Hydraulic system. Not to be neglected....

In 2024 the rudder cylinder was replaced with new, and the centreboard cylinder was installed.   A spare (new) centreboard cylinder is on board and the old rudder cylinder awaits rebuild.   The pump was serviced and a damaged pivot screw replaced.   The system was drained, flushed and purged of air, and fresh ethylene glycol was installed.   There are spare fuse discs and pump seals aboard.   

The hydraulic system on the 435 consists of a pump which operates two selectable circuits to raise and lower the centreboard and/or rudder.  It has a reservoir containing ethylene glycol  or propylene glycol hydraulic fluid,  and uses plastic hoses.    The fluid most commonly used is undiluted automotive antifreeze.      

Though it was not mentioned in the listing, Sakura's hydraulic system was not functioning properly. The rudder cylinder was siezed, leaking and corroded, and while the centreboard would raise properly, it would  drop freely when the control lever was moved to the down position. The pump itself was very stiff and the lever mechanism had excessive play.

    

On paper, the hydraulically-operated centreboard and rudder are a clever, well-engineered  system, and its 2-section Hydroem manual pump is a jewel.    Unfortunately, if the 435 has a weakness in real-world use, it might be this system.   While it might tolerate a sympathetic and mechanically aware owner who understands and maintains it, it will punish neglect.   

The system is prone to corrosion, particularly the rudder cylinder's shaft, especially if the rudder is left down and not cycled for extended periods.  It should be kept in the raised position when not in use.   It can be incredibly difficult to remove the close-fitting stainless steel pin that secures the hydraulic cylinder in the aluminum centreboard trunk.   I strongly recommend freeing and lubricating this pin every 2 years or so.  (An awkward job)   Sakura's issue with centreboard operation  mentioned above was a result of the system not having been correctly purged of air.  The owner should understand the principles of how the system operates,  and how to bleed the system.  The cylinders themselves are somewhat specialized and typical industrial hydrauliccs houses may not be comfortable servicing them.  It is telling that more recent Alubat models use a mechanical system instead of hydraulics.

All that said, as of September 2024, this system is in perfect working order, having been fully serviced with new or rebuiilt cylinders (and all bushings) installed.  I am now particularly adept at removing and replacing centreboard cylinders... (lol)  What follows describes the journey with details that might be helpful to others.  

It is also worth mentioning that the folks at Hydroem were very competent and helpful.  

How to replace the Centreboard Cylinder

This is detailed in a seperate post.

Bleeding the system.

In order for a hydraulic system to develop its full pressure and function correctly, it must be free of air.   Hydroem publishes instructions for purging the system.

I had to install and remove the centreboard and rudder cylinders several times, and found the bleeding process to be simple and intuitive.  I didn't refer to Hydroem's instructions, which I had read and forgotten.   

By installing one hose, extending (or contracting) the cylinder by pumping, then installing the other hose, then cycling the system, most if not all of the air can be purged.   At first when you cycle the system you will clearly see frothy air bubbles suspended in the clear green fluid as it enters the reservoir.  You will also hear an unusual "whoosh" sound.  Wait between cycles to allow the bubbles to rise and escape in the reservoir.  The fluid will become clear.      Cycle it again and repeat till the bubbles no longer appear. Ensure that you maintian the fluid level in the reservoir while you do this.  Easy.

Earlier Posts

Hydraulic Cylinders

I've had an interesting experience with cylinders.   (Some context:  The boat in the Caribbean, and I am in Toronto.  I was doing the refit during periodic vacation weeks, months apart)

I purchased the boat knowing the rudder cylinder had failed.   It was leaking and had a badly corroded shaft. I brought the cylinder home to Toronto knowing I could easily find a hydraulics shop for a rebuild.  The shop I selected rebuilt the cylinder, including turning a new shaft, all for a reasonable sum.   When I picked it up, they told me that the internal clearances were too tight, so without checking with me they machined the piston slightly smaller, free of charge.  It appeared to be in perfect order and it worked smoothly.   Months later, in Oct 2023 I  returned to the boat, installed it and lit leaked badly.  I emailed the shop, they apologized, and I let it drop.   I bit the bullet and spent the 1300euro on a new one from Hydroem.  When I returned to the boat in May 2024, I was surprised to find the cylinder did not fit into the upper section of the rudder housing.   The unit sent had raised welds whereas the original had been ground and polished.  Fortunately I had the tools and materials aboard to grind these welds flush.  The rudder, with its new bushings, pins, axles and cylinder is now working flawlessly. 

The centreboard cylinder  is contained in the centreboard trunk, suspended above the waterline and is therefore not as prone to corrosion as the immersed rudder cylinder. Once I replaced the fluid adn bled the system, I determined that the centreboard circuit was operating as it should.  No leaks. Nonetheless, I elected to remove and rebuild it rather than have it fail later at an inopportune time.  The process of removing it is described elsewhere.  

