Tender behind

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Gypsy
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Re: Tender behind

Post by Gypsy » Wed Oct 27, 2010 11:52 pm

When I said it recharges from the Mother Ship , namely our Mac , all I do is parralle it with the starting battery for about an hour .
Or I can run its charger on the inverter and recharge it like that , both work . The charger is a trickle charge , which is probably better on the battery .
Either way it is a charge from the Honda pushing the boat which is a 17amp charge.
Its using power that was generated as a byproduct of propelling the Mac.

When I get my solar cells mounted , the dinghy will be running on solar energy.

An electric motor is so much lighter , and so much easier to deal with overall , than a gas motor .
But You do sacrifice power for convience .
We do a lot of gunkholing as well , sooner or later , I'll probably get a larger battery .
It is fun , putting along , silently , watching the wildlife :macx:

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Catigale
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Re: Tender behind

Post by Catigale » Thu Oct 28, 2010 5:07 am

You can recharge occasional use but, completing the math exercise...

17ampsX12 volts is a nominal 200 watts, or about 1/3 HP

If the motor is used at a nominal 2hp rating pushing a dink, one hour of recharge replaces about 10 minutes of operation. I'll make that 20 minutes with factor of 2x... :D ...for the efficiency advantage of electric over gas...plus I get ton over use ellipses on my Ipad...

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Sumner
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Re: Tender behind

Post by Sumner » Thu Oct 28, 2010 8:38 am

Catigale wrote:......If the motor is used at a nominal 2hp rating pushing a dink........
Did I miss it or what? I can't see where he said it was 2 HP.

I'd like electric and the weight, but you still have to deal with the weight of a battery. Of course you can pick them up separately. Also for an extended trip where you might use the dink very much you are going to have to generate considerable electricity to do the same work as a few gallons of gas like you have pointed out,

Sum

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Catigale
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Re: Tender behind

Post by Catigale » Thu Oct 28, 2010 1:33 pm

You wont move a dink with much less than 2HP. Power is power - it doesnt matter if its electrical or internal combustion.

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Gypsy
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Re: Tender behind

Post by Gypsy » Thu Oct 28, 2010 2:50 pm

I used to have a formula that converted lbs of thrust to horsepower , but not anymore.
I use a 28lb thrust motor and it propels our two chubby butts about 5mph .
Weight was the reason I bought the wheelchair battery , but smaller, lighter, battery means decreased range. I can comfortably pass the battery up to the admiral as well as the motor.
The weight of the battery would probably equate to the weight of a gas tank . But the motor is much lighter.

I could use a small standard lead acid deep cycle battery and have a 20 mile range , but that would require more work , lifting the battery in and out.

But I still say the dink is powered by byproduct electrical energy. Recharging that battery does not burn a measurable amount more of gasoline , since the Honda engine is turning the alternator whether its charging something or not. I know the alternator becomes harder to turn when a load is applied to the elecrical system , but this would not be enough to measure . Soon , it will be solar powered.

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Catigale
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Re: Tender behind

Post by Catigale » Thu Oct 28, 2010 9:04 pm

You will burn exactly more gasoline than the fuel content required to deposit the used electrical power back into the battery, it turns out.

This energy isnt free, and will be the same amount of gas to power an equivalent HP motor, less losses.

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Re: Tender behind

Post by Hamin' X » Thu Oct 28, 2010 10:36 pm

The nice thing about a gas tank; it is much easier to put back into the boat when empty. Not so the battery. However, I am considering the Torqeedo for my dink:

Image

http://www.yachtproductsintl.com/catego ... goryID=185

~Rich

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seahouse
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Re: Tender behind

Post by seahouse » Fri Oct 29, 2010 1:21 am

Hey you guys! :D

You can't convert thrust to hp any more than you can convert the volume of a glass of water the the height of another glass of water. :!:

Thrust is force, and hp is power, so you would need to make an unreasonable number of assumptions to convert one to the other. It would not even be reasonable to connect two tenders together, one electric, one gas, with a rope, and see which wins because the propping alone (pitch, diameter, etc.) could very well determine the outcome without telling you much at all about how the two would compare in normal use. :?:

Yipes! Looks like trial and error is needed to compare the two power sources. And just what is the smallest gas outboard made? 2hp?

I think it's another one of those marketing conspiracies. :cry:

- Brian.

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Re: Tender behind

Post by Catigale » Fri Oct 29, 2010 5:45 am

The easy way to compare is to use the amps x voltage = power formula for the electric motor and then you can compare power to power of of course.

