What size gas generator do I need for my boat?

[deansst]

Hello newbie to the forum ,I have a 35 ft boat with an inboard diesel, I have 4 batteries on the boat the first battery is an interstate 8d-hc deep cycle and the other 3 are the 31 series cca700 ca 875 rc 190 wired in parallel, My batteries have gone dead after long periods of time at anchor running fish finder and live well pumps, If the batteries die I wanted to be able to get a quick jump start from the generator, is there a generator that has a quick jumper attached to It? or is it better to connect a battery charger to it ,let me know what size generator I would need for this thanks Dean.

[bob g]

i would want a generator long before the batteries even thought about going anywhere near dead

the batteries you describe will only take a couple dozen or less cycles to dead before they
are going to be about useless, they just aren't made for this sort of service.

without knowing what you have for loads its hard to spec a generator package, however
if it were me i would go with a 110-555jho prestolite/leece neville, and have it running soon after i had a need for all those loads. the alternator is rated for 160amps, and about 120amps hot continuous duty, maybe that would do the job.  if on the other hand you plan on running the batteries down and then recharging, you better have a balmar, xantrex, sterling, amplepower or other sophisticated controller/regulator or you will just end up torching the alternator.

far better to supply the loads directly from a battery buffered alternator than from starting batteries alone, provided your loads don't exceed about 120amps continuous for long periods of time "and" you have a controller as previously mentioned.  don't try and rely
on the oem regulator or you will likely have more troubles than you care to have.

ymmv
bob g

[DanG]

When you asked about a gas generator does that mean you are already carrying gasoline on board for other motors?

For house batteries you need to be kinder to them;  a low voltage alarm and/or cut-off in case you are not present when they are being abused might be a good start.

If you have petro-gasoline on board for a dinghy and you're looking to get an emergency kit together without a major retrofit its hard to beat the Eu Inverter Hondas; run a 40 amp 12 volt charger off the 120VAC output side of the Honda Eu1000 or Eu2000 suitcase style generators. Their fuel tanks seal up tightly for storage but I'd still be trying to store it weatherproofed on deck...

[deansst]

Guys thanks for the replies, What I wanted is to carry on a portable generator in the event the batteries die while sitting at anchor, and that I could jump start the boat just to get going, would the honda 1000 or 2000 be able to jump start the batteries so I could start the engine?

[Rover]

Hi deansst ,

First, you don't "jump start" your batteries, you jump start the engine. With the diesel, you need a fairly high amount of cranking amps to get her started. You would also need the power to be DC, so some real good charger with jump start capabilities.

If you are running down your batteries at anchor, you really need pursue better power management. The easiest is to use multiple battery banks, one of which you keep in reserve solely for engine starting. You also need a way to monitor your batteries so that you don't get into the predicament that your batteries get too low

I assume the diesel has a charging system (either alternator or generator depending on the age of the boat). Most boat owners use their engines  to keep their batteries charged up when away from a dock that has shore power.

I'm not a fan of putting gasoline generators on boats, especially if you don't have gasoline already on board , and I assume you don't because of the diesel. Gasoline brings with it a whole host of other problems, such as fuel storage. On a boat you will need to have it stored in a vented locker with a blower, something you don't have to do with diesel. 

just my two cents.

[bob g]

without beating a dead horse

the starting batteries you have are not made to be cycled to the point that they will not start the engine.

that type of battery can be severely damaged with as few as a dozen such cycles, i know this because i work with these types of batteries and diesel engine's.  the 700cca group 31 battery is about the cheapest such battery that the oem could install of that group size, they are very intolerant of being cycle hard.  i have seen them fail after a half dozen such cycles, this would leave you stranded conceivably.

your starting batteries should be kept separate from the work batteries, so that they can be counted on to do what they were designed to do.

it would be far better to add another 8D deep cycle to match the one you already have
(that is if it is still pretty new) and upgrade the charging system on the diesel engine you already have.  then start the main engine periodically as needed to recharge the pair of 8D's.  my bet is the system would be more fuel efficient than any honda gas powered genset and not have to have added fuel concerns relating to gasoline onboard the boat.

bob g

[deansst]

Bob the batteries are isolated from one another the 8d-hc I beleive is my house battery and the 31 series wired in parallel are my starting battery, they were the original batteries in the boat , I am glad you mentioned that the 31 series are cheap batteries, I wondered about that ,what would you recommend that would be a better batteries? I do not have room for another 8d and I think that is why the three 31s were in place, let me know Dean,

[Rover]

Please don't take this the wrong way, but how much do you know about your boat?, and what kind is it?. I've had numerous... right now I still own a small trawler ( full keel , only 25' , 35 hp volvo, built 1974)

Do you have a batter combiner/isolator off the alternator, do you have a battery selector? ( typically big rotary switch with off,1,2,all --- but can also be digital).

