Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 21-10-2017, 17:50   #1
Registered User
 
DumnMad's Avatar

Join Date: Mar 2012
Location: Nelson NZ; boat in Brisbane
Boat: 45ft Ketch
Posts: 1,235
Why do auto-pilots fail on long trips??

I've had a 2week and a 3week Tasman crossing where each time it was mostly without auto-pilot.

After research I conclude:
The waves got bigger,
The AP worked harder,
Not motoring so alternator not charging,
The battery voltage got a little lower,
AP pump motor took longer to get up to speed,
Higher starting mode currents in motor lasted longer,
Coils got hotter,
Motor failed.

On other threads I notice some have had this problem but after a while the AP is all good. I assume they had a good bi-metallic trip switch that saved the motor.
Maybe they also had wind or trailing water powered generator.

Does this make sense ??
__________________

__________________
DumnMad is online now   Reply With Quote
Old 21-10-2017, 19:00   #2
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29į 49.16í N 82į 25.82í W
Boat: Pearson 422
Posts: 12,324
Re: Why do auto-pilots fail on long trips??

The reasons you mention are all possibilities but if the motor in your AP is a bit undersized for the boat then that will exacerbate the effects of all these.

If a motor is rated for 35-45' boats and I had a 45' boat I would go for the next size larger. So far I've never burned out a motor on an AP, even on long cruises with limited charging which meant I was running batteries towards the low end of the charge range.
__________________

__________________
The water is always bluer on the other side of the ocean.
skipmac is online now   Reply With Quote
Old 21-10-2017, 19:33   #3
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 16,785
Re: Why do auto-pilots fail on long trips??

Get a CPT as a back up, mount the drive motor plate and the wheel pulley.
That way you can install the boxes and plug them in in just a minute and have an autopilot.
Additionally itís electrical consumption is almost nil, and as I believe itís drive motor is actually a Bosch OTR truck 24V windshield wiper motor being driven at 12V it will tolerate lower voltage better.
Now I am not sure about the drive motor, that is second hand, but seems logical to me.
__________________
a64pilot is offline   Reply With Quote
Old 21-10-2017, 19:44   #4
Registered User
 
DumnMad's Avatar

Join Date: Mar 2012
Location: Nelson NZ; boat in Brisbane
Boat: 45ft Ketch
Posts: 1,235
Re: Why do auto-pilots fail on long trips??

Quote:
Originally Posted by skipmac View Post
The reasons you mention are all possibilities but if the motor in your AP is a bit undersized for the boat then that will exacerbate the effects of all these.

If a motor is rated for 35-45' boats and I had a 45' boat I would go for the next size larger. So far I've never burned out a motor on an AP, even on long cruises with limited charging which meant I was running batteries towards the low end of the charge range.
Thanks, we have the larger 2 litre, 6amps @12v version.
I have noticed on blogs there are lots of AP failures between NZ and Pacific Islands and I presume good wind and big seas have something to do with it.
__________________
DumnMad is online now   Reply With Quote
Old 21-10-2017, 19:59   #5
Registered User
 
DumnMad's Avatar

Join Date: Mar 2012
Location: Nelson NZ; boat in Brisbane
Boat: 45ft Ketch
Posts: 1,235
Re: Why do auto-pilots fail on long trips??

Quote:
Originally Posted by a64pilot View Post
Get a CPT as a back up, mount the drive motor plate and the wheel pulley.
That way you can install the boxes and plug them in in just a minute and have an autopilot.
Additionally itís electrical consumption is almost nil, and as I believe itís drive motor is actually a Bosch OTR truck 24V windshield wiper motor being driven at 12V it will tolerate lower voltage better.
Now I am not sure about the drive motor, that is second hand, but seems logical to me.
Our back-up was 2 exhausted crew members who gained the benefit of really good experience

I understand the AP motor is like car starter motors which use a very high current for a short period. Wires can overheat and burn if the high power starter mode is continued too long. The motor can handle the lower voltage but not a lot of high current demand.
High power/high current as the revs go from zero to operating speed then it settles to a lower power /lower current when the motor has reached continuous running mode.
__________________
DumnMad is online now   Reply With Quote
Old 21-10-2017, 20:30   #6
ejs
Registered User

Join Date: Mar 2013
Location: From San Francisco
Boat: Able Apogee 50
Posts: 106
Re: Why do auto-pilots fail on long trips??

