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!

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

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.

I then made a "mark 2 dummy keel" which included wooden replicas of the guide plates. Using car body filler I took a cast of the inside of the bottom of the boat (where the plate rests) on the end of the dummy keel. This then gave a reasonable idea of the shape that the new guide plates should be (the old ones did not fit the boat accurately). In order to measure the inside of the keel box I made a simple measuring stick which would just fit inside the keel box (when held at right angles to the axis of the keel). This made it easy to express measurements as "stick+2mm" etc. I also made a thin plywood template with handles on it which just fitted inside the keel box. It was shaped to replicate the way the guide plates bear on the inside of the keel box. Using this template I then made 2 wooden templates which would just fit round it and therefore represent the keel box itself. If my keel with its new guide plates would fit inside these templates then it would fit inside the keel box.

New Guide Plates

It was then time to make the new guide plates. The old ones were 21mm thick, which seemed odd. However it seems that the acetal / delrin is normally supplied a bit oversize. I was relieved to find that the stuff I ordered as 20mm arrived as 21mm. The order of fitting the guide plates was:

  • Cut slightly oversize with circular saw
  • Plane bevels on the inside to match the shape of the main part of the keel
  • Drill fixing holes, counter-bore the fixing holes and fit to the keel. Drilling had to be done through the keel so that the hole in the delrin matched the wonkiness of the hole in the keel.
  • Plane front and back to the correct dimensions (checked using the templates described above)
  • Shape the bottom ends to match the boat
  • Round the outside corners
  • Put a bit of West epoxy in the bolt holes to make them more waterproof and discourage water penetration into the core of the keel. Wait for it to set.
  • Bolt on, bedded in a layer of silicone sealant
  • Measure again, followed by a little more planing.

New Front Pad

This required thicker material than the guide plates. The space available was 35mm, the existing pad was 25mm, so I ordered material 30mm thick, intending to use washers to fill the gap. Using the existing pad as a guide I cut the material to the correct angle to match the keel using the circular saw. I then shaped the edge which would bear on the keel using a small coarse halfround file and sandpaper, using plywood guides to keep the file straight. This took ages but seemed to give the right result. The other end of the block was left oversize pending careful measurement. The new pad did not quite fill the 35mm available, so I made some thin shims so that it was a snug fit in the bracket.

New hold-up strap

The metal strap which is used to hold the keel up is made of galvanised steel on my boat (however some later ones are stainless) and was quite badly rusted. I removed it and took it to a steel fabricator for his opinion. He did not have the right size of stainless steel in stock and said re-galvanising was not simple as the old galvanising had to be removed, so he made me a replacement in mild steel. This was not exactly the correct angle where it mated with the keel, so I took it back together with a wooden block which had a mould of plastic padding on it showing the exact shape of the old strap. He modified it – I should have made up the mould at the start as it only took a few minutes. I got the strap galvanised at a different place which makes boat cradles. I fitted the new strap bedded in a layer of West epoxy with milled glass filler, so that it was in contact with the keel all the way along. I used new bolts and put a bit of Duralac where the bolts went through the holes – it is supposed to reduce corrosion when fixing dissimilar metals.

New top roller

After the new hold-up strap was fitted it became apparent that the old top roller would not bear on the back of the keel box, so I turned a new slightly larger one from a piece of Delrin rod.

New Cables

Just before fitting the whole thing back in the boat, Fred Larkman reminded me that the cables were worn out and needed replacing. He soon made up new ones.

Overhaul Cylinder

I think there had been a little leakage from the hydraulic cylinder, so I took it to Ipswich Hydraulics for overhaul on the principle of doing everything possible to get the keel in good order. They fitted new seals throughout. The keel tends to very slowly go down when left up and held only by the hydraulics. I am not sure if this is caused by leakage at the cylinder or some other part of the system. So I also installed a valve in the aft locker at the start of the main pipe run to the keel cylinder. Closing this valve will stop the keel from slowly falling unless the cause is the cylinder itself.

