Wednesday, December 7, 2016

Propeller shaft hull penetration

                                                       Propeller Shaft  

Although a long time ago removed it was time to install again the propeller shafts and fix it to the engine coupling.
At the position where the propeller shaft enters the boat gave me the impression that there were issues with this part due to extra screws added into the wood. Also no gasket could be found between the shaft support and the hull.

The old bolt and nuts were removed and it was clear to me that there must have been water ingress into the boat, they were completely corroded.
These were still the original bronze bolts and nuts.

Everything was removed and the area completely cleaned from any debris, condition of the wood was checked.

As one can see from the next picture there is wasted wood and the condition could be better. Since the boat is this long ashore and has dried out completely, gaps between the planks, I decided not to change the wood in this area, due to the fact that I might end up with an issue when the boat is put in the water. For example if the new wood is wider than the removed wood the gap between the planks might not close.
The plan is now that after one or two years in the water the wood in this area of both propeller shaft penetrations will be replaced.

The penetration through the hull was protected with several layers of anti-fouling paint from inside out as well as from the outside.
The holes not needed anymore for fixing the hull penetration were closed with plugs.

The actual bronze propeller shaft hull penetrations were fully cleaned and sanded to remove any dirt or high spots.

Thin rubber sheeting was placed over the bronze piece and with a round hammer the contour of the bronze was taken over onto the rubber. One has to make sure that the rubber does not move during this process also the holes although not seen on the pictures are marked as well.

Next step was to prepare the new bolts and nuts.
It was decided to use stainless steel bolts and nuts and make them flush with the hull.
Actually threaded rods were made on the correct seize and the nuts were on one side fixed with thread lock, to prevent them from moving.

A small recess round was made in the hull at the positions where the nut would be positioned.
The threaded with nut rod was fitted with washer and small O-ring, to prevent as much as possible water ingress in the hole for the threaded part.

Before installing the fixing bolt it was protected with Sikaflex also to fill the hole where the bolt passes through with protective material.

The bolt was inserted by rotating the bolt by the nut to make sure that all the wood inside would be covered with Sikaflex.
It was made sure that all extra Sikaflex was removed from around the nut and the hole where the nut would fit in.

When the nut was pushed the last few mm at the same time two component epoxy filler was added around the nut and over the nut making it almost flush with the hull.
The nut and thread are now completely sealed from the water, while at the same time the nut is fixed in place giving me the opportunity when the boat is in the water and the wood expands to tighten the nuts on the inside when required.
Nuts are now only slightly tightened.

On the inside two extra holes were drilled in the bronze hull shaft penetration on the aft side to make sure that the whole unit would be flat on the surface and still be tight in place.
This way I do not require to tighten the bolts and nuts to much until the wood is expanded when the boat is placed in the water.

On the inside the stuffing box did get new packing as well as that when the shaft was connected to the engine that the rubbers of the couplings were replaced.
As described with the rudder stock the packing was cut with an angle to get a good connection between the ends so preventing that water would go through and one needs to tighten the stuffing box too much.

1 comment: