Things that go bump in the night.

Even as relative neophytes in the sailing world, Janet and I knew starting out that it's not wise to ignore strange noises.  Our experiences since July have reinforced our instincts in this regard.  That's why we decided we had waited long enough to address the strange thumping noise that could be heard in the boat whenever we anchored and there was any swell or current.

The noise first appeared in the days after we took possession of Maple.  At anchor we heard a consistent thumping sound that seemed to come from the area of the rudders.  A cursory examination suggested that the rudders were moving slightly in the swell in spite of the steering being locked.  Not ideal but our surveyor had investigated the play in the rudder prior to purchase and proclaimed it ok.  Surveyors are never wrong are they?  

Not willing to take his word for it, I contacted Robertson & Caine, the makers of our boat.  They suggested that at 5 years old, the rudder bearings may be worn and need replacement but that the movement was not something to be concerned about and the consensus on the sailing forums seemed to be that worn bearings were not a critical replacement item and could be addressed at the next regularly scheduled haul out.

We spent the next 6 months sailing, anchoring and growing accustomed to the thumping and bumping emanating from the rudders.  "How bad could it be?" we asked ourselves, while at the same time checking to make sure the rudders were still in place after every heavy workout we gave them. More digging online revealed that many other Leopard owners had experienced water intrusion in their rudders to the point where the interior core of the rudder was compressed and the rudder tangs moved within the blade.  

Maple's rudder construction.

This revelation introduced a new level of anxiety into our cruising for the remainder of the year and we agreed that we would make dealing with the rudder question a priority when we stopped in Turkey for the winter.  This would mean hauling out when the boat had already been out in February and had the bottom painted, and then again in October to replace saildrive seals.

Pre-haulout discussions with other cruisers identified a third possible reason for the play in the rudder; loose steering linkages.  After checking the linkages we considered this a remote possibility with the bearings being a possible cause and play in the rudder core/tang the most likely.  In order to confirm this the plan was to:

1- Drop the rudders when we hauled the boat

2 - Check the rudder bearings for excessive play side to side and up and down

3 - Cut small sections of the rudder to assess the degree of water intrusion and possible cause of the rudder movement

Dropping the rudders with help from cruising friends.

With the rudders dropped it was apparent, even before cutting into them that the problem was not the bearings or the steering linkages.  When gripped and turned, the rudder stock moved independent of the blade which is never, ever, a good thing.  In order to turn the boat the stock and blade must behave as if they are a single unit, anything else means that steering may not work when you need it most.

It looked like I would be opening up the rudders after all.  I needed to have a look to understand what was allowing the rudder stock to move.

Rudders opened up for inspection.

With some exploratory surgery completed I had my answer and it wasn't good.

The rudders are constructed using a 38mm diameter stainless post, this has 3 10mm diameter holes drilled through it which hold 3 tangs which are essentially 10mm steel bars.  Each of the tangs is encased in resin of some kind (probably vinylester).  The rudder is essentially 2 halves of cored  end grain balsa skinned with fibreglass which are stuck together with a resin layer in the middle that holds the tangs.

Unfortunately, the construction while robust, heavy and nearly bullet-proof was not completed well and there were major voids in the resin layer at the centre of the rudder.  In addition, a gap around the rudder post allowed water to enter the rudder and pool in these voids.  The end result was rotting of the balsa core in the top 1/2 of the rudder and crevice corrosion in the top 2 of 3 tangs.  Combined with the fact that the tangs were not welded to the stock and allowed to float and flex (read metal fatigue) this corrosion was bound to result in something breaking.

Both rudders had exactly the same issue.

For 6 months we had been sailing (sometimes in pretty heavy seas) with rudders that had lost 2/3 of their ability to move the boat.  Scary stuff.

After some discussion with a shipwright we met in the yard we landed on a fix.

1 - Carve out remaining rudder tangs
2 - Expose rudder stock for repair
3 - Insert new tangs in stock
4 - Weld tangs to stock to eliminate potential for metal fatigue
5 - Add plates to tangs to provide greater bearing surface within rudder (probably unnecessary)
6 - Fill rudders around new tangs with epoxy mixed with chopped fibreglass matt and cabosil filler
7 - Apply 2 layers of fibreglass to rudder to encapsulate and complete repairs
8 - Grind channel in top of rudder around stock and apply thick bead of Sika 292 (3m 5200 equivalent) to try to eliminate potential water intrusion at this critical flex point
8 - Barrier coat rudders
9 - Bottom paint rudders

And so the work progressed with assistance from Jeff on Nawii I got the rudders cut open completely and was able to get the welder at the yard to fabricate and attach the new tangs.

All that remained was to close it all up again.

The good news?  The rudders were very very hard to cut open and clean out.  These are strong little guys and generally well constructed.  Also, on a catamaran the rudders are not subject to the same loading as on a similar sized monohull, weather helm is not as significant and there is limited foiling effect. 

A combination of water intrusion/corrosion and metal fatigue are likely the cause of our problems.  I believe we have addressed these issues, and I now know exactly how the rudders are constructed and what to watch for.  

And along the way I've learned a lot about fibreglassing and other critical boatyard skills.