Question For You Guys Who Made The LiFePo4 Switch

Sharphooks

Sharphooks

Well-Known Member
I have a heavy boat. It is suitably powered but because it’s so stern-heavy it takes a while to get on step and once it’s there, it’s far from fuel efficient

Part of the problem is stern weight.. I have a Yamaha T25 and a pair of DF300’s but I’m not going to get rid of any of that weight. The easiest weight to address are batteries

I have 4 x 6 volt golf cart batteries that weigh 250 lbs. I’ve been told I can duplicate the 200 Ah of those batteries with a 200 Ah LiFePo that’ll weigh approx. 70 lbs

The golf cart batteries do their job just fine. It’s just a weight thing

Meanwhile——I can’t get rid of the pair of AGM start batteries (145 lbs) because using LiFePo batteries to start twin with Suzuki outboards is a place I can’t go

So, the question is:

In the grand scheme of things, will removing 180 lbs of stern weight offer any kind of significant performance change, enough to warrant the cash outlay for the LiFePo conversion?

thanks your comments
 
Do you need 200ah? If you switch to lifePO4 you can draw it down to 90% so theoretically you only need a 100ah? It will be lighter still but sounds like a small amount of weight in total to remove, compared to the full weight in your stern. You could also add a flexible solar panel to ensure you have extra juice and they are pretty light.

1500lb for engines, you would save 200lbs plus wiring, not insignificant but I would be looking for more to balance the boat.

What about bigger trim tabs could that be a solution?
 
The tabs are large Bennetts...they get the boat on step...eventually. If I go LiFePo, solar panels will be part of the conversion. I do long summer trips without plugging in...the refrigerator, a Scotty Hp, and a pile of marine electronics are a large part of the amp Hour requirements

The existing pod I wouldn’t want to monkey with——it’s proper for the boat and extends to the keel line

Yes, not a lot of weight moving batteries but getting any weight out of the stern hopefully will bump up performance and reduce fuel burn
 
Sharphooks said:
The tabs are large Bennetts...they get the boat on step...eventually. If I go LiFePo, solar panels will be part of the conversion. I do long summer trips without plugging in...the refrigerator, a Scotty Hp, and a pile of marine electronics are a large part of the amp Hour requirements

The existing pod I wouldn’t want to monkey with——it’s proper for the boat and extends to the keel line

Yes, not a lot of weight moving batteries but getting any weight out of the stern hopefully will bump up performance and reduce fuel burn
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I run one 12v 100ah agm from Costco for my hp downriggers, two screens, autopilot pump, fridge etc. but she does get pretty taxed with my smaller alternators. Separate start battery as well.

I have a small 12v agm you could throw in to try, I’m selling it for $95 but feel free to borrow it for a day.

My brother had 12” trim tabs on each side and now has 12” + 18”. Runs them off the same pump/ram.

You have already tried different pitch props? That helped for him too, completely different boat but heavy.

D8001B74-8A40-4A77-97E9-A68C2EABDCD0.jpeg
 
I’m running 16 x18.5” Watergrips on the Suzukis. They seem to be a very common pitch size prop for that horsepower outboard. If I do anything on the prop part of the set up with these outboards, it’ll probably be to get a pair of Sharrows. The biggest beneficiaries of performance with those props seem to be stern-heavy boats like mine. A friend I know has a 30 foot boat with twin Yamaha F300’s, also stern heavy and got on step with a bit of effort. The Sharrows cured that instantly and gave him 20% better fuel efficiency. He was lucky though—-Sharrow installed a pair of their props for free to use his boat as a promo tool when they were first making their name
 
Maybe add a whirlygig on a pole i here some of them make free power 😂🤔
Or maybe a small generator those are lighter than your battery set up
 
Changing batteries may not help, much. I think Bifmalibu has your answer: try dropping 2 - 4" of pitch on your props. On a smaller boat, granted, we changed the prop. Our experience was the same - a different beast!
 
There’s a prop shop, in Anacortes, that has very knowledgeable guy called “The Proptologist”. Their website is “Get a Prop”. He’s there in the mornings, taking calls. He used to work for Powertech and has propped 50,000 boats. I’ve been chasing the perfect prop, for 3 years. Partly because my tach was out by 300rpm. I had my mind made up on what I thought I should buy. Which was an expensive stainless 4 blade, to get better stern lift. I also have a stern heavy 30’ cruiser, that I stay/fish on for extended periods. So we have everything under the sun on board (including our cat and litter). But he steered me to a less expensive and better option. So far it’s a night and day difference, in performance.
 
be aware that you need a self heating LiFePO4 otherwise you will destroy the batteries in the winter when the temp drops below freezing and you charge them. I would get something like : https://dakotalithium.com/product/dl-12v-560-ah-lifepo4-dual-purpose-battery-with-can-bus/
117 lbs and 560Ah.
it has self heating and the ability to start an engine with 1000CCA.
get rid of all the AGM and golf cart nonsense and get 1 of these. plenty of power. its NMEA compatible so you can plug it into your chartplotter as well.
 
