Windlass Deck Repair

Performed: 2010
Editted: March 30, 2016

Prelude

It happened on our maiden voyage with Lyra from Lefkas to Israel. We entered Piso Livadi - Paros during a fierce Meltemi. Althoguh the water in the achorage were rather calm the wind was still very intense, probaby due to the tunneling caused by the sorounding hills. It was full so we tried to anchor Mediterranean style at the western breaker. Unfortunately the first attempt found us too far from it to get the line ashore. Very quickly the boat turned its bow to the wind so we decided to go for another round. While lifting back the chain my son, who was at the bow, told me that that it seems that the anchor got stuck. While I was trying to decide about the next step there was a sudden crack noise followed by the sound of 70 meters of chain streaming down the bow only to be stopped by the line attaching it to the boat. I went to the bow and found the windlass in an awkward position as if it was also about to go overboard any moment. After several futile attmpts to lift the chain by hand we decided to temporarily abandon it - we tied a fender to it, cut the line loose and went to find our luck at the crowded docks. A nice guy at the dock who noticed our situation moved one boat to make some space and we tied ourselves next to another boat which got in a bit before us - they were also out of luck as their genoa was completely torn apart because they could not furl it when the wind got too strong for it. Later we took the dingy and after an hour of free diving and hard work managed to get the chain and anchor on it and back to the boat. At that point we also understood why the anchor got stuck - we happened to be exactly where there were several flat rocks with narrow slots between them and the anchor found its way into one of them. The day afer I assesed the damage - the windlass "shelf" was completely broken and some of the bolts got disconnected from the windlass. Since we had several days of waiting we tried to fix it temporaily but failed, so the rest of the voyage was done with the second anchor (Danforth with 3m of chain and a line).

Analysis

The failure was the result of two major reasons.

Improper design and installation

The windlass shelf is a laminate of plywood and GRP. My observation is that the plywood is not marine plywood - the number of plys and their quality do not match those that I know for marine plywood.
The mounting holes of the windlass were too close to shelf edges or openings. The rear holes are too close to the opening for the chain (this is due to design of the windlass) and the front holes were too close to the shelf edge (the windlass should have been installed several centimeters backwards).
The mounting holes were not coated with epoxy/polyester and the poor quality plywood was left exposed to water and rotted.
All the threads for the mounting bolts were "eaten". In fact one of them was damaged so badly that the bolt simply fell out and the windlass was held by three bolts. The reason for this is that there was a stainless steel backing plate for the bolts. With such a large stainless steel electrode and galvanic corrosion it is easy to guess who served as the "sacrificial anode".

Improper operation

The boat served as a chater boat. Charter companies do not equip their boats with a chain snubber so it is most likely that throughout the years of service it was the windlass and shelf that carried the loads, pressing the windlass downwards and pulling it forward. This resulted in cracking the shelf and tearing the holes.

Repair

First I dismantled the windlass. This was not so easy. The electrical cables come directly out of the motor and go directly into the boat. To get to the connection point means removing somehow the liners in the bow cabin. Since I did not want to deal with it I simply cut them close to the motor - they will be extended later. What I found after removing the windlass was not a nice view - cracked and delaminated GRP and rotten plywood. I therfore cut everything until I reached "healthy" plywood' although still delaminated from the GRP. At first I glued the GRP back to the plywood using silica thickned epoxy and an array of clamps. Then I cut a piece of marine plywood to fit the cutout. both the plywood piece and the boat side shelf were sanded to create a scarf. The desired ratio of the  scarf length to thickness is at least 6:1 but due to space limitations I had to settle for a 2:1 ratio. The plywood piece was also glued with thickened epoxy. This was followed seven layers of fibreglass cloth, each a bit larger then the other to cover the whole area, and finaly a layer pigmented epoxy thickened with silica and microbaloons to make everything flat and level.

Meanwhile I also fixed the windlass. I gave it to a an aluminum welder to fill the old holes and make new threaded holes. The motor was dismantled, cleaned and painted. The old motor cover gasket was deformed so I made one out of gasket paste by Loctite. I also extended the cables using thick cabes and crimped copper sleeves, covered by heat shrink insulation.

New cutouts and holes were made in the now solid deck and this time they were epoxied for protection. Reading again the windlass manual I saw that the original installation placed it too low. The result was an improper angle which may expalin the frequent chain slips that we experienced prior to the failure. An 18mm plywood spacer was added to place the windlass as high as the chain locker cover allows and now the chain angle is as recomended in the manual.

And finally I made a chain snubber as described in http://www.bosunsupplies.com/snubber.cfm