Lapstrake Scantlings

[AWolfe]

Hi,

Long time lurker, first time poster. Here's my question: Are there any published scantling rules for traditional lapstrake construction? Riveted plank lapstrake has certainly been in use in work boats in the era of certification bodies.

I'm also interested in details of boats from the last few hundred years. I've come across the work of a swedish fellow who has taken lines off of many traditional craft (sadly with no scantling or fastening info), among a few others. Traditional rules of thumb? Directions to look? Magic formulae? Wild guesses!?

Thanks!

[Raggi_Thor]

Det Norske Veritas, www.dnv.com, published in 1970
"Rules for the Building and Classification of Wooden Vessels."
It costs 150NOK or approx 25USD.
I am afraid these rules are meant for larger crafts like fishing vessels.

The swedish fellow willprobably tell you the scantlings if you ask.

Wild guesses:
The thinnest plank thickness I can imagine for pine or spruce is abut 9mm or 3/8 inch. This is used in the smallest, lightest rowing boats around here, 14 feet weighing 90kg (170lbs?). Frames are about 2-3 feet apart and approx 2x4 inches solid timber. Light crafts from England has been made of 6mm (1/4 inc) mahogany with very light steamed oak frames.

Rule of thumb for light crafts?
Minimum 9mm planking for a 4m boat, increase by 1mm per meter LOA.
Minimum 3/8 planking for 14 feet boat, increase by 1/72 inch per feet LOA.

[CDBarry]

1983 DnV Small craft rules also have wooden scantlings.

[PAR]

General rules and scantlings for these type of hulls are dependant on several factors all requiring a more specifically defined requirement.

In other words, the planking can be thinner if closely spaced framing is used, thinner stock can be used if the planking is plywood, rather then solid stock. The type of structure used and method of fastening can effect choices used in the scantlings also.

Each designer, manufacture and builder of lapped hulls have developed techniques and strategies to address the issues that crop up in the process.

Lyman built many styles of lapped hull, using clenched plywood over closely spaced bent frames. Thompson did also, but chose to bolt the planks and tossed in wider spacing on the bent and also used sawn frames. Chris craft did similar, a number of companies elected to use roves, rather then clenches or bolts. A few outfits used all sawn frames. Some manufactures used varnish in the laps, others polyurethane, some butt blocks others scarfs. Traditional scarfs were fastened others just relied on the adhesive.

Each attempting to address the issues common to this construction method(s) Now epoxy as changed the game and a new form of lap hull, the glued lap is rising up, especially in small craft. The use has a lot to do with the construction of any vessel. A lightly built racer can't be used in comparison with an Alaskan trader, so it's difficult to suggest a general rule or set of guide lines that may apply to all the various forms of lap construction, without a more refined idea of it's needs and use.

[AWolfe]

Thanks for the feedback everyone. I'll see if I can find copies of those rules.

I'm looking for more information along the lines of what Raggi_Thor provided, observations or anecdotes indicating some sort of baseline in common practice.

Let's take a hypthetical case. 16 feet LWL. Double ended (form roughly following a snipa). 8 strakes per side. Oak keel, oak frames. Pine or spruce planking (or consider oak planking if you like). Fastened with rivet and rove - maybe 11 ga or thereabouts. One rivet every 6 inches lets say. Planks riveted through the frames. Caulked with tar and fiber in a groove.

Let's take two displacement cases. In the first, an unballasted rowing or light sailing hull of perhaps 600 pounds (with say two crew). In the second, a ballasted sailing hull displacing upwards of 1000 pounds.

So ballparking off of Raggi_Thor's comments, how far amiss would I be with the following:

First case: 1/2" planking. Frames every 18". Frames 2 x 2 1/2". Keel 2 1/2 x 4" stock.

Second case: 3/4" planking. Frames every 12". Frames 2 x 2 1/2". Keel 3 x 4" stock.

Looking for ballparks, observations on current or traditional practice, thoughts, comments, voodoo, etc.

Thanks!

[PAR]

There's a big difference between pine or spruce planking then oak.

I have a design here by John Brooks about the size you've asked and it is 1/4" plywood planking over sawn half frames on the topsides, using glued lap construction. Certainly would make a better sailor then a heavily planked, thinly spaced, heavily framed hull you've suggested. I also feel your rivet spacing is too wide, especially with materials that will move as much as this stuff will. I also wouldn't use the caulking as suggested, but rather rely on good mating surfaces and bedding compound or even varnish if you want real traditional.

How about 8" centers of 5/8" x 3/4" bent farming with 3/8" ply planks (1/2" garboards, maybe the whole bottom) having rivets on 2" centers below the waterline (3 each frame bay) and 2 5/8" centers above the waterline (2 per frame bay) for your ballasted sail hull. Use polyurethane in the seams instead of tar and cord, better yet, epoxy the seams and forget the roves and rivets and a bunch of the framing as well.

The light rowing craft you've described will not be light. I've seen light rowing hulls with 1/4" glued ply planking, which is half the spec you've supplied. Traditional light craft were sort of light, but didn't last long. Current materials and methods can produce a long lived light weight hull. Frankly, any 16' craft intended for ballasted sail or unballasted row doesn't need 3/4" solid stock planking.

Lets take a look at a traditional lap hull LFH's Carpenter, the tender to Walrus. She's little bigger then you want, but at 16' 3" on the water, close enough, 4'6" of beam and empty draws 5" Frame spacing is 7 1/2" and are 5/8" x 7/8" oak, using 3/8" cedar planking with 2 rivets per frame bay. Again half the dimensions you envision. This boat is designed to carry quite a load and handle rough conditions. He used a plank keel of 1 3/8" thick cypress that carried a 1/16" bronze plate shoe full width. She carries a cat ketch or cat rig has a small weighted board and has small, covered, lifeboat style decks fore and aft.

