Hydraulic autopilot question

[Colvic Watson]

The motorsailer we are buying has hydraulic steering - I've never sailed a boat with it before but apparently it can have a lack of 'feel'. Does this mean that it's similar to a non weighted power steering that is just always easy to turn? A big part of this question relates to the very, very ancient autopilot fitted (1977). The boat displaces 12 tonnes so that puts it firmly in the very expensive category for a new autopilot and the current one has had lots of work done to keep it going, but if the hydraulic system has no real weight on it, why not just fit a Raymarine wheelpilot type - expensive but at £900 versus £2,800 for the one rated for 12 tonnes displacement, it's a huge saving - plus second hand unit come up.

Thanks for help and suggestions.

Simon

 

[knuterikt]

There are two types of hydraulic steering used in boats.
1) Engine driven - these have a pump driven by the engine or by an electric motor. These systems has the same type of functionallity as the power steering in a car.

2) Manual hydraulic steering - this is basicly a rotating pump whit the wheel connected to the shaft on the pump. The power gain in this system comes from ratio beteeen the the fluid volume delviered by the wheel pump and the area of the piston. The longer you have top turn the wheel to get one degree movement of the rudder less force is needed on the wheel. This type is the most common and best suited for sailboats since it does not need external power.

If the system on your boat is of the second type, the problem you can encounter with the wheelpilot will be the speed (or lack of) the drive unit operates with. This in turn will give problem with holding the course.

 

[bendyone]

Just going through the process at the moment, the set up I have is a simple helm pump and ram. Fitted without NR valves you can still feel the rudder to a certain extent. However I am fitting a electric pump to be controlled by the autopilot so have had to fit NR valves to stop the helm turning when the pump runs. ie the electric pump operates the ram not the helm. Another point is to fit a bypass valve if you have an emergency tiller arrangement.
Go to a local hydraulic suppler not a marine place and you will get good advice and pay around 20% of the cost for the bits.

 

[castaway]

I bought a Mauritius 43 with hydraulic steering at the end of last year and have just returned from 2 week aboard. I was asking similar questions about how the system would feel before I left.

My boat has Vetus pump and ram and does feel a little 'dead' to the hand, however what I really like is the fact that once one has applied , say, 3 degrees of rudder the 3 degrees will say 'on' when you release the wheel.. I love this especially on a 15ton long keel boat.

My last boat had a mechanical linkage and on a long passage in a stiff blow I had to tie the wheel off rest my arms !

One odd thing with the autopilot is that when it is engaged the wheel is disengaged... so when the AP is disengaged and the 'Wheel' engaged the 'straight ahead' marker on the wheel is never in the same place !

The wheel pilot option would probably work for use only under power. Once again with my old boat (Moody Halberdier) I spent a great deal of time looking at the various options to replace the early 70's Pinta AP.... To replace with anything worthwhile was going to be, as you found, about £2500-£3k for a fully integrated system.

Regards Nick

 

[Colvic Watson]

Thanks for the replies

 

[Gordonmc]

This is the same thought-process I have been engaged on.
My boat (15 tons displacement) came with a Vetus wheel-pump; a ram of indeterminate make and a Cetrek-Bamar auto-helm controller linked to a electric-hydraulic pump.
I by-passed all the auto-helm kit and had the ram refurbished.
It seemed a lot more simple to get a wheel-pilot and I was looking at the Raymarine 4000 until I saw a line in one of the manuals; "Not suitable for hydraulic steering systems".
If anyone has installed a wheel-pilot on a hydraulic system I would like to benefit from the experience.

 

[gus]

A boat in the 12 ton range will not have the same 'feel' as a smaller boat. The size of the rudder and the forces on it mean that the mechanical advantage given to the helm means a certain loss of feel. I once had a similar boat with hydraulic steering and I fitted a Vetus autopilot which had an electrically driven ram. It was one of the best things I had ever bought as it was like having a permanent steersman.
How much you have to work your helm to control the steering of the boat will also depend on the design of your rudder. It should be hydrodynamically shaped and have a balanced front edge to make the steering lighter. It also helps if the rudder is quite large because you then have some real control forwards and backwards. An excellent example of the kind of control I and talking about is - cruising at 8 knots in a 38' long keeled motorsailer, fender over the side with the shout of 'man overboard' and being able to come about and be back alongside the fender in 18 seconds!!
Your steering is a whole system and getting it all to work together so that it gives you the control and amount of feel you desire will require some serious thinking.

 

[Pleiades]

12 ton boat is too heavy for an S1 or SPX5 wheel pilot, even without the Hydraulics. They are only rated up to 16,500 lbs laden displacement and that is only in flat calm gentle conditions, so methinks a refurb of the Hydraulics is the way to go. You might consider also fitting a second hand Hydrovane and a small Tiller Pilot however - that would give you a very reliable second rudder and second steering system for reasonable dosh - the Hydrovanes are good for several circumnavigations so the initial high cost is justifiable. No connection with either company other than as a happy customer - posted a Review of the combination here:-

http://www.sailers.co.uk/forum/viewtopic.php?f=6&t=315

Robin
Pleiades of Birdham
MXWQ5

 

[knuterikt]

One odd thing with the autopilot is that when it is engaged the wheel is disengaged... so when the AP is disengaged and the 'Wheel' engaged the 'straight ahead' marker on the wheel is never in the same place !
Regards Nick

It's not so strange, there are two different pumps that pump oil in/out of the hydraulic ram (by in/out I mean in different directions).

The wheel pump (powered by your hands only) has got return valves stoping the preassure from the rudder moiving the wheel.
This is the reason you can apply "3 degrees of rudder the 3 degrees will say 'on' when you release the wheel.. "
This also prevents you from feeling the pressure on the rudder ("feel a little 'dead' to the hand")

When you engage the autopilot the (normaly) electrical pump will pump oil in/out of the ram. The valves in the wheel pump will prevent the wheel from turning.

 

[knuterikt]

A big part of this question relates to the very, very ancient autopilot fitted (1977).

You did not say what kind of autopilot that is currently fitted.
If it is one with a electric operated pump you will most likely be able to reuse this part of the system.
The electric pumps tend to be quite pricy - up to 50% of the complete price.

The reason autopilots for larger boats are expensive is (partly) the high currents the will have to deliver to the electric ram or the elcetric pump but also the cost of the ram.

The "brain" of the autopilot normally reverses the polarity on the two powercables going from the brain to the ram/pump.

 

[Bosun Higgs]

I had a boat with hydraulic steering and with a wheel pilot for 7 years.

The lack of feedback comes about because most hydraulic systems are made for power boats and they incorporate anti feedback valves to prevent the rudder turning the wheel. If you were to remove these valves you would get feedback as you do with car hydraulic steering, but the lack of feedback can be handy at times. For example, I was able to turn the wheel over and then leave it whilst the boat went through the wind and I sheeted in the genny. Then go back to the wheel and centralise. However there is a disadvantage too - helming the boat was insensitive and no fun at all.

My boat was a Prout cat and unlike most monos cats are directionally quite stable and slow to turn. This gave real problems with the wheel pilot which couldnt turn the wheel fast enough to get the boat tacked through the wind, and quite often we lost all forward speed before we managed to tack. But it was effective at steering once on course even though the wheel was 4 turns lock to lock and the pilot spec said a max of two and a bit turns.