T-Pain Is On A Boat: Re: [Electric Boats] Re: Converting a small trimaran to electric drive

Wednesday, February 20, 2013

Re: [Electric Boats] Re: Converting a small trimaran to electric drive

Followed the link to check it out. Nice battery and made in America, (mostly), to boot.

Wish I had an extra $8 grande, I'd buy one tomorrow. Puts my 8 pack of Trojan T-125s to shame but since I only paid about a thousands bucks for an 8 kW pack I don't feel that bad. Looking forward to the day when you'll be able to buy Lithium for the cost of lead and it's coming. In mean time, I'll have to be content with my horse and buggy and wait for the model 'T's of batteries to hit the market.

Carter

www.archemedesproject.blogspot.com

From: James Sizemore <james@deny.org>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Cc: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Wednesday, February 20, 2013 7:24 PM
Subject: Re: [Electric Boats] Re: Converting a small trimaran to electric drive

Here is a 20kw lithium pack with bms and case for the below 8000, total package.

http://www.balqon.com/store.php#!/~/product/category=2897128&id=12658249

On Feb 20, 2013, at 2:07 PM, "Eric" <ewdysar@yahoo.com> wrote:

Hi James,

I converted my 30' ketch to electric a few years ago and had the opportunity to convert my F-27 trimaran to electric when the old 2 stroke outboard gave up the ghost. After considerable analysis, it seemed that converting to electric would be too large of a hit to the sailing performance for the trade to slower motoring capabilities with considerably reduced motoring range, not to mention the cost. And this was with a LiFePO4 battery bank like the one that I installed in my ketch.

You didn't identify which type of trimaran that you've got, but I'm pretty familiar with a number of multihulls. First off, I'm going to guess that your typical motoring speed with the outboard is around 7kts with about 3/4 throttle. If this is true, then you could expect similar performance with a Torqeedo Cruise 4.0 (about $4000US) running at around 3.5-4kW. I believe that you would need the "high speed" prop, I think that the regular prop hits max speed around 6kts. In any case, you'll probably need close to the full 4kW to drive the boat past 6kts.

So 4kW at 50V is 80A. Let's guess that to go 6.5kts, the Torqeedo will take 75A, I'll base all the calculations on those figures.

If you used regular flooded lead acid (FLA) batteries, sixteen Trojan t-105 batteries would give you 22.5kWh of rated capacity, they would weigh 1000 lbs and cost about $2400US. Many people believe that FLA batteries should not be discharged past 60% on a regular basis, so your usable rated capacity is 13.5kWh. Now throw in Peukert's Effect (the loss of capacity due to high amp loads) using 1.25 as the Peukert's exponent and your 1000 lb battery pack will last 2.66 hours or a range of 17.3 nm on a full charge.

Using AGM batteries is better. if you had eight Odyssey PC1800 batteries, they would weigh 1060 lbs and cost about $5200. The rated capacity is 21.4 kWh but AGM can be discharged regularly to 70%, giving a usable rated capacity of 16.8kWh. AGM are less effected by Peukert's Effect and using 1.1 as the Peukert's exponent, this battery pack would last 4 hours giving you a range of 26nm on a full charge.

Now let's consider Lithium batteries. If you bought thirty two 200Ah Lithium cells, they would have a rated capacity of 20kWh, weigh 500 lbs and cost about $8500. LiFePO4 cells can be discharged to 80% on a regular basis giving a usable rated capacity if 16kWh and the Peukert's exponent is down to 1.03. Now your 500 lb (half the weight of lead) will last for 4.1 hours and give you a range of 26.6nm at 6.5kts.

You mentioned using your outboard to charge your traction bank. Your outboard probably produces 6-10A at 12V. If we use the more generous 10A, your total charging output would be 120W. If you could rectify that energy up to 48V nominal without losses (technically not possible but let's play along for the conversation) it would take at least 133 hours to replace the energy that you used in your 4 hour cruise. If you use a 2000W portable generator (50 lbs and about $1000) through an onboard charger (about $500), your max charging rate would be 1500W (probably less), and now it will only take about 11 hours to replace the energy that you used during your 4 hour cruise.

So ignoring the costs, how do you think that your boat will sail if you throw another 600 – 1200 lbs of driveline into it?

Because of the math, a two hour range allows you to cut the weight and costs in half, but you're still looking at 300-600 lbs and multis don't like the extra weight. And your cruise range under power is closer to 13nm. For a lot of money. That's why my F-27 has a new 4 stroke 9.8 gasoline outboard. Cheaper, simpler, much lighter, more powerful, greater range, etc. I struggled with the 30lb increase in changing from 2 stroke to 4 stroke, but you can't buy small 2 strokes in California any more.

I can do different calculations if you want to adjust your requirements (slower speed, shorter range) but you can see where this is heading. Feel free to ask for more info, I'm glad to share my experience. BTW I have heard of successful electric trimarans, but they have been in the 40'+ range, the larger boats are better equipped to carry the extra weight.

Fair winds and smooth seas,
Eric
1964 Bermuda 30 ketch, 5.5kW Propulsion Marine drive, 8kWh Lithium batteries
Marina del Rey, CA

--- In mailto:electricboats%40yahoogroups.com, "jamesmccombs362" wrote:
>
> I am totally new to this electric concept, Mike, and would appreciate your opinion. I have a 31 foot trimaran at 6000 lbs. Currently I use a 9.9 outboard.
>
> What about keeping the outboard adding an electric motor and new prop (plenty of room for electric motor in the stern, enough battery power for 4- 6 hours cruising. Until litium prices come down I coould use the outboard to charge the batteries as it does now and make use of a genset for back up. ??? Any of this makes sense?
>
> Thanks in advance.
>