Sunday, December 18, 2011

NOTES OF AN ELECTRIC SAILOR: Tests from the harbor 2011

When I started this blog back in 2006 I thought it might just be a little online scrap book of travels with some photos. An easy place to put those memories and share it with anyone who happened by. It has since morphed into something a little bigger. In between my thoughts, photos, cruises and travels I also post things about products here and there. Those that work and those that don't work for me. I also use the blog as the name implies as somewhat of a log book of maintenance and boat projects on board BIANKA. This is one of those posts.

I had wanted to do some propulsion tests of BIANKA's electric propulsion system as soon as I splashed her for the 2011 season. But, that did not happen. But one morning a few weeks later I was having my usual 6 AM coffee in the cockpit. The air was still in the harbor, the water like glass and it was quiet and empty of any boat traffic. I thought well why not do some testing. Even though it would was not perfect conditions. It was midway to low tide so there would be some currents running and they do run oddly in this harbor. Probably would have been better to do it at the peak of the high or at low tide when currents would have been minimal. The boat had also been on the mooring for two weeks so I did not know how clean the bottom and prop were which could affect things somewhat. Anyway, I turned on the system slipped the mooring and headed out to the channel.  I made several passes between channel markers that were about 450 yards apart. One pass was made in each direction drawing 10, 20, 30, 40 and 50 amps from the battery bank.  I then averaged the speed of each pass and calculated the watts used. Here are the results:

1                  10            1.9           495
2                  20           2.8            984
3                  30           3.3          1458
4                  40           3.7          1933
5                  50           4.1          2417

Again these are the average of the two passes. One against and one with the current. I also did one additional test where I just throttled up to 5 knots and the power used there was 4346 watts. The test data pretty much confirms what I have noticed on board. Especially on pass number two. I can move my 8 ton 30 foot sailboat at about three knots just using power from my Honda 2000 eu generator and the Zivan NG-1 battery charger which is rated at 900 watts. The numbers show I could add an additional 48 volt 500 watt power supply into the mix.  I should then obtain the results of pass number three and still be within the power limits of the Honda 2000 generator. Which is good to know if I ever feel the need to add one. But, since BIANKA is a primarily a sailboat I have never felt the need for it.  I'm also using the same three bladed prop that BIANKA used with the diesel. It has a few dings here and there. I might be able to improve things a bit with a prop optimized for my electric propulsion system. But, I tend to be if it ain't broke don't fix it type of sailor. Anyway I'll try and do another test at the beginning of next season and see how they compare. Also it is good to have this data to compare if I do decide at some point to change the prop at some point. But, I'm very happy with things the way they are and have been for the past four years. So I really don't expect to be making any changes soon.

BLOG UPDATE:  After doing this test I pulled the boat for the season. I found the prop was not as pristine as it could have been as this photo shows just after the boat was pulled:
Usually I would have dived and cleaned it but, it being late in the season the water was too cold. I expect to have even better results in the spring doing the tests with a much cleaner prop.


Greg Martin said...

This is really good stuff! Have you done the official Asmo Marine test that the company prescibes? Sally Ruether has the test forms and can tell you all about it. Honestly, I haven't gotten around to it myself but have been meaning to. Everytime I feel like running some tests, I realize the conditions are less than ideal, my prop is dirty, etc. Before I run any official tests, I feel like I need to have a good way to control all the variables... but something is better than nothing, right!? This is really good. Thanks for sharing it on Electric Seas, too!

Capt. Mike said...


I have not done the offical ASMO test. Though I may try it this spring with a clean hull. When I pulled the boat after this test I found the prop was fouled with a sisel like growth. Which may explain the small increase in speed between the 40 and 50 amp data. I would expect improved numbers with a clean prop.