On 3/18/2015 8:59 PM, Wayne.B wrote:
On Wed, 18 Mar 2015 16:14:51 -0700 (PDT), Tim
wrote:

Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

===

That issue is known as "prop walk" and it is most apparent at very
slow speed before the boat gains momentum. Prop walk is caused by the
propellor acting as a paddle wheel. Since the prop/paddle wheel
rotation is perpendicular to the center line, a side thrust is created
instead of forward motion. The direction of "walk" depends on the
direction of shaft rotation. Since your boat is walking to the left
we can assume the shaft is rotating counter clockwise in reverse (when
viewed from behind the boat). Remember to think of the prop as a
paddle wheel at low speed. There are other more complicated
explanations for why prop walk occurs but the paddle wheel analogy is
the most intuitive to understand and the easiest to apply to problem
solving.

As Richard pointed out, the rudder has very little effect in reverse
until the boat gains some speed and creates water flow past the
rudder. This is not a problem in forward because the prop creates
plenty of water flow even when the boat is standing still.

Backing up a single engine boat is an art form not a science. Every
boat is a little different but some basic priciples apply. The best
strategy I've found is to apply a quick burst of power in reverse and
then shift immediately into neutral. Once you are in neutral there is
no more prop walk, and if you have built a little speed, you can steer
with the rudder. Sometimes you have to do this more than once.

Another strategy is letting the prop walk work in your favor and just
let the stern "walk" in the direction it wants to go. This implies
some maneuvering room of course.



Good explanation Wayne. I think many in this newsgroup are probably
familiar with this but it bears repeating sometimes. In cases of close
quarter maneuvering, "neutral" is always your friend. Like many I have
witnessed, it took a while for me to understand this. The natural
tendency of many is to "drive" the boat into the slip, often with
catastrophic results. Learning to relax, shift often to neutral
and let the boat take a "set" given the wind and current is much more
effective.

On Wednesday, March 18, 2015 at 6:00:15 PM UTC-7, Wayne. B wrote:
On Wed, 18 Mar 2015 16:14:51 -0700 (PDT), Tim
wrote:

Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

===

That issue is known as "prop walk" and it is most apparent at very
slow speed before the boat gains momentum. Prop walk is caused by the
propellor acting as a paddle wheel. Since the prop/paddle wheel
rotation is perpendicular to the center line, a side thrust is created
instead of forward motion. The direction of "walk" depends on the
direction of shaft rotation. Since your boat is walking to the left
we can assume the shaft is rotating counter clockwise in reverse (when
viewed from behind the boat). Remember to think of the prop as a
paddle wheel at low speed. There are other more complicated
explanations for why prop walk occurs but the paddle wheel analogy is
the most intuitive to understand and the easiest to apply to problem
solving.

As Richard pointed out, the rudder has very little effect in reverse
until the boat gains some speed and creates water flow past the
rudder. This is not a problem in forward because the prop creates
plenty of water flow even when the boat is standing still.

Backing up a single engine boat is an art form not a science. Every
boat is a little different but some basic priciples apply. The best
strategy I've found is to apply a quick burst of power in reverse and
then shift immediately into neutral. Once you are in neutral there is
no more prop walk, and if you have built a little speed, you can steer
with the rudder. Sometimes you have to do this more than once.

Another strategy is letting the prop walk work in your favor and just
let the stern "walk" in the direction it wants to go. This implies
some maneuvering room of course.

"Backing up a single engine boat is an art form not a science."

Yes, I found that out. and quickly. before pulling into a different landing than where my boat was slipped, I figured out in advance how to safely and effectually get out of there without harming other boats or whacking a chunk of dock.

Yes, a rudder boat is quite different than IO's.

On 3/18/2015 9:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 5:16:48 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

Speaking of 'trim' this boat had stationary trim tabs on it. They were cushioned by what looked like big shock absorbers.

For an old 27 ft. wooden cabin cruiser, it plowed water really hard till you got it up on plane and then it was really quite agile.
Speaking of getting up on plane it kinda reminded me of a fully loaded PBY trying to take off out of the water.

It seemed like it fought hard to plane out for quite a distance, but really it didn't take that long.

Too bad the plywood hull was starting to delaminate on the thing. I really had a lot of fun on that old tub.



Are you sure they were "stationary" and the things that looked like
shock absorbers weren't actually hydraulic cylinders? That's usually
how trim tabs are set up and controlled. If so, there should have been
a hydraulic pump and some controls to set the angle of the tabs.

