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Hull Renovation (Phase 2)

For those that have read the pages on Phase 1 of the hull renovation, you will know that in 1997 we spent an enormous amount of time and money replacing hull planking that was rotten or in poor condition.  Unfortunately, ARAMIS was still taking on water, not drastically, but enough to warrant installation of a back-up bilge pump.

 

Several of the seams, in particular those closes to the termination of the ladder frame were letting in water primarily whilst under sail.  The seams would seal up once in port but would continue to weep for many days after sailing.

 

In 2009, whilst out of the water for anti-fouling, we decided to remove fibreglass that had many years ago been stuck on the inside of the hull amid ships.   Much of this fibre had already come unstuck and was trapping water.  Causing a soggy sandwich and a cocktail of bacteria and moulds where causing odours and wood decay.  It was also apparent that some strengthening ribs, put in during previous hull repairs, where exacerbating problems with the hull's integrity

 

Having understood the problem, it was clear that it was not going to be a quick fix and it would take time to work out the best solution.

 

To allow us to profit from the boat after all the hard work and expense of the phase 1 renovation, we patched the seams on the inside the best we could with various gunks, gunges, foams and marine ply.  Nevertheless, our two bilge pumps worked overtime for two seasons.

 

The Solution

 

We consulted experts on possible solutions.  These essentially came down to the following options.

 

1.  Find some deep water and open the sea-cocks.

 

2.  Add ribs to tie the keel, hull planking and deck together.

 

3.  Skin the hull in glass or other fibre tissue.

 

4.  Bond splines in to the seams

 

5.  Skin the hull in epoxy and veneer.

 

Although Option 1 has crossed our minds several times we clearly could not entertain the resultant environmental damage.............

 

Option 2 was deemed impractical as it meant completely stripping out the interior and then refitting it to avoid the ribs.   This would have taken up much space and radically changed the character of the interior.

 

Many people recommended Option 3.  In fact several insurance companies seemed to favour fibre skinned wooden vessels.  Our view was that whilst this might cure the leaks, unless we were planning on laying up many layers of fibre, it might not solve the flexibility problems.  

 

Moreover, with the flexing, could we ensure a good bonding between the fibre and hull.   It is true that an exotic carbon fibre/epoxy combination does have its merits, nevertheless, soggy sandwich stories, plus our experience with the remedial patches already removed from ARAMIS led us to dismiss this option.  After all, we had a wooden boat not a "plastic" one.

You can clearly see the problem seam(s).  Exactly where the ladder frame terminates.

Analysis of the problem

ARAMIS is constructed using a top nailed strip plank technique.  The edge of each plank is shaped into a so-called half-moon.  When constructed there was probably no caulking in the seams.   The half moon contact area ensured a seal under expansion when wet. If caulking or adhesive was used in the construction they has long since dissolved.

 

If my understanding is correct, much of the rigidity of the hull comes from the expansion forces of the wet wood.

 

Over the the years, flexing of the hull under sail loads, combined with loss of integrity of the wood fibres along the seams has caused the seams to open too much and the copper nails to loosen.

 

The problem has probably been exacerbated by the hull drying out too much at certain times in its life plus attempts to drive caulking in to the seams to stem leaks.

 

You can see that unlike a more common strip-plank technique, where caulking is driven up against a wedge profile, driving caulking into ARAMIS's is likely to open the seam and further loosen the nails.

 

In any case, the combination of construction technique, the nature of the timber used and and use and abuse over the years has resulted in a loss of hull rigidity.

 

We can identify two main symptoms associated with this:

Issue 1

 

As keel loads are transferred in to the hull, rather than being shared across all of the seams and transmitted up into the deck, beams and carlings, the loads are concentrated at the end of the cross members that form the ladder frame (see below) with obvious effects.

Issue 2

 

The chain-plates where bolted directly through the hull with only a filler rib rather than any frame tied in to the keel. As hull rigidity was lost, the working of the chain-plates progressively opened the seams and loosened fixing bolts. The hull around the upper shroud chain-plates was in a particularly poor state.

 

We believe that this problem was exacerbated by the lack of mast partner blocks ; these were only soft rubber sealing blocks at the time of purchase.  Any lateral movement at the top of the mast may have caused too much movement of the chain-plates.  A bit of trigonometry shows that a 2cm leeward fall-away at the mast head would cause 3mm of movement at the chain plate if not restrained by the shroud tension and mast flex.  Clearly with the floppy hull the shrouds could never be adequately tensioned without opening the seams amidships and without partner blocks, the spring of the mast was not providing resistance.

 

The schematic on the right shows that in spite of the additional rigidity amidships formed by the beam and partial bulkheads, unless the hull was capable of transmitting the sail and keel loads into the this bracing, it served little purpose.

SplineVsmall

Option 4 consists of rabbeting each seam and gluing in splines (see right).

 

This solution might have its merits for a relatively small craft with wide planks, however ARAMIS has only 30mm planks and some 700m of seams below the waterline - a lot of work!

 

hanks to Gougeon Brothers Inc (West Systems) for the image and information on this technique]

Option 5 certainly seemed the most eloquent and durable solution.

 

Epoxy/wood laminates are commonly used in the construction of modern wooden sailboats; for example the Spirit Yacht range and the recent Fairlie creations. It also been used effectively in the restoration of historic vessels, particularly when the original hulls are in poor condition.

