Building the Ballast Tanks
from start to finish

Water Ballast for Dinah

Saturday, March 1st, 2008

Two or three other JOD 35s have done this before.  The plan is to add water ballast tanks to stabilise the boat when single-hand sailing, without a bunch of bodies hiking out to windward.

Designer Daniel Andrieu provided a JOD35wb stability study as shown in this wire-frame sketch:

JOD35 wireframe

JOD35 wireframe

Below is a rough sketch of the size and placement of the water ballast tanks:

ballast tank sketch (click to enlarge)

ballast tank sketch (click to enlarge)

In the sketch, the red box is a 12 volt centrifugal pump, the green lines are pipes to port and starboard tanks, the yellow line is a three inch crossover feed to enable dumping the 290 litres of water from one side to the other when tacking.

This is a very very simplified view, the actual plumbing will be a bit more complicated.

Other JOD35 owners have installed tanks such as these, port and starboard:

port side

port side

starboard side

starboard side

They elected to build their tank panels using glass fibre.  We have decided to use marine grade plywood and have chosen to install two baffles on each side, rather than just one.  We reckon the plywood panels will add extra stiffness to the boat and we reckon two baffles are better than one to keep the tank water from sloshing around too much.

Plywood for the ballast tanks

Monday, March 10th, 2008

Bloody expensive stuff!

Three sheets, 12mm, from Waller and Wickham in Baldoyle.  We could have used cheaper BS1088 waterproof and boilproof board, but potentially the plys have voids, allowing water ingress followed by de-lamination.  WE are taking a “to be sure to be sure” approach.

Robbins plywood

Making forward tank bulkheads

Wednesday, March 12th, 2008

Patterns for the bulkheads were drawn with light cardboard and then transferred to fibreboard which was then checked on the boat for a good fit. Tracing the contours on the underside of the deck and the inside of the hull was not easy.

Here, the fibreboard templates are being laid out on the ply for tracing.

cutting ply 1

Tools used to cut the plywood bulkheads. Jigsaw, steel straight edge and razor knife to scribe the straight lines for cutting, panel saw for the straight lines, drill with 8mm bit for tight curves where the jigsaw cant turn.

cutting ply 2

The two bulkheads, port and starboard, cut and ready for sanding on the surface and to round off the edges.

Cutting ply 3

These two inserts are needed to fill in the “rubbish bin” (clever builders those French) storage lockers on the after bulkhead.

Cutting ply 4

Epoxy coating the bulkheads

Thursday, March 13th, 2008

The ballast tanks will each hold 290 litres of seawater. The plywood MUST be PERFECTLY waterproof. Epoxy resin is the man for the job. Here the bulkheads and inserts are on the workshop table, sanded, dusted, cleaned with acetone. The table is covered with newspaper, but also several large sheets of acetate (from a friend’s printworks). Epoxy will not stick to the acetate, meaning we don’t have to worry about drips or overflow 0r the newspaper stuck to the underside after coating.

Epoxy coat 1

A plastic squeegee is used to spread the epoxy evenly over the surface. The panel at left has been coated. Room temperature of 20 degrees C permits three layers in a single day.

Epoxy coating 2

It is good practice to heat the plywood using a hot air gun to prevent “outgassing.” The gently heated plywood will draw the cooler epoxy resin into itself as it cools. Otherwise, bubbles will form as trapped air molecules in the ply try to escape.

Epoxy coating 3

The mixed epoxy is simply dribbled over the ply and then spread with a stiff squeegee.

Epoxy coating 4

The squeegee in use, after coating, wait a couple of hours and do the second coat, then after two or three hours (20 deg C) the third and final coat.

Epoxy coating 5