17 dead after duck boat sinks at Table Rock Lake near Branson, Missouri


#203

I just received word from Fergal Rogers, the director of Viking Splash Tours in Dublin, Ireland which explains the present situation regarding the approval by DNV GL.

We expect to receive road and marine certification in September of this year with the first vehicle going into service in Dublin in October. It has been a difficult project but the Salamander addresses all the concerns that a regulator may have. The hull design has been approved by DNV GL (Germanischer Lloyd) in Hamburg.


#204

Oh dear God. Are you next going to debate whether a five ounce African swallow can carry a one pound coconut in flight? Even gripped by the husk? Perhaps an empty water bottle attached with duck tape (no pun intended) will help.


#205

I wondered how the 8 sponsons were put on and firmly attached to the vehicle but this picture explains it. They are slid on in a rail like contraption. The signs of heavy use are visible.

The new Dublin bus type version also has sponsons which are stored on land in a kind of recesses on both sides on the top of the bus. I wonder why they have sponsons, as the Rotterdam and Amsterdam buses in service since 2011 and produced locally, do without them. I donot think that they are really necessary as these buses have a very substantial freeboard. Also there is the possibility to put ballast low in the bus to improve the stability as the ‘payload’ is situated higher up in the bus above the water line.


#206

Thanks for posting this. I too was wondering how the sponsons were attached on the ODIN. Any idea if they get locked in placed or are just held by the channel?


#207

Doodle_2018-08-03T12_27_41Z

From the looks of it they are only held in place, after they have been slid in, by the channel guides and then locked in with a vertical pin as shown in the picture. I like simplicity!


#208

I wonder about the “bus” in post A#192, are the sponsons moved manually or somehow flipped by some mechanical means?


#209

Interesting. I’d probably add a keeper chain to prevent the pins from getting lost, but it looks like a very simple and effective system.


#210

Good question. I donot see any vertical rail guidance system. I have asked Fergal Rogers today about why the sponsons. In my next e-mail to him I will add your question because I am also curious.


#211

Substantial freeboard does not necessarily mean good stability. The sponsons, if near or in the water when deployed, will add stability.


#212

IMG_2903

The effect of beam and freeboard on stability.

Let the draft, KG, and the beam, remain unchanged, but let the freeboard be increased. An increase in freeboard has no effect on the stability of the vessel up to the angle of heel at which the original deck edge became immersed, but beyond this angle of heel all of the righting levers will be increased in length. This is represented by curve C.

If the beam is increased by sponsons the effect in the same manner is shown by curve B.

With increased Freeboard:

  • GMT and GZ increase.
  • Range of stability increases.
  • Deck edge immerses later at greater ϕ.
  • KB decreases and BM increases.

With increased Beam.

  • GMT and GZ increase.
  • Range of stability increases.
  • Deck edge immerses earlier.
  • KB remains similar.

#213

Curve D would show the effect of enclosing empty water bottles within the hull.


#214

The area under the GZ curve is the amount of righting energy available to right the vessel.

The angle of heel at max GZ is the vessel maximum heel before capsize.

Increased freeboard will increase the amount of reserve buoyancy which means the vessel can take on more water and still remain afloat.

The vessel represented by curve C has the most righting energy, an ability to heel further without capsize and greater reserver buoyancy.


#215

Doodle_2018-08-03T17_05_07Z

Curve D shows the effect of enclosing empty water bottles within the hull.


#216

And here I’ve been harping on the crew to crush the empty water bottles down to reduce the space they take up as plastic waste! Should have been stuffing rose boxes and voids all this time! :drooling_face:


#217

Absolutely, and I guess the point is that these new amphibs were designed from the beginning with the increased freeboard. I suppose you could design add-on “freeboard increasers” (coamings I guess?) for the DUKW. Note the “Odin” DUKW you pictured has raised side panels above the deck but they end partway back and there are open gratings in the stern which defeat them as full coamings. These gratings are not part of the original design, which has a tailgate-like panel carrying the coamings all the way around.


Note also that the sponsons, if installed below the normal waterline, will not only increase the beam but also increase the freeboard. The picture of “Odin” afloat shows the bow sponsons out of the water but the stern sponsons slightly submerged.


#218

I think it almost impossible to increase the freeboard on a Dukw substantially without interfering with the passengers comfort and safety but sponsons are a good means to increase the stability.

Having the sponsons under the water line will increase the water resistance considerably. It is no coincedence that the sponsons are fitted above the water line. The speed is already low, 5 knots, but will go back to something like 2 or 3 knots. A tour will take ages then.


#219

You’re on to something. Crush them before stuffing them in the voids. The increased number of bottles should make the vessel practically unsinkable.:wink:


#220

The WAFI Handbook 2nd Edition suggests that a dinghy will benefit more if you make sure the cap is on tightly before crushing them. That way the air inside will be compressed and will provide even more cargo capacity and higher freeboard than a flat but weightless empty bottle.


#221

Back in 1916 the NTSB wanted a new Duck boat weight standard because of the Americans’ growing girth and proposed to raise it from 150 lbs per person to 185 lbs, that is 83.9 kg. I donot know whether this new weight standard was ever implemented and/or maintained since then.

What it means is that with a maximum payload of 2300 kg only 27 persons, 25 passengers and 2 crew, with an average weight of 83.9 kg each are allowed on board instead of the 31 persons that were loaded on the Branson Dukw. This comes down to an extra weight of 336 kg rather high up above the water line. As a result the boat will be sitting a couple of cm’s deeper in the water.


#222

This incident resembles others that we have disscussed. Chipping away at the margins, a couple cm on the freeboard, a couple on the aisle width, a relatively rare weather event, a recent change in management, maybe an operator with less then average skills.

I wonder about the CG weather limts, 35 kts and 2 foot seas. In hindsight that seems too high. I’d say the craft should be able to survive in twice the limit at least. In this case it looks 70 kts and 4 foot seas is too much. Limits of 18 kts and 1 foot seas make more sense.