I am building the USS California (Tennessee class) for BATTLE in the IRCWCC. It's my 4th ship overall, but it will be my first new ship in 7ish years, and my first ship using the modern tech that's out there. I ordered the hull and various components from strike as shown below, although I probably will only end up using about 60% of what I ordered based on personal preferences (Bose speaker sold separately). The beam on this thing is insane. I did a float test the other day to determine the center of flotation, as well as a "Tons Per Inch Immersion" equivalent to figure out how much freeboard I'll have based on the weight as I build. I think the target weight will be 28 lbs battle ready, so around 27 lbs before CO2 and BB's. The big decision I have remaining is propulsion and batteries. While I feel very comfortable making a reliable DC system, I'm leaning towards brushless based on what I saw at NE regionals the other week. I hope to get an order out either way this week to move forward on the project. I'm thinking approximately 800 kV direct drive (2 screws), with 11.1V new fancy batteries. The plan is to finish this thing before NATS, but I'll see how that goes (backup ship is ready)
Powering a larger ship with LiPOs could be a bit expensive, they also need special care and attention because they are more prone to causing problems if abused. I would suggest you consider running 20AH LiFEPO4 bricks (http://www.batteryspace.com/lifepo4...h-10c-rate-64-wh-6-0---un38-3-passed-dgr.aspx), also available in a handy 4 pack (http://www.batteryspace.com/lifepo4...-256wh-10c-rate-24-0---un38-3-passed-dgr.aspx). I run them in my HMS Prince of Wales, and I know a few other people that run them as well, without issue.
That's what is going in my DKM Scharnhorst. 40ah of long lasting stable power. The best thing about lifep04 cells is the discharge curve, instead of steadily dropping voltage like a lipo, or nimh/nicad, they hold voltage down to about 10% charge then just die suddenly. So no slowing down of the motors as the day wears on. I almost refuse to use any other type of cell chemistry.
We're talking about a few tenths of a volt. I wouldn't really consider that much of an advantage for our purposes. I don't normally use more than 25% of my battery capacity anyways.
As far as for our application, OK. But just comparing discharge curves, my point stands. There's also the fact that lipo's tend self ignite if damaged or improperly charged. They will also burn under water. I only use them when weight is an issue.
All batteries drop voltage during discharge, your statement made it sound as if LiPOs are comparable to NiCads or NiMH which is not the case. LiFE does have a slightly better discharge curve, so you would be correct there. LiFE is also heavier (an advantage for bigger boats), and does not have as high of a discharge rating. You do have to be more careful with LiPO batteries, but the newer ones are nowhere near as dangerous as they used to be (liquid electrolyte vs gel). Me and @Tugboat have already proven that LiPOs do not explode/burn underwater.
That goes for both LiFE and LiPO, and most other battery types. That's why there is a voltage cutoff feature on ESCs.
LIFE packs can be brought back from dead several times. Lipos can sometimes, but will be damaged either way.
That's lithium in general. However, I've been running LiPOs in my boats for 4 years now... plenty of water in the boat, and my fair share of sinks... no 'splodey...
I still wouldn't recommend people do it, as lithium in general, not just LiPO can be damaged by flattening.
I've had them burn from impact damage crashing a plane, also from puncture wounds. I was told it was almost impossible to get a Life to do that. Been using them as rx packs in planes for years, love em.