Generator capacity calculation

[Navatech]

OK, my Berty has a 20 KW genny... It's located in the lazarette and it's a pile of rust... It's not original to the boat... Originally these 46'6" Berty's were equipped with an 8.5 KW genny...

I have been looking for a long time for a used genny of around 12-15 KW... The reasoning being that the "original" 20 KW was too big and the OEM 8.5 KW would be too small what with all the additional stuff on the boat... I've also looked at smaller used (8-12 KW) units on the basis of availability thinking that I might just get by with a smaller unit if I managed my consumption...

However, I've had no luck finding a suitable and reasonably priced used unit... So, I'm thinking that possibly with the boat show deals a new unit might be a better solution all around...

The fly in the ointment is that if I'm buying new I don't want to buy too big nor too small a capacity... Too small and I'll need to manage my consumption which can be a PITA... Too big and I'll be wasting money in purchasing as well as running costs... Basically what I need plus some future reserve...

And here's the question to the membership: how do I calculate my "need" based on my existing equipment?!... Basically I have the following 110 Volt consumers:

* Water heater
* Battery charger
* 3 fixed AC units
* Carry on AC unit (used on the bridge when the "glass" is installed)
* 2 U-Line under counter fridge/freezer combinations
* Ice maker
* Galley triple element/oven combination
* Toaster
* Microwave
* 28" LED flatscreen TV
* 24" LED flatscreen TV
* Satellite dish
* Satellite receiver
* Cockpit fish fridge/freezer
* The Admiral's hair dryer

I currently do not have all the consumption details for each of these items but I can get them... Assuming I get them, HOW do I calculate my need?!...

[Harry Babb]

I think its as simple of adding up the Wattage of all appliances that you are currently running.....plus the wattage of anything that you forsee adding.....then add about 50% to your total........then go shopping.

Things that are "Hard Starting" such as refrigerator compressors and electric motors generally need 3 times their run current rating, to start up....that must be factored in your decision.

hb

[Yannis]

Nav,

I did the same exercise when I calculated the loads for my solar installation.


e.g. : (Hourly wattage for my fridge when it operates X time expected to operate during the day) + (Hourly wattage for "pump 1" when it operates X time expected to operate during the day) + ( Hourly wattage for "pump 2" when it operates X time expected to operate during the day) + (.....) + (.....) = Total wattage needed during the day.

Total wattage needed during the day / 12 volts - in your case 110v = Amperage required during the day.

Amps required X safety margin coeff. = Amps required by my solar source during the day.

(This safety margin should be taking into account the surge needs (=wattage for each surge X frequency that a surge need occurs for each appliance X time each surge lasts), and all other unexpected parameters like when you're sick and you use a lot of toilet pump, when your kids want to play an xyz tv game etc. There should be no problem with the hourly distribution of your needs during the 24h day as this variation is normally evened out by your batteries).

You have to be realistic in ALL above estimations otherwise you run the risk of either running out of power, or needing to carry a generator bigger than the boat itself.

I'm amazed however you're not carrying a dishwasher and a double washer/dryer combo, let alone the vacuum cleaner and the hood... !!!!

[RAWicklund]

Nav,
Do you currently have all them power suckers on your boat? If so, I would do a reverse engineering approach and turn everything on and measure consumption.

Get access to an amp clamp with a "peak hold" function. Measure amps with everything on and " peak" amps as you turn everything on.....namely ACs that have higher start crank amps. Take that data back to a couple dealers and see what they recommend and why.

Eyeball engineering looks like a 17-20 KW.....but just guessing since we don't know the btu's on ACs , water heater etc....

Ray

[Navatech]

I'm amazed however you're not carrying a dishwasher and a double washer/dryer combo, let alone the vacuum cleaner and the hood... !!!!

There's not going to be a dish washer on this boat... We'll be mostly using paper dishes... Any other items (pots, pans, cutlery) can be easily washed by hand... A washer/dryer combo is in the plans but will only be used in port (i.e. when hooked up to shore power)... There's not going to be a vacuum cleaner because whatever is currently carpeted is going to be redone... I don't see carpets as something that should be used on a boat... As for the hood, I have no idea what you mean by that...

[Navatech]

Nav,
Do you currently have all them power suckers on your boat? If so, I would do a reverse engineering approach and turn everything on and measure consumption.

Get access to an amp clamp with a "peak hold" function. Measure amps with everything on and " peak" amps as you turn everything on.....namely ACs that have higher start crank amps. Take that data back to a couple dealers and see what they recommend and why.

Eyeball engineering looks like a 17-20 KW.....but just guessing since we don't know the btu's on ACs , water heater etc....

I understand where you're coming from but this is a big boat... And, down in SEF (South East Florida) AC's aren't a luxury but rather a necessity... The U-Line fridges are actually less of a power hog then the previous domestic side by side fridge that used to be in the boat... Last but not least, while I certainly intend to fish the boat it's a family thing... If it were only up to me the boat would be a lean & mean fishing machine... However, I have 4 mates... 2 of them are young (late teens) men... The other 2 are very young (early teens) women... And there's also the Admiral... If I want to keep everybody together everybody needs to be happy... So, compromises need to be made...