Overhaul pulleys etc

As everything else had been taken to pieces I took the opportunity to clean all the pulleys, brackets etc. The bolts through the centres of the pulleys are high-tensile steel (not stainless like the fixing bolts) and so are prone to rusting even when greased. I replaced these bolts. (I have found that the pulleys in the frame immediately above the keel are prone to rusting and are stiff at the end of the winter. So I normally take them off and clean and grease them in the winter)

Tidying the inside of the keel box

It took a while to clean all the gunge from the inside of the keel box. There was quite a build-up of barnacles which showed where the guide plates had not been resting on the bottom of the boat. There was also a good deal of grease and other muck. The keel box is quite deep, so not all is reachable by hand and some of the cleaning was done using a stick with a solvent-soaked rag tied to the end. Eventually it looked pretty good and I repaired minor damage at the bottom and where the bottom pad bracket fits. I then put some West epoxy with graphite filler at the bottom of the keel box where the guide plates rub and where they rest on the boat.

Putting it all back together

Eventually I was convinced that the re-assembled keel would fit in the keel box, snugly but not too tight, and asked the yard to crane it back in. Fred and Steve soon had it back in the boat and as they had lots of boats to launch, they suggested I get on with fixing the wing back on. I started by connecting up the new cables, which is quite a fiddle. Putting the wing back on was more difficult than I had expected as the keel goes down at a slight angle but the bolts which hold the wing on are vertical. It was therefore necessary to move the wing about with levers and wedges to get it in the right place. Eventually it all went together and I could get the nuts on the main keel bolts. There seemed to be lots of washers and I did not know how many came of each bolt, so I shared them out according to the length of the bolts. Before tightening the bolts I put a good squeeze of polysulphide sealant all along the joint. After everything was tight I filled and faired the bolt holes with car body filler. This marked the end of our turn at providing entertainment at the boatyard. Everybody has stopped for a chat and to offer advice. We were lucky to have fine weather throughout – wind and rain would have made the job much more difficult and unpleasant.

Testing

It worked OK. It moved all the way up and down. It would even lift from the bottom of its travel when the boat was out of the water without the help of any lever – that was a definite improvement!

In Use

The keel seemed to work well once the boat was launched. One difference was that when lifting the keel the start of the movement was now quite smooth, whereas before the boat used to pitch very slightly at this point. When lowering the keel the last part of its travel was now smooth, whereas before it had finished going down with a few jerks.

However one thing was definitely not quite right. When lifting the keel right up. The holdup strap bumped on the frame at deck level and then scraped past the frame. After a while we dried the boat out alongside Ramsholt quay, removed the frame and put in a plastic shim at the front, so moving the frame back a little in the boat. Unfortunately there was only room for a thin shim of about 2mm, so the hold-up strap continues to foul on the frame. I hope to cut a bit off the strap in the winter. This will damage the galvanising which I will paint over with galvanising paint. What I should have done was to make yet another jig to record the exact position of the hold-up strap and make sure the new one was exactly the same.

Another thing did not become apparent until somewhat later. The keel could not be lifted all the way up with the hydraulics – it was about 25mm short of the end of its travel. This was a nuisance as it was not possible to stop it rattling when on a mooring or at anchor. I cannot explain this – I am sure the new keel cables would have been made carefully to be the same length as the old ones, but as I was in a rush I did not record the measurements. Anyway I now have new cables made a bit shorter which I hope will do the job.

After a while a strange squeal happened when lifting the keel. This turned out to be the delrin pulley at the top of the keel squealing on its axle (a 16mm bolt). This seemed to respond to a dose of Mclube.

Materials and Suppliers

  • Plastic: Delrin, white. In place of the original yellow acetal. Supplier: theplasticshop.co.uk
  • Steel: Hold-up bracket by Mike Jackson, near Bucklesham
  • Galvanising: Jacobs of Kirton (boat cradle manufacturer)
  • Fixings: Some from Larkman’s boatyard, some from SIG fixings, Ipswich
  • Boat Yard: Larkman’s, Melton, near Woodbridge

 

Jigs and Tools

Jigs:

  • Front pad measuring stick
  • Keel box measuring stick
  • Keel box template
  • Keel template, lower
  • Keel template, upper
  • (hold-up strap template would have helped)

Tools:

  • Vernier calliper
  • Plain callipers
  • Set squares
  • Straight edge
  • Power plane
  • Hand plane 
  • Sander
  • Electric drills 
  • Various hand tools