 

As far as restoration is concerned, the technique consists of gluing successive layers of veneer planking on to the hull. Normally, the hull would then be faired such that the sheathing is not visible and the hull shape is not significantly changed.

 

The only way to do this properly on a ARAMIS, would be to strip out, take off the keel and invert the hull in a suitable workshop such that the veneers can be laid diagonally across the entire hull (see the example right) and then fair and refit.

 

If ARAMIS had had a significant historical value and/or we had picked it up for a snip, then this would be the solution.  Unfortunately, our estimate was that this work would have cost at least three times the market value of the finished vessel and therefore an impossible choice.

 

Had there been extensive rot in the hull planks then this may have been the only option. However, as it stood in 2009, we had already replaced any rotten timbers and the hull was essentially in very good condition - except for the lack of rigidity amidships.

 

So, how to cost effectively restore the lost rigidity?

 

Finally, we decided to veneer sheath the hull, but on the interior, concentrating on the mid section where the keel and sail loads bare.

2010

Design1 Design2 Design3

These are the magic ingredients:

 

  • West Systems resin, hardener, microfibre filler

  • 60kg or so of mahogany 50mm x 4mm

  • many thousands of 12mm staples

  • 100 hours+

 

We made up a test section about 40cm square with two layers of 4mm mahogany laid with the grain at right angles. We brushed resin on the outside surfaces to harden them off.

 

We were astounded by the rigidity of this small section. We were only able to break it by driving a chisel in from the edge.  Even then, we could not separate the bond only tear wood fibres apart.

Lining1 Skin

Once bonded to the 25mm thick hull planking, we should be approaching Ferrari like torsional rigidity.

 

We did however have to ensure a good bond down on to the hull.  This meant removing all the old paint on the inside of the hull and cleaning it scrupulously with acetone and then roughing up the surface with 60 grit. We also made sure that the hull was extremely dry - force drying where necessary.

 

We had to remove all the bodged internal strengthening.  This meant chiseling through and grinding off semi-ribs, glued on ply and all sorts of other horrors.

 

We were careful to ensure a good bond to any structural elements; the main keel member, ladder frame, bulkheads, chain plates and any other permanent fixtures.

Skin2 Skin3

Stripping and cleaning in progress.

 

You can see that we will need a fair amount of fibre filler in the epoxy to fill the irregularities - even after substantial sanding.

Once cleaned, we started cutting and shaping the 4mm mahogany veneers to fit the hull.  In small steps, we coated the hull and veneers with a generous amount of the epoxy/fibre mix and stapled down the first layer with staples staggered every 4cm of so.

 

We were working with mix with a consistency of soft crystallised honey.  This allowed us to build up a thick layer, even on the nearly vertical parts of the hull, where necessary to fill irregularities.  To ensure a good penetration into the wood fibres of the 4mm planks, , we painted on a thin layer of resin/hardener mix without filler fibres immediately prior to the fibre-loaded paste.

 

Once stapled down, we scraped of the excess paste, pushing it well down in to the seams and between the veneer and structural elements.

 

If we were using this technique on the exterior, we would probably, for maximum strength, apply two layers of veneer diagonally across the existing planks and then perhaps a third layer following the original plank orientation for partly cosmetic reasons.

 

As we are using two fairly thick veneers and wanted the final layer to follow the original planks, we have bonded the first layer at right angles to the originals.

 

Initially we stapled across nylon packing tape so that we could remove the staples after the epoxy had cured by pulling the tape. Invariably, the staples broke and the remnants had to be pulled out with pliers.  

You can see the staples driven in to the first layer.

Skin5 Magwhite

Option 4 - bonding in splines

Option 5 - the most eloquent

Expensive sticky stuff

The first layer is down, and the second being prepared.

Skin9 Skin10

Under the starboard berth - ready for painting.

The main cabin bilge seen prior to painting

Where there were through hull fittings, we added an extra two layers of veneer to minimise the risks of opening seams when manipulating/abusing the sea cocks.

 

We estimate that we added about 70kg to the weight of ARAMIS, distributed nice and evenly amid ships.

 

Prior to putting ARAMIS back on to the water, the out side of the hull was lightly caulked throughout with oakum and red lead putty and then given a couple of coats of red lead prior to antifouling.

 

With 5000 miles under the keel since this work was completed we are still leak free.

 

The sailing capabilities of the vessel were transformed. It felt so much more responsive and much sharper about.  In particular, the mast no longer fell away to leeward so weather helm could be trimmed out and heel was greatly reduced.

 

In 2014/2015 we added a new through-hull for the galley saltwater tap, this gave us the opportunity to check how the laminates were holding together.  The core we took out was rock solid.  It was impossible to separate the lining planks from each other nor from the hull itself without tearing apart the wood fibres. Effectively, we had a super ridged 35mm thick hull throughout most of the vessel.

 

All in all, this was one of the most gratifying renovation projects as the results are so blatant.   We soon forgot the pain, hard work and expense.

Magwhite Magwhite

Backing off the stapling gun to make it easier to extract the staples meant that we were not getting the planks down hard enough.

 

Eventually we abandoned this idea and drove the staple in hard such that they were just below the surface of the veneer.  Once skimmed with the epoxy filler mix that oozed out of the joints, it was cosmetically good.

The main cabin bilge seen in 2013

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