Arctic Tern Electric Power

[Jamesh]

What by the way is the displacement of arctic tern in crusing trim.
What sort of power would you need for a 2200lbs sailing boat?
Perhaps 2 motors?
The batteries are easy to obtain and good ballast too.

James

[SeaB]

How about using a salt water motor, would not expect the regular motors meant for fresh water to do very well in salt water.

[mcdenny]

What by the way is the displacement of arctic tern in crusing trim. What sort of power would you need for a 2200lbs sailing boat? Perhaps 2 motors? The batteries are easy to obtain and good ballast too. James

I'd guess around 600#. Not much.

The 'how much power' question depends on how far and how fast you want to go. One cheesy trolling motor and one 50# battery would easily move your boat around in calm wind and still water for an hour. It wouldn't be practical outside that narrow definition though.

A decent system would be a 5 kW motor with four 60# 12v batteries. A better one would use 8 6v batteries

[kbowen]

This is what I don't quite understand, why would anyone put a resistor in parallel with a motor? That would just waste power. I can imagine putting a resistor in series with a motor which would be a crude but effective speed reducer. If anyone can verify that the speed coils are parallel to the motor, then the coils are probably acting as additional field coils in a shunt-wound motor. Contrary to intuition, a stronger field reduces the speed of a motor by increasing the back-emf of the armature. This would also explain why the current doesn't decrease at lower speeds as much as one would imagine; the extra juice is used to suppress the rpm.
Ken

Yes the lower speeds put a resistor in parallel with the motor. As the speed drops the load on the prop lessens so the current doesn't go up.

If I recall speed 5 puts all 12 v into the motor and speed 4 cuts that to 6 volts.

[kbowen]

Actually, I just thought of another possibility (which I can't test either because the motor is 1200 miles away)it could be that the field coils oppose the permanent magnet, that the lowest speed is the one with no field coils energized, and the coils weaken the field, increasing the speed. Someone from Minnkota needs to chime in here, or someone who can open up one of these motors and find out how they are wired.

This is what I don't quite understand, why would anyone put a resistor in parallel with a motor? That would just waste power. I can imagine putting a resistor in series with a motor which would be a crude but effective speed reducer. If anyone can verify that the speed coils are parallel to the motor, then the coils are probably acting as additional field coils in a shunt-wound motor. Contrary to intuition, a stronger field reduces the speed of a motor by increasing the back-emf of the armature. This would also explain why the current doesn't decrease at lower speeds as much as one would imagine; the extra juice is used to suppress the rpm.
Ken

[mcdenny]

Maybe I mis-spoke 😬. Probably the resistors are in series with the motor brushes.

[Oldad]

. Someone from Minnkota needs to chime in here, .

Good luck trying to get MK to speak on the issue. They have refused to reply to several requests I have made on their "help line" which is no help at all.

[ulav8r]

When I asked MK about the amperage of a 10 lb thrust motor bought about 1975, they replied within a week.

[mcdenny]

In case anyone finds this old thread, I've just refinished the boat to sell (check out Woodenboat website ad) as its been sitting unused for several years. Battery was dead as a doornail of course but the motor (installed used 8 years ago) and electronics still work fine.

[Rich Jones]

That is a fine looking vessel for a very attractive price. I hope someone snaps it up.
I also just sold two boats (canoes) that had been sitting around unused for years. Better someone else uses them then have them hanging in the rafters gathering dust.

[mcdenny]

Thanks Rich. I priced it to sell as I know it can be very hard to sell an owner built wood boat, no matter the quality.

In this case it sold right away to a guy from southern CA who saw it on the WB site a few days after to ad went up.

In related news I finally sold my second Harmony 25 (for about the cost of materials) after six years of trying.

[mcdenny]

The guy from Los Angeles changed his mind so the boat is not sold after all.

[mcdenny]

Just to close this out, the boat has gone to a new home in SW Michigan.

A shout out to WB as the new owner saw the WB ad that somehow showed up on the offcenterharbor website

[Pitsligo]

This is still a great thread, and I hope it stays around for a long time.

I'm in the process of sorting out how to put electric auxilliary power in my sloop, Bucephalus. Completely different beast than your Arctic Tern --19', deep keel, 3000# displacement-- so I'll need an entirely different approach than you used, but your innovation and technical expertise is both educational and inspirational.

