Thoughts on fitting an under deck autopilot


The Garmin GHP 12 Autopilot system. On the left the compass, next the ‘Brains’ and the display unit.

My Pacific Seacraft Dana 24 uses a Simrad TP30 tiller pilot which copes most of the time but just can’t cope when the conditions worsen or the boat is a bit over canvased. What this means in reality is that we tend to reef early to keep ‘Dave’ happy when we could be sailing faster if we had a more powerful autopilot. Since no one makes a serious tiller pilot I have recently been thinking about fitting an under deck pilot even though it would be far from an easy installation.

My first thoughts were that it could be possible although extremely difficult and even if a unit could be fitted it would use too much power. However, after much thinking and research I now think it is doable and feasible even. A system like this will be complicated to install, it will add weight and it will consume more power than the tiller pilot. That’s the down side. On the up side we get half the cockpit back and would even be able to lift the tiller up out of the way while sailing or motoring. The TP 30 is also noisy and its sounds can be irritating when quietly sailing. An under deck unit would be almost silent.

Because the unit is hidden under the deck it is not going to get wet and does not need to be placed on the tiller each time you want to use it. It would be much more powerful and able to cope with heavy tiller loads and unlike the TP30 could be adjusted in many different ways to maximise the performance and power usage.

One of the main problems with tiller pilots is that they are always situated right at the back of the boat and because the compass is inside the pilot it cannot react as quickly as a compass paced more forwards and at a lower level. It’s true that the TP30 can use a remote compass but that doesn’t disguise the fact that it is noisy and not very powerful. Read a review of the TP30 here

Is it even possible?

This discussion is about the possibility of fitting an under deck pilot to the Pacific Seacraft Dana 24 (read a review here) although many of the same principals will apply to most small yachts.

The first thing we need is a tiller arm mounted on the shaft under the deck to link to the autopilot drive unit. But how to attach a tiller arm to the rudder shaft? In order to do this, the rudder log (the fibreglass tube that runs from hull to deck level) would have to be cut down. So, drop the rudder about a foot and cut it down about 4" or 5" down from deck level. Then a stern gland would need to be fitted to the log much like the engine shaft in order to ensure that water cannot get into the boat. Even cut down the rudder log would be well above the waterline so it is possible that a gland could be dispensed with but fitting one would be the right thing to do.


This is the rudder log. It will need to be cut down to allow the fitting of an aft facing tiller arm. Cutting the log will weaken the boat but since the Dana is so over built and the gas locker is moulded in just next to it I doubt it will be a problem!

The tiller arm would then be mounted above the gland facing aft on the rudder shaft. I have found a company Jefa who make lovely alloy arms that will never break. Now, because the rudder log is no longer attached at the deck we have weakened the structure and are now relying solely on the bronze deck fitting to take the strain. This is no problem as it is ridiculously over engineered. Recently I have noticed some play at the top of my rudder and sometimes it makes a clicking noise as it moves. So what it really needs is a nylon bearing instead of a metal to metal loose fit.

Jefa Alloy Tiller lever

A typical Jefa arm. Made of solid Alloy, not cast. It splits apart for fitting. This model shows a slot for locking the arm in place but this won’t work on the Dana as the rudder shaft is a hollow tube. A different system for locking it on must be found.

The deck fitting would need to be removed and machined out to accept a nylon (or delrin or whatever would work best) bearing that could be easily replaced when worn.


This is the ridiculously oversized rudder guide. It will need to be removed and machined out to accept a bearing. This will make it very smooth and quiet and take any slight play out of the system.

So now we have a tiller arm. The battle is half won. All we have to do now is connect a drive unit to it. Sounds simple doesn’t it. Well it isn’t. Most drive units are only designed to move the helm 35 degrees either side of straight ahead making a total tiller arc of 70 degrees. Obviously this is enough for any boat when actually steering the boat when under way but the Dana has a very large tiller movement and in fact, when reversing every bit of that movement is required. This is a problem.

There are solutions but they are all compromises and it all comes back to the tiller arc. The way to increase the arc is to attach the drive unit on the tiller arm closer to the rudder. This will give us enough movement so that when we are mooring and need the full sweep of the rudder we can have it. But there is a down side to this and that is that it will reduce the power and torque of the drive considerably. But this need not be a problem as most drive units (even the smallest ones) are very powerful and even with their power reduced by half would be at least twice as powerful as the TP30.

