This bulletin board, hosted by the CDSOA, Inc., is the on-line meeting place for all Cape Dory owners and groups. We welcome everyone's questions, answers and comments about Cape Dory sailboat
I finally got a relatively calm day the other day to do some Speed vs Amp trials. I went cross current N to S then back S to N and averaged the speed readings for each amperage. The result turned out better then Electric Yachts estimates which give me more range then anticipated.
Speed vs Amps.png (33.27 KiB) Viewed 377 times
With 202Ah (@90% 182Ah usable) in the LiFePO4 battery bank and 79Ah (@60% 47Ah usable) in the AGM battery bank. The total Ah available is 229. At 4.5 Kts I will be using 40 amps which gives 5.7 hour and 25.75 Nm range. If I slow it down to 3.8 Kts then the amps drop to 20 and yields 11.5 hours and 43.5 Nm range. It should be noted that this data is taken in relatively calm seas and the current factored out. As an example yesterday I motored out of my harbor against a 1 Kt current, into a 17 Kt wind and 3-4 ft breakers. I had to use 80 Amps to keep her at 3 Kts. This was of course an extreme condition and I only had to do it for a few minutes. In open water I would never motor into those condition just set sail and tack though it like I did when I cleared the channel marker.
Here is MOONDANCE on her morning sitting just a bit high in the stern. I removed about 550 lbs of diesel components and added back about 250 lbs of electric components for a net loss of about 300 lbs. Note the new staysail on the harken fuller. I need to get a new staysail and figured that as I hope to be sailing into my 70's that the fuller would be a good add. It is awesome. Wish I got it sooner. I didn't have to get on the foredeck yesterday in 5-6 foot breakers to take down the staysail.
We are about ready to test the new install. We just need to connects the last two battery cables and then plug in the throttle, display, and current sensor wires. I do have a question for you guys though. We have the 48V system for the motor and we have a 12V system for the house loads. Does all of this get grounded together? Where did you fasten your ground? I'm thinking that one of the motor mount bolts might be a good spot. Any ideas or helpful info would sure be appreciated.
tjr818 wrote:We are about ready to test the new install. We just need to connects the last two battery cables and then plug in the throttle, display, and current sensor wires. I do have a question for you guys though. We have the 48V system for the motor and we have a 12V system for the house loads. Does all of this get grounded together? Where did you fasten your ground? I'm thinking that one of the motor mount bolts might be a good spot. Any ideas or helpful info would sure be appreciated.
Hi Tim,
Sorry for the late response. My desktop computer won't log onto the Cape Dory site anymore but my laptop and phone will, so I'm responding on my laptop. Anyone else had this issue?
Anyway I'm sure that you have already figured it out. I tied my ground to one of the motor mounting bolts. I'm not sure on grounding the 48V and 12V batteries together as I have two 48V batteries (202Ah LiFePO4 & 79 Ah AGM) that can both power the motor and a 48/12V converter on the AGM that powers the house panel.
Thanks Keith,
It looks like you got it right.
I had asked Scott at Electric Yacht for his advice and here is what he said:
The prop shaft is electrically insulated from the rest of the motor frame. This is primarily to reduce any chance of stray current corrosion that can occur with faulty ac wiring when plugged into shore power in a marina. You really don't want the shaft connected to your ac power grounding system if you can help it. With a conventional engine, you can' t separate the two.
You can connect the frame to your 12Vdc negative, which should also be connected to your 48Vdc negative and the ac safety ground per ABYC standard E11.
The mast bonding is a good precaution for reducing the likelihood of lightning damage. This is a separate issue from the internal wiring grounding scheme.
