CTP Autopilot problems

[a64pilot]

Originally Posted by MartinR

That is a little funny. They told me I needed the belt tensioner as I had a very short run meaning the angle was to big and there are not enough cogs engaged with the belt on the drive wheel. So I do use one, and the belt never slips. The photo down below is from the CPT home page. In my installation the drive unit is actually inside the wheel diameter.

If it was very short then I can see that there wouldn’t be many teeth engaged. Mine is right at the wheel rim, I had to space the big drive pulley away from the spokes to get enough clearance when the drive was disengaged, CPT supplied the spacers as part of the kit.
Maybe I do need a tensioner, but it never jumps unless something is wrong, like I got stupid when anchoring and left the Autopilot on and as the boat drifts back it jams the rudder hard over trying to keep the heading.

[Bill O]

Originally Posted by Exile

Yup. 0.4 amps. Remarkable. Of course, unlike a typical below decks ram, it's using the significant leverage of your wheel steering system as you've pointed out. But it also must mean you're adept at balancing your sails. Yes, I recall reading about the windshield motor. I also read from one of the links related to the PyPilot that its creator Sean favors using windshield wiper motors from auto salvage yards.

The 0.4 amps that is being quoted here is a value that a manufacturer has posted and not necessarily real for your boat. I'm not even sure what that value means, an instantaneous reading, Ah, what? .... and we all know how marketing can grossly exaggerate the facts.

While I believe the 24V motor is efficient, unless you actually measure the current draw over long term use/conditions on your boat, its just speculation. Going upwind in a well balanced boat/sail plan in moderate air, you should have very low power draw. Similarly motoring in calm conditions, would expect very low draw on the AP. Big following seas and heavier air would expect much higher power draw and eventually these conditions may overwhelm the AP.

I'm not really certain where the common misconception came from that all below deck APs are "power hogs", but again that is not always true. When we put in our very large below deck AP hydraulic pump, I similarly thought it would chew up a lot of power. Surprisingly its fairly low going upwind in moderate conditions (3-4Ah/10 hr.) and in more rigorous down wind w/following seas conditions (18-24 Ah/10 hr.) The pypilot does measure power usage, so these are real numbers in varying conditions on our boat. While one may think this is a lot compared to a wheel driven electric drive, our boat is 45K fully loaded and we push the boat fairly hard. All in all, IMO very miserly power consumption and easily replenished by the solar and wind gen.

Not sure the wheel driven electric drive could handle our boat in the more rigorous conditions and why we went w/the more powerful, robust hydraulic pump for our AP. May eventually install a electric drive to our helm sprocket (below deck) as a back up or usage under moderate conditions. This will avoid any belts which can break or jump under higher loads.

A64, you are correct 12V applied to the 24V motor is to slow it down for more precision in the AP control.


Bill O.

[Bill O]

Martin,
When you use the pypilot w/the CPT motor how much power usage are you seeing? I know your boat is totally different than ours, but more real data would be great.


Bill O.

[a64pilot]

I don’t understand why people think the heavier the boat, the bigger the AP required.
It’s not the size of the boat, it’s the force required to move the rudder. A skeg hung rudder can require large forces to move it, yet a much larger Spade as it’s balanced can require a lot less.
It’s a function of rudder forces, not boat size.

[hpeer]

A64,

I’ll be the first to say I have problems controlling weather helm and can get a very heavy helm at times due to poor trim. That a problem with ME, not the boat.

But I do have difficulty getting the AP to work at times die to weather helm.

Now since you are talking about the HELM FORCE it has encouraged me to think about my situation.

44’ LOD
49’ LOA with sprit
37’ LWL
40,000 lbs
Cutaway forefoot with keel hung barn door
(Now the interesting part)
1.9 turns on the wheel lock-lock
Small wheel with a 33” diameter

So when I look at a lot of newer production boats I see balanced spade rudders and HUGE wheels. No idea what there turns lock to lock are but I hear 3 is a typical number.

So I believe that my boat is an outlier not due to excessive weather helm, but because of the effort felt on the wheel. Even a little weather helm produces a significant effort, relative to a more typical modern production boat.

I just point this out as a how 2 different boats can produce I use very different experiences and present different challenges to sailors as well as AP’s, especially wheel pilots.

[Bill O]

Originally Posted by a64pilot

I don’t understand why people think the heavier the boat, the bigger the AP required.
It’s not the size of the boat, it’s the force required to move the rudder. A skeg hung rudder can require large forces to move it, yet a much larger Spade as it’s balanced can require a lot less.
It’s a function of rudder forces, not boat size.

There are other factors. In our case, it was more of a calculation of ram size and pump flow to properly move the rudder. The next size down was a bit too small and the larger pump that we purchased was a little on the too large size. What we've found it doesn't need to pump as much to move the rudder.
And yes we have a large skeg hung rudder. When we made our new rudder, did try to add a balanced lower section to help reduce the power needed to stern the boat. Seems to have worked.


Bill O.

[a64pilot]

Originally Posted by hpeer

A64,

I’ll be the first to say I have problems controlling weather helm and can get a very heavy helm at times due to poor trim. That a problem with ME, not the boat.

But I do have difficulty getting the AP to work at times die to weather helm.

Now since you are talking about the HELM FORCE it has encouraged me to think about my situation.

