The Rudder Job
 
Thursday, 12 May 2010

This rudder is from a 30 year old David Thomas-designed Quarter Tonner and it's a bit wet.  Wet on the outside is perfectly normal.  Wet on the inside is a problem.  The owner consulted a marine surveyor who suggested a repair would be a very good idea. And so it came into my hands, and leaked all over the back of the car when I took delivery.

My plan is to clean the rudder, dry it completely, epoxy and clamp the split trailing edge and then wrap it with lightweight e-glass and epoxy resin.  After fairing the cured surface, I'll primer paint it and return it to the owner, ready for antifoul and installation.

It weighs 27 kilos and has several layers of blue antifoul paint over yellow gelcoat.  And a lot of dirt and algae. 

Fifteen minutes with a good carbide-tipped draw scraper and most of the anti foul is gone.  Easier to do this in the rere garden...no need to sweep the floor!

Another five minutes with a random orbital sander and 60 grit paper.  I drilled a few 8mm exploratory holes to learn what is inside.  The gel coat is very thick and therefore brittle, but not oxidised. The trailing edge is cracked and the drill holes along the trailing edge go through solid layers of gelcoat, glass fibre and filler/glue.  Several white circles show that somebody has tried this job before...the white circles are drill holes plugged with filler.

Flipped it over and cleaned the other side.  I can easily insert a steel ruler into the cracked trailing edge.  The inside seems to be hollow.  I expected to find mushy wet foam filler.  The ruler is a printer's "em rule" or "pica stick" liberated from my time at the old Irish Press.

I pulled this mild steel bolt and nut out of each side of the leading edge, just below the top of the rudder.  Somebody in the past attempted to bolt the rudder halves tight together. Mild steel, in sea water...why would anyone do that?  It had rusted through in the middle. Bleh.

I now know the rudder is hollow, so I use a hole saw to cut a pair of 50mm diameter holes.  The holes allow me to peek inside using a pencil torch and a small mirror.  I see lots of moisture and dirty black glass fibre.  The blue bits are scratches and gouges in the gelcoat that have been filled over the years with blue antifoul.  I use the holes as access for a high pressure fitting on the garden hose to wash out the interior with fresh water.  Lots of bits of detritus flowed out from the inside.

Here is the core from one of the holes.  The gelcoat is about 1mm thick, very hard and brittle.  The rest of the layup is 5-6mm thick.  The black stuff on the bottom is filler-bog supporting one of the rudder shaft tangs.  More about tangs later.  I left the rudder to sit in the sunshine for a few hours after the fresh water rinse and then carried it into the garage.

I hope a bit of time with a dehumidifier will dry the inside of the rudder.

Old Fireball spinnakers serve as drapes to create a tent around the rudder and dehumidifier.  This is Friday morning and I'm sailing the Baily Bowl on Saturday and Sunday so there is plenty of time for the dryer to work.

Tuesday 18 May

The dehumidifier had very little effect after three days.  The rudder is still damp and sticky inside.  On Saturday, after racing the Baily Bowl in Dublin Bay, I bumped into the marine surveyor who had previously examined the rudder.  He was surprised to learn that it was completely hollow.  "Crack it in half" he suggested, " and then fill the halves with foam and glue it back together."  And so, Plan B begins: crack it, dry it, lighten it, fill with foam, fair the inside, glue together, wrap with lightweight glass and epoxy, fair, prime and return to the owner.

Using Mr Dremel with a grinding disk, a saw, hammer and chisel, four wooden wedges and a pound of patience, I ended up with this after about 20 minutes.

Remember the mild steel rusted bolt and nut I mentioned earlier?  Here is a close up of rust never sleeping on the inside.

This bit of filler/glue/bog which was wrapped around the shaft came away in my hand.  It's wet.  Very wet.  And it stinks.  An evil smell.

Here is the port side shell after chipping and grinding away junk using a chisel, angle grinder and flapper sander.  The black horizontal line is the bedding bog for the shaft.  I removed 1 kg of junk and the port side shell now weighs 3.75 kg.  Remember, the rudder weighed 27 kg when it arrived.

Interestingly, when the builder layed up the shell, he used yellow pigmented laminating resin.  The white areas are remnants of pigmented layup for tang supports.  The pencil line shows the orientation of the lowermost tang.

On the starboard shell, which has the shaft attached, much of the grey bog displays this sticky yellow substance.  Not good.  Did I mention the horrible smell?

Here is the shaft and leading edge on the starboard shell and the upper two of three tangs.  Powdery black stuff is failed filler / glue / bog which must be removed.  You can see the thickness of the layup in the hole at the top

Chipping away with the chisel, these and many other pieces were removed, totalling 3.75 kg on the starboard side.