[Yannis]

Nav,

The many exclamation points at the end of my phrase indicated a rather humoristic statement; I meant to say that your electric and electronic items on board seemed so many to me, hence my desire to tease you by trying to find the one or two devices that were not on your list; I had no wish to criticize or suggest what you should or shouldn't do.

By "hood" I meant the vapor aspirator above the stove; I'm not sure if the english is correct, probably not...
As for carpeting, I couldn't agree more.

[Marlin]

My 42' rybo has more demand than u are describing,4battery chargers, 1 70 amp power supply, ice chipper, have never had an issue with the 12 kw northern lights, the sister ship originally has a 9 kw and that would not keep up with the demand, my new boat has considerable more demand and has redundant 20 k w units, 6 refrigeration units in addition to 4freezer/ice chipper units,5a/c units,fyi

[Marlin]

What size service do u have on board 30 amp, 2-30 amp, 1-50 amp 2-50 amp power cords, if this current dockside system works, u should not exceed it or u may have to change the size of the boat service to accommodate a bigger genset,my opinion

[Navatech]

What size service do u have on board 30 amp, 2-30 amp, 1-50 amp 2-50 amp power cords, if this current dockside system works, u should not exceed it or u may have to change the size of the boat service to accommodate a bigger genset,my opinion

I have a 2 x 50 Amp @ 120 Volt shore power setup... With sockets on both sides of the boat...

[Yannis]

Nav,
Are you back from the US yet?

[Navatech]

Are you back from the US yet?

I've been back home but now I'm back in the US... But, if you need any help or information, just PM me...

[Marlin]

Watts = amps x volts, your main breaker or disconnect will determine what the ship is wired for,if u exceed that with demand, u will need to rewire/fuse your boat,I'm sure there r formulas that consider some percentage as a safety factor. So, 50 amps x2=100amps,x120 volts= 12000 watts, 12 kw should be compatible,I think my math is correct,taught school till the kids got smarter than me

[Navatech]

Watts = amps x volts, your main breaker or disconnect will determine what the ship is wired for,if u exceed that with demand, u will need to rewire/fuse your boat,I'm sure there r formulas that consider some percentage as a safety factor. So, 50 amps x2=100amps,x120 volts= 12000 watts, 12 kw should be compatible,I think my math is correct,taught school till the kids got smarter than me

While I'm planning on rewiring (will be going from a 32 volt DC system to a 24 volt DC system) and during that time I'll most probably rewire the 120 volt system too (simply because at that time it will be just a relatively minor additional step) but right now I just want to get the boat from PR to FL...

[Yannis]

Nav, rewire to 220 and bring her over here. Fishing in the US you'll do on some faithful's boat.

[Navatech]

Nav, rewire to 220 and bring her over here. Fishing in the US you'll do on some faithful's boat.

Not on your life!... This baby will chew through about 60 gallon of fuel an hour at WOT... It's unaffordable at US prices... At European fuel prices (double the US price) she'll just be a marina queen...

[Yannis]

How many nautical miles do you calculate your annual mileage?

If I arbitrarily assume that you cruise at 20 knots, at 70% of wot consumption, then you should burn 60 g x 70% = 42 gallons per 20 nm = roughly 2 g/nm.

For 800 nm(*) that you may do per year = 1600 g/year.

1600 g x 3.8 lit/g = 6000 l/year.

6000 l x 1.4 euro/l = 8400 euro/year.

So, if the price is double, your incremental spending would be around half of it, 4200 euros more.

Subtract from this the cost of moving yourself or (mega) family to the US so as to use the boat, how bad could the difference be ?

Of course, you know better if all the above may be depicting reality or not, as well as how much different the other costs are (marina, services, ....)


(*): I used my boat in 2014 for the first full summer. Normal to assume that I went farther and cruised longer than a "normal" summer. For two full months of cruising I made 800 nm. In somebody else's book this would be 20 days of summer vacation, PLUS, say, another 10 weekends per year (that I didn't do myself, as I only use my boat in the summer). I would assume it totals about the same yearly miles.

[Navatech]

Yannis,

Your calculation is valid but there are additional factors... Such as getting the boat to Europe to begin with... I was quoted 25-30K just to transport the boat from Fajardo, PR (St. Thomas USVI really) to Ft. Lauderdale FL... Transport to Europe would be at least triple... Then, I'd have to pay European VAT on the boat's value as well as the transport value... As for usage, once she's here in FL I plan on using her VERY often... The fishing here is year round and the weather is good enough most of the year too... In addition, I'll be able to use her as a live on while in the US (saving me more then 8K per year)...

[Yannis]

I understand.

For your info, prior to buying my boat I was looking into importing a B33 from the US, for which I was quoted in the neighborhood of $ 20K, CIF Pireaus. Yours should be a bit more because she's bigger.
The VAT is calculated on the actual value of the boat (...), however, you as an American, flying an American flag you may not have to pay it, if you keep the boat to yourself.
I have a spreadsheet with the costs that I had calculated back in '09, I can PM it to you if you wish.

[Navatech]

I'm not American by nationality... I have Dutch passport so EU rules would apply... 21% VAT on 120K (boat) and 40K (transport) would still be 33.6K... That buys a lot of fuel... I'd rather rent a boat in the Med then take mine there...

[Yannis]

Or come on mine ! Be my guest anytime, I accommodated 5 this past summer (4 inside, one...upstairs). But given that you have a lot of girls they may find it a bit crammed !