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Yesterday, a good friend brought to my attention a job posting where the owners of a beautiful sailing yacht were looking for a couple to take care of it. When I pointed out to him that the listing mentioned “experienced mechanic” as a requirement, he commented that I knew “enough to be dangerous.” I laughed at that adjective but think that it’s probably fairly accurate. 🙂

Not happy with our auto pilot’s performance on our last passage, or lack of performance to be more accurate, I took it upon myself to try to fix it yesterday. As I worked to disassemble the unit, I first likened the process to a surgeon performing exploratory surgery. When I got further into it though, I realized that it was more like a coroner conducting a post-mortem exam on some alien that had crash landed on Earth, that being because I had no idea what I was going to find inside the unit, having never taken one apart before.

As it turns out, the mechanical portion of the alien, I mean wheel unit, is pretty simple. Inside it there is a belt driven by a gear which, when a clutch is locked down, will turn the wheel. I had hoped to see something obvious that would indicate the problem but that was not to be. I can only guess that, even though the belt is still in one piece, the teeth on it are worn enough that, under pressure, they are slipping around the gear. Working on that assumption, I placed an order for 2 belts yesterday (one to put in and another spare) and am having them shipped to California where we can pick them up next month. We still have a lot of miles to cover between now and then so hopefully we can find some really settled weather to travel in that won’t make Wheeler, the auto pilot, stress too much.


  1. To steal a turn of phrase, a sailboat will turn an ordinary man into a mechanic.

    You seem to be holding your own in that department – kudos!

    I took the liberty of doing a bit of research for you. From what I gather, these autopilots (at least the older ones) love to eat belts at the rate of about one per week.

    Here is a link to the manual (PDF @ 1.44 mb):

    And to the archived threads regarding that model:

    Thanks for an enjoyable blog that I’m compelled to check out daily!

    • Thanks for the research and I’ll check that out. I think a belt per week might be stretching it a bit though, Zach. We have NEVER replaced the belt.

      • I agree – that seems like an awful lot of belts!

        Skimming the threads, that did seem to be the consensus. Failure seems to occur at roughly 200 hours / 1500 miles of sailing. Bear in mind that this information is from a decade (!) ago, but is probably still relevant.

        To me, it would be more important to glean the bits of wisdom for rebuilding and potential problem areas. There’s nothing worse than doing all the work, only to have some other nitpicky little bit fail and having to go through the exercise all over again. Just trying to save you some hassle and postpone Murphy’s Law a little longer, lol!

        I’ve learned the hard way (several times over) that it’s best to heed these recommendations for seemingly minor procedures and upgrades. If a problem arose for two other people, Mr. Murphy will appear, screaming like a banshee, at the worst possible time, if only to remind you that you skipped a step.

        The worst for me was not installing the recommended two additional grounding wires to a motorcycle harness. The fire department responded to the roadside to douse what remained of the bike. $3 in parts, or the cremated husk of a previously nice sportbike? Lesson learned!

        Back on point, here are the bits that apply to the autopilot repair.

        “First, the belt must be replaced often – about once a week at sea. $55 each at West Marine. But once you do that the unit is never the same. The engagement lever will flip itself to the unengaged position. I use shock cord to keep it engaged, but that’s one more annoying thing to do whenever turning the A/P on.

        Second, the unit has about 6 wheels inside that keep the two halves together. These break off. Glue works for a while. I finally thru-bolted these on with #10 bolts, and the units work much, much better and more reliably. But…. two 4000s are good for one summer (3000 miles) of sailing. ” – Date: Wed Aug 15, 2001 10:54 am).

        From a later post:
        “Also, when replacing the belt, remove the half dozen black wheels inside of the unit and apply grease to the bronze bearings. If you don’t, these bearings seize up and the mounts (plastic) break off. Be very careful to grease only the bearing; there must be no grease on the belt or the surfaces the belt runs against.

