Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Go with the biggest, 9.9 hp. On a windy day you will need all of that
on a 3,000 lb boat. You could probably get by with 6 hp in smooth
conditions buy it will not be enough to get through waves properly
when the wind is blowing hard. You should also get a special prop
with a lower pitch ratio than normal, and as many blades as possible,
like a work boat prop.


On 16 May 2006 14:27:35 -0700, "
wrote:

I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets hull speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Seem like the choice is between 9.9hp and 6hp. I don't want to run a
boat when I expect the wind will be blowing hard. In theory, this
means that a 6hp should be good enough. But I remember one time I ran
a boat and the day started quite well enough, and then in the afternoon
the wind started picking up. Sound like a 9.9hp is a better bet just
in case the weather unexpectedly changed right in the middle of a trip
in a 9.9hp-only lake. Now, I just need to find a way to dismount/mount
a 100-lb 9.9hp outboard by myself when I need to use the outboard in a
small row boat. Thanks for sharing the info.

Thanks for the info about prop with low pitch and many blades. Do I
need to change the prop back to the way it was when I move the outboard
to a small boat?

Jay Chan


Wayne.B wrote:
Go with the biggest, 9.9 hp. On a windy day you will need all of that
on a 3,000 lb boat. You could probably get by with 6 hp in smooth
conditions buy it will not be enough to get through waves properly
when the wind is blowing hard. You should also get a special prop
with a lower pitch ratio than normal, and as many blades as possible,
like a work boat prop.


On 16 May 2006 14:27:35 -0700, "
wrote:

I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

On 17 May 2006 08:10:51 -0700, "
wrote:

Now, I just need to find a way to dismount/mount
a 100-lb 9.9hp outboard by myself when I need to use the outboard in a
small row boat.

Try something like this:

http://www.yachtsofstuff.com/userPos...ff&cexs=ocmar3

You could probably build your own from steel channel.

Thanks for the info about prop with low pitch and many blades. Do I
need to change the prop back to the way it was when I move the outboard
to a small boat?

For optimal performance and motor longevity, the prop always should be
matched to the load. The risk of using a low pitch prop on a light
weight boat is over reving the engine and not making full boat speed.

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Calif Bill wrote:
wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets hull speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Glad to hear that you have good result using a 8hp with your slightly
longer and heavier boat. I probably will stick with 9.9hp instead of
8hp because there is hardly any price and weight difference between
them (according to the spec of Nissan outboard shown in Cabelas.com).

I would love to be able to use a 6hp in my boat as an auxiliary motor
because it is almost half the weight of a 9.9hp motor. But I have a
feeling that it may not be able to handle unexpected weather condition
if I have it in my boat.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Harry Krause wrote:
wrote:
Seem like the choice is between 9.9hp and 6hp. I don't want to run a
boat when I expect the wind will be blowing hard. In theory, this
means that a 6hp should be good enough. But I remember one time I ran
a boat and the day started quite well enough, and then in the afternoon
the wind started picking up. Sound like a 9.9hp is a better bet just
in case the weather unexpectedly changed right in the middle of a trip
in a 9.9hp-only lake. Now, I just need to find a way to dismount/mount
a 100-lb 9.9hp outboard by myself when I need to use the outboard in a
small row boat. Thanks for sharing the info.

Thanks for the info about prop with low pitch and many blades. Do I
need to change the prop back to the way it was when I move the outboard
to a small boat?

Jay Chan


"Now, I just need to find a way to dismount/mount
a 100-lb 9.9hp outboard by myself when I need to use the outboard in a
small row boat."

Free weights.

Good point. Now, I have thought of this for the second time, I think I
should be able to handle 100-lb motor. What was I thinking anyway? I
must have thought of lifting 100-lb overhead for 10 repetitions instead
of just lifting the 100-lb from one boat to the other. Now that I know
I should be able to lift a 9.9hp motor without hurting myself, I should
not hesistate to choose a 9.9hp outboard.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Wayne.B wrote:
On 17 May 2006 08:10:51 -0700, "
wrote:

Now, I just need to find a way to dismount/mount
a 100-lb 9.9hp outboard by myself when I need to use the outboard in a
small row boat.

Try something like this:

http://www.yachtsofstuff.com/userPos...ff&cexs=ocmar3

You could probably build your own from steel channel.

Thanks for the info about prop with low pitch and many blades. Do I
need to change the prop back to the way it was when I move the outboard
to a small boat?

For optimal performance and motor longevity, the prop always should be
matched to the load. The risk of using a low pitch prop on a light
weight boat is over reving the engine and not making full boat speed.

