Re: [Amel Yacht Owners] First Impressions: Firefly Batteries.

Danny and Yvonne SIMMS

Hi James
I haven't fiddled with weight distribution in the Amel to see changes but in my racing days, a lot. Weight in the bow, in my experience worsens pounding. Take a stick a yard (metre) long, hold one end and swing it downwards and suddenly stop it when it is a right angles to your body. Now add two pounds (1kg) weight to the outer end and try the same. Weight at each end of a boat causes hobby horse momentum by the same physics. The center of the boat is the pivot point, and up and down she goes.
That said, in a cruising boat the reality is we have a lot of stuff to carry and the lockers at each end are a tempting destination but I do try. All my considerable number of tools are in the perfect place, low down in the middle in the underfloor storage. I still have a lot of weight up front, I just wouldn't want the batteries there as well.
SM 299
Ocean Pearl

Sent from my Vodafone Smart

On 16 Dec 2017 7:31 a.m., "James Alton lokiyawl2@... [amelyachtowners]" <amelyachtowners@...> wrote:


Hi Danny,

   Thanks for the comment but  I am not so sure that I agree with the premise that carrying weight in the ends of the boat always makes the boat slower.   Have you sailed your boat with the weight spread out fore/aft versus concentrating in in the center of the boat to see if you could tell a difference?  Olin once told me to ignore the “logic” of keeping the  weight in the center of my Lokiyawl and he won a lot of races in his day.  Spreading the weight out fore/aft  does have the benefit of increasing the Pitch moment of inertia which can soften the motion and I think is a good thing in a cruising boat.   Perhaps when on the wind in short seas having the weight spread out isn’t a good thing but I am going to avoid those conditions when possible.   For off the wind or reaching on a cruising boat I don’t see how having the weight spread out has any real effect other than perhaps steerage but I would be interested to hear other Amel owners comments on this.  Whether I move the batteries forward or add more chain or trim ballast to counter the addition of the arch and panels the result would be similar.  Regardless,  I think that the boat is better sailed on her designed lines than being down by the stern and I don’t want to carry trim ballast unless I have to so I am trying to plan ahead to avoid that requirement.   I am really hoping that  when the time comes to decide on wether to move the batteries forward that I will be putting in Lithiums which will be lighter and due to the increased energy density I won’t need as many.   I would only consider a batteries that were spill proof in the forward cabin.  

On Dec 15, 2017, at 1:51 PM, Danny and Yvonne SIMMS simms@... [amelyachtowners] <amelyachtowners@...> wrote:

Hi James,

anyone who has seriously raced yachts will tell you to keep the weight out of the ends of the boat. Trim is altered by moving weight in the middle of the boat. The huge lazurettes in the stern are a tempting place to put lots of stuff, I try to avoid heavy items there and of course any weight there affects trim. There are heavy items that have to be in the front, anchors, chain rode.  I would not want to add all the batteries.



SM 299 Ocean Pearl

On 15 December 2017 at 16:17 "James Alton lokiyawl2@... [amelyachtowners]" <amelyachtowners@...> wrote:



   This is an interesting discussion,  I feel that I am learning a lot..the good the bad and the ugly….

   The batteries for the Maramu were installed in the engine room by Amel.  On the SM, the pass thru is wide enough to accommodate the batteries but I don’t think that this is possible on the Maramu due to space constraints.  In this location as you point out,  heat could be a significant factor in battery life.  (this is one of the reasons I installed an 8D Gel temporarily under the Vee bunk on the Port side.  The Gel battery is a very clean battery not requiring a battery box.)  I am considering future options to move the house batteries into the bow of the boat which would get them out of the heat of the engine room and also help trim the boat fore/aft.   The large draw items such as the thruster are in the bow so it seems like this might be something that could work…any input?  I am guessing (but do not know for sure) that since the degradatio n is a chemical process that the accelerated deterioration occurs only during the times that the engine is being used?   While damage was done during the heating periods, hopefully there is not ongoing damage when the engine room returns to ambient temperatures, so if this is correct unless one heats the engine room continuously for the life of the battery the life would not actually cut in half?    

    I have been reading that newer sealed  lead acid batteries used as starter batteries for cars are considerably more heat tolerant than those of the past.  The 2015 BCI Failure Mode Study reported an average life expectancy of 55 months under the hood and one additional year if the battery were kept in the trunk.  I don’t know if this benefit has been built into the batteries commonly used in our boats.

& #160;   Lead acid batteries are not too energy efficient so you might lose 15% of the power in charging the battery and if you discharge rapidly, you can lose up to 40%.  How much of that energy loss ends up as heat in the battery I wonder?  You make an interesting point about the Firefly batteries possibly running cooler due to the higher efficiency.  Again, it will certainly be interesting to hear your reports!   Thanks for sharing.


SV Sueno,
Maramu #220 

On Dec 14, 2017, at 7:12 PM, greatketch@... [amelyachtowners] <amelyachto wners@...> wrote:

Firefly specs the battery output up to as hot as 50C, but it does come with a caveat in their manual:

The optimum operating temperature for a lead-acid battery is 25°C (77°F). As a rule of thumb, every 8-10°C (14-18°F) rise in temperature will cut the battery life in half. 

That's a pretty standard rule of thumb that any chemist would use for a chemical reaction, and  I believe it is at least approximately true for all Lead-acid batteries.

Where Firefly might have a bit of an advantage is they have high charge efficiency, and very low internal resistance (specified as 4 milliohms) so they generate less internal heat during normal charge/discharge cycles.  They MIGHT run a little bit cooler in the same ambient environment than other valve regulated batteries.  On the other hand, a flooded cell that is generating gas will be losing a lot of heat that way, so I won't put money on it either way!

Bill Kinney
SM160, Harmonie
Fort Lauderdale, FL
Almost ready to be out sailing again!




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