Raymarine St4000 with Trim Tab Problem

[Alan Mighty]

Originally Posted by Rustic Charm

sorry about being a pain with everyone, but I really don't know anything about this stuff.

Ben, what about this one? I'm just trying to avoid having to change too much. If this will work I can make up nice Stainless bracket to use the current mount off the tow rail.

That is getting closer to what has been proven to work.


What's wrong with redundancy?


1) Buy a Raymarine ST1000, ST2000 or similar (Navico etc) small autopilot. Build your mount so the arm of the autopilot is perpendicular to the tiller of the trim tab. Have an attachment on the trim tab tiller so it can be slid fore and aft, so you can choose to run at the null point, or in heavier seas run with more damping.


2) keep your Raymarine ST4000 for your rudder tiller. That way you have steering redundancy: if the ST1000 or the trim tab fails, you use the ST4000 on your rudder tiller.

[Rustic Charm]

Originally Posted by Snowpetrel

Yes, thats what I was thinking. I assume thats not to scale. Id make it slightly longer than you drew it, nearer neutral feedback.

There are issues with overcentre things happening if the rudder turns too far, so test it with full rudder angles and fit rudder stops if needed to prevent nasty damage to the tab or the ram.

If you just u bolt on a big triangle of plywood over the entire trim tab tiller bit you can drill and adjust the ram attachment to perfect the ratios and feedback. When you have a combo that works build it from expemsive shiny stuff.

Personally id try Atolls approach first.

Whilst that isnt to scale , the ram from the auto pilot is directly over the axis of the rudder. Over the top hinge.

I think i can program rudder stops into the st4000. Ill check on that.

Im starting to think that no matter what i do ill have some engineering to do, so starting again with Atoll's suggestion might be just as easy. Yes.

But, if i can make this drawing work, i'll only have to have one bracket made. Because the current trim tab tiller remains the same. All i have to do is add another pin for the auto pilot.

[Rustic Charm]

Originally Posted by Snowpetrel

Also, you are goimg to have issues with the ram not being at its midships position due to the lomger distance. I cant remember if the raymarine is smart enough to quickly work out the "permenant helm" setting?

I have no idea what you are referring to with this post?

[Rustic Charm]

Originally Posted by Alan Mighty

That is getting closer to what has been proven to work.


What's wrong with redundancy? hmm yes, this gives me an idea.


1) Buy a Raymarine ST1000, ST2000 or similar (Navico etc) small autopilot. Build your mount so the arm of the autopilot is perpendicular to the tiller of the trim tab. Have an attachment on the trim tab tiller so it can be slid fore and aft, so you can choose to run at the null point, or in heavier seas run with more damping.


2) keep your Raymarine ST4000 for your rudder tiller. That way you have steering redundancy: if the ST1000 or the trim tab fails, you use the ST4000 on your rudder tiller.

So, if i use this one, i could retain the longer tiller on the trim tab, what i have now and drill a new pin into the same tiller back over the rudder axis. Then all id have to do is make a new simple bracket to mount the drive off the toe rail.

[Alan Mighty]

For simplicity and redundancy, I'd do this:

1. Keep your ST4000+ and its mount, so it can be used (mounted to starboard) to drive your rudder tiller. Keep it set to its standard operating sense.


2. Buy an inexpensive small autopilot (Raymarine ST1000, ST2000; Navico 550 or equivalent). Check gumtree, eBay, marina noticeboard etc.


3. Make a mount for the inexpensive small autopilot with the aim of mounting it to port (not starboard). Mount it such that the autopilot is perpendicular to the tiller of the trim tab and that it sits at the 'null point', in line with the pintles of your rudder. Mounting the small autopilot to port means you don't have to change its operating sense.


4. Make the attachment on the trim tab tiller so (i) the trim tab can be locked in line with the rudder for reversing the boat under power; (ii) the attachment point can be adjusted some small distance aft and forward of the null point.


Pros:


a. you have complete redundancy in case of failure of one autopilot. The ST4000+ is likely networked to your electronic nav system (gps, fluxgate compass, chart plotter). The small autopilot on your trim tab is then, apart from the need for 12VDC, self contained (i.e. has its own electronic compass). But the small autopilot can likely also be networked to GPS too).


b. when lightning threatens, your small autopilot can be stowed in your galley oven or some other metal box. That means that as long as you have 12VDC, you have self steering. As long as you have live batteries and wires to run, you can run a small autopilot on the trim tab.