Thanks for the link. Now I realize that I should be able to handle
100-lb motor without any problem. I didn't think this thoroughly.
Sorry about this. I think all I need is a mobile motor mount where I
can rest the motor on it while I move the motor from one boat to
another boat.

Also thanks for pointing out the need of matching the prop to the boat.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

wrote in message
oups.com...
Calif Bill wrote:
wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets hull
speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Glad to hear that you have good result using a 8hp with your slightly
longer and heavier boat. I probably will stick with 9.9hp instead of
8hp because there is hardly any price and weight difference between
them (according to the spec of Nissan outboard shown in Cabelas.com).

I would love to be able to use a 6hp in my boat as an auxiliary motor
because it is almost half the weight of a 9.9hp motor. But I have a
feeling that it may not be able to handle unexpected weather condition
if I have it in my boat.

Jay Chan


Actually a kicker and a small boat primary motor are dfferent beasts. I use
to use the 15 hp Mariner 2 stroke from my 14' 200# aluminum boat as a kicker
on the 21' boat. Got about 5.5 mph out of the motor, a lot of prop slip
when trying to push the big boat to hull speed. My 8 hp Yamaha T-8 pushes
the boat about 6.5 mph, or close to hull speed, at about 2/3 throttle. The
difference is the high thrust has a bigger leg, form an about 25 hp motor
with more clearance for the prop and swings a larger, higher pitch prop at a
geared down speed. My T-8 is not a candidate to wap between boats as it has
power tilt, electric start which all add weight. The 15 hp mariner 2 stroke
scaled about 85# and did troll OK, just did not troll as fast as the T-8.

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Calif Bill wrote:
wrote in message
oups.com...
Calif Bill wrote:
wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets hull
speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Glad to hear that you have good result using a 8hp with your slightly
longer and heavier boat. I probably will stick with 9.9hp instead of
8hp because there is hardly any price and weight difference between
them (according to the spec of Nissan outboard shown in Cabelas.com).

I would love to be able to use a 6hp in my boat as an auxiliary motor
because it is almost half the weight of a 9.9hp motor. But I have a
feeling that it may not be able to handle unexpected weather condition
if I have it in my boat.

Jay Chan


Actually a kicker and a small boat primary motor are dfferent beasts. I use
to use the 15 hp Mariner 2 stroke from my 14' 200# aluminum boat as a kicker
on the 21' boat. Got about 5.5 mph out of the motor, a lot of prop slip
when trying to push the big boat to hull speed. My 8 hp Yamaha T-8 pushes
the boat about 6.5 mph, or close to hull speed, at about 2/3 throttle. The
difference is the high thrust has a bigger leg, form an about 25 hp motor
with more clearance for the prop and swings a larger, higher pitch prop at a
geared down speed. My T-8 is not a candidate to wap between boats as it has
power tilt, electric start which all add weight. The 15 hp mariner 2 stroke
scaled about 85# and did troll OK, just did not troll as fast as the T-8.

Seem like your 8hp Yamaha T-8 High Thrust outboard is more powerful
than a 9.9hp (and 15hp) outboard for the purpose of trolling. This
means I cannot simply dismiss a 8hp motor just because its horsepower
rating is lower than a 9.9hp motor. There are some other factors that
I also need to consider.

What are the things that makes the Yamaha High Thrust motor more
powerful than a 15hp motor? Is the prop the primary factors because it
is bigger and higher pitch? If this is the case, I assume I can simply
replace the prop of a regular 8hp motor with a bigger and higher pitch
prop, and I should expect more trolling power from the regular 8hp
motor, right? Does the gear-box inside the motor need to be
correspondingly stronger in order to handle the bigger and higher pitch
prop?

Thanks for any info.

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

wrote in message
ups.com...
Calif Bill wrote:
wrote in message
oups.com...
Calif Bill wrote:
wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case
the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V.
The
boat is a center console. I guess I am asking for a motor that can
run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets hull
speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Glad to hear that you have good result using a 8hp with your slightly
longer and heavier boat. I probably will stick with 9.9hp instead of
8hp because there is hardly any price and weight difference between
them (according to the spec of Nissan outboard shown in Cabelas.com).

I would love to be able to use a 6hp in my boat as an auxiliary motor
because it is almost half the weight of a 9.9hp motor. But I have a
feeling that it may not be able to handle unexpected weather condition
if I have it in my boat.

Jay Chan


Actually a kicker and a small boat primary motor are dfferent beasts. I
use
to use the 15 hp Mariner 2 stroke from my 14' 200# aluminum boat as a
kicker
on the 21' boat. Got about 5.5 mph out of the motor, a lot of prop slip
when trying to push the big boat to hull speed. My 8 hp Yamaha T-8
pushes
the boat about 6.5 mph, or close to hull speed, at about 2/3 throttle.
The
difference is the high thrust has a bigger leg, form an about 25 hp motor
with more clearance for the prop and swings a larger, higher pitch prop
at a
geared down speed. My T-8 is not a candidate to wap between boats as it
has
power tilt, electric start which all add weight. The 15 hp mariner 2
stroke
scaled about 85# and did troll OK, just did not troll as fast as the T-8.

