Keel bolt and keel case renewal

The removal of Enfys’ keel bolts is described in  here. In this article, Bill Dowell continues the story by describing the installation of the bolts and the re-building of the keel case.

The original imperial 5/8″ and 3/4″ bolts were replaced with M16 and M20 and the holes were run through with long-reach drills to open them out. (For two of the centre bolts, the holes through the ballast keel were not true and the bolts had been bent when originally installed.)

New zinc-plated high-tensile hex head bolts were procured…

and were installed with a cotton grommet and bitumastic sealant around the outboard head.

As they were driven up liquid tar paint was poured in from above to completely flood the hole and encapsulate the washers and nuts.

The pair of bolts aft of the bulkhead and under the engine were fitted longer and set onto dense plastic blocks about 25mm high in an attempt to keep them above the bilge water puddle.

On the underside of the ballast keel the bolt head recesses were filled with mortar with a water-proofer added.

The exposed faces of the lower part of the centreplate case that is only accessible from under the boat were found to be a bit worn and ragged from the effects of immersion, lack of paint and the chafe from the centreplate. A simple scraper and wire brush on long handle was used to clean the barnacles and loose stuff off and the bare timber was treated with penetrating epoxy followed by a couple of generous coats of underwater primer.

A small paint roller on a long handle reached into all the corners (photo looks down into the slot under the casing, from above).

The centre-case under bolts were plugged-over and the upper part of the centreplate case reassembled with newly-made sides in iroko. Sikaflex was used for all faying joints and it was here that I discovered a problem: the Sika has a problem with the underwater primer and seems to ‘melt’ it so that the Sika does not stick.

Centre-case sides being fitted. There is a new front post (‘headledge’) as well.

Both sides in position

The slot capping was renewed.

New casing front installed

The centreplate case was finished off with new sill battens to help support the lower joints and cappings fore and aft.

A new capping piece was fastened down onto the lower casing with bitumastic sealing strip. Epoxy sealer was used on all faces that were potentially going to get wet or to be covered in sealant. The casing was varnished and the cabin furniture re-fitted.

We had reassembled the front casing upright post exactly as the original which had the athwartships through-bolt passing through the joint – there was no ‘stop-water’ in this joint and we just relied on the Sikaflex to seal it.

After she was launched water started weeping in and appearing from under the lower capping. At first we thought this was coming up from the lower casing and extra screws were added to force this down. After a period afloat the ingress slowed but it continued for the rest of the 2019 season.

In early 2020 whilst ‘Enfys’ was ashore we re-visited this part of the centreboard case and took the cappings off. Assuming that the problem was the joint below the front upright post (‘headledge’) we made and fitted a stop water block in this gap well-packed with bitumastic tar and held in place by a new clamping piece.

The slot capping had to come off again…

This is the piece inserted in lieu of a stopwater, all lathered up with tar, this time

Fitting the new piece…

… and the slot capping repaced.

The lower capping was cut down to suit and was refitted. This work was done on the eve of the March 2020 Covid19 lockdown and it was not until July that the yacht was finally launched. To my dismay she still leaked from this joint somewhere….!

There was still a weep from somewhere.

The trickle continued all the time she was afloat, and, in the end, we were about to beach her or get her lifted out when we decided to have another look at the casing joints behind the front capping. This was taken off whilst she was still afloat, and we found she was leaking from the joints between case sides and the front upright. This was simply packed with caulking cotton which finally stemmed the inflow.

In summary we shouldn’t have used Sikaflex for sealing these underwater joints.

Owing to lockdown over the winter 2020/21 we were unable to plan any further work on this but will probably eventually resort to dismantling the upper part of the case again and re-doing the joints with an alternative sealing method.


This article was re-published from the Enfys blog at Finesse 24 Sailing Yacht: June 2019 You can read about the renewal of the stern post too, which was carried out at the same time.


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4 Responses to Keel bolt and keel case renewal

  1. Pingback: Removing the keel case and bolts |

  2. Roger Rooke says:

    Thank you,
    Just about to inspect Drifter’s keel bolts while her engine is out for repair.
    Roger Rooke

  3. William Dowell says:

    Just a small comment: When we re—visited the job in early 2020 the new timber block was bedded on bitumen and not Sikaflex as the original job. It still leaked but not from that joint! This time it was from the case sides but these were caulked with cotton and are now tight.
    Bill Dowell

  4. Nick Ardley says:

    I have used the roofing bitumastic tar – comes in tins and stays soft…

    The owner of F24 Faith, had dribble problems with his centre plate case. He solved this by coating the centre plate side of casing going down with the same product.

    Another owner has fitted large section lower chock/case sides set bolted into keel wood. The 20 mm sides are set into these and sealed – what with I do not know. Chap said he was working at a boatyard when he did it all…

    Well done!

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