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Old 21-10-2016, 07:06   #1
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Retractable Rotating Saildrive?

It's an idle fantasy, as I'm pretty sure such a thing does NOT exist, but why don't we have retractable saildrives? Better, rotating ones?

The advantages for sailing would be so great, especially for catamarans.

I'm thinking about my next boat and still struggling with the second diesel engine.

How cool would it be, if the second diesel engine could do three different functions:

1. Generator
2. Donkey engine/backup/alternative propulsion
3. Vectored thrust/stern thruster for docking.


A roughly 20hp engine would be just right for all of this, for the roughly 60' boat I'm planning.

My mind rebels at the thought of having a second diesel engine which does nothing but drive a generator, like I have now. Poor use of resources.

A 20 to 25hp engine with about 8 to 10kW of DC generating capacity would be just the thing to rapidly charge a large LiFePo bank, and the engine would be well loaded in the middle of its RPM range.

20 to 25hp would be ok for a donkey engine for a roughly 23 tonne boat. Donkey engine not just for backup, but also for slow economical motoring in calm conditions, where the oversized main engine (150hp) would be operating below its best power output range.

I try to always sail, rather than motor upwind (and have worked hard to get my boat capable of doing that efficiently), so most of my motoring hours in my present boat are in dead calms and glassy seas, where I only need a fraction of the main engine's 100 horsepower, probably like 10. Often running it at 1500 -- 1600 RPM, which is suboptimal for an engine with peak power at 3900 RPM. It would be great to be using a smaller donkey engine for that.

A stern thruster is not essential for docking (I can move my boat sideways with just a bow thruster), but the more control you have, the better. It would make lots of docking situations feasible or safe, which would be risky or unfeasible without it.

An alternative might be to use a rotating electric saildrive and just drive it from the same DC generator which I use to produce electrical power. Does such a thing exist? Would be somewhat less efficient than a mechanically driven one, but might be much simpler and more feasible mechanically.
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Old 21-10-2016, 08:43   #2
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Re: Retractable Rotating Saildrive?

Letter (email) I recently sent to several firns in Europe tha are developing systems, and/or have some current small scale systems that work.



info@fischerpanda.de,
usa@oceanvolt.com,
mikko.hämäläinen@oceanvolt.com,
info@vetus.com
Dear Sirs,
I am working on a design for a 35-40 foot catamaran that I term a picnic/weekender catamaran. The concept will be somewhat similar to this one I found in Thailand a few years ago. I posted it on several boating forums a few years ago.
Weekender/Picnic PowerCat - General Catamaran Discussion | YachtForums: We Know Big Boats!





This particular catamaran was a powercat. I will be adding a sailing rig to it. I will also adding a trolling/fishing chair area to rear deck area,... so that pictured Zodiac dinghy will be relocated, and the two outboard engines need to be eliminated.

I need to repower this cat design, both for close quarters docking situations, and for some motor/sailing situations.
I have had a very long time interest in the rim-drive propulsion concept.
Rim Driven Propellers - Technical Discussion | YachtForums: We Know Big Boats!
What I have in mind at this moment is how I might adapt this to be my single primary propulsion propeller. I would like to mount it in the aft portion of a of the wingdeck of the vessel, and make it steerable upon demand, and also retractable when sailing. Naturally it requires an electrical supply, which as I understand it under present technology can come from a combination of battery power and a relatively small DE power plant. This power plant would be located in its own insulated (heat and sound) box up on the flat deck of the catamaran.

So here are a list of questions I have at the moment:

1) Can such a rim-drive propulsor be run continuous without overheating? It is my understanding that the Vetus unit can do that now.

2) Whether it is the Vetus rim-drive, or another electric drive motor, is it possible to operate such a 'DE system' with very little battery supplements?

3) How few batteries are required (in the interest to keep added weight down) ?

4) Is it possible to 'direct drive' this 'electric prop' with the DE power plant, or are batteries required.

5) I realize Vetus has its own DE power plant, but it appears that FisherPanda has an even greater selection of small DE power plants. Can these systems be mixed?

7) Should the Vetus rimdrive prove not powerful enough, what are the other alternatives that anyone would suggest??


As an example of why I might be considering this approach, I will offer this personal experience of mine. I was the original importer to the USA of French catamaran line,... the original model was a 37 foot boat called the Louisiane 37. I placed a 9,9 hp Yamaha 4 stroke Hi-Thrust outboard engine on it. It was a limited production outboard they made with an extra gear reduction in the output prop shaft so it could turn a bigger propeller. It worked pretty good as we got 7 knots out of the vessel in calm conditions. The engine was mounted in the center on a rear beam of the vessel, and soft lines were lead from the engine to the rudder arms so when docking the engine would steer along with the rudders. Maneuverability was VERY good. It made me a believer in 'steerable engine', verses twins,...an alternative to consider.





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Old 21-10-2016, 09:16   #3
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Re: Retractable Rotating Saildrive?

Put a big Minn Kota motor in you rudder ALA Hanse, and run it off of that 8 to 10 KW generator?

Its not done because of weight, expense and complexity and the amount of room it would take inside of the boat when you retracted the Azipod
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Old 21-10-2016, 09:28   #4
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Re: Retractable Rotating Saildrive?

There was a company making retractable leg saildrives. Were used on early cats with one engine in the center instead of one in each hull. I forget the name.
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Old 21-10-2016, 09:40   #5
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Re: Retractable Rotating Saildrive?