And yes if you have all the above, and are still having problems with starting your engine with a reserve bat, then your bat is probably long gone. (unless you leave your bat selector in the "all" position all the time, in which case, you are operating the bats as one bank even when charging).

[deansst]

The batteries I will be changing out they are at least 5 years old, on a battery switch . Last year a couple of times I forgot to switch from all too 1 or 2 on the switch and killed the battery, I wanted a back up generator just in case I killed the batteries, hook it up to a battery charger start the boat and go. the engine is a 450 volvo tamdc 74 diesel. The generator would only be on board for emergency back up power.

[Rover]

Its not the fact that it would only be on for a little while that causes the issues, its primarily the gas storage, even if its only in the tank on the generator, the fumes will seek the lowest part of the boat, from which there is no escape. Eventually , enough can build up to where a flash can occur.

If you wanted to add a generator, you could add a proper marine diesel genset if you have the room, course , not cheap.

I'd  definetly replace the batteries, possibly increasing the house bank size. 8Ds are normal in marine applications, but you can do better, 6 volt deep cycles in series/parralel etc.

You coul also add a 3 rd bank, though it if you use shore power (AC plug in at dock) to charge your batteries, you would need a 3 bank charger, 3 way combiner.

A side note on most marine battery chargers (my 3 stage Xantrex included), they are notorious for boiling off batteries over a period of time, you MUST check the fluid levels in the cells of the bats periodically, 3-4 mionths is a good interval.

All in all you have everything you need already (except new bats). If you continue to plan for contigencies, well , you're going to be out of pocke a lot $$. A lot of this is already built into the system that you have, you just need to pay attention to it and maintain it.

I mean if you add a generator, ok what if the engine goes out, hmm maybe need another one as backup (actually one with alternator may not be a bad idea) ...
 

[bob g]

5 years and a few deep discharges on the grp 31 700cca batteries is about all they are
good for, from now on they are too risky to depend on in my opinion.

the 700cca is the entry level grp 31 lead/acid battery, so you have a couple of choices

option 1, replace with the original spec battery and don't forget to switch them out when
not in use with the engine, or

option 2, replace with 925-1000cca grp 31 batteries at about 1.5 -2 times the cost of the
700cca batteries and don't forget to switch them out and get much better and more reliable service, or

option 3, replace the FLA batteries with grp 31 AGM batteries, some of which can stand severe discharges and will recover much better and give you better life, this would allow you to forget to switch them out when the engine is not running, however they will cost you about 250-300 dollars each.

option 4,  buy a small aircooled diesel engine, and drive a heavy duty truck alternator
using the oem regulator (which would be adequate for a backup charger) and use the fuel from the main engine which is diesel, not only available, but stores better, is always fresh, and safer than gasoline. 


me? i would pick option 1 or 2 (or maybe 3 if money is available) and couple with option 4 and you will be golden.

use an anderson plug to isolate the engine/charger from the main when it is not needed, that way you don't have to worry about draws, shorts or other backfeed issues, you can simply plug it in, start it up and do the charge, then unplug it.

bob g

[deansst]

To all who replied thank you for that, this is a great site keep it going people!

[roosaw]

I'd agree with others posts.  Get a selector switch and rewire so you can isolate the starter battery.  There are several alternate ways of keeping the house batteries charged up and it all depends on how you use the boat.  Cruisers typically go the solar-wind-alternator-big battery bank- lower the consumption route, day sailors can get by with bigger house banks and a battery charger that runs off shore power.  Drain the bats during the weekend and then let the charger fill them back up during the week.
It all depends on how YOU use YOUR boat though.  I have a spreadsheet that calculates the AH from loads, AH from production means and then shows the AH left in the banks.  useful for sizing your components.