Cons:


a. Cost of buying the small autopilot, running 12VDC to it, and fabricating a mount and the attachment to the trim tab tiller.


Other:


1. If you've not read Letcher's book or Eric Baicy's PDF, I recommend you do so. Both of them start by showing you a simple procedure to show how much your boat yaws. Different designs yaw to different degrees. In general, full keels (and their derivatives such a cut-away forefoot, swept back keels etc) yaw not so much and so work with a trim tab. Lightweight racers are more prone to yaw and are not as easy to helm with an autopilot.


2. Damping is a good thing. You need both mechanical damping (i.e. associated with the null point on the tiller of the trim tab) and electronic rudder damping set in the autopilot.


3. Be prepared to change damping for different sea conditions. Developed seas call for more positive damping than calm water. A beam reach or a broad reach requires more damping than a close reach. It's easy to change the mechanical damping, i.e. to adjust the attachment point on the tiller of the trim tab.


4. I prefer understeer to oversteer. So I usually attach my small autopilot aft of the null point. I can punch in a degree or two to compensate for understeer. Oversteer will destroy an autopilot just by wearing it out. Oversteer, by constant rudder correction, slows a boat down.

[Snowpetrel]

Originally Posted by Alan Mighty

For simplicity and redundancy, I'd do this:

1. Keep your ST4000+ and its mount, so it can be used (mounted to starboard) to drive your rudder tiller. Keep it set to its standard operating sense.


2. Buy an inexpensive small autopilot (Raymarine ST1000, ST2000; Navico 550 or equivalent). Check gumtree, eBay, marina noticeboard etc.


3. Make a mount for the inexpensive small autopilot with the aim of mounting it to port (not starboard). Mount it such that the autopilot is perpendicular to the tiller of the trim tab and that it sits at the 'null point', in line with the pintles of your rudder. Mounting the small autopilot to port means you don't have to change its operating sense.


4. Make the attachment on the trim tab tiller so (i) the trim tab can be locked in line with the rudder for reversing the boat under power; (ii) the attachment point can be adjusted some small distance aft and forward of the null point.


Pros:


a. you have complete redundancy in case of failure of one autopilot. The ST4000+ is likely networked to your electronic nav system (gps, fluxgate compass, chart plotter). The small autopilot on your trim tab is then, apart from the need for 12VDC, self contained (i.e. has its own electronic compass). But the small autopilot can likely also be networked to GPS too).


b. when lightning threatens, your small autopilot can be stowed in your galley oven or some other metal box. That means that as long as you have 12VDC, you have self steering. As long as you have live batteries and wires to run, you can run a small autopilot on the trim tab.


Cons:


a. Cost of buying the small autopilot, running 12VDC to it, and fabricating a mount and the attachment to the trim tab tiller.


Other:


1. If you've not read Letcher's book or Eric Baicy's PDF, I recommend you do so. Both of them start by showing you a simple procedure to show how much your boat yaws. Different designs yaw to different degrees. In general, full keels (and their derivatives such a cut-away forefoot, swept back keels etc) yaw not so much and so work with a trim tab. Lightweight racers are more prone to yaw and are not as easy to helm with an autopilot.


2. Damping is a good thing. You need both mechanical damping (i.e. associated with the null point on the tiller of the trim tab) and electronic rudder damping set in the autopilot.


3. Be prepared to change damping for different sea conditions. Developed seas call for more positive damping than calm water. A beam reach or a broad reach requires more damping than a close reach. It's easy to change the mechanical damping, i.e. to adjust the attachment point on the tiller of the trim tab.


4. I prefer understeer to oversteer. So I usually attach my small autopilot aft of the null point. I can punch in a degree or two to compensate for understeer. Oversteer will destroy an autopilot just by wearing it out. Oversteer, by constant rudder correction, slows a boat down.

All good except its a steel boat, and ive had no luck with the cheapies with inbuilt fluxgates on steel boats. The magnetic interferance thows them in any seaway.

