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Old 29-07-2010, 22:09   #1
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Viking Longship Design ?

While sitting here at the computer, I had the discovery channel on. They were discussing the advantages the Vikings had that allowed them to do what they did.
One of which was the over lapping planks creating a seam that traps/drags air under the boat, cutting down on friction.
They claimed 16 knots under sail in a replica with the square rigged single sail on an 80 foot boat.
BS, or fact?
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Old 29-07-2010, 22:28   #2
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I don't know if the Viking design used lapstrake planking or not. What I do know is that I had a lapstake planked 12 foot sailing dinghy when I was a kid and it sailed far faster than any of the other boats the kids and adults were using at the time. It was a lot more sea kindly as well.

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Old 29-07-2010, 22:35   #3
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Lapstrake is a beautiful thing.
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Old 29-07-2010, 22:49   #4
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When we crossed the Pacific, we met a viking longboat called Bifrost. The owner got the design from a museum where his father was a museum employee. He built the longboat and went sailing with a square sail. He claimed it was extremely fast. But then he claimed many other things, and I am not sure whether his claims held any water.

His long boat floated extremely well in Suva harbor.
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Old 29-07-2010, 22:49   #5
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So the design actually functions to increase speed?
Is there a known formula for the over lap to produce this effect?
They were using around 1 inch thick planking with what looked like a pretty heavy overlap.
Sixteen knots with that sail in weather that boat was built sounds impressive.
I was listening and not really watching. They put it against a 27 footer with the same amount of sail and the 27 footer passed it near the final mark.
Not much of a direct comparison, but still impressive for the time period it comes from.
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Old 30-07-2010, 00:44   #6
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The Longships were faster than anything else in their time, I know that much.

They had shallow draft, no external ballast, longwaterlines (narrow type hull) and a lot of sail area in a low aspect rigging. They were also relatively light-weight due to quite thin planking and frames.

In fact the hulls were extremely flexible, so all in all they were quite 'modern' in many ways.

And they had an another advantage of course, in a calm they had a large, strong crew to propel the boat with loooong oars!

So, compared to later shipbuilding, let's say in the midieval times, they were way before their time.

In Scandinavia , esp. in the north one could still see similar hulls,not too long ago, but a lot smaller, used as river boats. The Same people (Lapponia) used them.

I wonder where the Vikings got their inspirations and ideas from, since as far as I know, in their time they were far ahead of anyone else in ship desing and -building
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Old 30-07-2010, 02:21   #7
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Assuming an 80' longboat has 8% in overhangs (a reasonable assumsion) her LWL is 73.6, which we'll round to 74. Her typical S/L would be in the 1.3 to 1.4 range, placing her displacement mode speed at 11.18 to 12.04 knots. Since we know they used substantial beam/length ratios, commonly about 5:1, we can expect a much better S/L ratio. At 1.7 S/L (another fairly reasonable assumsion) her speed jumps to 14.62 knots. This is likely about what she can do, unless substantial under the 5:1 beam/length average. Some more assuming that she is and is an 80' boat with a 13' 4" beam (damn that's narrow folks) she would likely muster over the 1.8 S/L barrier and scream along at 15.48, which is close enough for a GPS to blink 16 knots occasionally.

The image attached shows a 80' x 16' and 80' x 13' 4" longboat, both having the same plan form and 74' LWL. Though possible the 13. 4" beam version doesn't seem as likely a candidate as the 16' beam version, if for no other reason then not enough internal volume for gear, crew and supplies. Though the longboats were "lean" they did carry some beam into the ends of the boat, particularly aft (as shown in the sketch) to have "bearing area" and cargo capacity.

In short, the folks talking about their 80' longboat doing 16 knots may be possible, but it's not especially likely, maybe skidding off the tops of swells she'd blast past 16.

Also testing has shown that lapped planking is at a disadvantage against smooth skinned hulls of the same shape, in side by side comparisons. Now, this has raised the hair on many lapstrake fans, who think they're "riding on a bunch of bubble ball bearings", but the sad reality is they're also generating more drag with the laps plowing on the forward ends of the planks and generating vortices off their trailing aft edges.