Also, be warned that just buying a huge alternator normally does not solve your battery charging issues.  The BATTERY controls how much current goes into them, not the alternator.  The max current that batteries will accept is 25% of their AH capacity.  A 100 AH battery then can only accept 25 amps max and then only when discharged well below 50%.  Most of the time they will only accept 10 or less (this example) so buying a 120 amp alternator is a waste of money.

If you would like a copy of the spread sheet email me at william-roosa@us.army.mil, it is free

[ed/il]

I did not read all the posts. I use a honda 2000 on my boat. Works for everything but the AC. Bring a few chargers and charge several at once. Do not use starting batteries for anything buit starting and running lights. If you do not take care of batteries you will need to replace every year. I have 8 batteries on my boat. I try to take care of them. My starting batteries last about 2 years. Might try AGM next. Going to mount solar once I figure out how to mount them. Where you located? New Orleans here. Good luck and have fun

[Rover]

A little honda 2000 isn't much till you bring fuel on board. The original poster as talking about a diesel boat and adding a gas gen ... different sets of rules and things to be aware of when doing so.  If you have a deep bilge and do not know of the risks of storing reg gasoline on a diesel boat (where there are no blowers typically)... same thoughts as adding propane to a boat with a deep bilge... bad idea, they make marine alcohol stoves for a reason, less chance of a big boom.

Rover

[divemaster1963]

I am with the others keeping a gas unit generator on the boat can be risky. May I suggest that possible have a extra starting battery that is held off your bank controller with a isolation switch. You can tie a small RV battery maintainer panel to the roof to keep the battery up. then if you should forget to switch the rotor to bank one or two and the batts discharge all you have to do is trip the isolated battery on to start the boat and then trip it off after the engines alternator kicks in. No missing with gas and permanent mounting with less transferring.

John

[ed/il]

Honda generator runs a long time on a 1 gallon or so fill up. Leave generator outside not in bilge. No more dangerous then a gas engine in a boat probably less. Solar is good option but I like both. There is sea tow insurance just in case. 

[wpowokal]

If you were to opt for a separate stand by battery on trickle charge, remember to exercise it occasionally or it will sulfate up.

Allan

[roosaw]

In getting back to answering the OP's original question.  You would be better off trying to run a small genset to drive the livewell pump and other assorted "at anchor" electrical loads than to try and get a battery bank big enough to supply the energy needed on one charge and still have enough to start the boat motor.
My rational is that you have a power boat (sailboats don't normally have livewells) so once your engine is running you have all the power you need and you really don't need deep cycle bats (once the engine is running).  outfitting your boat with solar/wind is not typically done.  it could be but most powerboaters don't (don't know why).  so that leaves us with large electrical loads of 24ish hour duration to be supplied by either batteries or a genset.  If you look at it from a weight standpoint the genset will win, if you look at it from a space standpoint the genset wins, if you look at it from a safety standpoint I think the argument could go either way (battery acid or gasoline are both pretty nasty on a boat).
If you get a diesel genset (assuming your boat motor is diesel) you can just tap into the boat fuel tank.  same applies for gas motor boats -sic go with a gas genset and plumb in the boats fuel tank.
As for size, I'm thinking you would have to do an energy budget for your boat while at anchor.  Some folks have to have air conditioning, freezer, reefer, lights, livewell pumps, stereo, electric stove........ and a 15 kW genset would not suffice, some just have a couple of led cabin lights and the anchor lamp and a hand crank bike generator will meet that need.

[ghurd]

My batteries have gone dead after long periods of time at anchor running fish finder and live well pumps,...

Returning to the problem at hand... big batteries going dead with small loads.

Uh, why run a fish finder sonar for "long periods of time at anchor"?
My Humminbird's (wally-world class, not the stuff probably found on most 35' boats) will run a week of 12 hour days with a used 7AH SLA, and still have a reasonably charged battery.

And uh, why run live wells for "long periods of time at anchor"?
Put a livewell timer on it and reduce the load by 80%?
Use a more efficient pump?
Use a more efficient pump AND a timer?

ie: Attwood V625 would move like 650GPH with about 0.75A at 12V, IIRC?
(The V-series may be completely replaced with the new series by now)
Then add an automatic timer.

The end result would be the mooring lights would use more power per day.

Just throwing it out there,
G-