440: Back-up Auto Pilot for Lagoon 440

[colemj]

Originally Posted by a64pilot

That is pretty much apples and oranges and we aren't talking about driving the rudder directly, but by using the mechanical advantage the manufacturer designed into the steering system.

No, it is apples and apples (and I meant wheelpilot, not tillerpilot, but the point is the same if the different boats are tiller steered instead of wheel steered).

Yes, the manufacturers design mechanical advantage into their systems, but that advantage is in the final form - often times the size of the wheel (look at those 6' diameter wheels on racing boats). Alternately, the length of a tiller is different. A wheel pilot generally does not come with several diameters of drive sheaves, or several gearing options. I now understand that the CPT offers two sizes of drive sheaves.

Your IP is a rack and pinion system, I believe, and those provide a great deal of backdrive resistance comparably. For cable systems, a boat caught a bit wrong can really produce a lot of backdriving force or create a turning resistance on the steering.

But my point was that there definitely are different forces on different boats and these are not all the same in the final form. If all were the same, we would all be using cheap wheelpilots (or tillerpilots for tiller-steered boats). Hence, there are different sized AP's for boats, and boats that will never be capable of being steered by a wheelpilot or tillerpilot.

Mark

[a64pilot]

Originally Posted by Paul L

So who do you plan on steering? You and maybe your partner for 36 hours in crap conditions? Do you think you'll be alert and a top-notch helmsmen part the way through this? Generally the APs stay more alert and steer better than a tired Mom & Pop crew.

As far as On average they don't, in most conditions it is fine. But get yourself in tough conditions, confused seas, up a little sideways and it can take a lot of effort to correct.

If the Wx is so bad that an AP failure could cause serious damage to the boat, yes I plan on steering, if that continues to the pint to where I'm beat, then I'll heave to for awhile or a drogue. (this from a guy with no actual experience, so reality may differ)
I have a CPT now, but plan on a below decks auto pilot as well, I plan on a rotary drive AP with a chain to drive the pinion gear shaft directly, that being more efficient than a Hydraulic model, but if this CPT continues to perform as it has so far, I may just buy another as a spare.

[a64pilot]

Originally Posted by colemj

But my point was that there definitely are different forces on different boats and these are not all the same in the final form. If all were the same, we would all be using cheap wheelpilots (or tillerpilots for tiller-steered boats). Hence, there are different sized AP's for boats, and boats that will never be capable of being steered by a wheelpilot or tillerpilot.

Mark

Agreed, one size fits all probably doesn't work for an autopilot, just the thought process is that the CPT wheel pilot and the Raymarine are the same, and they aren't.
Raymarine abandons the wheel pilot after the simple basic and inexpensive model, but the concept of an autopilot driving a boat through the same mechanism as the helmsperson does is valid, and it's easy to argue it's the safest and less risky way as you haven't modifies the factory steering in any way.

Still wonder why these Cats don't use hydraulic steering? From an integration standpoint I can see real advantages with it.

I've said a couples of time in this thread that a CPT isn't the way to go on a Cat, especially one of the size and cost of this one.

Somebody, it may have been you brought up a complete / redundant AP of the same make and model as the primary, but installed on the "other" rudder is the way to go on a Cat, and I think that is the most logical and covers more failure modes than any other way.

[Paul L]

Originally Posted by a64pilot

If the Wx is so bad that an AP failure could cause serious damage to the boat, yes I plan on steering, if that continues to the pint to where I'm beat, then I'll heave to for awhile or a drogue. (this from a guy with no actual experience, so reality may differ)........

`The best laid plans of mice and men. Stopping and heaving to is not always a good or available option. In my opinion on an offshore cruising boat that is relying on an AP and not a windvane, the AP should be tough enough to handle extended gale conditions. With a Mom & Pop crew, the AP will probably be a lot better than the crew in steering for long periods in those conditions.
The last big blow we were in was crossing the Gulfstream Nov last year with the crowd that was headed to the Virgins from Virginia. You really don't want to heave-to in the Gulfstream and wait to get hit by a front. The stream is way wide up there, so pushing through was the way to go but took a long time. There were a fair number of lost boats. Hard driving conditions were for about 30 hours or so. Real glad the AP could drive it.

