T-Pain Is On A Boat: Re: [Electric Boats] Diesel Electric?

Monday, February 17, 2014

Re: [Electric Boats] Diesel Electric?

Steve's suggestion is sound. Trying to turn an existing motor into a generator is going to be more trouble than it is worth. Sell the diesels and buy a good generator that will be sized correctly to power everything on your boat efficiently.

Vender alert

We have installed 48 volt systems, 72 volt systems and 96 volt system - and our manufacturer has installed 600 volt systems! While staying under 50 volts is what is noted in the ABYC standards for safety, it is better to use higher voltages on the more powerful systems in order to keep the amps lower as Steve mentioned. What we do on the higher voltages is install disconnects that will break the system into voltages under 50 amps when you need to work on it. Still, even 12 volts can be nasty! I've dropped a wrench across the terminals on a 12volt battery (not on purpose!) and it's pretty alarming how much power is there. Always use care when working on the electrical systems and around batteries no matter what the voltage.

Keep the continuous rating of the motors in mind when comparing the various system options. Depending on the speed you want to get for cruising, that will determine the kW size you will need to push the boat at a continuous speed which will also determine the size generator you will need as well. Also as Steve mentioned, since you will be motoring all of the time, the battery bank can actually be smaller in terms of amp hours. If the system is well designed then you will find that you can cruise efficiently with the generator and at anchor you will have plenty of battery power for your normal house loads. If you are running air conditioning or other large loads, then you need to factor that in and make some choices as to how that all fits into the equation.

Good luck on your conversion - the trawler is a great candidate boat for electric/diesel and I'm sure you will enjoy the boat more once it is powered by electric.

Sally Reuther

Annapolis Hybrid Marine

On Mon, Feb 17, 2014 at 11:24 AM, Steve Dolan <sdolan@scannersllc.com> wrote:

Hopefully your motor issue will not be a big thing but here’s some thoughts on the conversion. Not tech. stuff because there are others who are better at the math then me.

First off I’m running a bank of bats at 144V. I see no issue with this as long as you’re not dropping wrenches and such across the terminals. The real “ominous” voltage is 72V (Others claim not me). Running higher voltages isn’t a problem and is more desirable in larger boats and you drop Amperes down to the motors also decreasing wire size. At 7 knots I’m at 40A to each motor. If I was at 48V I’d be at around 160A.

If you’re going to install a genset in the future pull both motors and run everything off of it. Much simpler install and you would have the power for the inverter to 120V AC. Say around 21KW Genny. If you’re going to run all the time under power don’t even worry about a large bank of bats. You don’t have sails so the motors will have to do all the pushing. Have a decent house bank for anchoring and go from there. This is how many large ships run. I’m sure converting an existing motor to a genset will cost quite a bit. Sell them off and go for it.

I’m just throwing thoughts out there but my system works. I have 1 motor to worry about (genset) and use a hell of a lot less fuel (if any) doing it this way. Of course this is a sailing Cat not a power boat.

Steve in Solomons MD

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of cirejay@hotmail.com
Sent: Monday, February 17, 2014 10:55 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Diesel Electric?

I recently purchased a Gulfstar 36 trawler. It currently is powered by twin Perkins 4.236 engines, each with a nominal HP of 85. One engine developed some, at this time, unknown problem which I will have diagnosed in the spring, if it ever arrivesL.

The hull is the same as their motorsailer and as such is easily driven. Running on one engine and dragging the other prop, I time trialed it at an easy cruise of 6 knots and topped out at just over 7 (2 way, GPS).

My thought is to remove one engine and use the other as a generator to power twin electric motors and charge a good size battery bank. The engines weigh in at around 1,000lbs each so, assuming lead acid and just balancing the single engine, I come up with a bank of approximately 1.5 KW. (sound right?).

I’m thinking that the electric motors should be rated for about 30hp continuous each at 48 volts (trying to keep below the ominous 50 volt mark).

The boat does not have a genset at this time but I will be adding AC/reverse air so would probably be adding one if I did not go to the proposed configuration.

How will I use the boat: My partner is finally retiring this May and we plan to spend 3 months or so onboard each year while leisurely cruising the eastern US, possibly including the ‘great loop’. I am primarily a rag man and will keep the sailboat and use it for extended single handed trips as have been doing for the past few years. I have a couple of 50 watt solar panels on meander and love them so plan on a good size bank for the trawler.

Please, any and all, jump in with thoughts, questions, suggestions, etc.

eric SV Meander/MV Meander TOO