On Wednesday, March 18, 2015 at 6:14:36 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 8:59 PM, Wayne.B wrote:
On Wed, 18 Mar 2015 16:14:51 -0700 (PDT), Tim
wrote:

Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

===

That issue is known as "prop walk" and it is most apparent at very
slow speed before the boat gains momentum. Prop walk is caused by the
propellor acting as a paddle wheel. Since the prop/paddle wheel
rotation is perpendicular to the center line, a side thrust is created
instead of forward motion. The direction of "walk" depends on the
direction of shaft rotation. Since your boat is walking to the left
we can assume the shaft is rotating counter clockwise in reverse (when
viewed from behind the boat). Remember to think of the prop as a
paddle wheel at low speed. There are other more complicated
explanations for why prop walk occurs but the paddle wheel analogy is
the most intuitive to understand and the easiest to apply to problem
solving.

As Richard pointed out, the rudder has very little effect in reverse
until the boat gains some speed and creates water flow past the
rudder. This is not a problem in forward because the prop creates
plenty of water flow even when the boat is standing still.

Backing up a single engine boat is an art form not a science. Every
boat is a little different but some basic priciples apply. The best
strategy I've found is to apply a quick burst of power in reverse and
then shift immediately into neutral. Once you are in neutral there is
no more prop walk, and if you have built a little speed, you can steer
with the rudder. Sometimes you have to do this more than once.

Another strategy is letting the prop walk work in your favor and just
let the stern "walk" in the direction it wants to go. This implies
some maneuvering room of course.



Good explanation Wayne.

Yes to both of you. Very good!


I think many in this newsgroup are probably
familiar with this but it bears repeating sometimes. In cases of close
quarter maneuvering, "neutral" is always your friend. Like many I have
witnessed, it took a while for me to understand this. The natural
tendency of many is to "drive" the boat into the slip, often with
catastrophic results. Learning to relax, shift often to neutral
and let the boat take a "set" given the wind and current is much more
effective.

Neutral and patience. I have seen people 'drive' a boat into a sock. and I do mean DRIVE! They usually were stuck with dock damage fees and kicked out of the marina.

On Wednesday, March 18, 2015 at 6:22:58 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 9:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 5:16:48 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

Speaking of 'trim' this boat had stationary trim tabs on it. They were cushioned by what looked like big shock absorbers.

For an old 27 ft. wooden cabin cruiser, it plowed water really hard till you got it up on plane and then it was really quite agile.
Speaking of getting up on plane it kinda reminded me of a fully loaded PBY trying to take off out of the water.

It seemed like it fought hard to plane out for quite a distance, but really it didn't take that long.

Too bad the plywood hull was starting to delaminate on the thing. I really had a lot of fun on that old tub.



Are you sure they were "stationary" and the things that looked like
shock absorbers weren't actually hydraulic cylinders? That's usually
how trim tabs are set up and controlled. If so, there should have been
a hydraulic pump and some controls to set the angle of the tabs.

No Rick, there was no hydraulic pump or any way to attach hoses to them. Nor was there any trim controls. They looked just like a large diameter and squatty shock with a large and thick rubber boot wrapped around the center. On the trailer, I went back there and you could push up on the individual trim tabs with resistance, but weren't springy. Actually they did move up but with a lot of effort.

On Wednesday, March 18, 2015 at 6:24:47 PM UTC-7, Tim wrote:
On Wednesday, March 18, 2015 at 6:14:36 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 8:59 PM, Wayne.B wrote:
On Wed, 18 Mar 2015 16:14:51 -0700 (PDT), Tim
wrote:

Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

===

That issue is known as "prop walk" and it is most apparent at very
slow speed before the boat gains momentum. Prop walk is caused by the
propellor acting as a paddle wheel. Since the prop/paddle wheel
rotation is perpendicular to the center line, a side thrust is created
instead of forward motion. The direction of "walk" depends on the
direction of shaft rotation. Since your boat is walking to the left
we can assume the shaft is rotating counter clockwise in reverse (when
viewed from behind the boat). Remember to think of the prop as a
paddle wheel at low speed. There are other more complicated
explanations for why prop walk occurs but the paddle wheel analogy is
the most intuitive to understand and the easiest to apply to problem
solving.

As Richard pointed out, the rudder has very little effect in reverse
until the boat gains some speed and creates water flow past the
rudder. This is not a problem in forward because the prop creates
plenty of water flow even when the boat is standing still.

Backing up a single engine boat is an art form not a science. Every
boat is a little different but some basic priciples apply. The best
strategy I've found is to apply a quick burst of power in reverse and
then shift immediately into neutral. Once you are in neutral there is
no more prop walk, and if you have built a little speed, you can steer
with the rudder. Sometimes you have to do this more than once.

