We sail Phobos 21: Depth & speed instrument installation

It's always hard to decide for the in-hull or thru-hull transducer, but we wanted speed and sea water temperature numbers, so drilling is necessary.
Last week, I've finally completed the installation of the Raymarine i40 Bidata display (PN: E70066) and Raymarine DST800 analog tri-ducer (PN: A22154, made by Airmar) with depth, speed & water temperature readings in single thru-hull assembly.
The work on it begun since we arrived with the boat and firstly I had to decide the best place for the installation of the thru-hull. I wanted better access to it in case of emergency or when pulling the boat onto the trailer. After drilling the inspection hole and looking around the hull I decided to use the V-berth storage area bellow the mattress where we have the water tank already.

v-berth storage with water tank

view from the new inspection hole

This is a good spot because when you get some water here when you remove the transducer plug, it will stay there and will not travel all around the hull.Then I measured the best location in this storage more than 5 times and checking from the outside for any obstructions from the keel rollers and support pads to keep the transducer out of their path during launching/retrieving onto the trailer.
This is also the most front area where the bottom of the hull is still relatively flat to keep the transducer within 22° deadrise angle.

The major task then awaits me during the installation. I've drilled small the pivot hole to see if it's all good. Then I started drilling the inner layer from inside using the 90mm diameter hole saw. This is just wide enough for the hand to tighten the nut of the transducer and further operations. Then I drilled the same diameter on the fiberglass layer just a few millimeters bellow covering of the chopped lead ballast.

big hole in the inner layers of the boat - you can see the black pieces of chopped lead ballast

At first I thought that the lead ballast is somehow uniform matter, but turned out, it's made from small chopped pieces of lead. That makes sense as you cannot pour hot lead onto the fiberglass.
Anyway, that made the work a little harder because I had to take out some lead and created a dam from a cardboard to temporarily prevent other pieces to visit my hole :-) Lastly I had to drill 51mm hole thru the hull from the outside. I started drilling in reverse to prevent gelcoat chipping and as soon as I drilled thru the gelcoat layer I switched the rotation and finished the hole.

view thru the 2" hole from the outside

You can clearly see all 3 layers. From the left, its the inner layer, ballast cover and the hull. Of course the cardboard is not the best water tight sealant so I had to put 3 layers of fiberglass all around the perimeter between the hull and ballast cover.
Then I used the fiberglass circle I've drilled from the inner layer, drilled smaller 51mm hole and epoxied it to the hull as a backing plate to increase the hull thickness. I've wrapped the thru-hull housing with the plastic bag and screwed it to the hull so the backing plate is parallel with the hull.

fiberglass perimeter, backing plate and the thru-hull housing

sanded glass fibers

This is still not water tight. There are tiny holes in the perimeter fiberglass layer, but also there is still no seal between the hull and inner layer. So I mixed polyester resin with the chopped glass fiber and Cabosil to create a peanut butter like consistency, put into the plastic bag with a tiny hole in one corner and squeezed the resin between the inner layer and ballast cover layer like the confectioner.

final seal with the thickened resin

Then I've used the putty knife to spread the resin all over the perimeter and made it uniform.
As the last step I've just painted the hole with one layer of gel-coat and one layer of top-coat

final hole

In the same time I was drilling the hole for the display in the cockpit bulkhead. Always measure twice and check the surface is as flat as possible. Then drill the pivot hole and measure again.

57mm hole for the display

inside the head

Then it took me some time to think where to install the cabling. At first I wanted to pull it thru the ceiling, but it turned out to be impossible. Then I carved and varnished nice narrow planks of oak to build a conduit for the wires, but then I found out that I can very easily pull the cables between the inner and outer layers from the bulkhead under the seating just to the port cockpit hatch where I have a gas tank. I was so glad and there is plenty of space for other wires.

display and transducer cables in the port cockpit hatch board

going upwards just between the cockpit seating and the inner layer

When I tested the display mounting I've found out that the inner layer bends towards the deck layer so I've added small pieces of wood blocks in between.