Seem like your 8hp Yamaha T-8 High Thrust outboard is more powerful
than a 9.9hp (and 15hp) outboard for the purpose of trolling. This
means I cannot simply dismiss a 8hp motor just because its horsepower
rating is lower than a 9.9hp motor. There are some other factors that
I also need to consider.

What are the things that makes the Yamaha High Thrust motor more
powerful than a 15hp motor? Is the prop the primary factors because it
is bigger and higher pitch? If this is the case, I assume I can simply
replace the prop of a regular 8hp motor with a bigger and higher pitch
prop, and I should expect more trolling power from the regular 8hp
motor, right? Does the gear-box inside the motor need to be
correspondingly stronger in order to handle the bigger and higher pitch
prop?

Thanks for any info.

Jay Chan


The high thrust motors have a heavier gear case, gear down the prop speed,
and Run a lot larger prop.
http://www.yamaha-motor.ca/products/...=ov&model=1934

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

Calif Bill wrote:
wrote in message
ups.com...
Calif Bill wrote:
wrote in message
oups.com...
Calif Bill wrote:
wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case
the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V.
The
boat is a center console. I guess I am asking for a motor that can
run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets hull
speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Glad to hear that you have good result using a 8hp with your slightly
longer and heavier boat. I probably will stick with 9.9hp instead of
8hp because there is hardly any price and weight difference between
them (according to the spec of Nissan outboard shown in Cabelas.com).

I would love to be able to use a 6hp in my boat as an auxiliary motor
because it is almost half the weight of a 9.9hp motor. But I have a
feeling that it may not be able to handle unexpected weather condition
if I have it in my boat.

Jay Chan


Actually a kicker and a small boat primary motor are dfferent beasts. I
use
to use the 15 hp Mariner 2 stroke from my 14' 200# aluminum boat as a
kicker
on the 21' boat. Got about 5.5 mph out of the motor, a lot of prop slip
when trying to push the big boat to hull speed. My 8 hp Yamaha T-8
pushes
the boat about 6.5 mph, or close to hull speed, at about 2/3 throttle.
The
difference is the high thrust has a bigger leg, form an about 25 hp motor
with more clearance for the prop and swings a larger, higher pitch prop
at a
geared down speed. My T-8 is not a candidate to wap between boats as it
has
power tilt, electric start which all add weight. The 15 hp mariner 2
stroke
scaled about 85# and did troll OK, just did not troll as fast as the T-8.

Seem like your 8hp Yamaha T-8 High Thrust outboard is more powerful
than a 9.9hp (and 15hp) outboard for the purpose of trolling. This
means I cannot simply dismiss a 8hp motor just because its horsepower
rating is lower than a 9.9hp motor. There are some other factors that
I also need to consider.

What are the things that makes the Yamaha High Thrust motor more
powerful than a 15hp motor? Is the prop the primary factors because it
is bigger and higher pitch? If this is the case, I assume I can simply
replace the prop of a regular 8hp motor with a bigger and higher pitch
prop, and I should expect more trolling power from the regular 8hp
motor, right? Does the gear-box inside the motor need to be
correspondingly stronger in order to handle the bigger and higher pitch
prop?

Thanks for any info.

Jay Chan


The high thrust motors have a heavier gear case, gear down the prop speed,
and Run a lot larger prop.
http://www.yamaha-motor.ca/products/...=ov&model=1934

Thanks for the follow-up. Now, I understand that I cannot simply put a
large prop on a small outboard and expect it to have a high thrust
factor. The gear case needs to be strong enough to handle the large
prop.

Now, I have read up on this issue a bit more in this newsgroup, and I
realize that I should use a lower pitch prop in a motor for trolling
and a higher pitch prop if the motor is the main motor. What you were
saying about Yamaha High Thrust motor that can use a high pitch prop
for trolling probably has to do with its strong gear case, right? I
guess a regular small outboard that doesn't have a strong gear case
will have to use a low pitch prop (and run at a higher rpm) to troll
properly. If the small motor has a strong gear case, we will be able
to put a larger prop and a higher pitch prop on it to give a high
trolling power (and at a relatively lower rpm, right?). Seem like
strong motors that have strong gear case such as your Yamaha High
Thrust motor or a Mecury Big Foot are justified to price higher because
they can give out higher trolling power for the same horsepower rating.
If I run such a strong 9.9hp motor in a lake that only allows no more
than 9.9hp motor to push a heavy boat, I will be able to push the boat
faster than another similar boat that has a regular 9.9hp motor, and I
will have an advantage over the other boat in term of speed (not that I
will catch more fish than the other guy). Great!

