Ship Happens

[AntarcticPilot]

How about correcting "Nope" ?

Perfectly good colloquial English. Obviously, I use more formal English in the documents I correct, but they are academic texts that adhere to a fairly regimented style. But in the forum I can be less formal. English is defined by usage, so there's no way you can say that a particular common usage is more or less correct than another, but you can say whether a particular text adheres to the norms for its genre. French, however, is another matter, and the Academie Francais tries to regulate every last comma! It's on a loser in many areas, though.

 

[Keith 66]

Has any mention been made of the double diagonal hull construction? If that is a bit iffy (and likely to be, looking at the rest) then things could get really interesting.. Even more so than the grammar..

I dont recall from the early vids any mention of the double diag construction but from the videos you can clearly see extensive rot around the deck edges, covering boards & beamshelves extending into the frames.
Back in the 80's when i was learning the trade alongside a first class chippy, we worked on many double & triple diag ex navy boats, back in the 80's many were still in service as fishing boats converted into yachts etc.
Without exception all were "Getting a bit sore" as the local chippies said, rotten patches were common & bodging was normal. To take one plank on the inside out involves stripping every plank that covers it off. Because the planks run on opposite diagonals you quickly have half the side of the boat out. Bodging with epoxy doesnt work as the rot has always spread further than the repair.
We fixed one 36ft harbour launch that had broken its mooring & bashed on the seawall, the hole in her side was 4ft long. By the time we had stripped it out the uncovered area was 16ft long keel to sheer. Each plank intersection has 5 rivets so thats a lot of rivets.
Then you have the calico between the skins, it was put between the layers when built & soaked in linseed or white lead or a secret mixture from whatever yard built her! As these boats get old fresh water gets in the top & they start rotting, the voids between the planks offer a ready path for rot filaments to spread. It will & does spread from sheer to keel in short order.
Most were built from mahogany so will rot faster
This isnt naysaying or bullshit it is the simple truth of how any boat of this construction will die.

 

[Wansworth]

How about correcting "Nope" ?

He is on holiday?

 

[Birdy60]

I dont recall from the early vids any mention of the double diag construction but from the videos you can clearly see extensive rot around the deck edges, covering boards & beamshelves extending into the frames.
Back in the 80's when i was learning the trade alongside a first class chippy, we worked on many double & triple diag ex navy boats, back in the 80's many were still in service as fishing boats converted into yachts etc.
Without exception all were "Getting a bit sore" as the local chippies said, rotten patches were common & bodging was normal. To take one plank on the inside out involves stripping every plank that covers it off. Because the planks run on opposite diagonals you quickly have half the side of the boat out. Bodging with epoxy doesnt work as the rot has always spread further than the repair.
We fixed one 36ft harbour launch that had broken its mooring & bashed on the seawall, the hole in her side was 4ft long. By the time we had stripped it out the uncovered area was 16ft long keel to sheer. Each plank intersection has 5 rivets so thats a lot of rivets.
Then you have the calico between the skins, it was put between the layers when built & soaked in linseed or white lead or a secret mixture from whatever yard built her! As these boats get old fresh water gets in the top & they start rotting, the voids between the planks offer a ready path for rot filaments to spread. It will & does spread from sheer to keel in short order.
Most were built from mahogany so will rot faster
This isnt naysaying or bullshit it is the simple truth of how any boat of this construction will die.

Exactly my experience of it, the boat is not mahogany which is a saving grace but there are certainly huge areas of decay along the sheer but they do not seem remotely interested in how far it has spread and just keep on saying what great condition the planking is.

 

[clyst]

Exactly my experience of it, the boat is not mahogany which is a saving grace but there are certainly huge areas of decay along the sheer but they do not seem remotely interested in how far it has spread and just keep on saying what great condition the planking is.

HI Birdy, Not Mahogany ? Thats a surprise , what is it ?

 

[DownWest]

I was assuming it was plank on frame, until I thought I might have another look at the vids. No 73 has him 'replacing' some framing, but I saw the inner hull and thought Oh...

 

[Tranona]

Double diagonal was chosen because these boats were put together by non boatbuilding people. Planks do not need shaping - just cut to a constant length/width and riveted on to prefabricated frames and ribbands. Like many things in the war, speed of construction with unskilled labour was uppermost in the designers mind. Remember seeing grainy films of them being built in what I think had been a furniture factory. Never expected to last - many would be lost within months of launch and the end of the war would see them mostly scrapped with a few being re-purposed. Amazing any have survived at all.

