Electric pod drives

[Graham W]

It’s suggested on this webpage, towards the bottom, that a BC26 has been fitted with an ePropulsion electric pod drive https://www.cdtmarine.co.uk/epropulsion-pod-drive/.

That raises a couple of questions: if the BC26 is trailerable (just), how is that reconciled with a pod sticking out of the bottom of the hull?  It may not be a problem on the trailer itself, as it is probably quite far back.  But what about launching and retrieval in shallow water?

And if fitted with an E-175 battery, as suggested, how do they cope with recharging it if they can’t moor at a marina with a reliable electricity supply?  The battery weighs 87kg, so it’s not something that can be tucked under your arm for charging at a friendly local pub. 

Petrol generator?  Solar?  Wind turbine?  Hydrogeneration?  Apart from the first noisy and smelly method, it would take a very long time to recharge.  Full charging from the mains with the fan-cooled 30A charger takes 6 hours. With 100W from a large solar panel it would need around 90 sunlight hours - many days even if you live somewhere sunny.  According to ePropulsion, at 5 knots the Evo version of the pod would hydrogenerate about 200W, needing around 45 hours at that speed to fully charge.

[Sea Simon]

I guess my saildrive is perhaps similar in General Arangement to a pod drive? See photo (shown prop blades off)
Not much margin for error with the trailer! Mine has never been floated on/off, always craned/lifted.
I believe my trailer is almost a ton, empty? Another of CLHs finest...
All else aside I wouldn't  want to be immersing my double axle braked trailer in salt water. Parts are hideously expensive, never mind labour, for four wheel-lines...

But Eprop article is unclear if a pod drive, or more conventional outboard motor type drive is actually fitted. Notably no underwater photos. See screen shot. Can anyone identify this BC 26?
Seems to me, a BC 26 more likely to be fitted with a "Navy" outboard type motor, rather than a Pod?
I have professional experience with propulsion "Pods", much of it NOT positive.

Hydro Regeneration also not clear to me. It appears you need to be sailing at 5 knots to regen? Difficult to imagine how that is consistently  achievable, especially once pod prop is engaged to regen, the additional  drag must be significant? Obviously  it cannot be feathered or lifted, but could  probably freewheel if not in regen?
I'd be hard pushed to motor under diesel power (14 HP) at consistently in excess of 5 knots...certainly  not for 45 hours 

Wrt layout and charging, the best info I've  ever found is the hybrid Romilly site, which I've  mentioned here before.
All is achievable if you've the money...
https://www.roxane-romilly.co.uk/romilly/electric-drive-hybrid
The key seems to be "hybrid"? Gene +regen + solar + plug-in?

I envy the fancy "half timbered" Honda gene! (Perhaps £2K?)
http://www.romilly.nl/integrated-battery-assist.html

...and also some of the waterfront moorings adjacent to beautiful Dutch homes they also show...to plug my hybrid BC in to!

[Nick Orchard]

I hesitate to reply to this as I know of one electric BC26, but it’s not the one in the photo, so perhaps there are now two? The boat in the photo looks like 004 Eliza, which was originally owned by Nick Peters, but he sold it a few years ago. The photo is from a shoot for a magazine review, German I think. The boat that does have an ePropulsion motor is 001 Muddy Waters, but it’s not a pod drive. From memory of a conversation with the owner a couple of years ago I think Sea Simon is right and it’s a Navy 6. It’s mounted on a bracket on the transom that allows it to be lifted vertically clear of the water when sailing (or launching/recovery). It does have a hydrogenerator function, but you need to be going at a reasonable speed to use it. I know the owner was a little concerned that charging issues might affect how he used it, but I haven’t heard how he’s found lt in practice since we last spoke. Perhaps the new owner of Eliza has had the pod drive version fitted? Not sure why you would fit a pod drive if a Navy fits for the reasons already mentioned.

[Rob Johnstone]

It may interest you to know that Lockdown uses the 1kw pod drive. The pod is bolted to an inch thick block of plywood which slides up and down on two 10mm dia stainless steel rods which sit either side of the pod between the motor and the prop.. there's a clearance hole in the bottom of the boat for the pod linked to a slot for the prop. The top ends of the rod are secured to a cross member on the deck and the lower ends are epoxied into blind holes in the Hull. When in the down position  the fore and aft ends of the block butt up against wooden stops which take the thrust of the prop. The assembly is hoisted.by couple of pieces of 8mm braid which is epoxied into the block and secured in the up position by a cleat. Once the hoist ropes are release the assembly.falls to the working position under its own weight. The power cables are secured in a vertical coil to allow for the movement of the pod. I'll see if I can find a photo and post it later.

[Rob Johnstone]

Here's photo of the pod mounted in Lockdown, with the pod in the lowered (e.g. ready to motor position:
https://www.dropbox.com/scl/fi/6g8kcumexvekqbnrl00zk/20210325_122211.jpg?rlkey=5mlt9cljxom4bycxplsngg49t&dl=0

and here's a video of the mounting block moving up and down on the stainless rods. The block has a couple of thick walled delrin tubes epoxied to it which slide along the tubes

https://www.dropbox.com/scl/fi/sojgtusitvecftb9rgxs7/20210325_122402.mp4?rlkey=htjixgqsj8markjaa9lho0muh&dl=0


If you have problem gaining access to these send me an email rob.johnstoneatbtinternet.com and I'll mail you the pix.

[Graham W]

Rob,

I think your pod is basically the same as my eProp Spirit outboard, but without all the bits that get in my way when it’s tilted.  Your pillars are a neat idea and could be adapted for other trailerable boats.  Even better if the mounts could easily be removed for those that want to swap over to petrol outboards every now and then.

