Backup hydraulic steering - match pump to Cylinder?

[dial-a-monkey]

I'm planning on a long distance sailing trip and I want to have a backup for my LeCromble Schmitt(LS) Hydraulic pump and Cylinder.

The price LS want for a few random parts IS arrogant et ridicule!!
So I started looking for alternatives but discovered it's complex.

Any advice on matching a reversing pump to a double acting cylinder? can anyone suggest a good pump/cylinder combo? As it's just for a backup I'll probably buy used parts off ebay and service them before departure.

Did I miss any considerations below for a pump/cylinder match?

(1) Displacement of the cylinder VS stroke? (my LS max displacement is 432cc for a 485mm stroke) - how to match that against the pump? Should I aim for the current setup?

- Is it ONLY the rudder sensor that stops the pump from forcing the piston past the max stroke? what happens if it's faulty? - relief valve - then fuse?
- Does the Autopilot learn the pump rate (and adjust the PWM) and when to stop from the pump/rudder sensor?

(2)Speed of the pump? (LS is variable at 0.2 - 2 Ltr/min) is this figure crucial to avoid over active steering? should I aim for the same as the LS?

- What would be a good specification for ((Max Cylinder Displacement / Stroke) / by pump Flow Rate)?

(3)Current load - 8 to 13 AMPS
(4)Mechanical load (currently 750 Kg)

(5) Electronic bypass valve? I guess the reversing pump must have an electronic way to engage the cylinder or the manual/wheel steering would always force hydraulic oil through the pump damaging it? But B&G pumps don't seem to have it?!!

As always I'm very grateful for any advice - thanks.

 

[yoda]

As always the question is never easy to answer without more information. Let's make some assumptions:

You have a Raymarine autopilot, rudder feedback and control head.
You want spares that are interchangeable not fitted.

Looking at the final point the B&G ram and pump units I have seen have an unloading valve which while the autopilot is engaged is energised. when the autopilot is disengaged it allows the hydraulic fluid to flow as the helm is moved.

Thinking about the ram a spare ram will need to either be a direct physical replacement in terms of securing arrangement to the boat and quadrant or will need to be set up separately. In basic terms you need to ensure it is positioned on the quadrant to give full stroke just before you hit the rudder stops otherwise you will do damage, the distance from the centre of the rudder shaft is therefore dependant on the ram stroke. The capability of the ram is a function of capacity so you will need to have something similar to your current ram.

Of course the ram can only do it's job if the pump is up to the required job so will need to be specified for capacity against the ram size, required hard over times at a defined load.

There are some web sites that help with this but it takes some thinking about.

If I were you I would just buy a second pump and ram from LS or alternatively replace it all now with a matched ram and pump and keep the old units in case you have a problem.

Try talking to these guys, they may be able to help you out: http://www.marineelectronicservice.com/

Yoda

 

[Cardo]

I'll try and answer some of the more straightforward questions, based on my experience with a Raymarine pump, Vetus hydraulics and a Simrad autopilot...

(1) Displacement of the cylinder VS stroke? (my LS max displacement is 432cc for a 485mm stroke) - how to match that against the pump? Should I aim for the current setup?

You want the same (or very similar) stroke from the new ram, as this is the actual movement of the rudder. You could go for a different stroke if you attach the ram at a different point on the quadrant. Displacement is helpful if it's similar, but essentially the higher you go, the more the pump will have to pump to move the ram the same distance. Not the end of the world, but might cause the autopilot to steer a little more slowly, if it's already at the max turning rate.

- Is it ONLY the rudder sensor that stops the pump from forcing the piston past the max stroke? what happens if it's faulty? - relief valve - then fuse?

On my setup, yes. If the pump is pumping and there's no movement on the rudder sensor, it gives an error and stops doing anything in order to avoid damage. I guess if something went badly wrong and the pump kept pumping, the next point of failure would go... Be that fuse, hydraulic connection, ram, rudder stop.....

- Does the Autopilot learn the pump rate (and adjust the PWM) and when to stop from the pump/rudder sensor?

Yes, the autopilot needs to be calibrated for rudder sensor and then calibrates itself and learns the pump rate, etc. On my setup, I have to do a calibration using the Dockside settings on the pilot head. The autopilot will turn the rudders a maximum of 20º, well away from the rudder stops (at 35º).

(2)Speed of the pump? (LS is variable at 0.2 - 2 Ltr/min) is this figure crucial to avoid over active steering? should I aim for the same as the LS?

I would aim for something similar, but as long as the pump is suitable for your hydraulic system, then the autopilot should calibrate to pump at the required rate.

- What would be a good specification for ((Max Cylinder Displacement / Stroke) / by pump Flow Rate)?
(3)Current load - 8 to 13 AMPS
(4)Mechanical load (currently 750 Kg)

Sorry, too early in the morning for that kind of mental arithmetic

(5) Electronic bypass valve? I guess the reversing pump must have an electronic way to engage the cylinder or the manual/wheel steering would always force hydraulic oil through the pump damaging it? But B&G pumps don't seem to have it?!!