Another strategy is letting the prop walk work in your favor and just
let the stern "walk" in the direction it wants to go. This implies
some maneuvering room of course.



Good explanation Wayne.

Yes to both of you. Very good!


I think many in this newsgroup are probably
familiar with this but it bears repeating sometimes. In cases of close
quarter maneuvering, "neutral" is always your friend. Like many I have
witnessed, it took a while for me to understand this. The natural
tendency of many is to "drive" the boat into the slip, often with
catastrophic results. Learning to relax, shift often to neutral
and let the boat take a "set" given the wind and current is much more
effective.

Neutral and patience. I have seen people 'drive' a boat into a sock. and I do mean DRIVE! They usually were stuck with dock damage fees and kicked out of the marina.

" 'drive' a boat into a sock"

Er... "dock" sorry.

When I first bought and commissioned the Navigator I was a little
nervous about my boat handling skills, especially since I had gone
from a 28 footer to a 52 footer. To make matters worse the slip I had
in Scituate was right behind a floating fuel dock and I had to back
the boat about 150 feet from where I made the initial turn, passing
within 10-15 feet of the fuel dock (which often had other boats tied up
to it) and into the slip that only had 6 inches of clearance on each side.

Fortunately I hired a very experienced tug boat captain to go out with
me a couple of times and give me some lessons and tips on close quarter
maneuvering. The Navigator was equipped with thrusters but he refused
to let me use them. He's the one who really emphasized the "neutral is
your friend" concept and taught me to back the boat towards the slip in
a series of reverse, neutral, reverse, neutral steps, adjusting as
necessary with the shifters (not the throttles) to keep lined up with
the slip. It was well worth the short money he charged for these lessons.

On 3/18/2015 9:31 PM, Tim wrote:
On Wednesday, March 18, 2015 at 6:22:58 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 9:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 5:16:48 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

Speaking of 'trim' this boat had stationary trim tabs on it. They were cushioned by what looked like big shock absorbers.

For an old 27 ft. wooden cabin cruiser, it plowed water really hard till you got it up on plane and then it was really quite agile.
Speaking of getting up on plane it kinda reminded me of a fully loaded PBY trying to take off out of the water.

It seemed like it fought hard to plane out for quite a distance, but really it didn't take that long.

Too bad the plywood hull was starting to delaminate on the thing. I really had a lot of fun on that old tub.



Are you sure they were "stationary" and the things that looked like
shock absorbers weren't actually hydraulic cylinders? That's usually
how trim tabs are set up and controlled. If so, there should have been
a hydraulic pump and some controls to set the angle of the tabs.

No Rick, there was no hydraulic pump or any way to attach hoses to them. Nor was there any trim controls. They looked just like a large diameter and squatty shock with a large and thick rubber boot wrapped around the center. On the trailer, I went back there and you could push up on the individual trim tabs with resistance, but weren't springy. Actually they did move up but with a lot of effort.



Interesting. Never saw anything like that. Sounds like they were some
kind of passive trim tabs that relied on the stern "squatting" to
provide some lift. Actually, the primary purpose of trim tabs is to
stabilize the boat port to starboard (compensate a "list") depending on
loading. The ability to provide some "lift" assistance when trying to
get up on plane is really a secondary function.

On Wed, 18 Mar 2015 21:44:56 -0400, "Mr. Luddite"
wrote:

On 3/18/2015 9:31 PM, Tim wrote:
On Wednesday, March 18, 2015 at 6:22:58 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 9:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 5:16:48 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

Speaking of 'trim' this boat had stationary trim tabs on it. They were cushioned by what looked like big shock absorbers.

For an old 27 ft. wooden cabin cruiser, it plowed water really hard till you got it up on plane and then it was really quite agile.
Speaking of getting up on plane it kinda reminded me of a fully loaded PBY trying to take off out of the water.

It seemed like it fought hard to plane out for quite a distance, but really it didn't take that long.

Too bad the plywood hull was starting to delaminate on the thing. I really had a lot of fun on that old tub.



Are you sure they were "stationary" and the things that looked like
shock absorbers weren't actually hydraulic cylinders? That's usually
how trim tabs are set up and controlled. If so, there should have been
a hydraulic pump and some controls to set the angle of the tabs.

No Rick, there was no hydraulic pump or any way to attach hoses to them. Nor was there any trim controls. They looked just like a large diameter and squatty shock with a large and thick rubber boot wrapped around the center. On the trailer, I went back there and you could push up on the individual trim tabs with resistance, but weren't springy. Actually they did move up but with a lot of effort.



