High-Speed Pentamaran Yacht

[FAST FRED]

And that there boat lacked a lot in the beauty department

Some would agree the last truly great boats were built in the 1930'S

At least in terms of eye candy and liveabilty .

[BMcF]

Just an observation from someone who has messed about a good bit with some of the earlier "go fast" megayachts that incorporated CODOG or CODAG propulsion systems; The 20V diesels are typically rated around 8.5 MW...so this vessel, apparently a CODOG design, will be spending most of its cruising life with "only" 17 or 18 mw on tap. Seldom are the gas turbines lit off and the very high speed runs made...

And on those rare occasions, that the turbine IS lit, being CODOG that means the maximum power is in the 30mw area.

Still crazy numbers...certainly...but for all practical purposes the yacht is propelled primarily - and most all the time - by less than 20 mw coming from as pair of fairly efficient diesels.

[groper]

Thanks for that BMcF... do you have any other comments as to the probable efficiency of this hull configuration, in particular, 1 pair of airborne sponsons and 1 pair of immersed VS a more typical trimaran configuration?

[BMcF]

Originally Posted by groper

Thanks for that BMcF... do you have any other comments as to the probable efficiency of this hull configuration, in particular, 1 pair of airborne sponsons and 1 pair of immersed VS a more typical trimaran configuration?

I've only dealt directly with trimarans (including foil-assisted versions) and would expect that the resistance of this concept would be in line with those; in my experience, the added drag of randomly/rarely immersed "appendages" is negligible. So too is the added stability negligible, at least as far as motions affecting passenger comfort are concerned.

It looks, at least at first glance, to be a fairly good trimaran arrangement. Having worked with BMT-NG folks on other high-speed projects (not this one, so no dog in the fight), I would expect they have their sums right.

[peterAustralia]

I am not saying that I like it, but I can understand it.

If there was flat water and the boat is going fast, then the amas really only have minimal work to do, they just have to touch the waters surface creating very little drag, should the boat heel then they start providing buoyancy.

Of course flat water is not going to happen a lot. Would I prefer no gap betweent he 2 amas on each side, yes

Another way of doing it would be to have amas that ramp up, have an incline. So when water is flat only the aft few feet of the ama is in the water, should a large wave be encountered or the boat heels more of the ama touches the water.

What they are trying to do is decrease drag in the amas by reducing wetted surface by using small amas. When things get a bit rough much more of the ama comes into play. There is a logic behind it. I dont like the solution they used to apply their logic, but there is some logic nonetheless

[Number4]

I think the idea is that the second phase of the righting moment is further forward, and the load is spread across the hull.
Like the difference between a trike and a car going around a corner.

see page 5 & 6 of this....
http://media.bmt.org/bmt_media/resou...on03-03-05.pdf

[groper]

Originally Posted by BMcF

I've only dealt directly with trimarans (including foil-assisted versions) and would expect that the resistance of this concept would be in line with those; in my experience, the added drag of randomly/rarely immersed "appendages" is negligible. So too is the added stability negligible, at least as far as motions affecting passenger comfort are concerned.

It looks, at least at first glance, to be a fairly good trimaran arrangement. Having worked with BMT-NG folks on other high-speed projects (not this one, so no dog in the fight), I would expect they have their sums right.

I would agree, however im more interested in specifically the difference in sponson aspect ratio this arrangement employs... ie . why cut the sponson in half lengthwise when surely the same stability properties can be had by using a normal trimaran arragement with a longer ama waterline with less draft ie the same ama displacement.

It would seem, that they believe the shorter immersed ama, has better resistance properties, and therefore needed to add a second pair of airborne amas in order to meet heel stability requirements - otherwise why have them at all, its just more unnecessary weight of hull material?

If the short ama had an ideal slenderness ratio of around 25:1 then it makes sense to leave it at that, and suspend further bouyancy clear of the water. However, looking at the renderings (i know it doesn show much) it just doesnt look like the ama is anywhere near an ideal slender body dimension...

And why not rely on reserve ama bouyancy, rather than added appendages?
It just doesnt make sense at all...

[Ad Hoc]

Originally Posted by groper

It just doesnt make sense at all...

It is called satisfying the clients SOR.

[groper]

Originally Posted by Ad Hoc

It is called satisfying the clients SOR.

And the lack of further information or comment, speaks a thousand words... gotta love professional courtesy..

[Ad Hoc]

Originally Posted by groper

And the lack of further information or comment, speaks a thousand words... gotta love professional courtesy..

I take it then when you go into a car show room, you remain silent, and then expect the salesman to knowing exactly what it is you’re after, right down to your taste and budget without uttering a word.

Or conversely, you walk into the same show room and ask for super fast, but also super slow best fuel consumption, fastest accelerating, corners like a train on rails, turns into an all electric hybrid when run out of fuel and can carry 10 friends in comfort with room for a table to play cards and a drinks cabinet, take the hood down in summer, blast furnace heater in winter, cheaper to insure and spare parts that every one has knocking about in their garden shed and cheap as chips to buy...and so on and so on…and the salesman looks at you perplexed and you wonder what’s wrong with your simple request…

[groper]

Nope, you missed it... i meant the professional courtesy youve extended to the designer of this pentamaran....

[kerosene]

could it be that trimaran does not sound that sexy and revolutionary = thus the surfaces need to be broke into two separate pieces to create a "revolutionary" "new" design in the form of a pentamaran?

[daiquiri]

I still do not understand why is it necessary to have two separate and discontinued amas on each side, one submerged behind and one just above the water forward.

A single ama, divided in compartments and with a long bow overhang would imo perform all the required duties (be mostly out of water in calm seas and have a reserve buoyancy in case of damage), plus would make a much smoother resistance curve as it gradually submerges, plus would be much quieter (no wave slapping) when the ship is moored.

See the attached pdf, where shaded areas are simplified ama volume sections. A is an approximation of the actual configuration of this ship, B is the one described above.

[Ad Hoc]

Originally Posted by groper

Nope, you missed it... i meant the professional courtesy youve extended to the designer of this pentamaran....

And where do I suggest that??

[groper]

Originally Posted by Ad Hoc

And where do I suggest that??

If it were an amateur designer that put this idea forward rather than a NA, you would have been all over this like a fly on ***t, the multitude of threads that demonstrates this need not be referenced... But instead, you dont offer anything of any substance regarding this arrangement, good or bad. Professional courtesy implies, if you dont have anything good to say, then dont say anything... i really didnt think i needed to spell it out for you, but there you go...