Though in better shape than the rudder cylinder, it felt extremely stiff and could not be extended by hand.  I had it inspected at Hydrostore in Curacao, where Erik told me that it was way too stiff, and the clearances were too tight.  At my insistence he begrudgingly he replaced the seals, warning that he would not accept responsibility for the cylinder's operation.   (note -this was the second competent, professonal hydraulic specialist that considered the stock Hydroem cylinders to be too stiff - with too little clearance between internal parts.  I have since purchased two new cylinders and they were both like this, as was the rebuilt centreboard cylinder)   Wary after Erik's warning and my experience with the rebuilt rudder cylinder, and not wanting risk another months-long delay, I had also ordered a replacement cylinder from Alubat.   The replacement arrived and yet again, it did not fit.  This time, it was the flat section on the shaft that was too short to adequately to clear the flanges where it engages the centreboard.  Apparently there are two versions, and the wrong one was selected by Alubat.   Not sure how this would be made right, I reinstalled the original (now rebuilt) cylinder.  It works perfectly and I will grind the appropriate clearance on the other when I get a chance. 

So I now have a spare unused centreboard cylinder and will investigate rebuilding the improperly rebuilt rudder cylinder.   This was an expensive and time-consuming hassle, but I did gain some  knowledge and some experience with the system.

There appears to be something dimensionally different about the tolerances in these cylinders vs those commonly used in industry.  Until this is understood I would only order from Alubat/Hydroem unless the boat, owner, and hydraulics shop are all local so that issues can be quickly resolved.  Why are they different, and what is the specification?

2-section pump

Once freed up, the clever combination pump functioned properly though there was some play/wobble/wear in the handle mechanism.  I elected to inspect and correct this.   It is best to remove the mounting bolts to get at the screw that forms the lower pivot of the pump linkage, as it is awkwardly located in a counterbored recess in the back of the left side of the pump.  Upon disassembly it was found that a cut-down M5 hex head screw had been used for one of the pivots.  It was simply sitting in place, not secured.   As a result it was bent and worn, and jammed in place.  ultimately, it was extracted and a correct replacement cut.  Fortunately the threads in the pump housing weren't damaged.   This M5 SS screw must be cut to the correct length and possess the correct 10mm threaded and 25mm unthreaded dimensions for it to fit and function as intended. 

The use of the damaged screw led to some wear in the stainless steel link.  See below for dimensions

 The handles and screws will be secured with blue loctite.   I will add English labels for operation by guests.

Pump Fuses 

‘Pastille’ (losenge) in French, ‘fuse’ in English, this sacrificial disc is located in the pump and ruptures in the event of a locked centreboard (or rudder) encountering an immovable object, hopefully prevcnting damage to all involved.  

Many have suggested that DIY fuses are fine in this application, some are more cautious.   I thought I’d investigate….

The beer can is made of .007" aluminum, punch is 1/2” in diameter. 

Here are the factory-supplied parts - .006" thick copper, 12.4 mm diameter

I doubt the DIY approach would be a problem.

Original Posts

Update - April 2023

As noted below, I was able to free up and disassemble the rudder cylinder.  Though I was prepared to replace with new, I figured I’d bring it to a local hydraulics shop for assessment.   It needs a new shaft and seals of course - estimate is C$300-500.  Much better than €1300 plus shipping, taxes etc.    normally such things go the other way. 

The pump was stiff, and the rudder cylinder nearly seized. The centreboard would raise but  not lower with hydraulic pressure.     Definitely not hardware store items, and clearly suffering from age and neglect.  I’ll offend other owners if  I call it an OVNI weak point, but it’s definitely a talking point for most.  

Hydroem 2-section Pump

Here’s a link to my January 2023 attempt to operate the pump.  

https://m.youtube.com/watch?v=gES-mjiD7vU

When I returned in March I lubricated the pump and it began to work freely.  I inspected the copper ‘pastilles’ and they were intact, so the centreboard issue lies elsewhere.  

Hydroem Rudder Cylinder

On my initial inspection, the  rudder would not operate with pump pressure and would only budge (slightly)  if the rudder were moved by hand.  With some cycling, it eventually ended up gushing hydraulic fluid from around a corroded cylinder shaft.  

 In my return in March I commenced work on the rudder (documented elsewhere) and managed to excavate and remove the cylinder.

  It was quickly condemned by a very helpful Erik at hydrostore in Curacao as it could barely be moved and not disassembled.  I brought it home with me.

Hydroem, the manufacturer in La Rochelle France, quoted €1300 for a replacement.  

Somewhat curious,  I sprayed a liberal amount of PB blaster inside, and let it sit for two days.  (Old engine trick…)

Though stiff, it could now be moved more easily, and with some crisp hammer taps I managed to slowly get it extended, then apart.  Much to surprise, while the shaft is destroyed, the rest looks pretty good. 

Notes on Hoses

 The exact hose that i have in Nella (2006 – 435) is Synflex 3031-02 1/8″ . It was made by Saint Gobain in 2003.

Saint Gobain was taken over by Eaton (USA) in 2006 which is also owns the Danfoss brand–its still being made and its measured in inches.
The internal diameter is nominally 1/8″ but more accurately 0.130 inch
External diameter is 0.340 inch
Hose is available from Eurohydraulics (https://www.eurohydraulicsscotland.com/) –they are super responsive and friendly and expect a shipment of 3031-02 to arrive in about 6 weeks

Its also available from the Hydrasun (https://hydralink.hydrasun.com/PublicCatalogue/Page.aspx?i=11001) catalog. But at present they don’t have any in stock and its going to take “about 6 weeks” if ordered.