Thanks all- love learning from the chat here. My brief experiments with a 36lb thrust trolling motor (a little bigger thanTyler's 24 lb thrust Watersnake) on My M15 made me conclude that while it was great for an hour or two of fishing on a still lake while waiting for the wind, when the wind came up to even 10 knots, it failed to have the power to maintain decent way and steerage (in comparison, in its toughest test, my little 2 horse honda let me tow a stranded ski boat with 5 people in it off a rough lee shore in a 20-25 knot breeze with only a little whining in the worst of the waves). A standard trolling motor setup up to the task is a heavy proposition (though in a boat designed for it, it can be impressive- look up Thomas Hruby and his St Pierre Dory Daddy's Third) - and part of what I love about my M15 is how light and responsive she is. Tyler's 48v battery idea- with multiple batteries and a more powerful trolling motor might work, but weight and price will climb quickly (see if I can find the time to and brainspace to calc out what that might look like). The Torquedos and like are really coming along- I think they'd handle all the boat needs except for the range limitation, but until the range comes along, the cost is a barrier. So right now I concur w Dave that the current electrics are largely limited to protected daysailing and not a good match for Keith's gulf island crossing and most other open water work- however, I suspect ultimately we'll see the cost of a Torquedo style motor drop a bit and come with an option for portable generator/fuel cell to act as a range extender for times when range is essential (as so many daysail most of the time, and have only a few extended outings in a year). So for now I'll keep that 1985 2 horse going, and see what's on the market in a few years... On Thu, Oct 15, 2020 at 12:28 PM John Schinnerer via montgomery_boats < montgomery_boats@mailman.xmission.com> wrote:
Ah, missed the battery voltage, thought it was 12v. Do it all in watts then...
48v x 11AH = 528WH
Say moderate speed draws 12A, then 12A x 12.6V = 144W
528WH/144W = ~3.6H, at 12A draw, as you say.
There is also some loss of efficiency in all battery powered systems, typically at least 10% and usually more like 20%, so take 20% off the theoretical math to get a safer real world estimate.
Part of the efficiency loss with battery storage is in the recharging, which isn't an issue in this situation, so 10% loss might be realistic here.
Not bad then for what you put into it!
cheers, John
On 10/15/20 10:38 AM, casioqv@usermail.com wrote:
Hi John,
The motor draws 9-20 amps only max startup (stall/0 knots) at 12v on the low and high speeds respectively. This 11 aH battery is a powerful 48v battery for electric bicycles, so you have to multiply the amperage by 4x to compare with a 12v lead acid. The stepdown converter gives 1/4 the voltage and 4x the aH as output.
I estimate on high speed once cruising it draws about 13amps at 12v, so that would be approx (11.6*4)/13=3.57 hours of runtime. Let's say it draws only 6 amps at cruise on low speed, that would be approx (11.6*4)/6=7.73 hours of runtime.
Indeed, I did motor with it on low speed for over an hour, and the battery was still reading 100% on the built in meter it has (which only reads in 20% intervals), so it was definitely over 80% at the end.
Sincerely, Tyler
----- Original Message ----- From: "For and about Montgomery Sailboats" < montgomery_boats@mailman.xmission.com> To: "For and about Montgomery Sailboats" < montgomery_boats@mailman.xmission.com> Sent: Thursday, October 15, 2020 9:29:42 AM Subject: M_Boats: Electric motor range (was Re: changing Honda 2/2.3 prop)
The specs for that trolling motor say minimum draw 9 amps, max draw 20 amps.
So with your little 11 amp-hour battery, you'll get maybe an hour at minimum draw, and half an hour or less at max draw. Some basic electrical math:
11 AH divided by 9 A = 1.2 H.
Please don't head out on a 5 hour tour (or even a "3 hour tour" :-) without other means to get back if the wind dies...at medium draw (15A) you'll get about 40 minutes of runtime at best.
