What defines an Expedition Yacht?

As KIWI pointed out, Artic P (ex Artic) is a former sister of Lone Ranger (ex Simson). Artic and Oceanic were the last 2 large salvage tugs (total 4) of the older series left in this German Shipping company. A new type of even more powerfull tugs developed and build for that company, is the Nordic class. Attached you will find the particularies of ETV Nordic, just in case some of our members wants to convert her in to a yacht in some 21 years time.

This Tug is on charter by the German government for 21 years as an emergency standby tug in the German Bay. Because the German Bay is one of the highest frequented shipping areas in world, there is always a large salvage tug on standby in that area (24 h a day / 365 days a year). If one tug goes on duty, a second tug takes its place.

So after this charter you can buy it and convert it into a nice yacht.

Info, courtesy of Hamburg Towing and Savage Company.

Here is an example of the propeller and rudder arrangement of Oceanic, one of the 4 large Salvage Tugs. The 4 sisters are (were) Pacific, Oceanic, Artic and Simson. All retired and sold / converted, except Oceanic. She was on "deactivated standby" status at Bremerhaven and for the last time reactivated in 2011, when Nordic was in Dry dock for repair. She was for sale, as far as I know.

Those are some POWERFUL looking props, ...definitely not for a cruising vessel

another Multiplast vessel

Here is a very early concept power cat that Multiplast proposed. I think she was to be a 75' trawler cat. If I remember correctly I saw this model at their factory back in 1985 when I was searching Europe for multihulls to import to USA.

I made reference to such a 'trawler cat' on my website (that REALLY needs updating )
RunningTideYachts, Ltd. Photo Album of Design References Page 16

This was very early thinking (ahead of its time) about power catamarans.

Power Cat

Here is another powercat owned by a good friend of mine down in Fla. I posted a number of photos over here:
http://www.yachtforums.com/forums/123583-post41.html
http://www.yachtforums.com/forums/general-yachting-discussion/15706-new-yachting%3B-13-million-spend-3.html#post123586

She is perhaps to small for you HTM09, but if your were to consider an 80 footer she could be blown up in size. Nice enclosed upper-wheelhouse as well.

If you wanted to 'experience' such a powercat, I'll bet I could get you a ride on her. I'll send you a private message (sent you an email).

There is one other version of a propeller nozzle on the market for quite a long time now but not very well known. Called the Pivotable Rudder Nozzle. On this version, the focus is not on bollard pull, also it is thrust augmentating, her it is a combination of rudder and nozzle with less cavitation and good steering authority by vectoring thrust even at lower speeds. This type of nozzle is excellent for smaller displacement boats and yachts (roamer?). They produce a very small wake and very small prop noise. I have seen them being used on river boats, which regulary work on enviromental sensitive inland water ways and lakes. But they are also usefull on work boats and tugs. The openings in the nozzle are just one variation of this nozzle, in order to minimize recirculation. Below are examples of the principle and of the Dutch company Poseidon and their Pegasus nozzle, used for pleasure boats.

Interesting this thread has evolved into the heavy commercial tug school and the light avant garde multihull school.

I read over Brian's website and found a very interesting fact that I have often thought to myself... heavy displacement hulls tend to have more and uncomfortable motion in heavy seas... and Brian explains the reasons for this.

To me in very heavy seas the light multihull just seems better. Actually I once kayaked (very light single hull) across the English channel about 50-70 miles when I was young in 10-15' seas... in October... part at nighttime in pouring rain... nearing Brittany in the afternoon is was nearly as dark and still pouring. In thinking on the motion... rather be in the kayak in that than a destroyer in 30-40' seas. Heavens had a three week stint of that... could not manage to stand to get near the mess deck... besides at least once a setting it all ended up slammed up the bulkhead... oh, yeah and getting the short straw... replacing the mass head light at night in that mess (both bulbs out)... !

In light seas and moderate seas (only where I will go out purposefully) the heavy displacement feels more solid and the light displacement feels, well the only way I can describe it, is tinny... more jerky vibrations. Particularly multihulls as that is what I am basically referring to in the 'light". So the heavy displacement just feels more secure and the light an a light multihull feels a little insecure and shaky.

Now as to the "problème féminin" and the boat motion. As to that... the single displacement hull and very light weather... no real complaints... anything else and it had better be bolted fast in the berth! That tinny light feel and its the last time... breeze over about 5 knots no-way Jose'.
One time in the large monohull sail boat is too much... "pourquoi est-il de donner un pourboire?" or 'why does it have to be tipped' etc etc any slamming on difficult gybing there might be real fear... and very vengeful unhappy glances directed at you... and a forced trip to early mourning confession!

HTMO9... very interesting.

