therefore, the auxiliary outboard must be off to the
side. I am trying to figure out how close I should place the auxiliary
outboard to the main outboard. Does this really matter anyway? I have
a feeling that the rod that links the main outboard and the auxiliary
outboard together may dictate how close I can put them together.

3. I would like to know how deep I should position the auxiliary
outboard into the water. I have found two rules in the downloaded
owner manual of Yamaha outboard. The first rule says that we should
keep the cavitation plate at least 1 inch below the bottom of a boat if
the outboard is being used as a main motor of the boat. The second
rule says that we should keep the cavitation plate several inches below
the water surface if the outboard is being used as an auxiliary motor
in a sail boat (something to do with the sailboat tends to roll
around). How do these fit into my case? Because my boat has a semi-V
bottom, its sides are higher than the center. If I follow the first
rule, I assume I should position the cavitation plate of the auxiliary
outboard one inch below the bottom of the boat that is slightly higher
than the lowest bottom of the boat because the auxiliary outboard is
not centered in the transom. Is this right? If I follow the second
rule, I will position the cavitation plate in a different place than if
I had followed the first rule. Which one is correct?

4. I will mount the auxiliary motor on a motor bracket that can lift
the motor up or down vertically. But that motor bracket seems to be
designed for being mounted on a flat transom. But the transom in my
boat is slightly curved. How should I mount the motor bracket onto my
transom? Do I need to use some shims? How do people normally handle
this situation?

Thanks in advance for any info.

Jay Chan

Now if this was about...
How to position an Auxillary Motor on the Transom of a 18-ft SAIL Boat?