The 4000 has a remote fluxgate so it works if you nount the fluxgate compass someplace with a reasonable magnetic field. Maybe some of the higher end units will take a nmea feed but then you start to loose the simplicity and cheapness.

Also ive killed two cheap units with water ingress onto the circuit board. The 4000 puts most of the electrics away from the ram.

[Snowpetrel]

Originally Posted by Rustic Charm

So, if i use this one, i could retain the longer tiller on the trim tab, what i have now and drill a new pin into the same tiller back over the rudder axis. Then all id have to do is make a new simple bracket to mount the drive off the toe rail.

Exactly! And the new simple bracket can be a peice of driftwood lashed on with no 8 fencing wire. Drill a couple of holes for the ram to mount in...

Id make it so you could easily adjust the feedback from neutral (100%) through to strongly positive (about 60%) that way you can find the best feedback for your system, and even change it for different sea states.

The only downsides of this over atolls system are that the tiller arm length is short, and the autohelm may not be able to have its "gain" reduced enough to stop the system overreacting.

[atoll]

I designed this very simple remote control for the trim tab I have for my big boat,where the top of the rudder and trim tab control arm are situated just above the
water line.

this uses a standard morse push/pull control cable with custom"U"terminals on the ends of the cable with stainless pins for attaching the terminals to the control arm and ram end.
the ram end runs in a guide channel so when pushing it remains in alighnment with the cable end.

this attaches to the stern rail and uses a cheap tiller pilot with its own compass ,being raised it avoids magnetic issues associated with steel and ferro boats.

this system could also be used to attach to a wind vane.

[Rustic Charm]

Originally Posted by atoll

I designed this very simple remote control for the trim tab I have for my big boat,where the top of the rudder and trim tab control arm are situated just above the
water line.

this uses a standard morse push/pull control cable with custom"U"terminals on the ends of the cable with stainless pins for attaching the terminals to the control arm and ram end.
the ram end runs in a guide channel so when pushing it remains in alighnment with the cable end.

this attaches to the stern rail and uses a cheap tiller pilot with its own compass ,being raised it avoids magnetic issues associated with steel and ferro boats.

this system could also be used to attach to a wind vane.

That's the system I was going to use when, or if, I put a windvane up on the pushpit. never thought of doing it using an auto pilot.

[Rustic Charm]

After sleeping on this, I've decided to do two things.

I've got five days coming up over Easter, to do a sea trial of everything after being on the dry for six months. I'll 'try' putting the 'rudder sensativity' onto it's lowest function of 1. I'm not expecting great things, but I'll try it. If that doesn't work, then after I've finished testing everything else, I'll then take the current trim tab tiller off (it's bolted but dabbed with bit of stainless steel weld) and bring it and the main tiller home and make up a temporary bracket to mount it with Atoll's idea. I think that will be the least amount of work as I can mount it in ply to test it.

I'll get my welder guy to add a short tiller perpendicular tiller off the axis of the trim tab with an attachment point for the auto pilot tiller. Luckily I have a spare pin. I'll keep the origional trim tab tiller with the current mounting pole as I can use this if anything happens to the trim tab as a redundancy. This means I will have to mount the auto pilot slightly below on a slope to the trim tab tiller so that the long trim tab tiller flows over the top of it and doesn't interfere.

Atoll, how far out from the trim tab axis does the connection point need to be where I attached the auto pilot?

[atoll]

Originally Posted by Rustic Charm

After sleeping on this, I've decided to do two things.

I've got five days coming up over Easter, to do a sea trial of everything after being on the dry for six months. I'll 'try' putting the 'rudder sensativity' onto it's lowest function of 1. I'm not expecting great things, but I'll try it. If that doesn't work, then after I've finished testing everything else, I'll then take the current trim tab tiller off (it's bolted but dabbed with bit of stainless steel weld) and bring it and the main tiller home and make up a temporary bracket to mount it with Atoll's idea. I think that will be the least amount of work as I can mount it in ply to test it.

I'll get my welder guy to add a short tiller perpendicular tiller off the axis of the trim tab with an attachment point for the auto pilot tiller. Luckily I have a spare pin. I'll keep the origional trim tab tiller with the current mounting pole as I can use this if anything happens to the trim tab as a redundancy. This means I will have to mount the auto pilot slightly below on a slope to the trim tab tiller so that the long trim tab tiller flows over the top of it and doesn't interfere.