 

[Keith 66]

On the contrary, planks do need shaping, you cannot fit diagonal planks & edge set them as one edge will ride up & the error becomes cumulative. There are ways round this, either shape one edge as you go & fit next plank to it or cut all planks at a constant width, lay every other one with maximum gap at turn of bilge, lay filler plank into the gap & use a marking gauge set to the plank width to scribe both edges on the filler plank, trim on bandsaw & it will fit well. advantage of this system is you can do a whole stack at once & its fast.
I used to use this system when building cold molded boats.

 

[penfold]

Nothing to do with the available labour; it's double diagonal(and larger boats like minesweepers were triple) because it's partially monocoque/stressed skin, the frame doesn't carry all the loads, an HDML built with a carvel hull would be getting on for twice the weight and would be less stiff, may not even be a viable option due to movement and the extra timber used would not have gone down well with the Ministry of Supply.

 

[Tranona]

On the contrary, planks do need shaping, you cannot fit diagonal planks & edge set them as one edge will ride up & the error becomes cumulative. There are ways round this, either shape one edge as you go & fit next plank to it or cut all planks at a constant width, lay every other one with maximum gap at turn of bilge, lay filler plank into the gap & use a marking gauge set to the plank width to scribe both edges on the filler plank, trim on bandsaw & it will fit well. advantage of this system is you can do a whole stack at once & its fast.
I used to use this system when building cold molded boats.

Correct with round bilge, but these boats are hard chine.

 

[Tranona]

Nothing to do with the available labour; it's double diagonal(and larger boats like minesweepers were triple) because it's partially monocoque/stressed skin, the frame doesn't carry all the loads, an HDML built with a carvel hull would be getting on for twice the weight and would be less stiff, may not even be a viable option due to movement and the extra timber used would not have gone down well with the Ministry of Supply.

Double diagonal (or triple) does have that advantage, but low cost and simplicity of build were drivers as was the use of short planks compared with round bilge.. Hard chine lends itself to simple build by unskilled workers. As you say the hulls were light and boats faster and traditional round bilge would not have achieved the same performance. The logical development was of course the use of plywood for high speed hard chine boats but tht was not available earlier in the war.

 

[penfold]

Plywood was used extensively for frames; prefab of frames and planking by furniture manufacturers to Fairmile's and other designers plans allowed rapid assembly by boatyards with limited machinery.

 

[Birdy60]

HI Birdy, Not Mahogany ? Thats a surprise , what is it ?

Hard to tell from their video but when they were dry scraping it looked like softwood so would guess it could be larch, if they were lucky it might be pitch pine but unlikely, was she built before or during the war does anyone know?

 

[clyst]

Hard to tell from their video but when they were dry scraping it looked like softwood so would guess it could be larch, if they were lucky it might be pitch pine but unlikely, was she built before or during the war does anyone know?

We are told it was involved during D-Day ......... I would have thought some lower value African mahogany or Meranti . Who knows

 

[DownWest]

Hard to tell from their video but when they were dry scraping it looked like softwood so would guess it could be larch, if they were lucky it might be pitch pine but unlikely, was she built before or during the war does anyone know?

Very much doubt pitch pine for diagonal planking.
Since the Restorers are lookjng at this thread, maybe they can enlighten us? It would help in future comments.

 

[Rappey]

Double diagonal was chosen because these boats were put together by non boatbuilding people

The HDML was designed by W J Holt at the Admiralty in early 1939. During the war HDMLs were constructed, mainly by yacht builders.
HDMLs had a round bilge heavy displacement hull .
Most HDML hulls were planked in mahogany, but as the war progressed this became scarce and larch was used, although this tended to lead to leaky hulls. The decks were also of double-diagonal construction and generally made of softwood. Boats operating in tropical waters (including the Mediterranean Sea) were sheathed in copper below the waterline to prevent the attack of marine borers.
Medusa currently has teak Double diagonal decks, not sure if it had them originally.

 

[Keith 66]

Correct with round bilge, but these boats are hard chine.

Hard to tell from their video but when they were dry scraping it looked like softwood so would guess it could be larch, if they were lucky it might be pitch pine but unlikely, was she built before or during the war does anyone know?

Sarinda is round bilge not hard chine.
As for the softwood planking, she has had much remedial work done in the past i suspect the softwood planking is old repairs.

 

[clyst]

Sarinda is round bilge not hard chine.
As for the softwood planking, she has had much remedial work done in the past i suspect the softwood planking is old repairs.

I wonder why they complicated war time builds with round bilges . If thats the case it must have protracted cost in skilled/ semi skilled labour ect and extended build time .

 

[Keith 66]

Back then there were a lot of skilled shipwrights about, at least two yards locally Underwoods at Benfleet & Johnsons & Jago at Leigh built wooden boats for the war effort though you would never guess today from looking at where they churned them out!

 

[Wansworth]

Would the roundbilge builtboats be from pre war designs that within weeks or months as the war carried on hard chine designs were developed to speed up production and employ women in the building.