You can get a 50AH or 60AH or more lithium battery, and it will be much lighter than same capacity lead-acid, but it will also lighten your wallet by a whole lot more.
cheers, John
On 10/15/20 9:09 AM, casioqv@usermail.com wrote:
I've been playing with using a 12V trolling motor on my M15 along with a cheap "Golf Cart Voltage Converter" to use a 48v electric bike battery pack with the trolling motor. It seems to work very well so far, but doesn't have quite the thrust of a gas outboard... good enough for exiting the marina, but not for motoring into a chop. The weight and runtime is comparable to a Torqueedo but at a tiny fraction of the cost. I've never ran it empty, but I suspect I can motor for 5-6 hours on the battery at about 3 knots.
Here's what I have: -DPLANET 30A 360W 12v Golf Cart 48V 36V to 12V Converter ($35 on Amazon) -Watersnake T24 ASP Saltwater trolling motor - designed for Kayaks ($150 on Amazon) -2017 Rad City Battery Pack 48V, 11.6 Ah (557 Wh) (from my eBike, but $399 new)
Total weight of this setup is 14.1 lbs with 7.4lbs for the battery, and 6.7lbs for the motor (converter is small and negligible). This is comparable to the lightest gas outboard I think has ever been sold- the 1.5hp Cruise'N'Carry at 12lbs. I used to have a Cruise'N'Carry, and found it to be cheaply made and extremely loud, so not really viable.
A big 24v 80lb thrust trolling motor would probably push the M15 at near hull speed and into a chop, but would be much much heavier than a comparable gas outboard, and requires dual large heavy batteries.
Sincerely, Tyler '81 M15 #157 S/V Defiant
----- Original Message ----- From: "Rimantas Aukstuolis" <raukstuolis1@gmail.com> To: "For and about Montgomery Sailboats" < montgomery_boats@mailman.xmission.com> Sent: Thursday, October 15, 2020 8:18:41 AM Subject: Re: M_Boats: changing Honda 2/2.3 prop
What about those electric trolling motors? Hard to figure out thrust/power/torque comparisons. What little I know, comparing them to expensive Torquedo is that they use bulky 12 volt batteries vs lithium. Any thoughts? Rimas Aukstuolis
On Thu, Oct 15, 2020 at 11:14 AM Alex Conley <conley.alex@gmail.com> wrote:
Thanks for the caution re overpropping. I guess the real solution would be to change the gear ratio to turn a larger prop slower at a given throttle setting. Then you could use more of the engines range and gain both torque at higher speeds and a slower low speed- both on my wishlist. But not a mod I can see making- it’d be a whole new lower end... It seems most of the little outboards we use on our displacement sailboats are geared to get a little inflatable zipping around; have there been attempts to make an outboard geared for small sailboats, or is it just too niche a market? I’ll plan to live with my imperfect 35 yr old motor long enough to hopefully hit the point where the range/cost ratio of the electrics makes them a good replacement....
On Wed, Oct 14, 2020 at 8:10 AM Dave Scobie <scoobscobie@gmail.com> wrote:
Alex:
Somewhere a few years ago I read about a person changing out the prop on the small Honda - wasn't a Mboat. I can't remember any specifics.
The general consensus was the problem is the motor will likely be overstressed under the load - especially a concern with the powerhead being or cooled.
:: Dave Scobie :: M6'8" #650 :: SV SWALLOW - sv-swallow.com :: former owner M17 #375 SWEET PEA - m17-375.com :: former owner M15 #288 SCRED - www.freewebs.com/m15-named-scred/
On Wed, Oct 14, 2020, 8:03 AM Alex Conley <conley.alex@gmail.com> wrote:
Ive also searched for a high thrust prop for my 35 yr old Honda 2 hp but never seen one. In these days of 3D printers/milling, strong plastics and computer designs, it would seem there might be an opportunity for someone to work up some designs that could then be made on order.
-- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com