Quote:
Originally Posted by Cheechako View Post
There was a company making retractable leg saildrives. Were used on early cats with one engine in the center instead of one in each hull. I forget the name.
I remember those. But they swung up like an outdrive, IIRC.

I need something which would retract up into the hull, like a retractable bow thruster.

It might really need to be electric. This will kill the efficient calm weather motoring function because of the losses in the double conversion from mechanical to electrical and back to mechanical power. But greatly simplifies the task.

The same system can be used, maybe a smaller one, for a bow thruster. My present bow thruster is 10 horsepower and could be a little stronger.

That is actually very appealing. Run it directly from the DC generator which will be much easier on the electrical system.

So this looks a little different -- a retractable stern thruster which can be rotated and used as an electric drive. Obviously would have to be continuous duty rated, not like normal thrusters.
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Old 21-10-2016, 09:51   #6
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Re: Retractable Rotating Saildrive?

Quote:
Originally Posted by Dockhead View Post
It might really need to be electric. This will kill the efficient calm weather motoring function because of the losses in the double conversion from mechanical to electrical and back to mechanical power. But greatly simplifies the task.
It might not be as bad as you think, but why DC? High Voltage AC would be more efficient I would think. Hybrid cars electric motors are in the hundreds of volts I think.
I wonder what type and voltage the Azipods are run off of?
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Old 21-10-2016, 09:53   #7
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Re: Retractable Rotating Saildrive?

I found this on a Google search, Seems Hybrid electric is more efficient?

The podded design typically achieved a 9% better fuel efficiency than the conventional propulsion system when it was first installed in the 1990s. Improvements to the conventional design have shrunk the gap to 6%-8%, but on the other hand the hydrodynamic flow around the Azipod has been improved by fin retrofits and a dynamic computer optimization of the respective operating angles of the pods in multipod installations, yielding overall efficiency improvements now in the range of 18%.[4]
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Old 21-10-2016, 09:55   #8
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Re: Retractable Rotating Saildrive?

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Originally Posted by a64pilot View Post
It might not be as bad as you think, but why DC? High Voltage AC would be more efficient I would think. Hybrid cars electric motors are in the hundreds of volts I think.
I wonder what type and voltage the Azipods are run off of?
Yes, just ask Tesla or Edison!
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Old 21-10-2016, 10:10   #9
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Re: Retractable Rotating Saildrive?

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Originally Posted by a64pilot View Post
Put a big Minn Kota motor in you rudder ALA Hanse, and run it off of that 8 to 10 KW generator?
This. Seeing the video of the maneuverability of the Hanse with the motor in the rudder showed that it was indeed a very interesting idea.

The sheer amount of stuff that could break on a fully retractable saildrive would scare me. (Of course saltwater leaking into an electric-motor rudder is scary too)
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Old 21-10-2016, 10:14   #10
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Re: Retractable Rotating Saildrive?

Quote:
Originally Posted by a64pilot View Post
I found this on a Google search, Seems Hybrid electric is more efficient?

The podded design typically achieved a 9% better fuel efficiency than the conventional propulsion system when it was first installed in the 1990s. Improvements to the conventional design have shrunk the gap to 6%-8%, but on the other hand the hydrodynamic flow around the Azipod has been improved by fin retrofits and a dynamic computer optimization of the respective operating angles of the pods in multipod installations, yielding overall efficiency improvements now in the range of 18%.[4]
Well, you will have losses in the double conversion. You will have to make them up somewhere else, to get an efficiency gain. I bet they're counting gains from running engines at constant efficient speed and other things which won't be applicable here.

My next boat will definitely not be big enough for Azi Pods . My name is not Abramovich
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Old 21-10-2016, 10:14   #11
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Re: Retractable Rotating Saildrive?

The Minn Kota motor in a rudder ought to be able to be a generator too, if you chose to not go with a folding prop
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Old 21-10-2016, 10:17   #12
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Re: Retractable Rotating Saildrive?

Quote:
Originally Posted by a64pilot View Post
The Minn Kota motor in a rudder ought to be able to be a generator too, if you chose to not go with a folding prop
I'll have a spade rudder, and definitely won't want the drag of a fixed prop, or preferably any second prop or drive leg, which is why I wanted it to be retracting.

The main drive system will be a shaft drive with a Hundested manually variably pitch prop.
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Old 21-10-2016, 10:25   #13
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Re: Retractable Rotating Saildrive?

I did stumble across a retractable, ROTATING thruster:

OYS | Hydraulic 360 degree Vertical Retracting Thrusters from Ocean Yacht Systems - world leading suppliers of thruster and control systems to the superyacht and high performance yachting market.


It's hydraulic, and the smallest size is 33hp, which is a bit too large for me. But very much the right idea.

I remember now riding on small island ferries in Finland, propelled by small rotating hydraulically driven pods.

So there is some existing technology here.
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Old 21-10-2016, 10:37   #14
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Re: Retractable Rotating Saildrive?

Now this looks like exactly the thing!!!

Baltic Yachts introduce a retractable propulsion system! - Ocean Of News

Apparently made by Hundested!
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Old 21-10-2016, 10:47   #15
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Re: Retractable Rotating Saildrive?

Are you building a custom design? magnetohydrodynamic drive with closing bow and stern tubes!
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