Alex

[mcdenny]

Bumped to say that the pictures have been restored.

In my browsing through some newer build threads I see there is a growing interest in electric aux power for small sailboats and even some mention of “hybrid” rowing where the motor assists but does not replace the human effort. Also comments along the line of “ I love my electric bike so thought I’d try electric power for my boat “

I too recently got an electric bike and love it. The motor doesn’t at all replace pedaling, just makes it easier and flattens the hills. I stopped riding my regular bike years ago but now ride the E bike a lot. Some exercise is better than none, right?

What a wonderful thing it would be if E assist would mean more Whitehalls, Guideboats and the like stroking across the water again. Rowing upwind would be just as easy as downwind; an adverse tidal current, no problem; ship the oars and navigate facing forward through a little trickle of a creek.

[phiil]

53F54C35-2F17-4252-8CCE-6E8FFBCB7F97.jpg7840B5A5-6F71-417C-8D0A-9E11B0967CD6.jpg
Here’s the pod drive I built using a Bixpy motor. The foam block displaces the water in the well, and provides a little shock absorption in case of a hard strike. The whole thing lifts straight up for beaching. I will probably replace the Bixpy with a Torqeedo next spring. I’m driving a 16’ canoe and the Bixpy is really designed for a SUP or kayak.

[mcdenny]

Clever solution to water sloshing around in the trunk.

[The Jeff]

Thanks for updating the photos. It's a really well done setup and I'm definitely keeping it in mind if I ever build a bigger boat.

[rgthom]

Bumped to say that the pictures have been restored.

In my browsing through some newer build threads I see there is a growing interest in electric aux power for small sailboats and even some mention of “hybrid” rowing where the motor assists but does not replace the human effort. Also comments along the line of “ I love my electric bike so thought I’d try electric power for my boat “

I too recently got an electric bike and love it. The motor doesn’t at all replace pedaling, just makes it easier and flattens the hills. I stopped riding my regular bike years ago but now ride the E bike a lot. Some exercise is better than none, right?

What a wonderful thing it would be if E assist would mean more Whitehalls, Guideboats and the like stroking across the water again. Rowing upwind would be just as easy as downwind; an adverse tidal current, no problem; ship the oars and navigate facing forward through a little trickle of a creek.

Nice to see this inspirational thread come back to life. On my hybrid rowboat (good term), inspired by getting an ebike, it does assist the human power but in a different way. For the ebike I use the boost while pedaling, increasing my power output and speed. On the rowboat that does not work as well. Even double the power only adds a little speed, boats have that hull speed limit problem. The motor is like having a second strong rower, I alternate rowing and motoring to take a rest, see forward, get a snack, etc.
My main problem is it works too well. With on board solar I can cover 30 to 40 miles in a summer day on electric alone. I can avoid rowing completely and get lazy.

Rick

[pez_leon]

Thanks for restoring these pictures! It's an inspiring build.

Even double the power only adds a little speed, boats have that hull speed limit problem.

I think that's a big issue. Moving at 3 knots over ground against a 2.5 knot current would require pushing my 13' rowboat faster than any reasonable input will produce. The marginal gain from the motor won't result in much additional speed over whatever I can do. I would be curious to hear about a power assist for rowing upwind! Even just using the propeller to trim the boat onto the desired heading could be very helpful. I don't love the imbalanced feeling of constantly fighting the tenancy to turn into a side wind.


- James

[rgthom]

I think that's a big issue. Moving at 3 knots over ground against a 2.5 knot current would require pushing my 13' rowboat faster than any reasonable input will produce. The marginal gain from the motor won't result in much additional speed over whatever I can do. I would be curious to hear about a power assist for rowing upwind! Even just using the propeller to trim the boat onto the desired heading could be very helpful. I don't love the imbalanced feeling of constantly fighting the tenancy to turn into a side wind.


- James

My little motor works well in wind. As you say rowing into wind is tricky, the boat always tries to head off. My rowing technique is long slow pulls with a fast recovery before it turns. The motor is able to power into 20+ kts at around 3 kts boat speed at full power, much better than I can do rowing. Much better steering control too.