Another common reason is too much weather helm from lack of attention to sail balance.

Cheers, Eric
__________________
ejs is online now   Reply With Quote
Old 21-10-2017, 22:33   #7
Registered User
 
UNCIVILIZED's Avatar

Join Date: Jun 2014
Location: Up the mast, looking for clean wind.
Boat: Currently Shopping, & Heavily in LUST!
Posts: 5,629
Re: Why do auto-pilots fail on long trips??

There's what's been mentioned:
- oversize everything; wiring, motor, parts, etc.
- balance the boat via proper sail trim, & moving onboard "ballast" (heavy items) around


Also, build redundancy into your self steering. Such as a 2nd AP of the same make & model. Either operating in sleep mode along with the one which is driving the boat. Or to have as a spare for when the #1 pilot fails. And have spare parts onboard to repair the failed unit while the other one is driving.


Plus, of course, there are windvanes. They require no power, & can be as simple as $20 DIY affairs, to a homemade, purpose built vane, or one purchased off the shelf. Like a Monitor, or Cape Horn. And as a perk, their maintenance requirements are pretty dang low, as is their failure/breakage rate.
__________________

The Uncommon Thing, The Hard Thing, The Important Thing (in Life): Making Promises to Yourself, And Keeping Them.
UNCIVILIZED is offline   Reply With Quote
Old 22-10-2017, 03:27   #8
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,266
Re: Why do auto-pilots fail on long trips??

The motor gets overworked and fails.

You want a bigger motor next time.

Maybe 85% of all AP fails are motors/actuators undersized for the job. The rest is likely electronics and last are mechanical problems.

Cheers,
b.
__________________
barnakiel is offline   Reply With Quote
Old 22-10-2017, 03:40   #9
Senior Cruiser
 
Kenomac's Avatar

Cruisers Forum Supporter

Join Date: Jan 2012
Location: Somewhere in the Adriatic Sea
Boat: Oyster 53 Cutter
Posts: 8,447
Re: Why do auto-pilots fail on long trips??

Ask Murphy, he'll know why they fail.
__________________
Kenomac is offline   Reply With Quote
Old 22-10-2017, 04:06   #10
Registered User
 
Simi 60's Avatar

Join Date: Jun 2016
Location: Australia
Boat: Milkraft 60 ex trawler
Posts: 262
Re: Why do auto-pilots fail on long trips??

Commercial guys don't seem to have many problems, use what they use, not what weekend yachties buy at whitworths.
__________________
Simi 60 is offline   Reply With Quote
Old 22-10-2017, 06:22   #11
Senior Cruiser
 
atoll's Avatar

Cruisers Forum Supporter

Join Date: Mar 2010
Location: gettin naughty on the beach in cornwall
Boat: 63 custom alloy sloop,macwester26,prout snowgoose 37 elite catamaran!
Posts: 9,268
Images: 75
Re: Why do auto-pilots fail on long trips??

this is one of the numerous ways that God has found to punish yotties for not being good little dirt dwellers............
__________________
my catamaran building project updates http://www.cruisersforum.com/forums/...36#post2502136
atoll is online now   Reply With Quote
Old 22-10-2017, 06:27   #12
Registered User

Join Date: Sep 2015
Location: Out of Norfolk Va
Boat: Tartan 37
Posts: 421
Re: Why do auto-pilots fail on long trips??

Give your AP a break every couple hours for like 30 min. Don't sail overpowered. Going downwind when reducing sails drop the main first. We're lucky that upwind our boat will sail itself for hours. Also try slowing the response rate down, going from a 6 to a 3 will reduce the power by 2/3's from my observations.

Agree with oversizing anything you can, wiring is a low cost backfix you can do. This one is very important if you are running on voltages near the low end. A voltage drop of a couple tenths is a killer.
__________________
puffcard is offline   Reply With Quote
Old 22-10-2017, 06:50   #13
Registered User
 
Steady Hand's Avatar

Join Date: Jul 2014
Location: Crewing All of 2017 Available Globally
Boat: OPB = Crewing in 2017
Posts: 4,851
Re: Why do auto-pilots fail on long trips??

