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Old 03-09-2009, 23:27   #16
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Originally Posted by Ataraxia View Post
any chance you can get me a copy of the article?
PM me your address and I will U.S. Mail you the cut-out pages.

Here's a link to the "Geared Up" system mentioned in the article:
http://www.philbrooks.com/AboutUs/La...Northwest.aspx

and

http://www.gearedupsystems.com/
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Old 04-09-2009, 01:14   #17
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Originally Posted by Eleven View Post
If this is a 'new' installation then electric drive using submersible motors must be worth a quick costing out. It has the advantage of running one engine and both props for chugging along but at most efficient engine revs, and no shafts, gearboxes, rev matching etc.
Domestic power generation will be unlimited too and a dual installation almost guarantees water maker, etc.
It may take a bit more investigation to assess self adjusting props for electrics but lower prop drag when sailing is a big thing on longer trips.
Otheerwise simple one way couplings will rotate two shafts linked together. A forward reverse gear in each shaft could allow boat spinning but would be clumsy to operate.

Well the "quick costing out" proved to be very expensive. the comparaison between two conventional diesel engines and two electrical motors + a huge generator + a set of battery is quickly done. Nevertheless I am 100 % behind the idea, and if I could afford it would defintely go for electrical propulsion. For a multihull it amkes even more sense since you can bring you weights more midship which is better for a cat.
I need to mention that I do not want aircon nor a waterwater maker (they aklways break down) which makes the need of a generator useless.
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Old 04-09-2009, 01:21   #18
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Originally Posted by s/v Jedi View Post
Oh yes, I would investigate diesel-electric drive while building a trawler. This is proven technology with just one catch: your efficiency goes down as compared to diesel drive.

Two electric motors with shafts and propellers and two big gensets.

cheers,
Nick.

Nice but really I can't afford it, just as with solar energy it's the right thing to do and on the long run it might be cheaper but it s a very long run.
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Old 04-09-2009, 01:24   #19
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Originally Posted by lorenzo b View Post
When we were boat shopping we almost bought a Beebe 52 ft passage maker in Portland Oregon and had it hauled and did a sea trial. It had two Perkins engines stacked on top of each other connected by a rubber drive belt of the kind used in earth moving conveyor belts. You could engage either engine or both.The belt was incredibly noisy and the whole set up was awkward and weird. Made for a very strange engine room. The bottom engine was so low in the bilge it would have been a nightmare to work on.
We ended up not buying it because the surveys came back iffy and it had been used as an live aboard for too long without making a passage.
We settled on a single engine, a DD 871, with a reputation for running forever, and a bow thruster for docking.
Thanks very interesting comment I did indeed read about it. glad to know that it was not ideal, due to the specific design of our boat we will definitely go for two engines, 2 x 55 hp, rather than one 110 hp.
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Old 11-09-2009, 06:35   #20
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I can't find it right now, but I read of a guy that used a single engine and two hydraulic motors. A dual engine system would not be that much harder. A few more valves and hoses. Might end up with more money than electric, don't know, but that might be worth costing out, as well. Not sure about power loss as compared to electric.

There was also a guy that did a single engine with wide belts powering two screws. Belt tension and flapping were problems. After fine tuning and adding idlers, it worked well enough. But for various design problems in the boat, he scrapped it.

This evening I'll look for both of these and post them if I find them.

-dan
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Old 11-09-2009, 08:03   #21
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I believe the hydraulic system might be doable in you feel you would need the back up
If you loose an engine it will most likely be fuel related as modern diesels are very reliable. I would put some effort into a redunant fuel system if I were concerned
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Old 14-01-2011, 20:48   #22
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A single engine well protected by the keel and a shoe is what the majority of commercial boats use. KISS principle at work. Just keep the fuel and oil clean and a good old mechanical deisel will run forever.
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Old 14-01-2011, 21:32   #23
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If all you are worrying about is losing power on an ocean crossing, you could deal with this unlikely eventuality by incorporating a mast into the design and having some emergency sails.
Regards, Richard.
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Old 17-11-2012, 03:20   #24
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Re: One Engine Running Two Shafts

Guys,
Is this thread still alive? The original question presents a very interesting challenge. The real issues have more to do with getting the prime mover/movers operating at their thermal efficiency 'sweet spot' and aligning this all at the speed you will most often be running.
Lets go through the knowns:
Simplistically a single shaft will always present the most efficient, largest diameter, slowest speed and minimal drive line losses.
Hybrids sound nice trouble is you will never have enough radiant area to get the solar surface area you need to run at cruise and sometimes you want to run at night!! If your hotel loads approximate your drive power requirements then the equation changes, unlikely in a 50ft!! Works for large luxury ocean cruisers.
Oh were life that simple.

