'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.

Does it have one of those zinc rudder tabs right behind the prop? Is it
supposed to? Is it adjusted correctly?



Robin AndrePont wrote:
'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.

Robin,
You're probably not going to like this answer. Considering that there is
no slop in your steering system, (check this at the dock) there is a natural
tendency for a mono hulled boat to wander back and forth. On a 23' Maxium
I've driven it goes through a slow 30 degree arc, about 15 degrees either
side of straight ahead. If I get it centered it will swing through this arc
back and forth. If the channel is wide enough I just let it alone, if the
channel is narrow I have to constantly counter steer. This I am told is the
result of the curved hull trying to compensate for the low pressure that
develops on one side and than the other. At plaining speed these forces are
absent because the boat is out of the water for most part. The pontoon boat
I used to drive didn't exhibit these tendencies due to the duel hulls that
were for the most part straight and parallel. All in life seems to be a
trade off. :-)
Paul

"Robin AndrePont" wrote in message
...
'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.

On Sun, 13 Jun 2004 16:32:12 -0400, (Robin AndrePont)
wrote:

'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.

My 21'er does the same thing. I think only a keel would help, or a deep V hull.
I have noticed that the speed and direction of the wind will affect how well
the boat steers at less than six mph. I quit worrying about it a long time ago.

John H

On the 'Poco Loco' out of Deale, MD
on the beautiful Chesapeake Bay!

As stated, most single hull I/O engine boats do this. If you have
adjustable trim tabs on the boat - putting them all the way down will stop
this.
The single trim tab above the prop does nothing at slow speeds. It only
adjusts steering torque at higher speeds.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Robin AndrePont" wrote in message
...
'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.

"Robin AndrePont" wrote
I'm always fighting with the steering to keep
this boat in a straight line when going down
a river or entering a spring when driving slow.

I have a 70s vintage 18' tri-hull runabout and it wanders all over the place
when under power at slow speed, much like what you're describing. I always
just assumed it was natural.

It's the nature of the beast. Most v hulls wander at slow speed, but they
are so nice up on plane.

"Robin AndrePont" wrote in message
...
'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.

Robin AndrePont wrote:
'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.


Sounds like the standard "wander" that is typical of most sterndrive
boats at slow speed. My boats wanders at displacment speeds as has all
the io I have ever driven. After a while you get use to it and will
start to compensate before your heading really moved very much.

But me thinks this falls under "Operating as Expected" :-)

Capt Jack R..

Length: 18'
Model Name/Description: CALAE 1800
Boat Type: Stern Drive Power Boat
Hull Material: Fiberglass
Beam: 8'
Engine: 1
175 HP
Gasoline
Net Weight: 2,225



Robin,
You have a fiberglass boat I believe. If this was a wood boat then I would
guess a bow-in-the-hull.
My guess is that something in the outdrive is either bent or needs to be
checked for alignment, and I am no expert. My dads boat had a 2 blade skeg
on the bottom of the hull. I think the outdrive has a skeg at the bottom, it
could be bent. Try fixing the power steering and then post back to forum. No
I am not a know-it-all, I have owned a boat for 2-weeks. But I learned a lot
about boats trying to buy a used one. The first boat that I tried to buy had
a bow-in-the-hull and reason that I did not buy it.
After talking with my brother he said that person at his work had a wooden
boat with that problem and the boat tracked left-right.
Greg
"Robin AndrePont" wrote in message
...
'93 Thompson 18' Mercuiser Alfa one, 4.3.

When in Forward gear (slow) the back end of the boat is going to the far
left and then to the far right, none stop. Yes, I have a Trim Tab!
I'm always fighting with the steering to keep this boat in a straight
line when going down a river or entering a spring when driving slow.
With full throttle it's fine, does not pull. I can Trim it up, or Trim
it down and you can look behind the boat and see all the zig zag bobbles
from the boat. You can actually see the water pushing from the Propeller
and see the water go from one side to the other; however, the outdrive
it not moving. Weird, huh? There's no slack in the steering. it's all
tight. The Power Steering pump is bad but I don't think that would give
me this problem.
Does anyone have any ideas???!!
Thank you
plz... no e-mail.