All of the above are good possible reasons why the AP can fail.

The following is not an indictment of anyone who posted on this subject, simply a few observations and opinions. You may take them with a splash of salt water.

I suspect most casual sailors (occasional bay or protected water or relatively calm sea state) sailors depend on their autopilots for motoring or motorsailing, and so they are not stressing the AP as much as it can be stressed by higher winds and waves. Then, when going offshore in more challenging conditions the Autopilot fails after being stressed too much.

I would start with proper sail trim on the boat, to balance the helm as much as possible, BEFORE turning the AP on. Then, if the sea/wind conditions change to worse, consider then using manual steering when needed, reserving the AP for less challenging conditions.

Anecdote: I recently sailed on and helmed for hours (and enjoyed it) a fully loaded for cruising performance cruiser 42 foot boat on a close reach in 20-30 knot winds and the boat was so well trimmed by the skipper (a highly skilled sailor) that the helm required little more than fingertip (literally) control to steer. It was an example of proper trim and a balanced helm making the job of steering much easier. The boat was sailing with a reefed main and reefed jib, and still making 8-9 knots.
__________________
Ahoy All Sailors! Need experienced crew for a passage or delivery in Atlantic, Pacific, Caribbean, Med, PNW, ICW, coastal or across an ocean anytime in 2017? I am available on 24hr notice. See my CF Profile "About Me" page for details. Happy to lend a hand!
Steady Hand is offline   Reply With Quote
Old 22-10-2017, 07:23   #14
Head in a locker
 
Cavalier's Avatar

Cruisers Forum Supporter

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 856
Images: 1
Re: Why do auto-pilots fail on long trips??

Quote:
Originally Posted by Steady Hand View Post

I would start with proper sail trim on the boat, to balance the helm as much as possible, BEFORE turning the AP on. Then, if the sea/wind conditions change to worse, consider then using manual steering when needed, reserving the AP for less challenging conditions. .
+1

I routinely switch the AP to standby as part of the hourly checks, just to ensure that the sails are balanced. Apart from the reduction in stress on the AP, you also gain from a significant reduction in power consumption!
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is online now   Reply With Quote
Old 22-10-2017, 08:03   #15
Registered User

Join Date: Aug 2016
Location: Becalmed in the Med
Boat: Prout Snowgoose 35
Posts: 309
Re: Why do auto-pilots fail on long trips??

Presumably this needs to be split by type of final drive.

Tiller rod, wheel, or hydraulic, then perhaps by boat. I always thought that perhaps catamarans were a bit easier on the AP than monos.

With every autopilot there are a few main components.

Actuator unit
Drive pump or other steering
Compass
Display/controller

The actuator or pump are usually the only items ever likely to fail, and with modern systems they can be swapped in and out mixed and matched easily.

My old autopilot died on a crossing to Mallorca, but is was probably half as old as the boat, so 20 years say. It was made by a defunct company bought out by another now defunct company (marine companies don't tend to last it seems).

Unfortunately I couldn't just swap out the actuator (which was failing to provide power to the compass), because it was actually the compass that housed the brains of the system unlike the latest units.

I now have a modern Raymarine Evolution system and want to get components in place to allow me to make an easy switch should a failure occur. So that is fork out for a spare pump and ACU. Actually the ACU is so well protected by numerous fuses that I think the pump is the weakest link in the system especially is it doesn't get enough voltage.

In addition I want spare steering rams too. I actually had a ram fail on passage to Sardinia, and found the AP couldn't handle the boat under sail in 20 knts with only a single rudder.
__________________

__________________
mikedefieslife is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Auto pilots Soulsailor Marine Electronics 4 22-09-2016 01:33
Pelagic Auto Pilots? Sailshabby Product or Service Reviews & Evaluations 26 31-01-2016 20:57
For Sale: Replacement Transducer for raymarine auto pilots ceto Classifieds Archive 0 19-05-2013 09:45
Crew Wanted: Lady Sailor Seeks Old Salt Dog for Long Trips kiwiladysailor Crew Archives 48 02-11-2011 15:09
Auto Pilots islandtimemon Marine Electronics 5 21-06-2009 11:36



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:13.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.