March 29, 2018
This month we bring you part 4 in the refit and restoration of the famous Motor Gun Boat 81 (MGB 81) and we are still below deck. Our last article showed you the replacement of the aft and mid structural frames and longitudinal stringers, this month we carry on forward and take you back on deck for a look at some repairs and additions.
Repairs to deck sheathing have begun. The sheathing was sanded back and laminated, ready to be repainted at the same time as the vessel’s topsides, deck, hull and coach roof.
A few other minor repairs are still outstanding including the portside hardwood rub rail, the transom, the deckhouse and some of the deck hatches. These repairs will be left towards the end to avoid any damage, as we still need to fit the 3 new, Mermaid Marine supplied, FPT C13 825hp diesel engines, along with the rest of the interior.
We have added to the engine room’s fire suppression systems. Built inside the engine rooms ventilation covers are now simple yet effective fire flaps. With a quick pull of a pin, the handle will be released and the flap will close, cutting off all oxygen to the engine room along with the, soon to be fitted, 3 new, Mermaid Marine supplied, FPT C13 825hp diesel engines.
After assessing the work we could start removing the diagonals and deck beams, giving us access to the hull frames and outboard stringers-longitudinals. The removal of this was carried out in the same way as the midship cabins which can be viewed here in our last article.
In our last article, you may remember us laminating the hull frames. The final frames have been laminated for the forward end of MGB 81. Each new frame is made up of 12 planks, made from a flexible, light ash and a heavier stronger utile (hardwood), these are glued together to make a strong and flexible frame. Every pair of frames is a different shape, as the curve of the MGB hull becomes more pronounced as it gets closer to the front. This meant that every time a new set of frames is laminated the jig has to be adjusted, even if it is only by a few millimetres.
Above is a short video on the laminating, spiling and shaping of the hull frames.
This is the first of 5 videos showing the step by step interior restoration, the other 4 which will be following shortly, so don’t forget to follow the progress and updates on this project on our website here or you can register for our monthly eNews blog here.
Part 1 – Laminating, Spiling & Shaping Hull Frames – watch the video here
Part 2 – Fitting Hull Frames – watch the video here
Part 3 – Box Stringers, Longitudinals & Bunk fronts – watch the video here
Part 4 – Bunk Structure & Webs
Part 5 – Deck Structure & Flooring
We also produced 2 videos in which the 3 MAN 835hp engines were removed in order to make way for 3 new, Mermaid Marine supplied, FPT C13 825hp which will more reliable, fuel efficient, and lighter diesel engines. In case you missed it you can read the article and watch the videos here.
With the centreline sole bearers and diagonals removed we could start making new templates of the forward webs, and begin fitting the forward frames. (In total 300 webs and 48 frames had to be cut, shaped and fitted into place)
With the new hull frames installed it was time to start fitting the sole bearers, diagonal braces with the plywood biscuits/webs.
The forward londitudinals or stingers were fitted it the same way as the midship. The 14’6” foot beams were passed down through the forward hatch and along onto the starboard side, as anticipated the corner was far too tight for the port side longitudinals which were then returned on deck and eventually passed freely through a small hole cut the forward ship bulkheads.
The existing longitudinals originally butted up against bulkheads and were glued and screwed through and fitted in place. We have now cut through the bulkhead and fitted each stringer together in the middle, with a scarf join, to make 4 longer 23’ foot stringers rather than 8 x 11’6” foot box stringers. The ends are also now set into the bulkheads and fitted in place. These changes will make her more structurally sound and far more solid.
The lower section of the forward longitudinals really shows the shape of the hull as it continues forward.
With the Forward longitudinals/Stringers installed it was ready to fit the bunk fronts and box section
The forward zone out of the forward cabin longitudinal is now attached to the bulkhead with the addition of an alloy angle bracket, bolted and fitted to forward bulkhead longitudinal. Again this will make her structurally sound and far more rigid, as before it was only butted up and screwed in place.
Vertical uprights/groundwork were fitted to forward cabin longitudinal bunk fronts, in order to prevent the top longitudinal from sagging over time. It will also give us something to attach the additional box section to which we will mention a little further down.
The next job was to begin forming the bunk tops and the shape. Here you can see Mike Prince, one of our seasoned shipwrights fitting the bunk top bearers which will then support the bunk tops, similar to the sole boards covering the deck.
In order to attach the new structure to the original hull topside frames, we have fitted plywood biscuits. These biscuits will work in the same way as all biscuits/webs and pull everything together. As you can see it’s definitely not an easy job fitting these new biscuits!
This image shows the structure of the inboard and outboard longitudinal connection, along with the sole bearers and biscuits tying it all together.
Here you can see the structure within the bunk linking the longitudinal to the hull frame and bunk top which is then fitted to the existing topside frames.
The plywood webs or stiffeners are there to pull everything together. Every join between two frames, beams or diagonal is strengthened with a biscuit or web which has been glued and then screwed into place. This then pulls everything together thus preventing anything slipping out of place, while also stiffening up the frames and stopping anything from breaking or moving.
A new structure of box section is fitted prior to attaching the inner plywood panel. These smaller structures will hold the original wooden fronts to the bunks.
Finally, all of the new frames, diagonals, Longitudinals and deck beams were in place ready to be painted in the original blue/grey. We mentioned in our last article that this will be a pity because the laminates look more appealing in raw form, this is why we have decided to leave one section, under a removable sole board, unpainted and varnished. This way when it is back on show any visitors will be able to see how much work goes into laminating one of the frames.
With the sole bearers and sole boards back in place the structure was complete, it was possible to walk around her again without having to jump between the deck beams!
Not many jobs are now required below, the hole from where the starboard longitudinals were passed below need patching, we will be fitting a couple of additional bearers in the midship cabin for additional strength and support and finally a few more cosmetic touches including a new coat of white gloss for her walls.
The aim is to complete the restoration and undertake trials in mid-2018, after which she will be on show at the Portsmouth Historic Dockyard along with other famous historical vessels including HMS Victory, HMS Warrior and the Mary Rose.
Outstanding jobs still include;
Helm & interior
Repairs and Paint
Progress and updates on this project can be followed on our website here