If it's a hydraulic system similar to mine, you may find the pumps (be that AP pump or helm pump) have non-return valves built in, avoiding the need for bypass valves.
However, if you have a cable/mechanical steering setup, with a hydraulic autopilot, then there will likely be a bypass valve/switch somewhere.

As always I'm very grateful for any advice - thanks.

Say, where are you guys this winter? We're moored up over in Marina di Ragusa. Would be good to catch up with you guys before you disappear further off into the distance.

 

[maxi77]

My first thought is why do you want the back up parts? The cylinder itself is unlikely to fail though it's seals may. A lot easier to carry spare seals, lighter and cheaper and not that difficult to fit. Next you nead spare hoses, they are probably the weakest part of the system. Next key control valves, without them you are up a creek etc. As for the pump armed with a system diagram any decent hydraulic mechanic should be able to advise.

It may well be worth paying a hydraulic mechanic to give you a couple of hours of instruction on maintainance and first aid.

Also check out how your back up system works in a hydraulic failure

 

[ianj99]

Aren't you more likely to have power problems on a long trip unless motoring for hours a day to charge the batteries?

Would it not be better to spend the money on a self steering gear?

 

[dial-a-monkey]

G'day Peter. Thanks for your reply - and to answer. Yes I wanted to take just a overhaul kit BUT!

I got a quote for just an overhaul kit from the New Zealand rip-off-agent "Lusty & Blundell Ltd" which is "a few O-rings and a couple of cylinder seals - and a few other seals for the motor and 2 graphite brushes" for those few parts II would have to wait 6 weeks, and bend over and be kicked in the ass, II was quoted $1200 Nzd for the privilege- "yea right" as we say in Kiwiland.

I will try a few more of LS's rip off agents - elsewhere in the world - France might be the best option.

I also sent the quote/invoice to the head office of Lecromble&theft and asked Angela if she thought those prices were reasonable? - she wouldn't sell directly to me - and sent LS links to their competitors repair parts - basically the same type of parts for 30$. Waiting on the reply.

 

[dial-a-monkey]

G'day Tinkerbell! Wow it's been a while !! hows the TV reception there Hows Winter going? sounds like it's been pretty cold!!

First of all thanks for the great info it fits in well with what I had grasped .. will read it through a few times - but I think I have the jist - your practical approach rings true for me.

To be honest we snuck off back to NZ for the summer - and left the boat in Monfalcone up on the hard, it's a very relaxed here we've been out surfing and climbing a bit...but we are also busy planning for the summer in Euroland.. not far away now, eh!

We have a rough plan to head over the ditch this year - ohh - Dagmar's calling now -- Insisting I have to go cook dinner, have to go, she says hi!- NZ steak! yum, But I send you a message

 

[dial-a-monkey]

G'day Ian thanks for your reply..

I go this way as it's a simpler approach for me - to have spare autopilot parts used off ebay which are all cheapish - or buy an raymarine X-5 new and use a high-power H-bridge for the hydraulic ram - I know enough about electronics to find it easier than installing the windvave - especially as our stern would require a bit of GRP beefing up.

 

[dial-a-monkey]

Oh - power wise were saving all our pennies to get a 300 Watt - Watt&sea

 

[dial-a-monkey]

G'day Yoda, good assumptions, yes all raymarine, and thanks for the advice especially about the stroke vs end stoppers.

I would like to buy second hand LS - so far no second hand units have come up on ebay in the last 2? months, will keep an eye out tho.
There are lots of alternatives far cheaper like Seastar, B&G - and same for parts, cheaper easier to get = ebay

I could just drill 4 extra holes for a second cylinder/pump

 

[Cardo]

Be aware, the Vetus hydraulics documentation states the hydraulic ram should hit the stoppers before it reaches the end of the stroke. So having a ram that's too long (as long as it's not miles long) is not a huge problem, as long as the pump is size appropriate for the ram.

 

[yoda]

Be aware, the Vetus hydraulics documentation states the hydraulic ram should hit the stoppers before it reaches the end of the stroke. So having a ram that's too long (as long as it's not miles long) is not a huge problem, as long as the pump is size appropriate for the ram.

I can only assume that this type of ram depends upon an external feedback to the controller to prevent over extension otherwise you need very heavy duty rudder stops to prevent damage as it hits them. I wouldn't be happy with this.

Yoda

 

[Cardo]

I can only assume that this type of ram depends upon an external feedback to the controller to prevent over extension otherwise you need very heavy duty rudder stops to prevent damage as it hits them. I wouldn't be happy with this.

Yoda

As per earlier comments I made, the system relies on the rudder reference sensor to know where the rudders are, so the AP will never turn the rudders anywhere near the stops.

The idea of this is the the limit of the steering should be the rudder stops, and not the reach of the ram. I guess Vetus believe the rudder stops are tougher than pushing the ram to the extremes.