I happen to know a thing or two from my experience aerospace.
Those annular airfoil shapes are very low drag compared to a conventional wings or rudders as there is not tip vortex phenomena... where the circulation flow around the wing escapes the tip and creates drag by basically creating little tornados pulled along by the wing off its tips... these annular types of wing about 1/2 the drag typically of a convention blade situation.

They are also resistant to flow separations at high angles of attack. But they would not be practical on a high speed yacht! Note... if you looked at attached flow patterns on the ring wing surfaces you would see strong circulating currents on the wing surface at high angles of attack... these can be surprisingly predicted and calculated.

Very interesting not seen this on boats... !

The prop in there really complicates things particularly being at a critical point.... using the annular shapes for rudders without the props inside would still give much the same effect... very high rudder forces!

Oh, I forgot, they are mandatory item on SOLAS life boats or rescue boats if not equipped with outboards or waterjets. Reason: protection of people in the water. Outboards must have a protection ring around the prop.

picture of a Fassmer SOLAS life boat

I was against this prop protection ring on the SOLAS boats... why

You lose your protection from lurking sea monsters...

AND,

makes the boat more crowded for those already in the boat...

What's with the multis... any decent seas would be a worry! The tunnels would be under a lot of stress! In windy conditions you would have to worry about the vessel capsizing as well.

Great for cruising... but exploring the seven seas... you'll need big bulls, huge balls!

Far

Kitchen Rudder

Couldn't these also be referred to as 'kitchen rudders' (Kitchen rudders)
Kitchen rudder - Wikipedia, the free encyclopedia
The Kitchen Rudder is the familiar name for "Kitchen's Patent Reversing Rudders", a combination rudder and directional propulsion delivery system for relatively slow speed displacement boats which was invented in the early 20th century by John G.A.Kitchen of Lancashire, England

It made me think of that name that I was not that familiar with, but remembered that 'strange name', as we think of a kitchen as the galley in a house.

It also made me think of how useful such a system could be on these inland water canal boats of this subject thread I had almost forgotten about. Enjoy some pics and designs over here:
Inland Waterway Cruising; Boats, Barges, etc.

Perhaps you need to do a little more reading on this subject.

1) Multihull Design Considerations for Seaworthiness

2) Catamarans and Waves

3) http://www.wumtia.soton.ac.uk/sites/default/files/1779merged.pdf

4) Stability Part 3
Some years ago the Wolfson Unit at Southampton University conducted some model tests in their wave tank of both a power cat and a conventional deep V power boat to see which was the more stable in waves. People accept that a modern powerboat, like a Princess or Bayliner does not capsize, yet the test showed how EASY it was for a model powerboat to get rolled over by even relatively small waves. In comparison, NOTHING the Wolfson Unit could do would make the powercat capsize! Believe me, they tried everything!

5) http://www.wumtia.soton.ac.uk/about-us/published-papers

All well as long as "theory" matches up with "practice". Bring in the various levels of decision making/helmsmanship in professional and non-professional applications, and this will through a wrench into the theoreticists' world.

I don't buy the historical Fastnet analogy, especially without having multihulls in the race to have a direct comparison. Maybe there are better examples in the current Sydney/Hobart races, are catamarans the prime choice or do they take a back seat to mono-hulls?

I can fully understand your reluctance to accept the multihull as a 'seaworthy' vessel type. It just 'appears' to be more susceptible to being rolled over by a big sea, and in the early days of the sailing types there were a number of capsizes. It has struggled thru this 'non-acceptance' for many years. It is still a 'young technology in the scheme of things.

Even Lock Crowther (a most prolific multihull advocate and designer) was quite surprised at the initial tank testing he did in the breaking wave testing at Southampton. I can't find his original quotes right now.

BTW the catamaran hull form faired much better than the beamy trimaran form.

Not my cup of tea, but certainly focuses on the catamaran stability issue:

Stability Yachts no rocking or jarring movements 365 days a year of pure fun in the sun!!!

"The most stable position of a Cat is upside down"

The method in that picture will only work with a small cat. I know, big cruising cats always have an emergency exit in the salon floor (for save exit, when capsized). But how do you re-erect a large cruising cat, when upside down, lets say in open sea.

If have heart, they flood the forward hulls and re-erect them hadover???????

Sorry Brian, I was just using somebody's joke as a starter.

Honest question: Can you re-erect a capzised large cruising cat in open sea without external help (with some trimming tricks or whatever)????

I would say that the Nordhavns and other trawler like mono-hulls that have crossed oceans (the number has grown quite a bit in the last 10 years) have seen the slopes of many big waves and have met them successfully, with and without stabilization. Roll, hell yes, but no need for innuendo that assumes a different result.

Not disputing the fact that a wide-beam catamaran offers many advantages to roll when in heavy seas, just different strokes for different folks.