The foiling electric speedboat Candela C-8 has a similar idea, except that the pod has to reach down much further into the water when it’s up on its foils.  The result is that at rest, it has a large pinkish pillar sticking up at the back, which looks odd.  Yours for US$400k.

[Graham W]

From memory of a conversation with the owner a couple of years ago I think Sea Simon is right and it’s a Navy 6. It’s mounted on a bracket on the transom that allows it to be lifted vertically clear of the water when sailing (or launching/recovery). It does have a hydrogenerator function, but you need to be going at a reasonable speed to use it.

Nick,

The BC26 in Simon’s screengrab above is quoted as having a 3 rather than a 6, although they’re a bit vague about whether it’s a pod or a Navy outboard.  It probably doesn’t make much difference to the performance measurements that they were interested in.

As Simon has pointed out from his experience with his own unique 26, perhaps launching off slipways for a boat this size isn’t done very often.  Having a pod sticking out of the bottom of the hull may not be such a disadvantage if you mostly lift out, although it would create drag when sailing.  Rob’s idea of having a retractable pod on pillars is an interesting one and as with the BC26 that you know, a standard lifting outboard bracket on the transom could also be adapted for this purpose.

[Rob Johnstone]

Hi Graham,
Thanks for your comments. Originally I used stainless tubes for the slides but they very soon distorted and the unit jammed at half mast. Since switching to rods I've not (yet?) had that problem.
I think the motor is the same as your outboard "lookalike" but in a different casing. I use the spirit outboard battery that sits on a home made mount on the cockpit floor under the tiller. The pod can be controlled by a bluetooth remote control. I originally mounted that in the centre of the boat but recently changed it to be adjacent to the battery.

I find that the prop is quite noisy if left down when under sail and the unit will go into charge mode at low speed (I guess at about 3 knots for Lockdown has no instrumentation at all). It's very quiet under forward power but I think it tends to cavitate when trying to go backwards. I have some thoughts about how to adapt the mounting so that the pod can rotate to change the direction of thrust but, so far, the engineering of it has defeated me. I need to find some way of measuring the force produced by the prop......

Rob J

RobJ

[Graham W]

Maybe something like this might be adapted to work? https://seamarknunn.com/acatalog/Osculati-Sliding-Outboard-Motor-Bracket-EM4737600.html#SID=716

[Sea Simon]

Some interesting  ideas/info here.

Respect Rob, I didn't realise your pod install lifted. Well done!

Regarding drag etc...
on my Twin Disc saildrive, it's minimised by fairing the leg flexible mounting to the hull via a semi watertight, semi sacraficial outer rubber diaphragm. However, the white coloured  sticky-outy bit remains...which of course does not itself turn/rotate. The prop reverses, and the rudders steer...eventually 
Prop drag minimised by locking the drive in reverse when sailing, so forcing the two blade folding prop to streamline. This also protects the mechanical driveline against lube-related failures than can arise during freewheeling/windmilling. This can be a significant issue on larger commercial ships (wet lube bearings), probably irrelevant to electric Pods (at least at this size)?

Pod heading rotation. On larger commercial installs, this gets very complex very quickly...some larger ships have two fixed propulsion units, plus two more steerable "rudder units" in an attempt to overcome issues, and increase reliability/redundancy.
Siemens, etc al. have quite literally tied themselves in knots trying to solve power, and command signal transmissions even to medium size (8MW) Pods via slip rings and radio links. Not problematic on small Pods, but the mounting and thrust transmission  not simple either? This tech much more mature, as common with mechanically driven Pods from Aquamaster, Azipod etc. In the case below, Siemens basically  cribbed the mechanical aspects from Schottel. It didn't really work...


Not sure how much, if any, of this translates to the sort of pod application hereabouts, but..if you've a rainy/windy afternoon to fill have a look at the report of this fiasco involving early permananet magnet motor pods by Siemens:

https://www.gov.uk/maib-reports/loss-of-control-over-the-podded-propulsor-system-of-chemical-and-petroleum-product-tanker-prospero-and-subsequent-contact-with-jetty-at-milford-haven-wales

How about "off n oning" an 8MW pod, to regain control on a ship loaded with dangerous liquid cargoes?

[Graham W]

Watch out Rob!  Prospero, the ship in the accident report in Simon’s link had a pod system that was described as “innovative”.  This resulted in the ship’s pods behaving with a mind of their own, which in turn resulted in Prospero’s dramatic “contact with the jetty”.

It was a long time ago (2006) and I’m sure that systems have improved since then but are you sure that the Russians can’t take control of your wireless throttle?

[Rob Johnstone]

I think it more likely that the Chinese will be taking control, bearing in mind where epropulsion are manufactured!

[Sea Simon]

Control by "bad actors", Perhaps truer than you might initially  think? Although Prospero was "Engineered in Germany", by Siemens-Scottel, it was built in Shanghai....

There are rumours that our "security services" managed  to demonstrate that remote control was possible of one of the very large, electric pod-driven, prestigious cruise ships that frequent Southampton.

These sort of things meant that the electric pod drive systems had to be hurriedly and drastically improved, and "hardened", in terms of both hard and software.

Back to "our world" relevance? Perhaps?
One issue that emerged was, what happens when the pod strikes the ground? It should be "sacraficial", and break off, without the vessel sinking.
Another, what happens to any "waste energy" generated by windmilling Pods going in to regen mode, with nowhere to dump any power that is generated? This is also an issue for electric jack up rigs/self elevating platforms when they are lowering? (Some have large "load banks" to dump waste electricity  as heat).

Fascinating...at least I think it is!