Those that know me understand I've designed, built and repaired many lapstrake hulls. It's my favorite planking type, but it has no advantage over the same hull shape done smooth. Now, they do roll with less "frequency" then a smooth hull, as the laps do act as longitudinal flaps against this motion, but it's a minor consideration, unless you always sail in a beam sea.

If you contact me privately (email, IM, etc.) I can offer some lines for typical longboats.
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Old 30-07-2010, 02:45   #8
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Quote:
Originally Posted by PAR View Post
Also testing has shown that lapped planking is at a disadvantage against smooth skinned hulls of the same shape, in side by side comparisons. Now, this has raised the hair on many lapstrake fans, who think they're "riding on a bunch of bubble ball bearings", but the sad reality is they're also generating more drag with the laps plowing on the forward ends of the planks and generating vortices off their trailing aft edges.

Those that know me understand I've designed, built and repaired many lapstrake hulls. It's my favorite planking type, but it has no advantage over the same hull shape done smooth. Now, they do roll with less "frequency" then a smooth hull, as the laps do act as longitudinal flaps against this motion, but it's a minor consideration, unless you always sail in a beam sea.

If you contact me privately (email, IM, etc.) I can offer some lines for typical longboats.

Interesting information, thanks for sharing.

The lapstrakes, or klinker as we call them in Sweden, do cause turbulence in the water and thus drag, thats correct.

A klinker built Folkboat(for example) is SO much more beautiful than carvel/smooth ones though...IMHO
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Old 30-07-2010, 02:54   #9
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A planing powerboat hull uses the same idea. By having groves which allow air to be pulled in, the planing hull can reach the planing step easier and quicker than a standard hull.

The air helps to break the cohesion of water and hull
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Old 30-07-2010, 09:47   #10
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Quote:
Originally Posted by Ahnlaashock View Post
While sitting here at the computer, I had the discovery channel on. They were discussing the advantages the Vikings had that allowed them to do what they did.
One of which was the over lapping planks creating a seam that traps/drags air under the boat, cutting down on friction.
They claimed 16 knots under sail in a replica with the square rigged single sail on an 80 foot boat.
BS, or fact?
Being American TV I'd guess they just messed up the units . 16 km/h would be about 8.6 kts which actually is too slow.

The number ought to be around 11 kts given the standard 1.34 multiplier for a displacement hull (taking wags at dwl length and beam). The beam to length ratio doesn't seem small enough to make the multiplier 2.0 but maybe it is.

Planing klinker-built boats do indeed leave a bubbling wake, almost like a carpet of bubbles right behind. With a 100 Norse warriors (apparently a fairly standard complement !) rowing I guess they might have been able to get up on a plane with favorable wind and waves but the replica was probably manned by modern wimps who weren't rowing for their lives.

Ormen Långe was about 165 feet long and would probably have been a sight to see. I think that was the "mother of all" long ships.

Something that I find surprising is that the longboats could apparently be sailed against the wind with their square-rigged sails.


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Old 30-07-2010, 11:46   #11
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If I recall correctly, the fastest 24 hour run in a reconstructed longship is about 223 miles in 24 hours, thus an average speed of 9.3kts or so. A reconstruction of the very light Gotstadt ship attained a speed of ten to eleven knots.

There were a number of differing types, based on the number of rowing benches in the Gulaþing Law: the karvi with 6-16 pairs of oars, the snekkja with 20 pairs of oars, the skei with 30 oar pairs, and the enormous busse with 34 paired oars.

The skei types were generally few in number and presumably the ships of prominent jarls and kings, and the busse were atypical and appeared in the later viking-age dynastic wars. The snekkja type was the most common of the longships built for raiding and wars. In general, the length to beam aspect ratio was 6 or 7:1 in the excavated examples of most known finds, while the huge Hedeby longship (30 pairs of oars) had a ratio of 11.4:1.