I like the electric motor concept, but since i wont have a generator the recharge issue is problematic for me for a week long cruise with heavy dink use.

The thread above hopefully gave people a sense of what the recharge load needs to be - it isn't small.

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Re: Tender behind

Post by grady » Fri Oct 29, 2010 9:59 am

Power is power you can make the same power/thrust/HP/torque or whatever with a gasoline engine or electric motor.

To use the least amount of gas you will need to get a gasoline outboard. Anytime you convert energy from one form to another there is a loss. nothing is 100% efficient. pressure to motion, motion to electricity, electricity to battery, then battery to electricity, electricity to motion. it is more efficient to harness the motion the first time and convert it into thrust.

Generally the gasoline option is lighter also. I do prefer the electric option and now battery and motor technology is finally getting close.

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Gypsy
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Re: Tender behind

Post by Gypsy » Fri Oct 29, 2010 11:15 am

An electric motor is a much more effiecent machine verses gasoline , when it comes to converting energy to propulsion .
This is one reason many large boats are going to a generator / electric motor setup verses straight
oil burning engine.

If you desire more range in your dinghy , you simply bring more battery . Like you would gasoline cans .

I had a 4hp electric motor , a Minn Kota , it would lift the front end of my 17' aluminum canoe with two people in it.
But it would suck the bottom out of a battery very quickly.

The advantages to an electric motor are many , and thats why I prefer them , always have.
But their one disadvantage is speed .
But if I were interested in speed I wouldn't have traded a 220hp V8 engine for a sailboat with a 50hp Honda , now would I ?

One of my gentle memories , is anchoring the big boat on the Sauwanee River Florida and following one of thier canoe trails in the dink . With the electric motor , we were able to sneak up on all kinds of birds and other wildlife.

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Re: Tender behind

Post by Boblee » Fri Oct 29, 2010 6:36 pm

Sorry I just can't see how Fuel (gas ) driven motor with a prop attached is less fuel efficient than a fuel motor driving a generator which drives an electric motor either direct or even worse through a battery.
There are advantages in using an electric motor but they are not 100% efficient and nor are generators.
I did see something on yachts using electric drives but they rely on recovering excess enegy from forward motion provided by fuel or air (sail) with some solar, wind generation etc thrown in.

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Re: Tender behind

Post by DaveB » Fri Oct 29, 2010 7:23 pm

Powered a inflatable 9ft.6 in. with a deep cycle Sears best Lawn mower size battery with a 40 lb thrust elect. outboard. Ran fine in calm water at setting #4 out of 6 doing 3 knots . Doing Max. 6 only got me to 3.5 knots with 2 people aboard and would run out of power in less than 1 hr useing the 4 setting.
My Suzuki 2.5 gas 4 stroke will outdo the Elect. at full throttle in less than 1/2 throttle.
Full tank last over 3 hrs at 1/2 throttle on the Suzuki, weighs 32 lbs with tank filled. Add the weight of elect. motor,battery and caseing and see the diffrence.
Sold the Elect. Motor.
Dave
Catigale wrote:You wont move a dink with much less than 2HP. Power is power - it doesnt matter if its electrical or internal combustion.

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TexasDan40
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Re: Tender behind

Post by TexasDan40 » Fri Oct 29, 2010 8:06 pm

I don't have a tender, but there have been times when I wish I had one.
I do pull my kids behind Alpha Sail often. This is from about 2 weeks ago before the water started getting too cold in Kemah, Tx.
Image
Te :macx:

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Gypsy
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Re: Tender behind

Post by Gypsy » Fri Oct 29, 2010 11:22 pm

Ran fine in calm water at setting #4 out of 6 doing 3 knots . Doing Max. 6 only got me to 3.5 knots with 2 people aboard and would run out of power in less than 1 hr useing the 4 setting.
I think you were a victim of the dreaded "Hull Speed" 3knots was the hull speed of that dink

All the modern Cruise Ships use Diesel generators to power electric motors that actually turn the propellars


With just a 28lb thrust we could max out at 5mph and cruised at a bit less ( 4mph) and we cruised for about 5 miles before the battery would show signs of running down.
I guess its different strokes etc . I wouldn't care to have a gas powered dinghy . I enjoy the quiet gentle ride of an elecric dinghy . I also enjoy the ease of stowing the equipment and not having to have gas for two different engines . Recharging is done from byproduct electricity and soon to be solar.
But it may not be for everyone

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