Sol Purpose

Haul out for bottom job and thru hulls

It has been three years since the boat had its last bottom job and I had a problem with the height of the bottom job anyway.  With full water, diesel and holding tanks the waterline was above the bottom job and so there was a heavy later of algae/barnacles forming.  I decided to have the bottom job raised by 8 inches to give myself some breathing room as we would have considerably more “stuff” on the boat when we set off due to provisioning and moving all essentials from storage.  This meant that I had to sacrifice the boot stripe but that was a small trade off and didn’t bother me enough that I felt the need to have the boot stripe redone.

Whilst the boat was out of the water I also wanted to get a project done that has been nagging me for a couple of years… replace all the below the waterline thru hulls.  There was nothing obviously wrong with them apart from the fact that, like 95% of all boats today, they did not meet ABYC standards.  Almost all thru hulls consist of a parallel threaded thru hull with a tapered ball valve attached directly to it.  This means that only one or two threads are ever used to hold the ball valve in place.  ABYC H-27 standard states that “A seacock shall be securely mounted so that the assembly will withstand a 500 pound (227 Kg) static force applied for 30 seconds to the inboard end of the assembly, without the assembly failing to stop the ingress of water”.  For more details on this specification and a test showing that a brand new parallel thru hull to taper ball valve installation fails this test see this site

As our boat is 20 years old I felt pretty confident that our current condition was far worse.  The thought of something heavy shifting in a bad sea and shearing off a thru hull made the decision to replace them all with proper backing flanges bolted to the hull an easy one, just not a cheap one 🙂

I could wax lyrical about the whole project but it would essentially be pure plagiarism.  I followed the excellent instructions available at the Compass Marine how to website, specifically this link…

I cannot praise this website enough for the extensive project list and excellent instructions given.  Suffice to say that with their guidance I was able to replace 4 x 1.5″ and 2 x 0.75″ thru hulls in two days of work.  This included removal of the old thru hulls and backing plates (they were thin and held on with sealant) as well as all surface preparation, dry fitting, epoxying, sealing and clean up.

The new backing plates were made of 0.5″ G-10 which is an absolute bear to work with.  The link above does not exaggerate at all.  I was unable to use a hole saw for cutting out the plates from the sheet as the work required of the drill for a 6″ disk was just to much, and this was with a drill press.  I ended up using a jig saw and several blades and only used the drill press for the inner hole to take the thru hull.  It took me one and a half days just to cut out the backing plates, drill their central hole and tap and thread the holes necessary for the mounting bolts.  Naturally I did all that work before the boat was hauled.

Below are a couple of pictures of some of the stages of the project.


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