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Saturday, October 27, 2012

Burmese Long-Tails

In our last post we looked at Paul Wilson's photos of Philippine bancas. This time we'll view Paul's images of longboats from Myanmar. (I've always heard such boats referred to as "long-tails," but it appears that both terms are in common use.)

Here's Paul's description:
The Myanmar (Burma) photos were pre-digital scans of some photos I took while working/touring there in 1999 or 2000.  The photos are of longboats in Inle Lake in central Burma.  I was interested in the articulated drive mechanism.  Unlike the longboats in Thailand, the engine is stationary with a universal joint at the transom.  The pipe in the wash from the prop is for water cooling to the engine. Very simple and effective.  I loved these boats and their chug, chug, chug with their big Chinese diesels.  The long bow allows them to extend out over the shore for easy loading and unloading at the market. 
Much more here: http://en.wikipedia.org/wiki/Inle_Lake 
I don't have any photos of them but the leg rowers of Inle Lake are fascinating so give them a google if you haven't seen them before.
http://www.youtube.com/watch?v=dmSYpWIzidYhttp://www.youtube.com/watch?v=gpScZKmDkLo
I agree. This leg rowing is fascinating stuff.

It's plank-on-frame construction, but I'd bet money that it's shell-first. Substantial ceiling or floorboards allow cargo to remain dry and possibly protects the planking from damage. Interesting to see a shiny new engine in a boat type that probably dates back centuries. (Click any image to enlarge.)
A rubber hose connects to the front of the water intake pipe and curves over the massive transom. By pushing down on the tiller, the driveshaft and prop can be raised. The gunwales extend far beyond the transom: I'd like to know the reason for this. 
Steering combines the forces of directed thrust (i.e. changing the angle of the prop, as on a sterndrive) and  the rudder just ahead of the prop. These steering systems don't look cobbled together: someone is clearly manufacturing them to a standard pattern.
With numbers like this, it's clearly an economically practical design that suits the needs of the society.

In contrast, Thai longtails mount the engine right on the transom, atop a pivot. This is mechanically simpler, in that it eliminates the universal joint for the driveshaft. It has a substantial downside, though: placing the weight of the engine entirely on the transom must make the boat very stern-heavy. It also orients the prop shaft at a downward angle, which reduces propulsion efficiency. To minimize this problem, the shaft is very long (making the angle shallower), but this "solution" compounds the problem of a long, awkward extension behind the stern. The Burmese arrangement, with its horizontal prop shaft, is shorter and inherently more efficient.
Thai longtail. (Source: Kellerna, via Wikipedia)
Thanks again to Paul Wilson for the Myanmar photos.

8 comments:

  1. The leg rowing thing is remarkable. I trust the tourists give them something for their performances!

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  2. Gav,
    I believe they're not doing this for the tourists: it's just the way they fish. I really don't know how they'd react to a "tip," but I'm picturing how a Gloucester or New Bedford (Massachusetts) fisherman would react if you too a picture of them working and then offered them a tip. A beer? Maybe. But I think they'd be offended by any implication that they're "scenic".

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  3. Dear Paul,

    its an interesting read, would you know anyone who knows from where to buy these engines and propulsion system used on burmese long tail boats.

    would request for your help.

    regards,
    Jitendra Rami
    rami@westcoastmarine.co.in
    +919820369980
    Mumbai, India

    ReplyDelete
  4. Even though the above comment is spam (it's from an Indian brokerage that specializes in ultra-high-end yachts, and the commenter's intention is clearly just to get a link on this blog -- too bad for him), it did cause me to do a little Googling, and I found: 1) this superb article on how to build your own longtail: http://longtailboats.webs.com/apps/blog/entries/show/5452276-the-long-tail-motor,
    and 2) the interesting fact that longtail engines are commercially available in the U.S.. Here are a couple suppliers: http://www.mudbuddy.com/opencart/index.php?route=common/home
    http://www.explorebeavertail.com/mudmotors.html

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  5. Hi, my name is Ronald, I am a marine engineer and I work on container ships. I am intrigued by the shaft mechanism on the Burmese boats. I assume that the shaft from the engine protrudes from the stern through a "stern tube", and from there a universal joint connects another shaft which bears the rudder and propeller assembly? Does this mean that the universal joint is immersed in seawater, and is not lubricated? Also, how do you know that the Burmese solution is more efficient, since it uses a universal joint in the shafting system while the Thai long-tail does not?

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  6. Hi Ronald. From the photos, it does appear that the primary output shaft passes through a stern tube. This seems to be fairly high on the transom, and it looks like the universal joint is above the waterline, although this could change if the boat were heavy-laden. I don't know about lubrication of the universal, but I wouldn't be surprised if they just slap a handful of wheel bearing grease on it every now and then.
    I also don't know whether the Burmese or Thai system is more efficient overall. In favor of the Burmese method is the straighter shaft angle and the more centered placement of the engine's weight which would lend toward better hull trim. On the Thai side is the absence of an energy-robbing universal joint. I don't know which of these factors would be greater. (On the Burmese boats, however, it looks like the final drive shaft and the primary output shaft would be in fairly straight alignment when the boat is traveling straight ahead, so the universal wouldn't rob much power under those circumstances.)

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  7. Hi my name is Brian, just back in the UK from Myanmar and a few days on Inle Lake. I am curious to know the function of the twin tubes in an H shape on the top of every longtail mechanism I saw, regardless of age, tourist or working boat. Must say we enjoyed barrelling along as tourists on the open water, and also just chugging through the villages.

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  8. Brian: In the third photo, it looks like the upper tube faces forward at its aft end, and the lower tube faces aft, and that both of them have hoses on their front ends that lead to the engine. I'm not sure, but guess is that the upper tube is cooling water intake, and lower tube is cooling water exhaust.

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