double planking

[kialoa]

ok
I am restoring an alden ketch (45') originally single planked. I am considering double planking the bottom but have a few questions as to the details.
I know the garboards and perhaps first broads are generally single. after that typical construction might be inner planks of cedar with outer planks of lets say mahogany. do you screw fasten the inner planks to the frames and then the outer planks just to the inner planks or all the way through. Don't builders also use fastenings from the inner plank between frames into the outer plank? and lastly do you need to use something like irish felt and some preservative as a layer between?

[ishmael]

Why? Why are you contemplating double planking?

It's good, when originally applied. The longitudinal ro haw keeps old boats in shape. But I have a hard time imagining it working well as a repair.

Occasionaly someone posts something in this section that goes over my head. This is such a time. I'm not saying you are wrong, but I just don't get it.

[kialoa]

ish
exactly what i was thinking, it does seem to keep a wooden boat in shape. this is not really a repair but an extensive rebuild. new forekeel keel sternpost and knee, new floors frames and interior. most of the bottom planking will be replaced

[Tim B]

Wouldn't adding a layer of planking significantly change the boats weight and therefore sailing trim? I am only familiar with double plank in small racing sailboats (<20ft). The builders of these boats that double planked used plank thicknesses that were about 1/2 of that the builders using single plank used. Are you planning on replanking the whole boat? Replacing the original layer with planks 1/2 the thickness?

[Andrew Craig-Bennett]

This is covered in detail in Nevins' Rules, I think.

Certainly the outer plank fastenings pass into the frames. Garboard single, maybe also first broad. Outer planking thicker than inner.

Only reason I can see for an amateur to do it would be to make each individual strake easier to manhandle. Lighter, and you could probably avoid some steaming. You might be able to get away without a helper.

But it still doubles the man hours needed for the job.

Strictly an American thing, don't know of any British boat built thus.

[Thad Van Gilder]

hm...wasn't the guy who invented double planking british...used it on lifeboats...
I am having a moment. I can't think of his name, but I read the book that he wrote 100 years ago.

-Thad

[Andrew S/Y Rocquette]

ROCQUETTE is double carvel planked. Seams overlap the centre of the underlying planks. Inner layer spruce, outer mahogany, total thickness just under one inch - which is a bit light for a 30.5 foot waterline, 43 foot LOA yacht. All resourcinol glued and bronze-fastened to the frames and I think from memory also fastened in places from the inside skin to the outer with screws (while the glue dried mainly).

As both planking runs are fore-and aft, there were strains where after 40 years the outer planks dried and split along their seams (Med sun!), and therefore split the inner planks. Thus we've routered and splined all these cracks, then veneered three diagonal layers of wood, 2x 45 degrees, final outer fore and aft.

Not sure this would have worked with a traditional carvel hull, as the plank movements would likely set up too many stresses for the veneers to cope with.

[ 01-13-2006, 04:18 AM: Message edited by: Andrew S/Y Rocquette ]

[Andrew Craig-Bennett]

I stand corrected! But I still think that double fore and aft planking is a very unusual construction in Britain.

Certainly double diagonal, or double planking with an innner diagonal layer and an outer fore and aft layer, was extensively used in Britain but more for lifeboats, Naval small craft and police launches than for yachts. In these vessels both skins of planking were often teak, copper fastened to each other with oiled calico between.

[PeterSibley]

Ashcroft system if I remember correctly Thad.

Rocquette , how thick are the diagonal veneer layers? The Carrs did a similar job on "Curlew " in NZ , she was single layer carvel and rough.The result was reportedly very successful.

[Andrew S/Y Rocquette]

The veneers were 3x 1.7 mm, so totalling 5.1 mm (around 1/5 inch)...have a look here (http://www.yacht.ro/frame.php?lang=en&linc=race) at her website for some phots.

Andrew

edited to add for ACB: not aware that this was at all a usual British practice, so think you're very much right. ROCQUETTE was a major departure for Campers and her whole design and build was quite innovative. Suspect their experiences during the war with the type of craft you mention, plus the GELYCE launches going back to the 1920s, plus the flying boats they worked on all contributed to the method.

p.p.s.: Peter - you're restoring the 1924 CE Nicholson ketch I think you've posted about? Please tell me more!

[ 01-13-2006, 08:49 AM: Message edited by: Andrew S/Y Rocquette ]

[Dan McCosh]

I would wonder about the effect of only double-planking below the water line. It would seem to do some odd things to the torsional stiffness of the hull.

[Andrew S/Y Rocquette]

Originally posted by Dan McCosh:
I would wonder about the effect of only double-planking below the water line. It would seem to do some odd things to the torsional stiffness of the hull.Think you're right - it might lead to hard spots on the hull...

[Thad Van Gilder]

Ashcroft... that's it!

[John Gearing]

Check with the guys at McClave, Philbrick, and Giblin down near Noank, Connecticut. You can probably google them successfully. They are the pre-eminent Herreshoff restorers IMHO in the USA and should be quite familiar with double planking as some of N.G.H.'s boats were double-planked (although IIRC, Herreshoff doubled above the W.L. only?). Ed McClave is, in addition to a fine boatbuilder, an extremely competent mechanical engineer who has applied quite a bit of his engineering knowledge to boatbuilding. Plus, they are all really great guys who will most likely help you if you ask them nicely.