restoring a traditionally built boat it is important to replace parts
of the structure of a similar size to those that are being replaced or
missing. Those sizes are termed "scantlings"|
The dominant source of this type of information for traditionally built workboats in Australia is the USL Code. It would probably be OK for traditionally built workboats in other parts of the world.
Here I give a bit of a spiel about what it is and how to use it.
There are different codes applicable to traditionally built sailboats. Common ones there are Herreshoff's rules or Nevin's rules. Or for modern boats the ABS (American Bureau of Shipping) code.
Here were some fellows restoring a 35ft Sydney harbour ferry.
Originally Posted by darrenyorston
I am not sure how thick the deck is however there are a couple other areas where I can see the thickness and I would say either 6 or 8mm. Could be different though as they are on a different part of the deck.
That sounds WAY to0 thin - would expect 3/4 or thicker ply or even thicker planks for a boat this size.
Despite the archaic nature of the document the USL code will give you a lot of info regarding the minimum dimensions of different parts.
the last paragraph mentions a downloadable copy - click that link - you have to enter some details to gain access but it is free. Go down the list to "Wood"
Open the document and go straight to the tables. Note that they often give alternatives of using either timber planking or ply for different parts. Read the notes under each table carefully before using its contents.
It will give the right sizes for a trawler - but will be to heavy for a yacht or light motorboat.
The thinness of the decks may indicate that some of the work was done by people who didn't know what they were doing - so I would suggest doing some study so that you know how things should be done in this style of boat. (Rabl's book on Wooden Boat Construction would be a good start - also the one by Bud McIntosh).
It also might call into question the knowledge of the surveyor - if he didn't notice the decks were only 6 or 8mm - yet suggested that you go ahead and repair them. He really should have realised that they were too thin. Check the USL code above - I think you will find that they should be around 3/4" ply or thicker for your length of boat.
There are some short cuts if you use epoxy - but get the West Systems "Guide to wooden boat restoration and repair" - it will set you back about $10 but will show how to repair ribs etc without upsetting the existing structure.
I probably wouldn't suggest going the whole epoxy hog with your boat - but if you put down a properly engineeered ply deck and substructure all glued together with epoxy then any upper works etc could also be modern epoxy/timber construction.