I have a design that is a bit smaller at 12' but the scantlings are 1/2" x 5/8" oak frames on 6" centers, 5/16" cedar planking, plank keel 5/4th's stock, 7/8" centerboard and rudder, 2 rivets per bay.

What are you attempting to do?

[Raggi_Thor]

"Traditional light craft were sort of light, but didn't last long." ?
It is true that the typical light double-enders that I mentioned didn't last long as workboats around 1900, mostly because of no upkeep or treatment (oil, varnish) at all. However there are still some 100 year old boats around. Thanks to better care and penetrating oils they now seem to last forever.

More modern example:
The norwegian "Grimstadjolle" designed by Sam Berge in 1943 has proven to be strong enough to last for some decades. MAny boats wehere built in the fifties and sixties.
The hull planking is 12mm (1/2 inch) pine with bent frames of oak 26x35mm (1 by 1 1/2) placed approx 350mm (14 inches) apart.
LOA 17.5 feet, outside ballast is approx 170kg iron, sail area 10m2.

[AWolfe]

What I'm trying to do? I'm trying to build a "sense" of lapstrake. I've got a feeling of what's "right" with plywood & fiberglass, some sense of what's right with carvel, some sense of strip construction, etc. But with lapstrake, the published materials are few and far between (compared to more contemporary materials), and the people that engage in traditional style clinker building are also more thinly scattered - and plans with construction details are also a little harder to come by.

I thought I would pick the collective brain around here, as there seems to be some experience and knowledge present.

Incidentally, I've been checkout out the Nordic Folkboat minimum scantlings as specified in the type rules. Yet another take on slightly more contemporary lapstrake.

[PAR]

I didn't mean to offend, AWolfe, just asking. I tend to like the lighter side of lap construction, personally thinking it's the only reason to chose the method. Lap construction can provide a light weight watertight hull with the added benefit of the nicely lined off laps looking very nice. It's not the fastest method, nor the easiest, but is well loved and with some current applications in materials and techniques, very dry and long lived. With the additional fore and aft stiffening added by the laps, very good for trailered boat construction. Again, purely personally I think, any heavily planked and framed lap design would be better served in carvel.

On hand I have the scantlings of a few dozen small and medium sized lapped craft of different configurations, all showing frame spacing, planking type and thickness, etc.

John Brooks does a class at the WoodenBoat School, Brooklin, ME, he does glued lap, but may have some sources that may be of help to you.

[Raggi_Thor]

There is a common problem with bent frames that brake in traditional lapstrake hulls. The clinkered/clenched strakes has no transverse bending moment so the frames has to take it all.

The Folkboat is lighter than the newer (grp) IF-boat, isn't it?
I think glued lapstrake in plywood is a very nice method.
One possibility today is to have all the strakes cut on a cnc router. In 1993 I had to do a lot of programming in AutoLISP (AutoCAD) to unfolf the 3D strakes to 2D patterns, now it's done rightaway in Rhino 3D :-)

[PAR]

Of the traditional types of wooden construction, lapped hulls have great longitudinal strength, the method permits very thin planking, very good resistance to vibration, can shrink and swell without leaking, requires no caulking and can afford very light weight framing. It also is hard to repair and demands very good workmanship from an experienced builder.

Any lightly framed craft, be it lap or other wise will suffer from broken bent frames, plus a bit of broken other things as well. Light construction is just that, it's durability isn't the design priority lightness is. Some of these older craft have survived, but likely through uncommonly good care or luck.

Building a lap hull in any other fashion, doesn't suit the method as well as it would others methods.

Batten-seam also provides very good longitudinal strength and vibration resistance, no caulking needed, very thin planking and is leak free. It also has special framing which is heavier, is difficult to repair and is costly to construct.

Carvel requires heavier framing and planking then lap, needs caulking, produces a smooth hull, is easy to repair and is generally liked by most builders from a cost and ease in building view point.

Strip planking is easy to build, requires few if any frames, no caulking necessary,is leak free, also very strong and inexpensive. It also is very heavy, difficult to repair and requires thicker planking then the other methods.

There are many types of planking variations, all having their good points and bad. My only point is, lapstrake planking is the strongest of the types when light weight is considered well up on the design criteria list. Building with heavier then necessary planking would be better served living on a carvel hull or other type, where it's bulk can be of some advantage in the design.

The two design's I listed on a previous post here, clearly show the lapstake's ability to work with seemingly ridiculously thin planking. The L. Francis Herreshoff design was drawn up in the 1930's the other the 1990's, both showing what can and should be done with lap construction. No additional advantage can be gained by increasing the planking thickness. The boat will just be heavier then it needs be and will perform like it.

[rxcomposite]

Lloyds Register of shipping used to have Rules and method of construction for wooden boats. I think it is obsolete publication but you can inquire from them.

I have a copy of the 1981 publication.

[Dutch Peter]

Originally Posted by rxcomposite

Lloyds Register of shipping used to have Rules and method of construction for wooden boats. I think it is obsolete publication but you can inquire from them.

I have a copy of the 1981 publication.

RX, I think you mean the LR Yachts and Small Craft Rules. These indeed include rules for wood constructions. Hang on to that copy, the rules are not printed anymore!!

[PAR]

The typical Lloyds spec scantlings for lap hulls produced heavier then necessary craft. They had to insure them, so error on the heavy side was a simple business decision.

[rxcomposite]

Dutch Peter,

Yes it is. It says Rules and Regulations for Yachts and Small Crafts. As i look closer, the print says May 1979 for the hull construction.

I have the new Rules. Its named "Classification of Special Service Craft".