Solar Boat (Electric Motor) Calculations for canals

  • 03 Jul 2013 00:42
    Reply # 1331954 on 1298446
    Deleted user
    Good luck with your project .  We took a different tack, going with a Honda generator to make a series hybrid, just in case we needed the power and for the coffee maker.  This month, since it is a new system, we are going to measure output and recharge rates, so we can have the option to not depend on shore power for recharge.  The solar panel went into the Potomac, but we had better luck with a wind generator.  The data for that will come soon with more points to measure.
  • 02 Jul 2013 06:20
    Reply # 1331245 on 1298446
    Glad to hear of your success! 

    Batteries are a nuisance, but a necessary one. 
    Without them, solar panels give a poor return.

  • 29 Jun 2013 20:52
    Reply # 1329786 on 1298446
    Deleted user
    Shore power would certainly be a bonus.

    My approach is very much to try to match the solar input to the electrical need. In an ideal world I don't think I would have a battery at all, both for weight and replacement costs.

    However I do have a spare 110ah battery so I am using that as the electric motor battery for now.

    The setup I have just rigged is to leave my electrics almost as they were; starting battery and leisure battery with split charging from the engine.

    I have added in the spare battery into a rear locker and put a 12v two pin socket after the solar charge controller and fuse.

    So now I can connect the solar to either my leisure battery, or to my motor battery. It's not ideal as I still can't charge the electric motor battery from the diesel without physically swapping batteries.

    I'll play around with it as it is for a bit, and then maybe investigate triple battery relays if its successful.

    Mainly because it was cheap (£100 ebay) but the folding aspect is useful too.

    I just did the first run and got 2.3 knots at full tilt, about half that at half speed, so almost exactly as predicted.

    Lovely and quiet :)

    Last modified: 29 Jun 2013 20:55 | Deleted user
  • 21 Jun 2013 18:02
    Reply # 1324016 on 1298446
    Hi Sam and Kurt,

    Following on from your point, Kurt, about overnight shore power, it is widely available in the inland waterways but not always where you want it. Berlin, as mentioned by Sam, has many free 24 hour mooring spots right through the city but none have power. Its a short run out of town to numerous yacht clubs where power is available. We have been cruising in Germany this year since 30 April and could have had shore power every night if we wanted. Being on a budget we have gone for anchoring and free mooring spots. In France there are number of towns and villages that offer free moorings, power and water to encourage boats to stop. 

    All the very best to mehitabel and her crew during your trip to Tonga. Good luck with the reef passages in particular. Although not as warm or as colourful as Tonga we have been cruising inside the Baltic Islands of Usedom and Rugen. Its been quite amazing how extensive the lagoons are and how far inside them you can go. There is no tidal flow on the Baltic but the wind can build up masses of water up rivers and lagoons and then it flows out. We have experienced some of these flows and a bit of power comes in handy. Inland rivers obviously have current but so do many canals, a fact that needs to be taken into account.

  • 20 Jun 2013 20:40
    Reply # 1323211 on 1298446
    Hi Sam,

    I just sorted out, finally, that this is about you and Joker, as well as the camber question under Flat Sails... You've probably read JRA Newsletter #61 by now and seen the two articles I did that are somewhat related to your pursuit. Which I hope will go very well!

    We're sailing to the tropics soon, weather-permitting, with no diesel but with 680W of solar panels and a modest wind generator. I'm sure we'll need patience at times, waiting for a full charge before risking a pass or a windward channel here or there in Tonga, but at sea we should be able to motor-sail a little each day if we want to.

    In your situation, you'll have the backup of a diesel, and be able to ration your electric charge for day-by-day progress. Have you considered the availability of overnight shore plug-in charging? Low speed is key in conserving power, and yes, quiet is a wonderful benefit. I bet you'll go a little faster than you've predicted, for the Watt. If not, it's likely because of a too-small propeller.


