Pod Drives for Displacement Superyachts

[Willallison]

I've noticed that a couple of the more recent Mega-Yachts have been fitted with ABB Azipods, but these are all in the 70+ metre class.
Are nthere smaller pod-drives - either diesel electric systems or "direct drives" like the ZF / CMD/ Volvo units - that are designed for smaller displacament craft. I'm thinking in the 40 - 50 metre range, but would be interested in infor on units for smaller vessels as well.
The only stuff that seems to be around is either very small (like the Mastervolt ones) or very large (like the aforementioned ABB ones)

[Ad Hoc]

Will

Funnily enough, we're doing a design with a Volvo IPS drive, smaller 20m boat.
http://www.volvopenta.com/volvopenta...ine_range.aspx

They range from 250 to 850kW

[Willallison]

Yes - they've really taken off in the planing and even semi-displacement segments, but there's precious little out there, or so it would seem, for displacement installations.
Of course, the gains aren't there in terms of drag, but there are other advantages... worth a look if nothing else...

[MechaNik]

Hang on, what am I missing here? I thought there were a lot of options on pods for displacement craft in that size range. Just how little power are you thinking of using and the potential speed range?
ABB only go as low as 1MW but they are proactive in yacht supply and offer complete solutions.
Rolls Royce have a huge diversity of solutions with pods ranging from even lower power ratings to the ridiculous side.
I believe there are other suppliers out there too.

Schottel provides a range of pods, which is not very surprising, did they develop the principle some decades ago.
But the reason that we don´t see pods on smaller yachts is simply that those boats are thought to go remote places and owners like to keep draught as low as possible. (Bermuda restriction)
Just my 2C of course.

Regards
Richard

[MechaNik]

Yes how to forget that originators so quickly and a pretty full range too.
However they do promote their drives for restricted draft. I would think it pertains only to the counter rotating twin prop units vs a conventional single screw?

[Willallison]

Thanks Gents... just the sort of links I was after...
Richard... not sure why the draft would be any different to a conventional shaft installation... both would be dictated by the diameter of the prop(s), which would in turn surely be determined by the needs of the particular vessel...? I could well imagine that the pod systems would be limited by the model range of the manufacturers though... but that's just the sort of info I'm looking for.
The downside of course is that they can be vulnerable to damage... and very difficult and expensive to repair... just the same problems as with the CMD / IPS / ZF units...
In terms of power... I would expect that we are looking for the equivalent of a pair of 700 shp shafts... speed is up to 15 knots and displacement probaly around 280 tonnes... all approx

Originally Posted by Willallison

Thanks Gents... just the sort of links I was after...
Richard... not sure why the draft would be any different to a conventional shaft installation... both would be dictated by the diameter of the prop(s), which would in turn surely be determined by the needs of the particular vessel...? I could well imagine that the pod systems would be limited by the model range of the manufacturers though... but that's just the sort of info I'm looking for.
The downside of course is that they can be vulnerable to damage... and very difficult and expensive to repair... just the same problems as with the CMD / IPS / ZF units...
In terms of power... I would expect that we are looking for the equivalent of a pair of 700 shp shafts... speed is up to 15 knots and displacement probaly around 280 tonnes... all approx

Well Will, ........Pun intended

it is not possible to install a pod drive of equivalent power at the same draught of a conventional drive. That was the answer.
All the tricky and finicky snakeoil solutions have at least ONE disadvantage over the prop / shaft design. Commonly one thinks about hull "pockets" of some sort. A idioty.
You are the NA, I am just a boatbuilding clown, get the theories together yourself, its easy. The last leg of the "Z" is the gear, and that is always below a prop shaft level of a conventional.

No pods on yachts.....

Well, my 2c only, of course.
Regards
Richard

[MechaNik]

Will, the first and only pod drive Superyacht I have been on was in about 2002. It was Alumercia from Heesen and it may make a good reference for your project should you continue on that route.
I remember thinking at the time that this must be they way superyachts will go, and surely systems will be better adapted for them. Alas time has proven me wrong and there are still many negatives to pods. Have you seen what they weigh? For a lighter displacement boat as you suggest they may pose more problems than thought of.
If you went to diesel electric they might make more sense, but DE doesn't make sense to me on a yacht either.

[MechaNik]

Actually if your looking for something different why not investigate Voith schneider propellers. They are looking at superyachts to use their full motion control system, for zero speed and under way plus D.P using the main drive.
It would make more sense if you came down on your top speed, but since when have super yachts made sense?

[Ad Hoc]

Originally Posted by apex1

All the tricky and finicky snakeoil solutions have at least ONE disadvantage over the prop / shaft design.

Indeed they do.

But, if the design, with pods, satisfies the performance and costs issues and the client wants it....why flog a dead horse. You give what s/he wants.

If the units do not meet the performance and costs requirements, then it is a no brainer.

It is certainly not a common sight....doesn't mean one can't do it..if the Will is there...pun intended

[Mat-C]

Originally Posted by apex1

Well Will, ........Pun intended

it is not possible to install a pod drive of equivalent power at the same draught of a conventional drive. That was the answer.
All the tricky and finicky snakeoil solutions have at least ONE disadvantage over the prop / shaft design. Commonly one thinks about hull "pockets" of some sort. A idioty.
You are the NA, I am just a boatbuilding clown, get the theories together yourself, its easy. The last leg of the "Z" is the gear, and that is always below a prop shaft level of a conventional.

No pods on yachts.....

Well, my 2c only, of course.
Regards
Richard

Willallison may be an NA, but I'm not... could someone please tell me what this one disadvantage is? The Pod installtions that I've seen - IPS and Zeus certainly haven't suffered from excessive draft - they look much the same as shaft drives to me...???

[powerabout]

Broward built a few 100 footers with pods a few years ago

[Willallison]

I've been looking into these units a little further. Both Schottel and RR have units that might be suitable.... thanks again for the suggestions.
Draft certainly doesn't appear to be excessive, unless you go for the largest diameter props... in which case the same problem would arise with conventional shaft(s).
As MechaNik correctly pointed out, weight could be more of an issue... the serious commercial units weigh in the vacinity of 5 tonnes, though in the context of a quite large vessel this can almost certainly be accomodated.
Don't get me wrong... I'm not trying to make the case for pods in yachts... but it is the task of the designer to examine all the options... that's all I'm doing at this stage.

Powerabout... I think the Broward installations were for higher speed applications weren't they?

Once again... thanks for the RR & Scottel leads... if there are any others that might make sense, please let me know...

[MechaNik]

Steerprop is one that supplied a lot of data for a conference I went on for Dynamic positioning. They made some pretty big claims from real life tests using their CRP units compared against open props. Mechanically a CRP pod is more sound than a single blade because of opposing forces in the gear drive. CRP is really what has brought pods back into the light as it is easier to achieve than on a normal shaft.