Replying to all discussions in this single post... thanks, guys!
Steve:
Hi Steve. I have a very high performance Kurt Hughes cruising catamaran which has no engines at all. To give you an idea of the type, it's just like a Gunboat 48. Very similar numbers. It's a blank canvas. Brand new build... which is the reason I'm considering the electric propulsion. There are major advantages to being able to support massive HVAC loads easily if already producing power to move the boat.
My wife and I do charters for a living and this is our new charter boat. We run a professional galley in the "crew hull" and serve 3 gourmet meals per day, plus snacks. Our guests also run hair dryers, we microwave and guest comfort (massive HVAC systems) is a top priority.
We charter in North America and the Caribbean. I've consecutively owned a boat for the past 20+ years and have lived aboard full time since the early 2000's when we started chartering. So "world cruising" with extra demands for charter guests is probably the best way to sum up the usage.
Budget? I'd have to say no more than a typical diesel installation. Same cost as installing a pair of Yanmar 3YM30's and a genset. That would be my maximum budget. That means the packaged products are not in my price range. If I go electric, I have to build it myself using industrial components, not overpriced marine stuff.
I actually agree with those naysayers... sorry! :) Performance is my top consideration here. My goal is to have props clear of the water when sailing. It makes a huge difference... a coupe knots... having no props there. A couple knots is nothing at 20 knots, but it's quite a big deal at 6 knots. My main goals for going electric are:
1) Having props clear of the water when not in use
2) Producing enough electricity to run HVAC - for instance, shut down one side's propulsion and send the extra energy into HVAC.
Ken:
I'm not sure what you're suggesting. Were you suggesting a pair of 4HP Parsuns? I had looked at taking two pairs of Torqueedo 9.9's and that wasn't enough. Aren't the Parsuns less strong? Forgive me if I'm not understanding. I'm still learning the electric propulsion stuff.
Carter:
I was hoping to size the electric motors such that they produce the same amount of power as the pair of 30HP Yanmars would. My usage of the boat is detailed above. That was my original question... how to find electric motors that would have the same rating as a given HP diesel engine.
A detail I should have mentioned from the start is that I am looking at a diesel electric system only. No massive battery banks, as the cat needs to be kept on a diet. The *only* reasons I'm looking at diesel electric are:
1) It's a way to have props out of the water when not in use. Outboards are also another way and that way is on the table too. I'm trying to evaluate if outboards, custom inboards that have retractable props, or diesel electric is the way to go. That is the purpose of my posting here.
2) We have massive HVAC and house loads. We need a large power generator in general, so stealing some from propulsion to power house loads is attractive, so diesel electric might make sense there.
--- In electricboats@yahoogroups.com, Steve Dolan <sdolan@...> wrote:
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> Sean,
> What make, model and drive system (sail or shaft)is your cat and do you have a budget in mind? How are you going to use the Cat? Puttering around, Coastal, or World cruising?
> I have the Solomons Technology system with what was known then as the twin 74's motors:
>
> Power output 9 kw
> Torque 74 lb-ft (100 N-m)
> Voltage 144 vdc
> Max, current draw 64 amp
> Weight 144 lb (65 kg)
> Width at bracket bolt holes 16.5 in (419 mm)
> Width at motor mount centers 20 in (508 mm)
> Length, casing 14 in (356 mm)
> Length with shaft 18 in (457 mm)
> Max. prop diameter* 18 in (457 mm)
> Max. displacement 16 t (14.5 mt)
> Max. monohull length** 45 ft (13.7 m)
> Max. catamaran length** 52 ft (15.8 m)
>
> Each side is really 2 motors bolted together and offer redundency, they can operate on 1/2 of the system.
>
> I'm not a fan of the "POD" systems on this size boat, to many things can go wrong and typicaly this size boat tends to go out in "bigger" stuff adding loads that could damage components hanging down there. There is a boat (Green Motion) that does have a retractablepod system, I believe in the 50' range. Most of the naysayers out there seem to be WAY overly concerned about drag for some reason and the possible loss of 1/2 to 1 knot of speed having a prop under the boat. I never understood this, don't most ICE boats have one of them under there? I regenerate power anytime the boat is moving above 3 knots and it really kicks in at around 8 knots. If I retracted a pod I would get nothing back plus I have know idea what the difference is between 6 and 6 1/2 knots is nor do I care. I would rather have the free charging.
> I do know a guy selling a DEMO system (Alex) for a good price if your interested in Florida. He probably could be talked into helping on the install as well. BUT the systems aren't cheap. Let me know if your interested an I can put you 2 in touch.
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> Steve in Solomons MD
> Lagoon 410 SE
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> Hi Sean,
>
> There are two different rules of thumb for converting ICE to electric drive. The first is based on the HP of the existing engines. Typically, you can convert HP at 2.5-3HP ICE to 1HP electric. Using this conversion, each of your 30HP engines can be replaced with 10-12HP motors or 7.5 to 9kW drives. (1HP = 750W). The problem is that this conversion is dependent on how well the IC engines were sized to your boat.
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> Alternatively, most displacement boats typically require 1kW for each ton of displacement. So using that conversion your 9 ton boat would need 9kW of total drive to power at 95% of regular hull speed. However, your catamaran desn't act just like a regular displacement monohull, and cats typically have more windage than a monohull of similar displacement, so your power requirements will probably be higher.
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> So while I believe that 9kW is too little for your boat, you should get safe propulsion to reasonable speeds with 15-18kW of electric drive as listed in the first paragraph.
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> Hopefully Steve, a member here with an all electric 41' cat, will weigh in with specifics about his boat, I think that you would see similar results with similar drive units.
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> I believe that pods look good onthe design board, but some pod owners have reported problems with pods that are submerged 24/7. Many successful electric conversion have been done with inboard style drives, retractable outboards or drive legs have also worked well. I'm not saying that pods are inherently bad, but they haven't built a solid reputation to date. Properly designed and executed pods might be able to change that perception, but the cost might be higher than some of the regular electric drive conversions.
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> Welcome to the group!
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> Fair winds,
> Eric
> Marina del Rey, CA
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> --- In electricboats@yahoogroups.com, "seansullivanjobs" <seansullivanjobs@> wrote:
> >
> > Still working on this design...
> >
> > I'm exploring the use of off the shelf, submersible electric motors to spin props (pod style) for a 45' sailing catamaran with a max loaded displacement of 18,000lbs.
> >
> > Could anyone help me figure out how to convert the twin 30HP Yanmar diesels that are specified to the appropriate HP or KW of electric motor?
> >
> > I had thought it was about 15-20KW electric, but had this whole debate on and electric unfriendly forum where they kind of sand bagged me.
> >
> > Can you guys help me figure out what the appropriate electric motor sizing is to replace a 30HP Yanmar 3YM30?
> >
>
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