DESIGN COMPETITION - converting 97-ton sailboat to electric propulsion

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DESIGN COMPETITION - converting 97-ton sailboat to electric propulsion

International Rescue Group's flagship is a 78-foot LOD (length on deck), 75-foot LWL (waterline length) ketch at 97 tons full displacement vessel. We are hauling her out in Rio Dulce, Guatemala in a month and will remove her old unreliable and uneconomic Volvo 450HP diesel (always stupidly overpowered!) and replace with an electric or diesel-electric hybrid system.

We are a charity run by 100% unpaid volunteers so we don't have much money, but some donations have been earmarked for a refit.  We are not broke, but we are not rolling with cash either and most of the work will be done by volunteers (especially me). Cost is always a major factor, but we do have an IRG T-shirt, IRG cap and lots of public kudos for the design winner, WHOO-HOO!

Please submit your ideas in the COMMENTS below. Here are the design specifications and objectives:

  1. In light air we have determined using hip-towing and outboard motors (small propellers) that 20HP thrust moves the vessel at 1.8kt and with 50HP thrust at 3.5kt which is 84nm per day and quite satisfactory for a blue-water sailboat. In experimenting we find that 20HP is enough to motor-sail in light air. 
  2. In another experiment, in light air we reached 3kt being towed by another 40-foot sailboat with a single 35HP diesel engine at less than full power. Our guess is that if that 35HP was driving our boat alone we would reach 4kt and possibly more.
  3. When power is applied through the single propeller shaft rather than inefficient vectored hip-towing using small propellers, we expect better speed than in the above experiments.
  4. As a charity we do not expend fuel while there is wind. If we cannot make VMG progress due to adverse wind direction we heave-to or anchor rather than burning fuel.
  5. We apply sound seamanship to avoid lee shore or adverse current situations rather than apply raw power and burn fuel.
  6. Power propulsion is generally only required when maneuvering into ports or anchorages, motor-sailing or when on mission making way in light or no wind conditions.
  7. When we remove the Volvo engine and transmission it will open up a 7-foot stand-up almost rectangular engine room of 12 feet wide by 8 feet long and a very deep bilge in the center 4 feet deep by 3 feet wide, 6 feet long which could house a large battery bank keeping weight low.
  8. We have two 240v AC 50Hz single-phase output Northern Lights diesel generators, one is 16kW and the other is 20kW. We use one generator to drive large watermakers for disaster relief missions when at anchor on-site.
  9. The vessel has a large cockpit over which we can install a 2kW solar panel farm. This could be possibly extended to 4kW.

Location: Rio Dulce, Guatemala
Members: 2
Latest Activity: Sep 6

NOTES ON DESIGN SPECIFICATIONS

I am frequently asked why most sailboats of this size have 200HP engines; my logic is that the manufacturer is providing enough power to reach hull speed plus reserve. THIS IS NOT REQUIRED IN OUR APPLICATION.

Discussion Forum

TRADE-OFF ANALYSIS

Started by Captain Ray Thackeray, IRG Sep 5. 0 Replies

I constantly get asked "Why not just replace the existing diesel engine and transmission? Here are the trade-offs:DIESEL-ELECTRICTwo existing generators AC 240vReliableEasy to maintainInstall two AC…Continue

TYPES OF MOTOR

Started by Captain Ray Thackeray, IRG. Last reply by Captain Ray Thackeray, IRG Sep 3. 2 Replies

AC or DC? What options are available? What are the trade-offs? There are so many options and ideas. Used 240v AC electric motors are cheap and could be driven directly off the generators. Similarly…Continue

BATTERY DISCUSSION

Started by Captain Ray Thackeray, IRG. Last reply by Captain Ray Thackeray, IRG Sep 1. 1 Reply

Lead acid, AGM, Lithium-ion oh my.Continue

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Discussion Forum

TRADE-OFF ANALYSIS

Started by Captain Ray Thackeray, IRG Sep 5. 0 Replies

TYPES OF MOTOR

Started by Captain Ray Thackeray, IRG. Last reply by Captain Ray Thackeray, IRG Sep 3. 2 Replies

BATTERY DISCUSSION

Started by Captain Ray Thackeray, IRG. Last reply by Captain Ray Thackeray, IRG Sep 1. 1 Reply

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