        I have two ST4000s, and found that these wheels are a problem. Last year I bolted the broken ones together using #8 bolts and lock nuts, which worked just fine. I recently ran bolts through all of the wheels just to be sure there’s never a problem again. If you do this, please do not tighten the bolts too much; the wheels must spin freely.” (Date: Fri Sep 28, 2001 10:32 am)

        • I did read it all. Fortunately, the belts can be purchased for much cheaper than what West Marine sells them for. The link that I included in this post sells them for 20 bucks each and they shipped the order the same day I placed it (yesterday).

          The wheels that they mention appeared fine on our unit. I am not about to take them off to grease them as it defies my “don’t #$@! with it if it ain’t broke” philosophy.

          As for the clutch, our’s disengages as mentioned. And here I thought that I was the only one who had improvised a solution for that (while underway I might add). 🙂

          One point about the belts wearing out so quickly. There are obviously some conditions that the auto is just not designed to handle. Forcing it to try to work under those conditions are definitely going to lessen the life span of the belt and/or the entire unit.

          • Great! Just trying to lend a virtual hand. I know internet access can be sketchy. 🙂

            “don’t #$@! with it if it ain’t broke” – how true. Reminds me of an old biker saying: Carburetor is a French word. It means “Don’t **** with it.”

            Hopefully the repair turns out just fine.

            I agree on the life span issue. Some people just like to abuse equipment, and have the cash to throw parts at it.

            Cheers, and thanks again for a great blog.

  2. I see the autopilot as one of maybe 3 things I wouldn’t like to sail without! I hope you get it fixed soon – you’ll figure it out!

  3. hi, I’ve been reading your blog from the very beginning, (of the blog) that is, a very interesting story you two have, as a wannabe cruiser the one thing that seems to be missing that would really help all of us ( i know this could be personal) is how much does it really cost to get going and then on average to stay out there, would be great if you could comment on that via email. thanks and best to you both

  4. Yes, the 200 hours seem true.

    No, I’ve not had trouble with the handle. Still perfect (1997, just put in its 3rd belt since 2008)–I replace them before they break).

    I do use sailcoat on the non-friction belt surface. The wheel spins better when the auto is off.

    I’ve greased the bronze parts and there are some signs of wear. I did have to over size and re-tap one screw.

    The plastic wheels seem fine.

    I generally hand steer off-the-wind when there is a swell. It just seems to be working too hard. Also hard on the wind.

  5. Mike, if you haven’t got it, I suggest you google for the Raymarine User’s Manual for the ST4000.
    Mine is on the boat so I can’t quote it directly but I seem to remember that they stress 2 things. Washing out thoroughly with fresh water after use so as to remove salt crystals. This obviously for mono-hulls where the a/p is outside, so not really relevant to you. The other point is the correct adjustment of the belt. This is explained in the manual and is done with the small cam that I am sure you can see. On one model you have to turn the cam to retension the belt as it stretches slightly and starts to slip. On another model you slide the cam and tighten a screw to keep it in place.

    They stress that the a/p is designed for certain loads that depend on boat weight and steering mechanism. If these are exceeded, the a/p will fail due to motor burn-out, or simply that the belt will slip.

    I can’t imagine where the “1 belt a week” idea comes from, unless the system is badly set-up, severely overloaded, used in very bad weather, or all these. I would expect more like 3 to 4 years use, perhaps 2 years minimum if you are cruising hard almost every day. I’m sure on your courses they will have told you always to hand steer in really bad weather, ie f7 and upwards. This because the helmsman can be pro-active and adjust before the wave hits, whereas the a/p can only react, maybe very strongly, after the wave hits.

    Good idea to have spare belts anyway, but from your picture, yours looks fine.

    Good luck.


  6. Hi we had a similar issue with ours we also had the chain drive snap & had to get a new one, be careful replacing the main auto drive belt as ours was chewed up after we put it back together & had to replace that as well, the reason it got chewed was one of the outer screws was loose & the whole thing came out of line. We are now having issues with the Head & had to strip it completely but looks like we need a new one & will sort that out in St Martin. good luck with it all

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