As to sailing into the wind, or at least very close to it, this was possible due to the innovation of shaping poles (beitass) which could be rigged to sockets in the deck and points on the edges of the sail to shape the sail when sailing close to the wind.
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Old 30-07-2010, 13:23   #12
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Saw the same thing years ago, probably the same show. The first time anyone recreated a full size longship, they did indeed find that the lapstrake design caused "bubble injection" which is banned by most modern racing rules because it makes hulls faster and could cause some very expensive r&d programs.

So yes, the longships do that and yes it works. Odds are the Vikings had no idea this was happening, or if they did, it wasn't why they started using lapstrake construction. Wood was a scarce and sacred (literally) commodity for them. The designs probably evolved from "this is what my father did" combined with the technology, tools, and resources they had. Remember, things like metal fasteners would have been even more expensive. Somewhere on this planet, someone has tried every possible way to build a boat. What worked--got built more often.

With their penchant for sacking and burning ("Viking" is after all a verb!) it is little wonder that the rest of the world didn't spend a lot of time recording the wonders of Norse innovation and technology. If they'd had any desire for conquest--as opposed to plunder--we'd probably all be drinking meade out of skulls and horns by now, or else serving them up to our masters.
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Old 30-07-2010, 13:34   #13
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With their penchant for sacking and burning ("Viking" is after all a verb!)
Most vikings were traders. Viking horns are a Hollywood myth.

Not sure where you got the idea that Viking is a verb unless your reference is the humor site: Viking - Encyclopedia Dramatica

Keeping the record straighter to defend our ancestors' reputations




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Old 30-07-2010, 14:29   #14
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The first time anyone recreated a full size longship, they did indeed find that the lapstrake design caused "bubble injection" which is banned by most modern racing rules because it makes hulls faster and could cause some very expensive r&d programs.
Absolutely ridiculous. Testing has clearly born this out and one must remember that air is less dense, therefore less buoyant then water against the hull, so the boat actually settles deeper, increasing wetted surface, frictional and parasitic drag, etc. I was one of those nut jobs, that actually drilled a few thousand holes in the hull of a production daysailor in the late 1960's, in an attempt to prove this theory. Of course, I was just as wrong back then too, but I was also young and didn't have a few engineering degrees yet, to help understand it all.

Anjou, the steps on a stepped powerboat face the opposite direction then they do on a lapstrake hull and they are oriented perpendicular to the plank runs seen on lapstrake hulls. Lapstrake powerboat hulls sometimes have the bottom planks lapped in the opposite direction to help with flow separation at speed. It looks a little weird, but it's an effective method to improve top speed.

No longboat has ever planned unless we've grossly misjudged the hull shaped employed. We know they used boats with 5:1 or better beam/length ratios, which makes them efficient rowing and sailing machines. For them to plane off, they would have to sacrifice this efficiency and flatten out the buttocks quite a bit. All examples uncovered have shown fairly steep buttock angles, so they couldn't plane without an atomic reactor aboard.

If they crested a swell and skidded down it's face, the boat would momentarily surf, but it's stern would dig in like a plow and she'd stop really quickly, once the sea leveled out a touch. This isn't plane mode, this is falling (literally) or skidding (literally) and gravity is doing the work, not hull shape or S/L potential.

Yes, beam/length ratios in excess of 5:1 will force you to toss the 1.35 S/L ratio formula out the window as the physics just stop applying. This is why multi hulls easily crush this theoretical threshold. Sharpie hulls (typically 6:1) have proven this for considerably longer then our understanding of Viking longboat shapes. Sailing canoes and other craft have also born this fundamental flaw out of the LWL limited speed restraint.

The basic problem with the longboat is her aft sections lack bearing area to keep her stern afloat at these (and above) speeds and their buttock angles prevent clean separation, so a suction is created, which pulls the stern down into her own wake. 1.7 S/L would be a reasonable limit, which places her fairly bow up at 14.62 knots in our hypothetical 80' longboat above. She couldn't sustain these speeds for long, but she could "burst" out every so often, when the sea state and conditions permitted.
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Old 30-07-2010, 14:51   #15
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Yes, ive seen the steps which are cut across the water flow direction. Roughly one third aft of the bow.
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