  • 13 Jun 2013 10:28
    Reply # 1317101 on 1298446
    Deleted user
    So I took the leap and just got a 55lb trolling motor for £100 off ebay.

    I'll try it on the boat and see if it really does move us and then decide if the additional solar is worth it.

    If not it will still be useful in the tender.. I'll let you know how I get on.
  • 02 Jun 2013 12:38
    Reply # 1307344 on 1298446
    Deleted user
    Hi all

    Thanks for the replies.

    Kurt is this your article:'s%20motor%20system_.pdf

    Or is there another one? 

    I guess my next step is to borrow an electric outboard and see if it really will push us along.


  • 26 May 2013 19:47
    Reply # 1301762 on 1298446
    Hi Sam,

    I give you my hearty encouragement. About your calculations, I have little to offer that would apply to your boat, different as it is to ours. 
    (see article in JRA Newsletter #61)

    However, the principles are similar, and so will be your need for patience.

    Best of luck!


  • 22 May 2013 02:33
    Reply # 1298539 on 1298446
    Hi Sam, you should go talk to the guy's on the Yahoo Electric Boat Forum. The the guy's there really know their stuff and they are doers, not dreamers. So you will get real world advice.

    I do not normally recommend Yahoo forums to anybody but this one is a exception. It's heavily moderated by a chap that really knows his stuff so misinformation is quickly discovered and pulled.
  • 21 May 2013 23:58
    Message # 1298446
    [Webmaster edit: Sam Rossiter posted this in the General Forum. I've moved it here, cos it's a bit techie! Brian.]

    Hi all

    So I'm thinking I don't get enough funny looks from other boat owners yet..

    I have a small boat 26ft, 2000kg and plan on doing a fair bit of canal work, might even head for Berlin. Not in any particular rush. Engine noise also annoys me. So I'm doing the maths on a solar/electric auxiliary (for canals only obviously)

    I'd obviously still have the diesel for strong currents etc.

    ==Required power==

    Reading this suggests that a 55lb thrust is equal to about a 2hp petrol outboard, which would get us moving, albeit slowly

    I'm looking at the Flover 55: which looks like it might give me maybe 2 knots at full tilt using 45amp @ 12v £170

    "You will draw about a quarter of the charge from your battery at half speed" So maybe a knot at 11.25 amps.

    ==Engine inputs==

    I have a 50amp alternator that does nothing but use diesel once the batteries are charged.. So by running the engine in bursts; an hour of fast noisy donk, a couple of hours of slow quiet electric I can use that 'spare' power.

    ===Battery discharge==

    I don't want a discharge below 20% = 12.42v So I can take 24amp hours between engine recharges.

    So without any solar input I can do 1 knot for two hours before needing to recharge via engine.

    ==Additional Solar inputs===

    I already have 100w of thin solar panels on board.

    Based on average cloud cover let's assume 50% output of the panels

    So I might get 50watt/ 4.16667amps from my existing solar.

    If I got 200 additional watts of solar which would cost about £380

    I should get 150w/ 12.5amp from my this solar, which would move us along at a knot on a cloudy day.

    On a full sun day (If ever!) I would get 25amps and maybe manage 1.5- 2knots.

    The panels would be rigged on temporary lines between the stanchions when in  'canal' mode, then stacked in the forepeak when in 'proper boat' mode.

    ==Cost comparison ==

    So total system cost would be about £600. Expected UV life of flexible panels 5 years, so 20years if used outside for only 3 months a year.

    Based on diesel at today's prices:

    10 HP/ 1 litre/ hour @ 5knots

    1000 miles = 200 hours = 200 litres (ish) x £150p / litre = £300 fuel cost

    So in 2000 miles I would break even. Plus the value of doing it silently which is worth something to me..

    Any glaring calculation errors?


    Last modified: 21 May 2013 22:52 | Sam Rossiter
    Last modified: 30 Jun 2013 20:39 | Anonymous member
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