Atoll, how far out from the trim tab axis does the connection point need to be where I attached the auto pilot?

if the length of travel of the ram is 17cm.
then have a 8.5cm control arm on the trim tab.

this will give 45degrees of travel each way(from center position on the tab. this should be plenty(centers are tab axis and pin)reducing this length will give more than a total 90 degrees travel of the tab,extending less.

the inboard bracket on the tiller arm can be mounted out of perpendicular if clearance is a problem,(ie make the centers longer than 8.5cm) but when fitting make sure the ram is extended to half its travel length so the trim tab remains centered.

( you will have to check the ACTUAL length of travel on your ram,then devide by 2 to get the optimum trim tab arm length)

edit: I checked raymarine for st4000 ram,and it is giving me 31.6cm ram travel length,so optimum trimtab lever arm would be 15cm which will give slightly more than 90degrees of travel on the trim tab

[Rustic Charm]

Originally Posted by atoll

if the length of travel of the ram is 17cm.
then have a 8.5cm control arm on the trim tab.

this will give 45degrees of travel each way(from center position on the tab. this should be plenty(centers are tab axis and pin)reducing this length will give more than a total 90 degrees travel of the tab,extending less.

the inboard bracket on the tiller arm can be mounted out of perpendicular if clearance is a problem,(ie make the centers longer than 8.5cm) but when fitting make sure the ram is extended to half its travel length so the trim tab remains centered.

( you will have to check the ACTUAL length of travel on your ram,then devide by 2 to get the optimum trim tab arm length)

edit: I checked raymarine for st4000 ram,and it is giving me 31.6cm ram travel length,so optimum trimtab lever arm would be 15cm which will give slightly more than 90degrees of travel on the trim tab

I don't quite follow what you have written in red?

[atoll]

Originally Posted by Rustic Charm

I don't quite follow what you have written in red?

I was over thinking ,in case you did not have clearance with the ram mounted perpendicular to the tiller!

but looking at your photo,both the ram and the tiller are quite slim,so making the bracket 15 cm out,and the trim tab lever arm 15cm would give sufficient clearance.

on hind sight ,and taking into account that the st4000 ram is a very powerful unit making the trimtab lever arm less than 15 cm, would give a faster response time,and less power draw.

so a 12.5cm lever arm on the trim tab would give a 120 degree movement of tab and 25% reduction of power use and 25%faster response time assuming the ram has roughly 30cm of travel

[Rustic Charm]

Originally Posted by atoll

I was over thinking ,in case you did not have clearance with the ram mounted perpendicular to the tiller!

but looking at your photo,both the ram and the tiller are quite slim,so making the bracket 15 cm out,and the trim tab lever arm 15cm would give sufficient clearance.

on hind sight ,and taking into account that the st4000 ram is a very powerful unit making the trimtab lever arm less than 15 cm, would give a faster response time,and less power draw.

so a 12.5cm lever arm on the trim tab would give a 120 degree movement of tab and 25% reduction of power use and 25%faster response time assuming the ram has roughly 30cm of travel

ok cool I'll make the trim tiller with holes so I can adjust the 'pin' that the ram go's on to anyway. Ben suggested that so I can play around with it. And I should be able to do the same thing with the ram end.

okay, I now have a plan.

Though my main tiller is ****. I need to make a new one that looks nice.

[atoll]

Originally Posted by Rustic Charm

ok cool I'll make the trim tiller with holes so I can adjust the 'pin' that the ram go's on to anyway. Ben suggested that so I can play around with it. And I should be able to do the same thing with the ram end.

okay, I now have a plan.

Though my main tiller is ****. I need to make a new one that looks nice.

that's great ,and yes making say three holes in the trim tab lever at say 10cm,12.5cm and 15cm will give you that dampening/amplifying effect from null point(15cm) that alan talked about.

also as alan pointed out there is very little force required to move the trim tab so the shortest lever will give the fastest response,and least power draw.

the only issue I can see is if the wind drops and the boat stops moving with the ram still trying to steer.
which might bend the trimtab lever if it is at its maximum travel before the ram is fully extended?

does the auto pilot have the rudder angle sender unit attached,as this might confuse it,as it is not actually moving the rudder?