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post #37 of Old 10-25-2013
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Re: Islander 36 electric inboard? diy

Hi Miatapaul,

In a way you are right that about 800 Ah@12 V takes a Islander 36 only 40 minutes at full speed. If you use your engine that much you probably belong to those who should go for a diesel solution.
Our previous stock of customers don't use their motors that way. What they usually need is enough power to get out of the harbor and start sailing, something to get them out of dangerous situations and last but not least something to get them home when there is no wind.
The first one is easy. It usually takes about 10 minutes at various speeds to get out of the harbor and start sailing. The energy used can easily be regenerated while sailing. With our system and a boat speed of about 5 knots this will take about 45 minutes.
The second one is also easy because those situations usually last from a few seconds up to maybe 10 minutes.
Finally the third one, which is also easy. If weather is absolutely calm then you don't need much energy to drive the boat in 3 knots. For everyday use and the Islander this will work for about 5 hours. Now weather is seldom absolutely calm which mean that you have at least a little bit of wind to sail on. Start the motor at low speed and you will gain a few knots at the same time as energy consumption is very low. I would guess that you in 1 knot of wind would have a boat speed of at least 3 knots and enough energy for at least 15 hours and still have the emergency half of the batteries left…

Worth mentioning is that the Islander 36 is a quite heavy boat where quite a lot of energy is needed to get it moving. A more easily driven boat will get much better performance on the same amount of energy.

The other half of your reply is about money.
In Sweden we are talking about the same money to go from diesel to diesel as when going from diesel to electric. If you start from scratch with an empty hull then going electric is cheaper.
What you mustn't forget is costs for maintenance. In the diesel world you have costs for filters, lubricants, winter conservation and so on. These costs does not exist in the GreenStar world. Therefor I usually say that you should put the cost for batteries in in this maintenance account. Our GS12-100 batteries usually last for about 8 years in a sailboat. In the Islander example you should then put the cost of one battery each year on maintenance account. Compare this to the maintenance cost of the diesel and don't forget to include household and start batteries… Left to compare after this is the cost of bought liters (or gallons) of diesel and bought kWh of electricity...
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