If it were only that simple. Unfortunately as well as reducing the power you speed up the movement of the drive unit so the corrections to the helm would be very sudden and it is possible that the boat would over steer and the pilot would not be able to catch up and no amount of adjustment would help.

A delicate balance needs to be found. Thankfully physics comes to our aid and immediately rules out certain types of drives. The most common type of drive seen is a linear drive either electric or hydraulic. It’s basically a cylinder with a powered rod that moves back and forth. The problem is that even if you moved the attachment in close to the rudder the drive unit would not be able to articulate with the extreme angle needed on the Dana which I have measured to be 60 degrees either side of straight ahead! Almost double the standard amount.

So linear units are out. What’s left? Well Jefa do some lovely drive units but they are heavy and expensive and use about 4 amps an hour on average which is too much for a small cruising sail boat. This unit has to mount close to the tiller arm and that means there would be an additional 12 kilos right at the back of the boat which is not ideal.

Here is the Jefa autopilot unit. Very strong, beautifully made and compact. Sadly also very heavy at 12 kilos. It also uses a lot of power. The clutch alone takes 1.4amp/hr making this unit a bit of an overkill for a 24 foot boat!

Now I was running out of ideas. Luckily I came across the Octopus cable drive unit from a Canadian company. In fact Simrad offer the exact same unit as a drive option on their autopilots so that must be a good sign. The unit weighs about 4 kilos and can be placed up to 6 feet away from the pilot. It is not as powerful as the Jefa unit but still adequate for the Dana. The plus points of this kind of unit are many.


The Octopus Type RS for sailing boats. Allows remote mounting and a lighter weight. It uses a flexible cable to ‘push/pull’ the rudder. This is the most likely candidate so far.

Most autopilot systems need a rudder feedback unit installed but the Octopus unit has it already built in. This simplifies the installation considerably. Thanks to the push pull cable it can be fitted either vertically or horizontally well forward of the rudder keeping weight out of the stern. Plus it uses considerably less power. Average consumption should only be a couple of amps at most. Obviously the less work the pilot has to do the lower this figure will be.


The Autopilot brain

Having solved the tiller arm and drive issues we now have to decide which autopilot to use. Most pilots can be set up to work with any drive so you have a large choice. Personally I do not like the look of the Simrad autopilots or their displays and I have vowed never to have a Raymarine product on board my boat ever again there are fewer companies to choose from but there’s still a fine choice. There’s B&G, Jefa make one, Coursemaster from Australia do a range. There’s the French company NKE who supply most of the French racing boats but my favourite so far is the Garmin unit. It has a colour screen and many options to change all the settings to maximise the efficiency of the package.

This unit has a separate compass that can be placed in the optimum site for best performance, a separate CPU and the display. The display can be placed next to the engine controls to keep from cutting holes for it elsewhere. It will be a minor inconvenience to have to reach down to start and stop the autopilot but that’s about the only down side although there is a wireless remote control option which would make the unit even easier to use and offers the ability to steer the boat from the foredeck or from up the mast if solo and navigating through coral reefs. It has a range of 45 feet.


The Garmin colour screen. It has different settings for day and night viewing.

The new pilot will enable tacks and gybes to be adjusted to suit the boat among other features. But best of all it will be powerful enough to leave a bit too much sail up if we feel like going fast and it will steer the boat better when it’s surfing down waves in a gale. The unit will be kept dry and this will ensure that it lasts a long time. The added bonus is that we get back one half of the cockpit which is normally taken up by Dave and his ugly cable.



There is a lot to be said for the TP30 tiller pilot. It does steer the boat most of the time using very little power. We would be lost without it. The down side is that it is not very adjustable and it is always in the way and out in the elements and when the conditions worsen it starts to struggle.

An under deck unit will work better, be more adjustable and able to steer the boat even in extreme situations. Being under the deck it is protected from the elements and this will ensure a good reliability. On the down side it weighs more, probably about 10 kilos all said and done and we’d surely keep Dave and Dave 2 as back ups anyway. The autopilot is the most essential bit of kit on the boat after the sails! It will use more power but because the unit is so adjustable it can be tuned so that it can keep the boat on course with the minimum of tiller movement.

