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[piker]

hi guys, i have just bought a one of these  http://www.aquacraftmodels.com/boats/aqub20-ul1-superior/index.html    "minus batteries."

i know nothing at all about electrics.  i,m a complete newbie and know nothing   would these batteries listed below.  [scroll down the ebay page]   be ok. 

thanks in advance  paul

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140457086021&ssPageName=STRK:MEWAX:IT

[andrewh]

Paul,

Reasonable question   Looks like a vivid boat!  Where do you aim to run it?

 The reference you gave says:

Requires: (2) 7.4V, 3200mAh LiPo batteries & 4 "AA" alkaline batteries.

I guess that the 4 AAs are for the transmitter.
Forgive me if I am teaching you to suck eggs - but a bit of explanation of the "bits" of this might be helpful to others, if not to you
7.4 V is code for two Lithium Polymer (LIPO) cells in series, ie their voltage adds up to 7.4volts
3200mAh is the capacity (size of the fuel tank) and 3200 mAh means milliAmp hours. 
So this is the same as 3.2Amp Hours
So (at the very simplest level) they will supply 3.2 Amps for one hour or 32 Amps for 1/10 Hour or any other combination that multiplies to 3.2
UP TO the safe limit of thos particular LiPo cells  - which is expressed as something like C30 or x30  - this means they can safely be discharged at 30 times the nominal 1-hour rate (in this case 3.2Amps)
So if you got 3.2Ah cells rated at C30 they could be discharged at 30 x 3.2 Amps or about 90Amps

Right - now what is the required current for your boat?  It has a 60A speed controller so the max current must be equal or less - say 50A
Which would be equivalent to about 20C or x20 - which is a "normal" type of LiPo
All the cells in the Ebay auction are C30 type and 5000mAh (5Ah) so they are over twice the capacity reccommended - so they will weigh twice as much

So please have another look around and find some close to the specified 3200mAh  - they will be the right size and weight!
Do you have a LiPo charger? - you will need one
Do you have, are you able to add the right sort of comnnectors to the cells when you get them?

From the specs of the speed controller the batteries are clearly wired in series - ie both batteries of 2 cells are in series giving about 14V nominal.

I hope some of this spiel is helpful - there may well be Mayhemmers (notoriously helpfull people ) close to you who could help
andrew

[mattycoops43]

That sounds pretty spot on to me. You can generally go up a bit from recommended capacity, but going to 5000 will be a big change in weight and size. I would think 4000 would be the absolute max and may require mods to fit. measure up the space where they will go, and make sure the cells will fit.

matt

[Tombsy]

Nice boat!
I have the same one.
The batteries you show would work but I'm not sure about the quality.
I would stay with at least 30c batteries, 40c is better and 5000mah will give you about 4 minutes run time safely.
I am using these batteries now and they are faster than my other 20c-30c packs.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10305

The boat comes with Dean's connectors the batteries you showed have no connectors so you would have to add them.
The HobbyKing batts have 5.5mm bullets and it would be better to change the boat connectors to bullets as well.

There have been a couple of fixes on the later versions of the boat but some things to consider are:
Pressure test the cooling system the early versions had leaky motor cooling jackets. If it leaks it's probably better to get an aftermarket one.
Reinforce the turnfin mount by getting some epoxy in the bolt holes.

Consider adding a Low-voltage-cutoff the esc cutoff is set a too low. I added a Dimension LVC from Kintecracing that is at 3.3v per cell.
If you run the batteries too low they will be ruined, I use 4min for a safe runtime and our races are less.
The new nanotech batteries have a higher C but there are none in stock right now.

Brushless esc's like to run wide open throttle, you can puff the capacitor on the esc by running at part throttle. The newer boats have a bigger cap so it's not as big a problem.
I added 2 more caps to my esc it's an easy fix.

There are lots more set up and race prep tips if your interested.
The best prop I've found is the Grimracer 40/52/3 blade it's good for close to 50mph with 40c batteries.

Kintecracing.com has lots of good stuff.

[piker]

thank you so much for taking time out to help me out guys
very good of you.

 all is becoming clear--- ish now.
paul
ps i dont have a charger or batteries as yet,

[mattycoops43]

4 minutes? from a 5000mAh???? With a 60A esc??? Is that right?

[dreadnought72]

Seems a little bit low to me. But not much.

Going with Andrew's 50A suggestion (the motor's got to be less than the ESC's rating!) a 5 Amp Hour battery would give you a tenth of an hour - say 5 to 6 minutes full speed.

Andy