In designing 10/10/10 I started out with a single shaft, when you consider the power speed equation which really goes exponential at about 8knt it means a single engine is never operating at its thermal sweet spot in the 7knt area where most time in practice is spent. In effect any drive line efficiency is rapidly offset by this thermal efficiency loss apart from the long term impact of under loading the engine.
For a given HP in the water is it possible to design a single propeller as the optimal in this class of boats? On the surface - excuse the pun - it appears so. Maybe not. In 10/10/10 to get the propeller efficiency, with the single shaft HP required artificially drives up the draft, with this wetted surface area, therefore more HP per knt, pushes the engine to operate at poor thermal efficiency, during the majority of applications, means the engine sits in the middle of the boat above the sole line and presents internal layout inefficiency (a real advantage of hybrids). Additionally the shaft angle is higher, affecting propeller efficiency, there is limited redundancy and no shaft steering.

In effect when I ran the numbers for 10/10/10 it was more efficient for all speeds to run twin screws/engines outboard of the draft centre line' allowing a horizontal shaft, with a concomitant reduction in draft. A double reduction is required to get a total reduction of 6:1, 2:1 from a curvilinear belt drop shaft to the gearboxes which are 3:1. All this forgets the drive line complexity of actual building and twin shafts come at more than twice the price!!

Shaft speed and propeller diameter (efficiency) dominate the whole equation. Getting 80%+ compared with the average 55% propeller efficiency allows true gestalt in the whole design equation.

Now back to the question. Being able to run in cruise mode turning both shafts from a single engine would provide the absolute best drive line. When considering this in the design, which I rejected, the issue was not the cross connection complexity, modern curvilinear belts can easily handle, it was the fact that to make it work an ability to declutch the non working engine from the drive line was required, and this was the killer in the equation.

With the benefit of hindsight should I have gone with a single offset engine driving two shafts through two separate gearboxes? Small modern, not yet available for marine application, common rail direct injection probably provide a broader 'sweet spot'. Setting aside the loss of redundancy, the clincher in my decision was the need to fit the engines, as low as possible, and the reduction pulley/belt between the frames which are 600mm. The GFC provided at very reasonable price two three cylinder engines combined with the stub shaft they have 20mm clearance between frames. Would it be the perfect world I probably would have gone with a modern CRDI single engine driving both shafts.

Just some thoughts!!
Geoff
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Old 17-11-2012, 05:19   #25
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Re: One Engine Running Two Shafts

Greetings and welcome aboard the CF, Geoff.
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Old 18-11-2012, 02:10   #26
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Re: One Engine Running Two Shafts

Thanks mate,
In the event I could not get the theoretical perfect engine and as the engine was on the critical path reality of production over design elegance kicked in. I failed to mention, in what was an abbreviated discussion on a complex issue, an important precursor to the solution was that early in the design development decision I had decided to go with bilge keels and these formed a logical direction to drive the power train. Hence twin shafts.

Also I omitted the decision to use a slotted shaft with a twin blade carbon fibre propeller driven by a need for both production and hydrodynamic efficiency.

The bilge keels provide the opportunity to 'dry out' in a tidal area and enhanced dynamic stability. Also the initial launch which will be across the beach down the road will be much easier with a hull sitting horizontally on three points, forward on the keel and down aft on the bilge keels.

I am hoping I never have to 'fix it' rather suggesting when 'doing' it is likely that you might reflect on things you might have done better. Suggesting self introspection is always good for the soul.

Hope this helps.
Geoff
PS My old lap top died, about time, just got a new Windows 8 lap top and have not worked out how to attach some pics, this might help the discussion. Just another work in progress.
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Old 18-11-2012, 09:18   #27
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Re: One Engine Running Two Shafts

As a Prout man I applaud your bilge keel choice. It's the right way for cruising.
I would add a mast at the back of the cabin, for mast head lights of course, and radio and maybe radar where height matters. Some basic sail rig would be good for storm and a boost when the wind is right.
Interesting to hear the considered pro's and con's of various systems.
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Old 19-11-2012, 02:49   #28
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Re: One Engine Running Two Shafts

Testing have I attached a photograph
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Old 25-11-2012, 02:08   #29
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Re: One Engine Running Two Shafts

For information. Here are some more pics of the propeller and the moulds used to make the blades.
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