So what I find interesting is the concept of the Wye Island Race. I just watched some videos of Arrowcat going around Vancouver with one $1000.00 plus fuel stop in I think a day some 650nm at 27.7 mph average speed.
I would expect that if it could be done that cruising electrically even if assisted by generator a voyage such as that would be a nice three day weekend and might make a consolidating point electrically considering we have a strong green influence in and around Vancouver.
My calculations came from me running this formula awhile back. I presume I made incorrect assumptions:
WPA = LWL x BWL x hull fineness factor
This formula gives an approximation. BWL can be approximated as Beam x .90 and the hull fineness factor (my term) is about 68% for fine ended sailboats and 71% for full ended sailboats
POUNDS PER INCH IMMERSION (PPI): The weight required to sink the yacht one inch. It is calculated by multiplying the LWL area by 5.333 for sea water or 5.2 for fresh. The PPI usually increases as the hull sinks into the water as the LWL area is also increasing due to the shape of the hull above water.
WATERLINE AREA: The area of the LWL, usually expressed in square feet. It is not always easily obtained but can be calculated roughly for a sailboat by the formula : .67 x LWL x Beam. It is more accurate if you have the Beam WL rather than the Beam(Max), of course. Knowing the LWL area is essential in working out the following calculations.
So substituting once again:
.67x25.5x14 = 239.19 for hull one
.67x25.5x14 = 239.19 for hull two
478.38 = LWL Area
PPI = 478.38x5.33
PPI= 2550 lbs or if only calculated using one hull then 1275lbs which seems more realistic.
So have you explored any solar aspects for your boat?
I would not like to be pulling 100 amps from my pack when it is around 20% or less as if there is even one cell that falls below that magical 2.6v number faster than the rest it will die very quickly and you will be out cash and running on a very degraded cell that will lack in capacity at the top end. I have two 72ah calb sitting right here that for one reason or another ended up over charged or undercharged.
Now I really want to go out into the garage and pull the top of my Ray and get a picture of the motor as apparently these etek motors are hard to find brushes for. Plus I wanted to photograph the 36v on the motor and show it to you. I traced the original motor to a floor cleaning company that installed them in their sweepers. I also discussed them with John I believe from Montenergy.
One of my motors had some oil spill back from the leg on the journey here and oil got up in the motor parts but I sprayed the hell out of it with some type of safe cleaner and then ran it and then used it later in the year and all seemed good but I may be in for a surprise with that motor considering the above.
I explored the concept of going with light packs based on 72ah cells something similar to this:
Which to me denotes that although you can slam these little cells with current things do get hot.
Whereupon I finally get to the question does it take you 80amp to the motor to do 5 knots in your boat?
I'm calculating my pack conservatively at 384 useable amp hours based on: http://www.pbase.com/mainecruising/lifepo4_on_boats&page=1 where his initial baseline test reveals his same 400ah cells are actually good for 420ah. So in my case I have 4 12v sets so I may see 384 amp hours and I only factor at 80% usage.
I'm hoping to get 5 knots at 30 amps for the miracle result but more often think in terms of 40amps for projected time at 9.6 hours and like you frankly who would want to motor non-stop for nine hours if they were not going somewhere they needed to be.
Worst case I've built a brick and it takes me 80 amps to get 5 knots then usage gets me 4.8 hours and the boat becomes heavily reliant on alternative charging sources while underway - solar and generators wind included if need be.
Arden
---In electricboats@yahoogroups.com, <matwete@...> wrote :
A couple points:
1) The standard ol' ETEK is rated at 48v, 8HP----not sure where the 36v rating you refer to comes from…I ran with a 36v PbA pack for 10 years (from mid 2003 until late 2013). My lithium batteries charge to 48v and are depleted completely at 31v. The lithium pack is Uber-stiff in terms of voltage---even with 1 fully charged battery, I could pull 200amps at 48v from the battery at full throttle without the battery flinching. Right now I have 7 batteries in parallel and will eventually have 10. I could see going to a 96v system at some point if there were good reasons to do so. In the meantime, I'm still running with the same 1st set of brushes on this motor with 2 spare sets…
2) Added weight and range: I've run with as little as 180# and as much as 800# (2 strings of 36v T-105) over the years. I didn't like 800# of batteries in the back and the boat didn't sit well in the water. With lithium, I'm able to spread the pack out fore- and aft- without having to vent the batteries during charging, so going with 800+# of lithium and the added displacement isn't that big of a deal. OTOH, even a 420ah pack would be better than the old lead acid pack I had---I don't really need 2x this…however, with 840ah and my typical usage, I don't think I'll be hauling around a genset except once every couple years, if that. It's crazy---on a full charge, I could run 9 hours at 80amps (5kts) and do 45-nmi…with that kind of range I probably should host the West Coast version of the Wye Island Challenge by offering a race around Sauvie's Island on the Columbia River…that's probably about 43 miles---but then, who wants to motor for 9 hours straight? J Certainly not my ETEK.
Are you sure you displace 1800#/inch? For my hull, it's about 700#/inH20…
-Myles
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Saturday, November 7, 2015 3:38 PM
To: electricboats@yahoogroups.com
Subject: RE: [Electric Boats] Looking for a great fishing story!
A 41v nominal pack voltage denotes your really honing in on the 36v aspect of your motors still I assume to be the same as my footprint being an old etek. Mine actually say 36v on the motors themselves. So I was a little shocked to say the least when I opened them up but apparently they do well way beyond 36v.
Besides I guess a mont709 is the direct replacement more or less so affordable electrical is where it is at. If I'm reading your configuration right you simply flick a switch to go from 48v to 36v which is a very effective controller. Do you have reverse?
Our boats are of a very similar displacement and construction mine being plywood epoxy as well. I estimate that I'm 3500lbs bone dry as in 12 years on the dry.
That is exactly the scenario that is playing out for me as well regarding obtaining and upgrading lithium. It was suggested by the vendor to simply buy a lesser pack and see how the weighting works out with the boat and then if need be double the pack size later on if needed or wanted.
I'm weighing in at around 530lbs for my 400ah 48v pack. Truth be told though with all the other gear I'm probably adding more like 1200lbs on to the final dry weight when it gets picked up in the slings. I'm hoping the travel lift has a guage on it to weigh me.
Are you concerned with the added weight in relation to expected returns or has your experience absolved you of all the range anxiety you may have?
I know roughly that every 1800lbs or so I drop an inch at the waterline.
Arden
Posted by: albert682@yahoo.com
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