Obviously it’s a costly item and I don’t suppose there will be much change from £2500 but that compares to the cost of a decent wind vane. It’s also quite a mission to install but I think it would be worth it in the end. It is at least possible. In any case when was anything worthwhile easy?

If anyone has any thoughts, comments or questions I’d love to here them.


Simrad TP30 Tiller Pilot Long Term Review


Dave steers Doolittle mid Atlantic. Note his burgundy jacket, later changed for a beige one to keep him dry and cool.

Over the last couple of decades I have had a love hate relationship with autopilots. My last boat was a long keeled classic with a steep angle on the rudder and this caused no end of problems and over the years I tried and consequently destroyed most of the autopilots on the market.

By the time I had bought the Dana 24 I had ruined no less than 10 pilots and not one of them worked very well. When it came to buying an autopilot for ‘Doolittle’ I thought long and hard about buying an under deck unit but the way the Dana rudder is would have meant serious structural changes would have needed to be made. Then there’s the fact that under deck pilots are very complicated and consume a lot of power.

In the end it just didn’t seem worth it and besides, maybe the Dana with it’s vertical rudder and more modern shape would allow a modest tiller pilot to work. After a terrible experience with Autohelm (now Ratheon) I vowed I would never have anything to do with that company again so I went with the Simrad TP30.

Most autopilots make outrageous claims about the size of boat they can be used on. The TP30 is rated for boats up to 42 feet long so I figured that it should be about right for a 24 foot boat. Maybe if you are just using it in gentle conditions or motoring these claims are correct but I can’t imagine the TP30 steering a 42 foot yacht sailing in rough conditions.

Whether a tiller pilot works well on your boat will depend on how easy it is to steer when you are on the helm. If you have to put a lot of pressure or input in when sailing then the tillerpilot will struggle. If on the other hand, the boat is light on the helm and easy to steer (like most modern boats) the chances of an tillerpilot working are much greater.

On my last boat, the only way the pilot would hold a course was to set it up on it’s maximum gain (the speed of response to course change) and minimum sea state. The only trouble with this was that the tillerpilot was working like mad the whole time and this in itself caused problems. For some reason electronics manufacturers love to make everything black. I don’t know why they do this but when you are sailing in the Med in the summer, temperatures can get very high indeed. With a black horizontal surface soaking up the heat of the midday sun and the pilot working overtime, the pilot gets ridiculously hot. In fact one time in Sicily it got so hot that the cog spun on the motor shaft and rendered the pilot useless.

Suffice to say, I learned a lot about steering and tillerpilots over the years. The other thing I discovered is that the worst thing you can do, apart from using a tiller pilot on a classic yacht is to let them get wet. They don’t like it!

If you want your pilot to last the secret is this. Adjust it so it doesn’t work very much when steering the boat. By that I mean, do not load it up with excessive weather helm. If you are sailing you should reef the main very early so as not to load up the helm. Adjust the settings so that the boat can swing about a bit before the pilot starts steering. Don’t let it get wet or hot. I know that this is asking a lot but if you ignore this advice you will have all sorts of problems.


Pic shows the cog wheels. Two magnetic pins are pressed into the larger cog. If they slip out, they will smash the Hall sensors on the PCB.

The unit itself is mostly made of plastic and frankly isn’t very tough and there a few design faults which can render the pilot useless. The biggest problem are the magnetic pins in the larger cog wheel. These tell the pilot where the arm is and without them simply will not work. What normally happens is this: The magnetic pins start to work themselves out and then they smash into the delicate Hall sensors which are fitted to a small PCB. When that happens the pilot won’t work. It would be wise to always carry a spare PCB with the Hall sensors on it. It is easy to replace and very likely to get damaged sooner or later.

Another problem that you may experience is the slipping of the motor cog which is only pressed onto the motor shaft. Most of the time this cheap way of attaching the cog is sufficient but if the tillerpilot gets hot and is working hard it may very well start to slip and then the pilot will not work.

If you do buy a TP30 or the latest TP32 (which I assume is pretty much the same design inside) get used to the idea that you will have to take it apart on a regular basis. They claim that all you need to do is smear a bit of silicone grease on the shaft every now and then but this won’t be enough.


There are ten cross head screws in the underside of the pilot, unscrew them all and open the pilot like a book. (see pic). There is no need to dismantle the unit any more than this. The motor simply lifts out for easy access to it’s ends.

