Leisure Keels - Admirably Solid After 45 years

A Reassuring Inspection of the Keel Bolts on a Leisure Yacht

Preamble:

Many Leisure yachts are over forty five years old. The vast majority have twin keels, secured to the hull by by stainless steel studs or bolts

However, there are no recorded issues with the keels or their fixings. The keel design of Leisure yachts has proved admirably durable.

Consequently there has never been an article published on the removal of the keels on a Leisure yacht until now.

Leisure owner Neill, had taken on the restoration of Leisure 17, Eva B, and noticed some rust on the top of the port keel joint.

Concerned that the keel fixings were possibly corroding with age, Neil decided to remove the port keel for a closer look.

Fortunately Neil photographed and documented the whole procedure and his article below should provide reassurance to all Leisure yacht owners,

The original builders of the first Leisure 17s, Cobramold, secured the cast iron keels to the fibreglass hull, using stainless steel studs.

These studs were screwed first into tapped holes in the metal keels.

The cast iron keel, with the studs protruding, was offered up to a reinforced fibreglass section of the hull where matching holes received the studs.

A suitable jointing compound was applied between the keel and the outer hull to form a watertight joint.

Then inside the fibreglass hull, the studs were secured by nuts and washers and the keel was drawn up to its final position as the nuts are tightened.

Finally inside the hull, Cobramold poured resin over the protruding studs, washers and nuts to protect them from corrosion from water in the bilge of the yacht.

This method of fixing meant that the stainless steel studs and securing nuts were now invisible - and remained so for the past  45 years

Removing the odd stud (or keel bolt) for inspection is not an easy task since the studs were tapped and screwed into the cast iron keel and any attempted "inspection" could end up compromising the water tight joint between hull and keel.

Checking the keel bolts on Leisure 17SL Eva B

This article describes how Neil set about checking the keel fastenings on his 1982 Leisure 17SL

The work was carried out in the open, without the cover or convenience of a workshop.

Please note that the weight and scale of the keels may not make this method suitable or practical on larger Leisure yachts.

Keel Removal

My first  task is to raise and support the hull of the yacht sufficiently, so that the keel can be "dropped" when unbolted from the hull.

The fixing studs protrude into the hull by around 40cm, so that having the hull raised by just 150-200cm is sufficient.

Eva B was already on a trailer and the yacht was jacked up on one side as shown above.

Please take the utmost care when jacking up and supporting the hull. Any mistake at this stage may be irretrievable!

Inside the hull, a Dremel was used to remove the resin which covered the the nuts on each securing stud. The securing nuts were not too difficult to remove once freed from their resin covering.

The original washers were left in place. The washers were all at different angles. Apparently this was to avoid "point loading" occurring if they were aligned all the same way.

I intend to reinforce the area around the stud holes and washers with further layers of fibreglass and a new set of washers,

I undid all the nuts. Outside at the top of the keel, I carefully cut along the seal with a hacksaw blade. I then used hardwood wedges to gently prise the keel away - and its weight helped it to drop free.

The keel root on the hull showed just minor delamination and water penetration of the outer laminate.

The keel was taken to a local fabricator who removed the studs which came out relatively easily from their tapped holes.

Dimensions of original keel studs on a Leisure 17

The original studs were 1/2” whitworth 12 tpi 75mm in length

Since about 40mm of the 75mm was inserted into keel, this only left 35mm for washer and nut.

However 75mm would not be long enough as I intended to add a locking nut, and a new, second washer and extra fibreglass reinforcement.

The old keel bolts were all in very good condition, probably A4 (grade 316) stainless, and showed no signs of any corrosion.

However I decided to replace the studs with A2 (grade 304) stainless and the reasons are explained in detail at the end of the article.

I had 5 new studs fabricated by BA-Bolts.co.uk They are 1/2” Whitworth 12tpi, 125mm in length (actually 100mm would have been a better choice).

Retaining the old washers and adding strength

Inside the hull, I carried out thickening and stengthening of the fibreglass by adding 3 layers of chopped strand matting (csm) /300g woven roving.

I thought that the old washers, left in position, will benefit from being strengthened by this.

I added the new, larger washers and two nuts per stud. These are surface mounted so they are visible.

One of the old studs (at the rear) came into the hull very close to a stiffener. The washer was fitted at an angle which meant it cut into a hollow stiffener. There was not enough room to add a new, larger washer there.

Replacing the keel

First the keel root on the hull was gel coated and left to cure. This should provide a water proof base. All stud holes holes were also coated in gel coat.

I then roughened the surface to provide a key and help the final sealant make a best fit and provide a watertight joint.

The keel was then offered up for a "dry fit", checking alignment and gap and lowered back down again.

Nitoseal MS600 was used to provide a watertight and flexible joint between hull and keel.

https://www.sealantsupplies.co.uk/product/fosroc-nitoseal-ms600

The sealant was now applied to keel and hull root. The keel was again offered up and held in position whilst the nuts inside the hull were tightened in order.

Finally the keel was drawn up fairly tight to allow the sealant to squeeze from the joint and the joint left to "cure" for 5 days before a final tightening of the nuts.

Tip: Have plenty of white spirit and a towel! Use masking tape at the top of the keel and the bottom of he hull root to provide the sealant with a neat line.

Neil, Leisure 17SL, Eva B, Fife

Reasons for using stainless steel  A2 in the new  keel studs

There were several reasons, the cost,   the intended use of boat (day sail light conditions) and also that the tensile strength was comparable to A4. 

A2 has a slightly more forgiving flex than A4 .

A4 to be optimal, it’s protective composition must have oxygen to react.

A4 for deck fittings is a must where it self heals with oxygen present.

In underwater situations without oxygen A4 could simply react/ corrode like A2.

Providing that my keel sealant works it should be dry and airtight below the waterline . 

As as an additional measure, I painted the base of the threaded holes in the keel with two part zinc-rich epoxy,  to act as barrier if water did get in.

The zinc in epoxy acts as a sacrificial element but I guess this needs oxygen to react.

The most vulnerable spot I think for corrosion is actually where the studs will be on show in the hull locker. A salt water and oxygen rich environment could cause rusting .

Re-encapsulating the nuts and washers would make them airtight but would defeat the purpose of the project which was to have any corrosion in plain sight!

I have chosen A4 stainless nuts and coated the new washers with two part epoxy zinc-rich coating.

I will be watching and inspecting the hull fastenings inside the boat's lockers as the season progresses!  

Neil, L17SL, Eva B, Fife

Footnote from the editor

["The molybdenum content of A4 stainless steel also helps it to strongly resist attack from chlorides, such as those found in seawater.

For this reason A4 is sometime referred to as being of 'marine grade' and why it is so useful in this demanding environment, especially above deck" ]