Electric Conversion log for Kahleesea - Page 25 - SailNet Community
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post #241 of 271 Old 06-10-2019 Thread Starter
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Re: Electric Conversion log for Kahleesea

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I have my zinc installed just forward of the strut to prevent exactly this issue. Looks like you don't have a struts, so something just forward of the stuffing box will work also. A hose clamp will do it.
I have no struts and I cannot lie. You otha brothas can't deny, when a boat sails by with an itty bitty brace and her rigging in your face you get sprung...

I thought about having a strut installed so I could put a bigger prop on, but that would mean a new prop shaft. The prop guy told me to do that would be about $2500, so it wasn't worth it.
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post #242 of 271 Old 06-10-2019
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Re: Electric Conversion log for Kahleesea

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It's a long way out *now*.

When I installed it there was only a 3/8" gap from the cutlass bearing. If you look at the pic I posted of the decals, you can see the prop where it's supposed to be.
Ahh. That explains it.

Mike
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post #243 of 271 Old 06-13-2019 Thread Starter
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Re: Electric Conversion log for Kahleesea

Update 6/13/2019


Looks like the coupler screws failed, causing the prop shaft to slip out of the coupler. Probably my fault for not setting them correctly. Luckily, no damage to the prop or shaft, and only minor damage to the rudder.

My insurance deductible is $500, which is more than it will cost to replace the coupler professionally, so no claim required.

Looks like the prop just scraped the paint on the rudder. A little touch up and it should be fine.

Overall, I think I dodged a bullet. Maybe I had enough karma points built up that I could cash some in.
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post #244 of 271 Old 06-17-2019 Thread Starter
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Re: Electric Conversion log for Kahleesea

Update 6/17/2019

The hard coupler should be going on in the next day or two.

I spent all day Saturday trying to replace the bilge. Removing the old and installing the new is no problem, though the bilge is very deep. I can barely reach the bottom of it while face first on the floor.

I was able to fix the cold machine. It now runs as well as it ever did. Turns out that when I reconnected the batteries after the conversion I missed one connection. The boat used to have a massive 8D on the opposite side of the house batteries, so I didn't reconnect those terminals when I put the house bank back in. Little did I know that the cold machine was wired into the hot terminal on that side. I just reconnected the hot from that side to the house bank. I'll put that on the list of things to change in the off season. It works fine as is for now.

The bilge seems to be wired backwards. The red/brown and orange/brown from the switch on the panel are reading as grounds, not hots, according to my multimeter. Also, the hot lead to the bilge seems to have been severed, and I can't find the break, nor can I find the lead from the battery that goes to the bilge. I really hope I don't have to run a new line from the battery to the bilge. Getting a line through that conduit without a string to pull it would be... problematic. There's about 8 feet between where the cable disappears into the bulkhead on the bilge side and where it would come out in the rear battery compartment that runs through conduit behind the head. There's no access to it anywhere in the middle that I can find.

But did I mention that the cold machine works again? At least now I can have cold drinks while I sweat my ass off trying to rewire the bilge. Hooray!
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Re: Electric Conversion log for Kahleesea

I really enjoy this thread, especially now that we are starting to get real life numbers on power consumption.
Looking forward to much more, after the repairs are done 👏😁
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Re: Electric Conversion log for Kahleesea

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I really enjoy this thread, especially now that we are starting to get real life numbers on power consumption.
Looking forward to much more, after the repairs are done 👏😁
Please keep in mind that the numbers are for my boat, my motor, and my prop.

There are so many variables that you can only draw general conclusions in regards to other boats, even if they had the same 27' waterline.

Now, if someone could come up with an app that you could plug in your prop size/pitch/blades, your LWL, your motor efficiency, and your boat weight and plot a consumption curve, that would be pretty darn useful for electric converters like me.
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Re: Electric Conversion log for Kahleesea

"Now, if someone could come up with an app that you could plug in your prop size/pitch/blades, your LWL, your motor efficiency, and your boat weight and plot a consumption curve, that would be pretty darn useful for electric converters like me."

That would be Lotus123 circa about 1983. These days it would be an Excel spreadsheet. (Or any free similar.) "Apps" are one-trick ponies. There's also a "Propellor Handbook" by David Gerr which should have all the necessary formulas in it.
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Re: Electric Conversion log for Kahleesea

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"Now, if someone could come up with an app that you could plug in your prop size/pitch/blades, your LWL, your motor efficiency, and your boat weight and plot a consumption curve, that would be pretty darn useful for electric converters like me."

That would be Lotus123 circa about 1983. These days it would be an Excel spreadsheet. (Or any free similar.) "Apps" are one-trick ponies. There's also a "Propellor Handbook" by David Gerr which should have all the necessary formulas in it.
I found a spreadsheet online that does well enough. It allows me to change a range of inputs to change the outputs. It's still backwards to what I need, but I can make it work.

Strangely enough, when I put all my info in for my electric drive, it spits out that I need a 15" 3-blade with a 17" pitch... which is exactly the propeller I have. I know for a fact that this propeller isn't the most efficient choice, but it's the most efficient that I can fit in my available space.
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Re: Electric Conversion log for Kahleesea

"I know for a fact that this propeller isn't the most efficient choice, but it's the most efficient that I can fit in my available space."
Space can be a limit. Some years ago a friend re-propped (IIRC) and with the new prop swinging that much closer to the hull, you could hear an almost subsonic thump thump thump as the blades spun by and forced water against the hull.
I'd be surprised if the spreadsheet recommended what you had versus what you think would be better. Could be the spreadsheet isn't up to par. Might be worth using Gerr's book, or asking a prop shop, and trying to reconcile the difference.
Certainly is convenient that at least one "source" is saying you don't have to spend money.(G)
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Re: Electric Conversion log for Kahleesea

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Space can be a limit. Some years ago a friend re-propped (IIRC) and with the new prop swinging that much closer to the hull, you could hear an almost subsonic thump thump thump as the blades spun by and forced water against the hull.
I'd be surprised if the spreadsheet recommended what you had versus what you think would be better. Could be the spreadsheet isn't up to par. Might be worth using Gerr's book, or asking a prop shop, and trying to reconcile the difference.
Certainly is convenient that at least one "source" is saying you don't have to spend money.(G)
The rule of thumb for props is leave 15% of the diameter between the prop and the hull. This applies with props running at ~1000 RPM. Apparently it scales downwards, as in the slower the max speed of the prop the closer you can get to the hull.

I had a lot of help from the local prop shop. He was enthusiastic about propping an electric boat and worked with me to come up with the right prop for the boat. My old prop was a 2 blade 15" with a 12" pitch. My new 3-blade prop generates ~50% more thrust at the same speed, so I can spin it more slowly. The old prop made revolutions for 5.5 kts @ ~950 rpm, and maxed out @ ~1300rpm. The current prop makes revolutions for 5.5 kts @ ~750 rpm, and maxes out @ ~1200 rpm.

One of the major differences between the two systems is that the electric is 92% efficient from ~25% power up to ~90% power. The Yanmar was most efficient at around 2500rpm. Going to WOT would at least double the fuel consumption but only increase the power output ~50%. Going WOT on the electric only increases the current. There's no decrease in efficiency until you hit the top 10%, where it slowly declines to ~90% efficiency at 100% power.

Economically, the electric system is 5x cheaper to run than the diesel was, calculated at the Yanmar's peak efficiency, and about 40x less polluting.
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