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You are here: Skip Navigation LinksHome > Articles > Modifications/maintenance > Parker 31, 325, 335 > Parker 31 keel overhaul

Parker 31 Keel Overhaul

Author: Pat Morgan, P31 21 Phun
29 December 2011

Introduction

This article describes my experience of overhauling the keel. It goes into a lot of detail which is only likely to be of interest to someone contemplating a similar job. Don’t try this at home unless you really need to!

This article may also be read or downloaded in PDF format (925 Kb)

Symptoms

  • Twice during the 2010 season the keel had refused to lift. On those occasions the way we lifted it was to dive down and put a rope round the wing, pull it tight and fix it to the stern cleats then press the "lift" button. This procedure is inconvenient at the best of times and not possible in many situations. It is only possible because Pam is a good swimmer.
  • When beating, after tacking and pulling in the sails, as the boat powered up there was often a marked “clonk” as the keel settled into a new position on the new tack
  • (Not really recognised as a symptom until afterwards!) Since we first bought the boat it has not been possible to lift the keel when the boat is out of the water and the keel is fully down. It has always been necessary to put a lever underneath and lift it up and back. Once started the keel would lift OK

Analysis of the symptoms

I felt the non-lifting issue, although it only occurred twice, was trying to tell us to do something. Maybe we would get to the point where the keel would not lift at all. This would severely hamper our use of the boat and would render many safe harbours inaccessible. Something had to be done!

Dismantling

We lay the boat up at Larkman’s Boatyard at the top of the River Deben. I asked them to take out the keel so that we could examine it carefully and decide what to do next. In order to take out the keel, you first have to remove the wing from the bottom of the keel. The mast had been removed for the winter, as usual. The yard insisted that the keel job should be done before replacing the mast, for reasons of stability. Our boat spends the winter in a high cradle, which allows the keel to be lowered completely, so I put large blocks under the ends of the wing and removed the filler which covers the nuts securing the wing. I left the job of removing the wing to the yard as they are practised at such things – and arrived a few days later to find the main part of the keel laid on blocks on the ground near the boat. Tip: It would be more convenient to have the keel a little further off the ground, maybe on a pair of strong trestles about knee high.

Observations

The movement of the keel is controlled by:

  • Guide plates, made from acetal. These go at the 4 corners of the top part of the keel and slide inside the keel box which is built into the boat. When the keel is right down the ends of these plates rest on the inside of the bottom of the boat, and the keel lift cables go slack. · Bottom roller which is mounted on a metal plate let into the bottom of the hull just in front of the keel. On our boat this had been replaced by an acetal pad and so I call it the "bottom pad" from now on.
  • Top roller which is mounted on the hold-up bracket fixed to the top of the back of the keel. This rolls on the inside of the back of the keel box.
  • The keel does not rise vertically, but at a slight angle. The top roller and the bottom roller / pad ensure that the keel is correctly lined up with the keel box and stop the keel from just hanging down vertically.

Looking carefully at the keel and the inside of the keel casing I made the following observations:

  • The bottom pad did not seem to rub on the front of the keel when the keel was right down.
  • The bottom pad only projected a very small amount (about 1 mm) from the plate that holds it. The pad itself appeared OK, but the sides seemed to have been a bit splayed out by the keel.
  • The front right guide plate was quite worn near the bottom at the front
  • The front left guide plate did not appear to bear on the front of the keel box. It also did not appear to bear on the bottom of the boat when the keel was right down.
  • The two rear guide plates appeared to be OK except that they were nowhere near the bottom of the boat when the keel was right down

Analysis of the Observations

It seemed that the bottom pad and the top roller were not quite doing their job of keeping the keel correctly aligned with the keel box. With the keel right down, and the pad and roller at their closest, the keel was allowed to tilt forward at the bottom until the front right guide plate took the load. The extra force on the guide plate made it more liable to jam.

The fact that the rear guide plates did not touch the bottom of the boat suggested that when the keel was right down, it was supported in the fore-and-aft plane only by the front right guide plate. Also the front pad and rear roller were always under pressure as the bottom of the keel was trying to swing forward.

The Plan

Replace all the wearable parts, carefully made to what I considered was the right size. That meant replacing the front pad and the guide plates and possibly the top roller. Any fixing bolts would also be replaced and also anything else which looked in any way suspect. It is difficult and expensive to remove the keel, so it is not a good idea to skimp on a few nuts and bolts. All must be A4 stainless steel.

Details of what was done

This section is just a narrative of what I did. This may not be the best way of doing the job.

Measurements

I made the following measurements on the keel before removing the guide plates:

  • The amount the guide plates overhang the top part of the keel at front and back
  • Overall thickness of the guide plates
  • Total thickness of the keel complete with guide plates
  • Overall measurement over the keel guide plates at right angles to the front/back of the keel, at top, middle and back of the guide plates
  • The amount the front pad projects relative to the front of the keel box

One feature of this project is that it is not possible to keep trying things on for size. You do not know if it all fits together until the new guide plates etc are attached to the keel and it is put back in the boat. When it’s back in the boat it is impossible to see how well the guide plates fit in the keel box and how well they mate up with the bottom of the boat when the keel is down.

Another feature is that I knew the new guide plates and front pad must be different sizes from the existing ones, so could not just copy the old ones.

Making Jigs

Mark 1 dummy keel with the 
old guide plates attached
Mark 1 dummy keel with the
old guide plates attached
I was concerned that I might make the new guide plates the wrong size or shape and wanted a way that I could try them on, so I made a "dummy keel". This was initially a wooden dummy of the top part of the keel (to which the guide plates attach). I then attached the original guide plates to the wooden dummy. This was not completely successful as I could not work accurately enough to make the dummy exactly the same as the original part of the keel. This was caused by my own lack of skill and also because the bolt holes in the keel for securing the guide plates were not true.

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