Monday, December 02, 2013

NOTES OF AN ELECTRIC SAILOR: Harbor Test 2013 Part One

Back in early June I had just splashed BIANKA but, had to wait for the boatyard to step the mast. Since I had nothing else pressing on board I thought I would take the opportunity to do some testing of the electric propulsion system both without and with the mast installed. So that's what I did. I made several runs between two buoys in the harbor that were 450 yards apart. I did a similar test back in the fall of 2011. Though I conducted these tests with a cleaner bottom since the boat had recently been splashed.

The mast on my 30 foot Nonsuch weighs about 300 lbs which is pretty heavy compared to a lot of other boats the same size. So I was curious to see what effect the mast weight might have on the boats performance. Like the test I did in 2011 I made two passes between the buoys. One going east and then turning around and making another pass going west. They were made at various current draws from the 48 volt battery bank of 10, 20, 30, 40 and 50 amps. The two passes were averaged to take into account any tidal current pluses and minus to the speed.
Here is the graph comparing the speed both with and without the mast on board:

As you can see there is a slight difference at the low end and upper end of the speed data. But, only about a  quarter of a knot or so. The sweet spot seems to be right around 3 to 4 knot range where both graphs are pretty close. Out of curosity I took the data from the Harbor Test of fall 2011 and added it to the above graph's data:

What's interesting to note is that the 2011 test data was taken at the end of the season just before I pulled the boat for the winter. The hull and prop had not been cleaned for probably a month or more:
So that growth seemed to have had some effect on that test data. 


John Morrison said...

I presume the results from the first graph indicate that once you have the mass of the mast moving, it begins to exhibit some momentum, hard to get going, easy to keep going.

I know that when I removed my offshore anchor chain (some300lbs worth), the waterline on the bow rose about 3 inches. Perhaps the resulting drop in wetted surface accounts for the very minor improvemnet in speed once underway?


Capt. Mike said...


Nice thing about electric is you can start off very slow with a lot of torque and keep the prop slip to a minimum while starting off. Really helps when coming into a dock.
Yeah I think the 300lb mast on the bow does lower the bow a bit but, as the graphs show has little affect on boat speed compared to a fouled hull and prop. Which is good to know.