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zurk said:
be aware that you need a self heating LiFePO4 otherwise you will destroy the batteries in the winter when the temp drops below freezing and you charge them. I would get something like : https://dakotalithium.com/product/dl-12v-560-ah-lifepo4-dual-purpose-battery-with-can-bus/
117 lbs and 560Ah.
it has self heating and the ability to start an engine with 1000CCA.
get rid of all the AGM and golf cart nonsense and get 1 of these. plenty of power.
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LOL, where's a 560 Ah battery going to fit on a 30' boat, not to mention being way oversized for the needs of that size boat? We have a 100 Ah LiFePO4 house battery and can stay on the hook for two days without worrying about a charge while running the fridge and VHF radio. And any reputable battery brand will have a built in battery management system to prevent charging and damaging the batteries at low temps. Yes, you can get heated batteries, but those are meant for if you plan to operate in sub-zero temperatures regularly. Not too many days like that on the coast and even fewer that I'd be taking my boat out in.
 
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I don't know if removing the weight from near the transom will lead to an appreciable improvement in performance, but it can't hurt.

If you have any questions on the LiFePO4 battery and charging system itself, let me know. I replaced my 100 Ah lead acid house battery with a 100 Ah LiFePO4 and at the same time moved it from midship on the port side to near the stern on the starboard side. I noticed that port side now rides a bit higher, but I either use a bit more trim tab, or keep a bit more water in the fresh water tank (located on the port side). I didn't notice any difference by putting the small amount of weight near the stern.

As others mentioned, you'll get a better usable capacity our of lithium ion battery so you can drop the capacity if you feel your 200 Ah lead acid battery is sufficient. Maybe consider a 150 Ah unit? Several brands make that size.

The DC-DC charging system so you can charge the house of the engines is a fairly straightforward instal. Picture of mine attached. I also installed a Victron smart shunt battery monitor and highly recommend. It syncs your phone over bluetooth and gives the current state of charge (amongst other information). The DC-DC chargers also link through the same app.

IMG_4222.jpeg
 
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I am in a similar situation. Too much weight in the back along with a 300 pound dinghy.
I am going to move my 4 AGM golf cart batteries(500AH) forward into the cabin. Will get the 320 pounds about 10 feet farther forward.
We actually moved them temporarily as a test and it made quite a difference.

I have 340 watts of solar from 2 panels sewed onto back cover. It provides all I need for power. We recently went to Bamfield and brought a 5 cubic foot freezer along with onboard fridge/freezer. Ran it off the inverter with microwave, coffee machine, toaster. Only went down to min 85% on the batteries. Never plugged in over a week.
Only my port engine charges the house so when running off starboard the solar keeps house batteries fully up even though running all electronics, downriggers and fridge/freezer. Its a really cool system and not expensive to buy and install.

Sharp Hooks. Not sure why your start batteries are so big. I run group 24 start batteries for my diesel. They only weigh 46 pounds each. moving up to Group 27 or 34 only gets you more capacity but no more cranking amps. I also have a combining switch I can engage. I use that for cold starts.

Couple other things you could do is bigger anchor and more chain. That's weight right at the bow so would have the most effect
 
Very helpful comments, Gentlemen. Sir Reel: those two G31 AGM dual purpose start batteries were installed due to the power draw of the Optimus electro servo-motors that steer the boat. Last summer it was not uncommon for me to troll for 15 hours off the kicker motor with the main outboards powered off For days on end.

As those servo motors draw power from the G31 start batteries I need to have those back-up Amp hours for when the Suzuki alternators are quiet. In my last boat ( A pair of G24 flooded single purpose starters) I saw how quick those servo motors can draw down voltage
 
LiFePO4 are certainly lighter, like half the weight of comparable Ah flooded. I just replaced the AGMs from our cabin solar system with Lifepo this past spring, and very much appreciated the lower weight on the multi-step moves between the various land and marine travel modes. Just make sure you have the appropriate charge controller for your new batteries, lead acid units have a different charging curve and their controller won't get you past about half capacity if connected to Lifepo.
 
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