The portside is now cleaned and cleared of junk, reducing weight.  You can just see the rounded tips of the upper |(at right) and lower tangs peeping through their glass fibre and bog containments.

The stainless steel tangs were very nicely welded to the stainless steel shaft as you can see here on the middle tang.

Time to start re-assembly.  Here is a piece of light weight finished fibreglass tape, leftover from a previous project.  In the background is a mix of WEST 5-minute epoxy, magic stuff, brilliant for a quick non-structural fix.  The square of tape will cover the inside of the two big holes.

And here they are, glued in place, ready for filler on t'other side.  The apparent bend in the stainless steel shaft is an optical illusion provided by the camera.  The filler bog grey is original colour, black is dirt from wetness over 30 years.

I used a mix of Isopon P-35 car body filler to fill the drill holes and smooth off a number of cavities in the original bog.  The stuff is easily mixed, waterproof, dries quickly and is easily sanded.  At the right, the top of the starboard shell, there was a goof during original manufacture and a piece is missing.  Later, I'll sand and shape the Isopon filler to make up for the failure.  Notice all the air bubbles in the original grey goop.

More later
 
Tuesday 25 May
Had to wait a few days for my supplier to re-stock two part polyurethane closed cell foam.

Below, pieces of foam strips have been glued in place on the port side, ready for some chopped strand mat to provide a bit of support for the shaft tangs.  The original pieces fell away during the clean up.  I used polyester resin with talc as thickener for the glue.


The foam strips have been cut from a lump of builder's foam.  Cheap and simple.

Chopped strand mat cut to size and ready for laminating.  Will provide stiffening support for the shaft tangs.

Ready for foam.  These two innocuous chemicals, when mixed, will make closed cell polyurethane foam.  A 50/50 mix, I'll have 60 seconds to stir and then pour into place.  The mix will expand about 25 times by volume. 

The mixed chemicals have foamed to fill the starboard side.  Very artistic. Tracy Emin might be proud.

On the port side, I used a section of an old Fireball spinnaker pole to protect the rudder shaft channel from being filled with the foam.  The rudder shaft is 38mm diameter, the pole is 41mm diameter.  The three mill difference is nothing. You can see the three tang supports, chopped strand mat over foam strips cured in place.

Here, the foam has cured and I use a saw to slice away the unavoidable excess.  I am reminded of the Jeremiah Colman story: He made his millions not from the Colman's Mustard people ate, but from the mustard they left behind on their plate.  Filling nicely.


Had to leave this job for a couple of weeks, Round Ireland Race prep for Dinah was required, along with a bit of SB3 racing.

Now prepared for gluing the two halves together.  The starboard side, now clean and dry, weighs 20 kg, most of which is stainless steel.  All the foam has been sanded on both halves and they dry-fit quite nicely.  These lengths of timber laths will serve as clamps while the epoxy cures, botled together with M8 x 100mm bolts and nuts.  Sheets of old print film are laid underneath the rudder to catch epoxy drips.  

First step is to coat both halves with neat epoxy resin and let it sit for two hours.  It is wondrously warm here in Dublin so I have used West epoxy with slow hardener.

I have mixed up several small batches of epoxy resin with Microfibres added to make the consistency of peanut butter.  A generous dollop is spread on all mating surfaces:  around the circumference and on the shaft and tangs.  Because I have used the WEST slow hardener, there is no chance of exotherm.

Both halves have been carefully mated and the clamps tightened up.  A bit of long scrap teak to take up the gap on the trailing edge, one on each side, providing a good clamp.

A very satisfying epoxy ooze!  Happily, good ooze all round the joint.  I'll leave it alone to cure for 48 hours.  A long strip of acetate film is taped to the underside of the trailing edge to trap the overflow ooze.  It will help to extend the trailing edge by 6 mm, more later.

Starboard side, the two holes and a few other nicks have been filled and the trailing edge ooze has been sanded.  Very hard stuff to sand!  Which is good.

I have scribed a line to delineate the new trailing edge and I'll sand and shape to the line.

Mr Dremel and a pair of Sur Forms make the job a bit easy.  Not much, but a bit.  White gelcoat filler is now used to fill any small bubbles or hollows in the new trailing edge.   Then, sand it again!

Starboard side in the sunshine...

...and the port side.  This side had a strange hollow which was "so not fair" (see the Ben and Jerry Ice cream advert) so I filled it with gelcoat and sanded smooth with a long board and using a long straight edge as a guide.

Hanging around...two coats of International Primocon, a very good general primer for underwater use, then wetsand and ready for antifoul. 


Total weight: 24 kg, saving of three kilos!
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