Doug:
I'd love to have electric drive, but the math really doesn't work for me. Battery technology is not in my opinion mature enough yet. The experiences people are having with lithiums in the marine environment so far that I've read about do not sound good long term. The power to weight ratio is good, but people are having issues with charge controllers, and the actual management of batteries for max life is still not totally worked out to my satisfaction. Cost of these batteries is quite high still. I've looked at the life expectancy of lead acid batteries based on depth of discharge, and the online charts show something interesting. The life cycle penalty for deeper discharge is actually fairly small when one looks at the total charge stored and discharged over the life of the battery. In other words, 2 batteries doing the job of 4 will only last a bit less than half as long as 4 batteries doing the same job. As I recall it's about a 20% life penalty. What that means is that I can use half the number of lead acid batteries and change them out slightly more than twice as often, for half the cost, and half the weight. Golf cart batteries for example can be had from Batteries plus with a one year (no pro-rate) replacement warranty. What that means is that if I were hitting the US annually, I could optimize my battery bank so that I would have free annual replacement. That might mean having two battery banks, and running one to death every 6 months or so...........
I've always loved western red cedar....... It's a wonderful rot resistant wood. Juniper is better yet, but obviously not available as a suitable boat building material ;-(
I seem to be running down two tracks. One is to build a lengthened and greatly modified KD-860 derivative, and the other is to build a Woods Sagitta, and pull out the stops on weight reduction. The latter is the preferred route. Sagitta offers the option of strip planking only below the knuckle, and ply above it, or strip planking the whole thing. This would lend itself to doing the bottom either in strip planked 10mm cedar, or strip planked divinicell, and building the upper of full length infused sandwich panels laid up on the flat. The latter option would be easier in terms of finishing the inside...... I can't imagine trying to fiberglass the inside of something as large as an entire Sagitta hull. Achieving the seal to vacuum bag or infuse the exterior of a hull bottom built on bulkheads would be a bit of a challenge, but I don't see it as insurmountable. It looks like it would require a seal strip along the edge to stick the bag to, and of course the seams between the planks to be very well sealed. I really need to find somewhere to do an "infusion clinic", or lacking that option, I need to do a lot of experiments. Perhaps a "pilgrimage" to the West Systems operation.....
I don't want to end up "twisting in the wind", trying to figure things out. I'm toying with a number of wild ideas, which generally upon reflection simply are not practical. There are details I won't know until I actually buy plans and do a bit of modeling.
What I lack, really is a good comparison between cedar strip construction and equivalent strength foam. Everything I read involves plywood, and of course elimination of the stringers is not factored in. In any case, the cost of foam skyrockets pretty rapidly as it gets thicker. $97 a sheet in case lots for 3/8, $121 and $144 for half and 5/8, and of course more glass and epoxy. If I were a "money is no object" sort of guy things would be different ;-)
H.W.
On 06/28/2018 10:00 AM, 63urban 63urban@gmail.com [harryproa] wrote:
I'd love to have electric drive, but the math really doesn't work for me. Battery technology is not in my opinion mature enough yet. The experiences people are having with lithiums in the marine environment so far that I've read about do not sound good long term. The power to weight ratio is good, but people are having issues with charge controllers, and the actual management of batteries for max life is still not totally worked out to my satisfaction. Cost of these batteries is quite high still. I've looked at the life expectancy of lead acid batteries based on depth of discharge, and the online charts show something interesting. The life cycle penalty for deeper discharge is actually fairly small when one looks at the total charge stored and discharged over the life of the battery. In other words, 2 batteries doing the job of 4 will only last a bit less than half as long as 4 batteries doing the same job. As I recall it's about a 20% life penalty. What that means is that I can use half the number of lead acid batteries and change them out slightly more than twice as often, for half the cost, and half the weight. Golf cart batteries for example can be had from Batteries plus with a one year (no pro-rate) replacement warranty. What that means is that if I were hitting the US annually, I could optimize my battery bank so that I would have free annual replacement. That might mean having two battery banks, and running one to death every 6 months or so...........
I've always loved western red cedar....... It's a wonderful rot resistant wood. Juniper is better yet, but obviously not available as a suitable boat building material ;-(
I seem to be running down two tracks. One is to build a lengthened and greatly modified KD-860 derivative, and the other is to build a Woods Sagitta, and pull out the stops on weight reduction. The latter is the preferred route. Sagitta offers the option of strip planking only below the knuckle, and ply above it, or strip planking the whole thing. This would lend itself to doing the bottom either in strip planked 10mm cedar, or strip planked divinicell, and building the upper of full length infused sandwich panels laid up on the flat. The latter option would be easier in terms of finishing the inside...... I can't imagine trying to fiberglass the inside of something as large as an entire Sagitta hull. Achieving the seal to vacuum bag or infuse the exterior of a hull bottom built on bulkheads would be a bit of a challenge, but I don't see it as insurmountable. It looks like it would require a seal strip along the edge to stick the bag to, and of course the seams between the planks to be very well sealed. I really need to find somewhere to do an "infusion clinic", or lacking that option, I need to do a lot of experiments. Perhaps a "pilgrimage" to the West Systems operation.....
I don't want to end up "twisting in the wind", trying to figure things out. I'm toying with a number of wild ideas, which generally upon reflection simply are not practical. There are details I won't know until I actually buy plans and do a bit of modeling.
What I lack, really is a good comparison between cedar strip construction and equivalent strength foam. Everything I read involves plywood, and of course elimination of the stringers is not factored in. In any case, the cost of foam skyrockets pretty rapidly as it gets thicker. $97 a sheet in case lots for 3/8, $121 and $144 for half and 5/8, and of course more glass and epoxy. If I were a "money is no object" sort of guy things would be different ;-)
H.W.
On 06/28/2018 10:00 AM, 63urban 63urban@gmail.com [harryproa] wrote:
Stone
I have been struggling with similar issues. Ultimately I want a solar electric cat to cruise on relatively long term. Strictly electric no sail. (Gunkholing canals rivers etc.)
I found a dirt cheap tornado that was being sold as plywood and glass that i was going to use as a test bed and learn a few things from. I got it home and started stripping it down only to find that it is cedar strip core and so far have found zero rot.I will continue on with the test bed idea but the beauty of cedar strip is that it is infinitely remodelable. So I may just slowly build this one out until I have what works for me.
Nick b.
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Posted by: StoneTool <owly@ttc-cmc.net>
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