The most important thing you must do is push the magnetic pins out and glue them in properly with superglue. If you don’t do this, then one day the pins will ease out and smash the Hall sensors.

If you hear your pilot squeaking during use I recommend taking it apart and putting a drop of machine oil at either end of the motor itself. While the unit is apart put more grease on the worm drive and replace the belt if it is not tight. There is no tension device on the belt so if it is stretched it may slip.

You can take the panel off the electric part of the tiller pilot but this seems quite well sealed and in any case if the electrics do fail, there won’t be a lot you can do anyway so I suggest you leave it alone!

You can buy a spares kit which includes a new seal but I have found that if you don’t try to remove the seal when you open the unit it lasts for many years. In fact fitting a new seal is quite tricky so best not to touch it at all unless it is obviously broken.

To stop the tillerpilot over heating in the sun and to reduce the chance of water getting in make a jacket for it using a pale coloured material. Since our tillerpilot (Dave) has had a jacket he has been much more reliable. This is probably the most important thing you can do to keep your pilot working for as long as possible.

If you are having problems with the pilot suspect the electrical connections. If the pilot doesn’t get a good solid voltage it will cut out and behave erratically. Always check the socket, wiring and plug first before doing anything else.

So that covers the problems you are likely to have and how to avoid some of them. Let’s discuss the pilot itself.

At this point I have to say that we have had Dave on Doolittle for 6 years now and he has steered the boat across the Atlantic and has now done about 13,000 miles. This is most impressive for a plastic tillerpilot but there is no way he would have done this if not for his jacket and the regular oiling and greasing of his innards. He has had a new belt installed but apart from that he is original. The shaft is a bit pitted and corroded where some salt water has got in at some point but so far (touch wood) he is still working.

I think this says more about the Dana 24 than the quality of the TP30 in my opinion. The Dana is a very easy boat to steer and she will practically steer herself in most situations so Dave never has to work very hard and this must surely be the main reason why he is still working. That said, he has steered us bare poled before a gale mid Atlantic for 24 hrs and did an alright job.

The TP30 has an NMEA input so it can be made to steer to a waypoint but we always simply put the boat on a heading and press the red button. The controls are simple and the unit has coloured leds that light when you press a button. It also beeps so you know that the button has been pressed correctly. There are just 5 buttons to press for all the adjustments.

Dave can be used as a stand alone autopilot using his built in compass or you can fit a separate compass somewhere else on the boat. If you have wind instruments the unit can steer the boat by using the wind. There are also adjustments for gain and seastate.

There is an auto tack feature which when pressed tacks the boat through 100 degrees. Sadly this amount cannot be adjusted so when heading upwind I find that I have to head down 10 degrees or so before I press the tack button or the boat almost has the wind on the beam after I have tacked. It really is a shame that there is no simple way to adjust this to suit your boat’s best upwind angle.

It wasn’t cheap. At the time it cost about £450 which is a lot of money for a plastic tiller pilot but it does seem to work fairly well for most of the time. Basically the times it doesn’t want to work well are the times when if you took the helm you would have a hard time too. It’s quite powerful but not very fast nor is it predictive. It has to wait for the course to change before putting the helm over. To some degree the way you adjust the gain and sea state can help but the bottom line is that it has limitations.

No doubt a proper hydraulic under deck unit with separate compass and computers would be a much better way to steer the boat in more extreme conditions but as a compromise the TP30 isn’t bad. It is easy to fit. All I have to do is plug it in, drop the pin into the support and the other end snaps onto a pin on the tiller. It uses very little power and obviously the less it works the less power it will use but in any case I would be surprised if on Doolittle it takes more than 5 amps over 24 hrs which is brilliant.

Rather than drill a hole in my boat to fit it I simply added an Antenna mount bolted to the pushpit. It works very well.


A simple clamp on antenna mount is bolted to the stanchion and allows tillerpilot mounting without making holes in the boat. This has worked for over 13,000 miles so far.


If you have a modern boat that is easy to steer and light on the helm, the TP30 should work quite well.

It takes very little power and is quite powerful albeit rather slow to respond and move the helm.

It suffers a few design faults that can be easily sorted out. It also needs regular maintenance to keep it going.

It can be connected to NMEA, it can steer by separate compass or wind. There is a remote control as an option.

Don’t make it work hard and get hot and whatever you do, keep it away from water!