[colemj]

Originally Posted by a64pilot

Still wonder why these Cats don't use hydraulic steering? From an integration standpoint I can see real advantages with it.

There are several disadvantages to hydraulic steering - mono or cat. Loss of helm feel and loss of a tie-bar are big ones on cats, although a hydraulic tie-bar can be designed. With dual rudders, alignment and loss of alignment can be issues with hydraulic systems.

They do make autopilot integration, circuitous routing and multiple helms easier, though.

Mark

[a64pilot]

You can do hydraulics with a tie bar, truthfully I think it would be near to impossible to do without a tie bar.
Even modern outboards are hydraulic steered, I believe it's they only way you can get a Mercury Verado for instance.
Should be able to have two completely separate hydraulic systems with the drive units stacked, each one driving a different rudder, only common part being the wheel and tie bar, just can't see maintaining perfect rudder alignment without a mechanical connection myself.
I think it's probably mistrust of a modern system that keeps buyers away from hydraulic steering, funny too as I see Cats as being very modern.

How are the very high end boats like a Gunboat steered?

[colemj]

Probably the biggest reason is loss of helm feel - there simply is no feedback to the helmsman. Outboard-driven boats don't need helm feedback.

I don't consider hydraulics as being equated to a modern steering system, nor mistrust in the consumer. Usually they are considered more of a compromise in a sailboat.

No clue on Gunboat steering, but other performance boats like Outremer, LeRouge, etc use a tiller...

Mark

[coldar1]

Thanks for all the replies and discussion. Very interesting reading. With proper sail trim, our lagoon 440 is very easy to steer by the helm wheel, and as purely a back-up, I think the wheel mounted unit will do the job. We are hoping for following winds for most of the Atlantic crossing which means we should be flying our para-sail. On our boat, that makes the wheel loads even lighter. Under virtually all conditions we have sailed in the last 18 months of continuous cruising, we set the auto-pilot on setting 5 or 6 to reduce the rudder response and even sitting in the compartment right alongside the electric/hydraulic motor and pump, you can hardly hear a sound so it isn't working hard. My biggest fear is the electronics failing, not the motor, pump, or ram. Looking at the issue purely on a Risk Management basis where Risk is a likelihood - V - consequences and we have 100% redundancy with our wheel steering if we loose hydraulics, I'm starting to think the consequences of an auto-pilot failure being having to steer by wheel, is an acceptable risk. My crew may have different ideas, but that I can deal with. "Floggings will continue until morale improves"!

[a64pilot]

No reason why hydraulics can't have feel or feedback, My outboard did, the wheel would pull to port or starboard depending on engine tilt, just like teleflex steering.

[DavefromNZ]

For info our L450 auto pilot has failed three times on me. All occasions were downwind with waves making it work hard and we were over canvassed so the balance was not so good. I think the hydraulics may have overheated as the warning was "drive failure". After about 15 mins it worked ok again.

Hand steering the L450 is very hard work both mentally to keep it on track and the forces on the wheel are huge.


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[robert sailor]

Hand steering any boat that has too much sail up is usually pretty hard offshore, reef early everything is easier.

[colemj]

Since it wasn't a Lagoon AP, it would help to know the brand and model of the AP and the drive unit.

Mark

[DavefromNZ]

I have all Raymarine gear. The Autopilot is SPX30.


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[colemj]

Thanks. Do you have a hydraulic drive unit? These packages usually use the electromechanical drive and not hydraulic. Perhaps they supplied you with the Type 1 drive instead of the Type 2 and it is a bit small for your boat? Also, check to make sure the wiring is sufficient to provide 40A for the distance it is run - most installations are greatly underwired.

The drive unit error is usually due to either insufficient voltage or an inability to get the drive to move when supplying current. Wiring or too small a drive for the boat will cause these things in rough conditions, but not in more calm ones.

Mark

[DavefromNZ]

We have the standard Lagoon 450 hydraulic drive unit for the auto helm.