Jay Chan

Help Sizing an Auxiliary Outboard Motor for a 18-ft Boat
 

wrote in message
oups.com...
Calif Bill wrote:
wrote in message
ups.com...
Calif Bill wrote:
wrote in message
oups.com...
Calif Bill wrote:
wrote in message
oups.com...
I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in
case
the
10-years old main motor dies (2) Trolling for fishes (3) Use it
in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor
should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it
has
16-ft at the water level. It is 12" draft. The hull is a
semi-V.
The
boat is a center console. I guess I am asking for a motor that
can
run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more
than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run
the
boat off shore (the boat is a "bay boat" and should not be used
off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than
9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I
can
use a small and light weight outboard motor that I can mount it
in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan


I run an 8HP Yamaha High Thrust on a 21' 3400# boat and it gets
hull
speed.
You want a High Thrust for kicker, and probably a 6-8 is fine.

Glad to hear that you have good result using a 8hp with your
slightly
longer and heavier boat. I probably will stick with 9.9hp instead
of
8hp because there is hardly any price and weight difference between
them (according to the spec of Nissan outboard shown in
Cabelas.com).

I would love to be able to use a 6hp in my boat as an auxiliary
motor
because it is almost half the weight of a 9.9hp motor. But I have a
feeling that it may not be able to handle unexpected weather
condition
if I have it in my boat.

Jay Chan


Actually a kicker and a small boat primary motor are dfferent beasts.
I
use
to use the 15 hp Mariner 2 stroke from my 14' 200# aluminum boat as a
kicker
on the 21' boat. Got about 5.5 mph out of the motor, a lot of prop
slip
when trying to push the big boat to hull speed. My 8 hp Yamaha T-8
pushes
the boat about 6.5 mph, or close to hull speed, at about 2/3 throttle.
The
difference is the high thrust has a bigger leg, form an about 25 hp
motor
with more clearance for the prop and swings a larger, higher pitch
prop
at a
geared down speed. My T-8 is not a candidate to wap between boats as
it
has
power tilt, electric start which all add weight. The 15 hp mariner 2
stroke
scaled about 85# and did troll OK, just did not troll as fast as the
T-8.

Seem like your 8hp Yamaha T-8 High Thrust outboard is more powerful
than a 9.9hp (and 15hp) outboard for the purpose of trolling. This
means I cannot simply dismiss a 8hp motor just because its horsepower
rating is lower than a 9.9hp motor. There are some other factors that
I also need to consider.

What are the things that makes the Yamaha High Thrust motor more
powerful than a 15hp motor? Is the prop the primary factors because it
is bigger and higher pitch? If this is the case, I assume I can simply
replace the prop of a regular 8hp motor with a bigger and higher pitch
prop, and I should expect more trolling power from the regular 8hp
motor, right? Does the gear-box inside the motor need to be
correspondingly stronger in order to handle the bigger and higher pitch
prop?

Thanks for any info.

Jay Chan


The high thrust motors have a heavier gear case, gear down the prop
speed,
and Run a lot larger prop.
http://www.yamaha-motor.ca/products/...=ov&model=1934

Thanks for the follow-up. Now, I understand that I cannot simply put a
large prop on a small outboard and expect it to have a high thrust
factor. The gear case needs to be strong enough to handle the large
prop.

Now, I have read up on this issue a bit more in this newsgroup, and I
realize that I should use a lower pitch prop in a motor for trolling
and a higher pitch prop if the motor is the main motor. What you were
saying about Yamaha High Thrust motor that can use a high pitch prop
for trolling probably has to do with its strong gear case, right? I
guess a regular small outboard that doesn't have a strong gear case
will have to use a low pitch prop (and run at a higher rpm) to troll
properly. If the small motor has a strong gear case, we will be able
to put a larger prop and a higher pitch prop on it to give a high
trolling power (and at a relatively lower rpm, right?). Seem like
strong motors that have strong gear case such as your Yamaha High
Thrust motor or a Mecury Big Foot are justified to price higher because
they can give out higher trolling power for the same horsepower rating.
If I run such a strong 9.9hp motor in a lake that only allows no more
than 9.9hp motor to push a heavy boat, I will be able to push the boat
faster than another similar boat that has a regular 9.9hp motor, and I
will have an advantage over the other boat in term of speed (not that I
will catch more fish than the other guy). Great!

Jay Chan


The high thrust were originally designed for sailboats. Displacement hulls,
and that is what a small kicker is for on a fishing boat.