Printable View
Hi,
Can anyone advise what timber I should use to replace the ribs in the pic below, and how can I curve them.
I don't have a steaming machine in back yard. :)
It is only for cosmetic reasons, not structual.
http://i1101.photobucket.com/albums/...ps0aefdf0d.jpg
"Steaming machine" is easy to make. You just need something that makes steam, and a box to hold the steam and the framing stock. You can see one I whipped up in these two posts: here and here.
That one runs out of water in the jug after 15-20 minutes, so is not ideal for doing timber thicker that 7mm or so. Usually you want about an hour of steaming time for every 25mm of thickness.
Solutions:
either have another jug you can boil water in, and then have a tube so you can refill your first jug with water that is already boiling, without interrupting the process, or
use a bigger jug, or something else big that will boil water.
Suitable timbers: Silver Ash (Flindersia schottiana), Sydney Blue Gum (Eucalyptus saligna), Spotted Gum (Eucalyptus maculata), Blackwood (Acacia melanoxylon). Umpteen others too, but these are some of the best. If the boat will be in the weather all the time, probably Spotted Gum or Sydney Blue Gum for their greater rot resistance compared to the other two.
Those ribs are on fairly close centers, so they'll be relatively dainty. I'll guess they're about 3/8" (9 mm) thick by ~1" (25 mm) wide. You probably don't have to steam most of these, but can get them in with just a heat gun. Many will likely just press into place.
When bending ribs in, you should over bend them a little bit, so when they spring back (they will) after being released from clamps, braces, etc., they'll lay down nice and where you want. A block of wood under each end at the rails, will usually be all you need to over bend the ribs. I'd remove every third or 4th rib and replace them wholesale, then skip the next and continue replacing the ones that haven't been. The idea is to leave enough ribs in place so the hull doesn't distort any more then it has (there's quite a bit of distortion there). Once you have 50% of the old ribs replaced and fastened with new ones, you can safely remove the remaining ribs wholesale and replace them, knowing the new ones will hold her shape during the rest of the process.
Green lumber (unseasoned) bends the best. Naturally seasoned bends okay, especially if the moisture content is raised up above 17% - 18% (preferably more). Kiln dried stock is the worst to bend and must be soaked, to lower the breakage percentage to tolerable levels. If you have kiln dried or seasoned stuck, blow 18% moisture content, dig a pit, line with a plastic tarp and fill with water. Toss the stock in it, after it's rip to dimensions and weight it down in the water filled pit. Leave them this way for 24 or more hours, then use the heat gun or steam box on them. These soaked ribs will be much more compliant this way.
James,
I used to think steam boxes were for "serious" boatbuilders, until I had to bend some carlins for a Heron. I saw a lot of lash-ups on utube, some really hairy.
Bunnings sell a Wagner wallpaper steamer for $99. I made a 2.4 m box out of cheap timber, tossed the pipe from the steamer in the top, it reached to the bottom and supported the timber above the condensation. Worked perfectly, and I got some thick gardening gloves from Bunnings too.
Now why was I panicing?
Another option - lamination. In the 1970's we used to build 16' racing skiffs, hand laminate the ribs and frames, then sheath with diagonal veneers. Great to see you putting the effort into restoring the old girl.