Chris Craft Constellations by Murray, Uniflite & Pacemaker

The Cost of “Anchoring Out” Versus Staying at a Marina


Introduction

The main reason for buying an inverter is that it makes your Connie free from dependence on shore power. Saving money by avoiding marina slip charges is one motivation for wanting an inverter but another is that it also allows you to cruise in more remote areas (the boondocks) where shore power may not be available. The purpose of this paper is to estimate the costs for operating with and without an inverter i.e. in the boondocks vs. at the marina. It also describes several modes of operation.

Battery Bank Size

If costs were no consideration, we could make the inverter battery bank large enough to carry the electrical loads of your Connie for the whole day. But that would require 32 6 volt 225 ampere hour golf cart batteries at about $140 each or $4,480. The cost is prohibitive and it would be extremely difficult to even find a space to store the batteries.

Therefore, the inverter battery bank we discuss here consists of only four 225 ampere hour golf cart batteries which are recharged on five hour intervals. This keeps the cost of the batteries down to about $560 and the cost of the whole system including the inverter and charger down to about $2,200.

Operational Modes

There are four modes of using your inverter which are described in the sections below:

Mode 1: Anchoring Out with the Generator Running 24 Hours per Day

A Connie has five air conditioners which produce 68,000 BTU per hour of cooling. In my experience on a sunny hot summer day in Maryland you need all five units going full blast to keep the boat cool. And even with all the air conditioners going the upper salon will probably be in the mid-80s. The total power draw is 52 amps at 120 volts or 6,240 watts.

This is only 6,240/20,000 = 31% of the 20 KW Onan generator’s total capacity so the generator can probably easily handle the air conditioning loads in addition to all the other loads.

Even with all the loads (air conditioning plus other) running on an anchored Connie, the generator is only at about ½ of full load and burns about 1.2 gph. At $4.00 per gallon (current in 2013) that’s a cost of $4.00 x 1.2 = $4.80 per hour or $115.20 per day.

Mode 2: Anchoring Out with the Generator Running 8 Hours per Day and an Inverter Running 16 Hours per Day

This mode assumes that you have an inverter and that the generator will be turned off from Midnight to 7:00 AM, from 9:00 AM to 12 Noon, from 2:00 PM to 5:00 PM from 7:00 PM to 10:00 PM. At all other times the generator will be on. It is also assumed that your inverter is capable of handling the loads during the generator-off periods.

Air conditioning can be on at all times when the generator is on but not when it is off. Even with all the loads (air conditioning plus other) on the generator is only at about ½ of full load and burns about 1.2 gph. At $4.00 per gallon (current in 2013) that’s a cost of $4.00 x 1.2 = $4.80 per hour or only $38.40 per day for an eight hour day.

Mode 3: Anchoring Out with the Generator Running 15 Hours per Day and an Inverter Running 7 Hours per Day

It is assumed that the generator will be turned off only from Midnight to 7:00 AM. At all other times the generator will be on. Air conditioning can be on at all times when the generator is on but not when it is off. Even with all the loads (air conditioning plus other) on an anchored Connie the generator is only at about ½ of full load and burns about 1.2 gph. At $4.00 per gallon (current in 2013) that’s a cost of $4.00 x 1.2 = $4.80 per hour or $72.00 per day for a 15 hour day. The cost in this mode is $55.50 less than at the marina so it is still a considerable saving.

Mode 4: Marina Costs

I selected the Anchorage Marina in Baltimore to estimate costs. It is not the cheapest but is typical of the better marinas which offer swimming pools and other amenities. For daily transients their rate is $2.25 per foot which is $112.50. A 50 amp hookup is an additional $15. Total cost is $127.50.

Discussion

Mode 1 doesn’t require an inverter but is almost as expensive as staying at a marina and also requires that the generator be run unattended all night which is probably not safe. So I doubt it would ever be used. The bottom line is that if you don’t have an inverter you simply don’t anchor out. You go to a marina.

Mode 2 is obviously the cheapest. It saves $89.10 per day over the marina cost. If you used this mode 10 times a year you would save almost half of the inverters cost. In two years it would have essentially paid for itself. In ten years you would have a profit of $6,810.

Mode 3 is more expensive because the generator is on at all times except during the midnight to 7:00 AM sleep period. It represents the situation which would occur if it was so hot that the air conditioning had to be on all day and into the evening. The air conditioning and generator would be off only during the sleep period. This is basically an emergency only mode but is still much cheaper than staying at the marina.

Mode 4 is the Marina Mode where we pay for a slip in a marina. It is the most expensive way to go. But anchoring out all the time gets boring so I expect most people will continue to use it about half the time even if they have a an inverter.

Some readers may say that operating with an inverter is too regimented. You just don’t want to be constrained to turning the generator on and off every few hours. But the alternative is either doing without electric power most of the day or running the generator 24/7. You could buy 32 golf cart batteries for $4,480 and reduce your charging cycles to once per day but I doubt many of you would want to do that. And when you contemplate where you would store all those batteries that option will probably leave your mind entirely.

This is my second attempt to make this post. In the first attempt I had a table and the Forum editor entirely scrambled the text. Without the table the post seems to have worked.

CaptOlin, 3/17/2013