Riveted blocks inside clinker hull?

[Anastasia]

In exploring my hull and thinking about what work this novice should embark upon this winter, I found something I haven't yet read about yet. Maybe you folks can help me figure this out.

Inside the hull of this antique 17 ft clinker, I notice wooden blocks riveted to the planks. On the outside of the hull where these blocks are straight cracks in the paint where two pieces of wood joined are together. A couple of the planks are cracked and likely in need of repair.

This boat was made in Norway in the 70s. I wonder what this joinery practice is? Could the wood just be butted up to one another rather than having scarf joints?

Like I said I am a novice and don't have much money to spend. I would prefer to do the work on the boat myself with the help of my family. I understand that clinkers are difficult to repair, but I am naive and brave... a dangerous combination. Maybe you can help tame my daringness.

Thanks for your consideration!

[landlocked sailor]

Those are probably butt blocks, just like in carvel construction. Repair of clinker boats is not an onscure art. Walt Simmonds is an old master and his books are a great place to start. Look at http://www.duck-trap.com/repairs.html ,Rick

[Thad]

They are "butt blocks", but they probably back short scarfs riveted through the block.

[nedL]

Butt blocks are 100% normal & standard practice, even in 17' lapstrake boats. When you don't have planks long enough to go from stem to stern in one piece you use them where the two plank lengths meet. They are not at all necessarily a sign of repair work. Typically there is no tapered scarf there, just 90 degree cuts at the end of each plank. (If you use a tapered scarf then you don't use butt blocks - usually). Nothing wrong with having them in your boat.

[ishmael]

What the others said. Though lapstrake is typically scarfed and either riveted(older construction) or glued, butt blocks aren't unheard of.

Here's a question, does anyone know why butt blocks are typical in carvel planking and scarfs in lapstrake?

[rbgarr]

Sometimes you'll see yachts, particularly those finished bright, that have full length planks. It's more expensive and difficult to build, because handling a very long plank takes more people, but looks better when varnished, especially as planking ages and water intrudes (often at first) at plank ends and at buttb locks and shows as darker spots.

The reason IMO you see butt blocks on carvel boats, but not lapstrake, is that on the inside of a carvel planked boat the butt block overlaps the plank above and below the planks butted. This strengthens the joint by preventing the butted planks from springing out of the fair curve of the hull. BTW, in some locales, work boats have wider and sometimes thinner frames: to butt and fasten planks to with out having to go the extra step of making and fitting butt blocks.

In a lapstrake boat, a butt block would be too complicated a carving to do that effectively (if the butted planks were cut off at 90 degrees), so the scarfing technique is an easier way to do it in the long run. Another advantage is that a fastening can go through the laps and scarf on the top and bottom of the scarfed plank, giving it more support and holding the feathered edges together.

[ 09-19-2003, 10:57 AM: Message edited by: rbgarr ]

[Alan D. Hyde]

All the joints in strakes on Chris-Craft Sea Skiffs were joined by butt blocks.

These are well-designed and well-regarded rough water lapstrake boats, strong but light-weight for their size.

I'm not aware of anything wrong with the technique, as they used it.

Alan

[Keith Wilson]

Yep, butt blocks. I'm now in the process of replacing both sheerstrakes on my Townie (17' lapstrake daysailer) because serious rot started in the exposed end grain at the butts. In fact, the starboard sheerstrake had two butts! Well, in 1964 they were trying to compete with fiberglass boats and were, shall we say, economical to a fault in quite a few areas. :( Keep 'em well sealed.

[nedL]

On the Jersey shore (where lapstrake botbuilding reigned for over a hundres years) I knew of only one builder that used scarfed joints. Square plank ends & butt blocks is how it was done.
Butt blocks are actually easier on lapstrake construction than on carvel. Lapstrake planks are not 'backed out' on the inside as on carvel planks, so there is no need to contour the mating surface of a lapstrake butt block.

Take a close look & you can see them on this 1951 Ulrichsen skiff being rebuilt after hurricane damage. All the butts are original & none were added during the rebuild.
http://www.imagestation.com/picture/sraid16/pfdd3e6d2eba1c9d2b0c157ad3cd3df72/fdf21df4.jpg

[ 09-19-2003, 12:58 PM: Message edited by: nedL ]

[Anastasia]

Hey, thanks. I did not know there was so much to learn about butt blocks on clinkers.