435 Centreboard Cylinder Removal

The following is based on my experience with my 2001 OVNI 435 #6.  It may not reflect any changes to the 435 through the years.   Any input to improve this document is welcome.  

Specific tools required 

• Flare (helpful) and 14mm open ended wrenches
• Hammer and drift for 10mm pins
• small 90 degree pry bar to assist with removing covers.  

The centreboard cylinder is situated within the centreboard trunk, positioned horzontally above the  centreboard.   It is not necessary to remove the centreboard to remove the cylinder as there are access covers on top of the trunk for this purpose.   

In order to remove the centreboard cylinder, you will need to first gain access to, then remove the two pins that secure the cylinder.  The forward pin fastens the cylinder's piston rod to the centreboard.   It is the extension and retraction of the piston rod that raises and lowers the centreboard.   The aft pin anchors the cylinder base between reinforced areas on the opposite sides of the centreboard trunk.  Once both pins are removed, and you can disconnect the 2 hydraulic hoses and lift the cylinder through the access cover. 

In preparation, the centreboard must be safely supported in the fully-retracted position. Lower the board slightly to ensure the cylinder is no longer bearing the board's weight, and can be safely removed. 

Gaining Access

To access the hoses, first remove the plywood cover opposite the galley fridge.  This cover fills the triangle between the main bulkhead and the settee corner.   You will see the hoses and the acrylic  cover though which they pass into the trunk, via cable glands.  (which may have become brittle and broken with age)    

1. Remove the cable ties securing the cables to the bulkhead.   
2. Note the fore/aft orientation of the acrylic cover.
3.  Slack off the gland nuts and remove the cover screws.  
4. Gently pry the cover free and slide it up the cables.   It is through this opening that the cylinder will be withdrawn.  

The 10mm forward pin is accessed from the top and sides of the centreboard trunk in the forward cabin.

1. Remove the plywood trim covers from the top and starboard side of the CB trunk and lift the plywood berth board to gain access to the two upper aluminum covers on either side of the trunk, and the acrylic cover on top.  
2. The aluminmum covers are secured by M4 philips screws, and sealed with Sikaflex.  You will likely need to use a small pry bar to break the cover free of the sealant.   
3. With the covers removed, you will see the cylinder's piston rod end where it engages the CB via the 10mm pin, itself secured with two cotter pins.  If you do not have complete access to this, the board is not fully retracted.  

The 10mm aft pin is accessed by removing  two small aluminum covers located on either side of the centreboard trunk, roughly opposite the fridge.  The starboard side cover is concealed beneath a plywood trim panel, the portside cover is under the  forward end of the settee, most easily accessed by unscrewing the removing the plywood panel that forms the seat.  

1. Remove the plywood trim cover and unscrew and remove the plywood panel that forms the forward dinette seat. 
2. Remove the square aluminum covers. The 10mm pin will be seen seated in its close-fitting hole.  

Once all the covers are removed clean the area as much as possible. Remove any residual sealant.

Removing the Cylinder

Removing the forward pin first allows the piston rod to be fully retracted which is necessary for removal, but also eases the next steps and ensures that the more difficult-to-remove aft pin is not binding in the cylinder. 

1. The forward pin is secured by cotter pins. Remove one or both of the cotter pins and drift the pin out.   
2. The pin should yield to moderate taps with the hammer and punch.  If not, first use the hydraulic pump to ensure that the cylinder is not still loaded with the weight of the centreboard.  If badly corroded or bent it may be difficult to remove.   
3. Once the forwad pin us removed, using the hydraulic pump, select the position used to lower the board, and pump to fully retract the cylinder's piston rod.  
4. Carefully drift the aft pin out with a hammer and drift, from starboard to port.  This pin may be extremely difficult to remove due to corrosion, the amount of contact area, and the pin's the close fit in its holes.   Once this second pin is removed the cylinder will be lying loosely on top of the centreboard, connected only by the hoses. 
5. Disconnect the hoses using an open-end 14mm wrench for the nut and a second flare wrench to prevent the hose from turning while doing so.   Some fluid will be released as the fittings are loosened.   
6. When both hoses are disconected, tape the ends to prevent any debris from entering the system.

The cylinder can now be removed.

Reassembly

(If you are reading this you already know about sealants, and where and how Tefgel/Lanolin must be generously applied.)

Reassembly is generally the reverse of the above, with a few additonal hints.   

1. Before proceeding, ensure that the piston rod is fully retracted and that the holes in the cylinder base and the piston rod are in the same plane, by rotating the rod as required.  It'll probably be stiffer than you expect, and may require some leverage.  
2. Place the cylinder in the trunk in the correct orientation.   (base aft, fittings up)   
3. Switch the hydraulic pump to the "raise" position, and cycle it until it spurts fluid from the aft hose.  This helps ensure the hose is free of debris and excess air.    
4. Connect the aft hose only.   
5. Insert the rear pin to secure the cylinder base to the CB trunk.    
6. Use the hydraulic pump (still in the "raise" position) to slowly extend the piston rod.  Guide the rod end between the centreboard flanges and pin it in place.   Do this slowly and be careful not to overextend the cylinder.  (You will need two people to do this efficiently.)
7. Celebrate the fact that you've mostly purged the cylinder of air.
8. Switch the pump to the "lower" position, and as before cycle the pump to purge the forward hose. 
9. Reconnect the hose, and switch the pump back to the centre "locked" position.
10. The system will now be operational but must be fully purged of air.   
11. Once you are certain the system is functioning and connections are leak-free, replace and seal the aluminum covers and acrylic covers.  Do not reinstall the trim, tighten the glands or secure the cable ties.
12. After the boat is launched, fully cycle the hydraulic system.   With the board down, secure the hoses with new zip ties and tighten the cable glands.
13. After ensuring that there are no seawater leaks, replace the trim and cosmetic covers.

Misc photos and notes

The photos below show the flanges on the centreboard, between which the cylinder's piston rod is pinned.  If you are replacing the cylinder, ensure you order the correct part as it changed during the 435's production run.   

The photo below shows the two configurations of cylinder ram.   Note the different length of the flat section.   

The photo below shows the aft pin, and how it engages the cylinder base and the reinforced sides of the centreboard trunk   Note that I cut this access hole myself in order to saw off the pin as it could not be removed otherwise.   

The photo also shows the two nuts used to secure the hose to the 90 deg. male fitting on the cylinder.  The upper (in the photo) nut is held firm while the nut adjacent to the fitting is turned.