44’ LOD
49’ LOA with sprit
37’ LWL
40,000 lbs
Cutaway forefoot with keel hung barn door
(Now the interesting part)
1.9 turns on the wheel lock-lock
Small wheel with a 33” diameter

So when I look at a lot of newer production boats I see balanced spade rudders and HUGE wheels. No idea what there turns lock to lock are but I hear 3 is a typical number.

So I believe that my boat is an outlier not due to excessive weather helm, but because of the effort felt on the wheel. Even a little weather helm produces a significant effort, relative to a more typical modern production boat.

I just point this out as a how 2 different boats can produce I use very different experiences and present different challenges to sailors as well as AP’s, especially wheel pilots.

I agree, and I believe that the large wheels on newer boats are to some extent due to marketing, how many photo’s do you see of the intrepid sailor sitting down behind his almost car sized wheel?
None, but you see many in full foulies braced against a man sized wheel
However it seems that big wheels take up a lot of cockpit space too.
I’d even go so far as to say that the dual wheel thing may be more to do with easy access to the swim platform for boarding the boat than anything else.
Mine would be sitting in the cockpit in shorts, no T shirt sipping a coke while on watch while Otto holds a better course than I would.
On my boat a smallish wheel is necessitated by its simplistic steering design, the wheel is mounted directly to the pinion shaft, and since the rack is under the seat connected directly to the rudder shaft , that sets the wheel diameter max to be twice the seat height, or the rim has to go under the floor.
As the rudder is a Spade you can get away with a small wheel diameter. Mine is 24” and lock to lock is 1.5 turns, and it’s easy to turn. Crank in a lot of weather helm and it gets harder of course, but not real hard, and that’s due to it being a Spade rudder, and even all Spades are not created equal, some are more balanced than others, with a big wheel you may want less balance to get more feed back.

Wheel size I think matters greatly for a CPT, the CPT can apply 80 something ft lbs of force, with my wheel being two ft, that equates to a force on the wheel of 40 something lbs, but if my wheel was four ft., it’s only 20 something lbs, and that’s not a whole lot, so I think they work better on small wheeled boats with the assumption that the builder has kept forces to where they are tolerable with a small wheel.

[hpeer]

Then there is also the SPEED with which that force is applied. Fewer turns lock to lock means faster.

But also girls in Bikinis with their hands held high On the wheel has some visual Appeal. ��

So after what I wrote above I dashed into the cockpit with the idea of maybe replacing the wheel sprocket for a smaller one and increasing my turns lock to lock.

No such luck, I’m already at just 6 teeth, REALLY small.

Dang!

The only other thing would be to get a bigger quadrant, no room for that. Which lead me to this thought, if you have a tiny lazaret, and tiny quadrant, then maybe you need a huge diameter wheel?

[Exile]

Originally Posted by Bill O

There are other factors. In our case, it was more of a calculation of ram size and pump flow to properly move the rudder. The next size down was a bit too small and the larger pump that we purchased was a little on the too large size. What we've found it doesn't need to pump as much to move the rudder.
And yes we have a large skeg hung rudder. When we made our new rudder, did try to add a balanced lower section to help reduce the power needed to stern the boat. Seems to have worked.


Bill O.

I would think your ketch rig is another factor making it easier to balance the helm. Beautiful & unique traditional boat, btw. Always nice seeing boats like this brought back to life.

[MartinR]

Originally Posted by Bill O

Martin,
When you use the pypilot w/the CPT motor how much power usage are you seeing? I know your boat is totally different than ours, but more real data would be great.


Bill O.

On average 0.2 A. Very much dependent on how the gains are set.

[a64pilot]

Originally Posted by Bill O

There are other factors. In our case, it was more of a calculation of ram size and pump flow to properly move the rudder. The next size down was a bit too small and the larger pump that we purchased was a little on the too large size. What we've found it doesn't need to pump as much to move the rudder.
And yes we have a large skeg hung rudder. When we made our new rudder, did try to add a balanced lower section to help reduce the power needed to stern the boat. Seems to have worked.


Bill O.

Sorry, I didn’t include the info that I should have, I was speaking to wheel pilots and didn’t state that, sorry.

But even wheel pilots are rated by boat size, and to me that doesn’t make much sense, I know smaller, lighter boats than mine that have heavy wheels, while mine is very light, not that mine is big, it’s not, but I feel sure that a Raymarine wheel pilot would work on mine for instance.

[Bill O]

Originally Posted by MartinR

On average 0.2 A. Very much dependent on how the gains are set.

True and the gains are set differently for the conditions for better response.

[a64pilot]

Still an average of .2 is half of what was claimed.
Now what’s missing of course is I’d assume his boat is easily helmed and well trimmed, take one that isn’t and the power used is going way up.
Still .2 is nothing

[MartinR]

Originally Posted by a64pilot

Still an average of .2 is half of what was claimed.
Now what’s missing of course is I’d assume his boat is easily helmed and well trimmed, take one that isn’t and the power used is going way up.
Still .2 is nothing

Yes, my boat is very well balanced and rudder forces are very low even though she is quite long. The distance between rudder and keel is long also, which means the rudder has plenty of leverage, so only small corrections are needed to maintain course.

Also this is the power consumption using the pypilot controller. I have no figures for the CPT controller, but I would guess, the consumption is slightly higher, but still very low.

[a64pilot]

Curious, why would you think the CPT controller would be any different?