Interesting. Never saw anything like that. Sounds like they were some
kind of passive trim tabs that relied on the stern "squatting" to
provide some lift. Actually, the primary purpose of trim tabs is to
stabilize the boat port to starboard (compensate a "list") depending on
loading. The ability to provide some "lift" assistance when trying to
get up on plane is really a secondary function.


===

Another useful thing that trim tabs can do is keep the bow from
bouncing around and pounding in a chop. That's a delicate balancing
act between speed, wave angle, out drive trim, etc.

On 3/18/2015 9:55 PM, Wayne.B wrote:
On Wed, 18 Mar 2015 21:44:56 -0400, "Mr. Luddite"
wrote:

On 3/18/2015 9:31 PM, Tim wrote:
On Wednesday, March 18, 2015 at 6:22:58 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 9:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 5:16:48 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 7:14 PM, Tim wrote:
On Wednesday, March 18, 2015 at 3:55:00 PM UTC-7, Mr. Luddite wrote:
On 3/18/2015 6:51 PM, Mr. Luddite wrote:
On 3/18/2015 6:10 PM, Tim wrote:
Greg's thread made me think about my old Chris-craft Cavalier and how
it was set up. It had solid shaft propulsion. And looking from the
back, it had the rudder just left of the prop. I wonder why it was set
that way instead of being directly behind the propeller instead of
offset the way it was. Also I wonder why only one prop instead of two.
It was a bugger to back out of a slip .

When underway everything was fine and would steer well regardless of
speed or direction.
Any ideas?



Tim, Wayne can probably provide a better answer but I believe what you
are referring to is an "offset rudder". In theory it makes the rudder
more effective by putting it in "clean" water rather than directly in
line with the prop wash. Not uncommon.


BTW, when backing out (or into) the slip, the rudder has virtually no
affect on steering. Slow speed turning relies on the prop wash hitting
the rudder.

Richard, I discovered that when It was demonstrated to me. Yes, at a very slow speed, the boat would back to the left only regardless of how you set the rudder, and that provided to be a royal pain in a few cases.

I hadn't thought of the "clean" water theory, but that does make sense now that you mentioned it. That was the only rudder boat I've ever owned. since then it's been I'O's.



BTW, "prop walk" also occurs when moving forward which is probably the
most important reason for having the rudder slightly offset. The wash
over the prop compensates for the prop walk so with the rudder centered
on a single screw the boat doesn't try to make a slow turn due to prop walk.

Similar I guess to the little, adjustable trim rudder on an IO or outboard.

Speaking of 'trim' this boat had stationary trim tabs on it. They were cushioned by what looked like big shock absorbers.

For an old 27 ft. wooden cabin cruiser, it plowed water really hard till you got it up on plane and then it was really quite agile.
Speaking of getting up on plane it kinda reminded me of a fully loaded PBY trying to take off out of the water.

It seemed like it fought hard to plane out for quite a distance, but really it didn't take that long.

Too bad the plywood hull was starting to delaminate on the thing. I really had a lot of fun on that old tub.



Are you sure they were "stationary" and the things that looked like
shock absorbers weren't actually hydraulic cylinders? That's usually
how trim tabs are set up and controlled. If so, there should have been
a hydraulic pump and some controls to set the angle of the tabs.

No Rick, there was no hydraulic pump or any way to attach hoses to them. Nor was there any trim controls. They looked just like a large diameter and squatty shock with a large and thick rubber boot wrapped around the center. On the trailer, I went back there and you could push up on the individual trim tabs with resistance, but weren't springy. Actually they did move up but with a lot of effort.



Interesting. Never saw anything like that. Sounds like they were some
kind of passive trim tabs that relied on the stern "squatting" to
provide some lift. Actually, the primary purpose of trim tabs is to
stabilize the boat port to starboard (compensate a "list") depending on
loading. The ability to provide some "lift" assistance when trying to
get up on plane is really a secondary function.


===

Another useful thing that trim tabs can do is keep the bow from
bouncing around and pounding in a chop. That's a delicate balancing
act between speed, wave angle, out drive trim, etc.



Never had to worry about that on our Grand Banks. :-)
7 kts was about it for cruising. When we did the sea trial
when we sold it the buyer's surveyor asked me to "open her up" ..
meaning full throttle. He laughed because when I did so I said it was
the first time I had ever done it and the first time I ever saw the bow
lift a little. It maxed out at just over 9 kts.