Dinghy Motor

[Art]

I ran that gasser at around 22 knots, so when I towed that one time I ran at 22 knots, but I did notice the throttle was pushed forward more. Not until I checked fuel level (routine) did I come to realize using more fuel.
One time and done.

Steve

To push a boat at 12 knots through the water, compared to pushing it at 6 knots, takes many more than just twice the horsepower; as well as much more fuel volume per hour.

That's because the drag-scale coefficient of water friction compounds algebraically not linearly as speed through water increases.

So... with me towing a boat at 6 knots compared to you towing at 22 knots... the water friction drag increase is not 3.75 X [such as the liner speed increase]... but rather - algebraic drag increase equals more in the range of 8 to even 10 X [depending on the towed boats hull design and weight].

Our LOA 14'8", lightweight [700 lbs. including the engine] Crestliner V-bow entry, flat bottom with ridged-set trim tabs and its o/b's skeg out of water is a really easy tow at slow [6 knot] speed.

What size/weight/hull-shape boat were you towing at 22 knots? Towing at that speed... I understand considerably increased fuel use.

 

[SteveK]

Art, I understand. I do not tow because of that one experience. My original question remains. Still curious what towing a tender like yours relates to fuel consumption with/without. I know you cannot answer. Maybe someone else.

 

[angus99]

One of the problems I have with your set up, other than the fact my boat is in such a tight location, I physically couldn't have a dinghy sticking out like that, is that being the cheap sob that I am, I know at my marina I would be paying for the extra footage every month until I left said marina. And also paying at visiting marina's while cruising so your Defever 44 would be charged out at maybe 50 feet. It likes those really nifty bowsprits you occasionally see on sailboats, when I see them I also see $ sign at the marina.

My marina staff go around on occasion measuring over all boat length, including goodies attached, to determine if they are charging the right amount.

Luckily, where we dock, we pay for the slip, not our boat length. A 50-foot slip accommodates nicely, with a small amount of anchor overhang, and we pay the same with or without a stern-mounted davit. Likely that will change when we’re back on the Loop and paying transient rates again.

The dinghy butler looks nice. The only problem for me would be that it completely eliminates any access to the swim step.

Not completely in our case, Dave. Ours is mounted to brackets I installed under the swim platform—for all practical purposes, it looks to be on the swim platform and the hinge points are about one foot aft of the transom. When deployed and the arms are down, we have full use of the platform—we just have to step over the arms (easy) and under the hoist rope (getting less easy as I approach “middle age” ). With the arms up, it’s no more of an obstacle than the Seawise or any other stern-mounted system.

 

[dhays]

Not completely in our case, Dave. Ours is mounted to brackets I installed under the swim platform—for all practical purposes, it looks to be on the swim platform and the hinge points are about one foot aft of the transom. When deployed and the arms are down, we have full use of the platform—we just have to step over the arms (easy) and under the hoist rope (getting less easy as I approach “middle age” ). With the arms up, it’s no more of an obstacle than the Seawise or any other stern-mounted system.

I see. I didn't notice that in the photo.


My Seawise is mounted in such a way that I can easily walk on the swim platform from the Stb side to almost the port side without obstruction. The line that secures the bow does cross the swim platform on the port side so it has to be ducked under.


The PO had it installed. Initially, it was installed so that the forward supports for the SeaWise were mounted against the aft transom. This effectively blocked it off on the stb side. It was then changed so the supports angler forward to the swim platform itself. So now no obstruction.


It doesn't take too long to raise and lower the manual SeaWise. I've considered using an electric winch handle that I still have left over from my sailboat, but I've never bothered. I just might as I age however..

 

[cardude01]

I’m late to this thread, but I also recently bought an Epropulsion Spirit 1.0 Plus motor. It took forever to get it because of supply chain disruptions, but I’ve been impressed so far.

I have used this motor on my little trimaran sailboat and on my fiberglass catamaran lake/river boat. It pushes both of those easily, but like others have said it’s definitely not fast. I was using a little Tohatsu 3.5hp engine for these boats, and while it would push them faster it was noisy as hell, and even with stabilized fuel that damn outboard rarely started and ran right. I’ve rebuilt the carb countless times but it’s still very temperamental.

Here’s a little video of a test of the Spirit motor on the heavy fiberglass lake/river boat. The motor gives surprising range. We have used this boat for hours at night trying to shoot gar with a bow.

 

[Art]

I’m late to this thread, but I also recently bought an Epropulsion Spirit 1.0 Plus motor. It took forever to get it because of supply chain disruptions, but I’ve been impressed so far.

I have used this motor on my little trimaran sailboat and on my fiberglass catamaran lake/river boat. It pushes both of those easily, but like others have said it’s definitely not fast. I was using a little Tohatsu 3.5hp engine for these boats, and while it would push them faster it was noisy as hell, and even with stabilized fuel that damn outboard rarely started and ran right. I’ve rebuilt the carb countless times but it’s still very temperamental.

Here’s a little video of a test of the Spirit motor on the heavy fiberglass lake/river boat. The motor gives surprising range. We have used this boat for hours at night trying to shoot gar with a bow.

View attachment 121823

Gee - 3 to 4 mph; that top speed? What happens if you need to go against a current?

 

[cardude01]

Gee - 3 to 4 mph; that top speed? What happens if you need to go against a current?

Yeah I don’t take these two boats on any rivers with any current to speak of. The fiberglass catamaran is just a boat to putt putt around on and enjoy nature, and I use the motor on the sailboat to get it out of the channel into the bay.

If one is looking for speed these elec motors are not what you want. I have a 15hp Efi Suzuki for my dinghy motor on the big boat because I do want some speed from time to time, and so far that thing always starts on the second pull.

 

[sbman]

I'm still above 50% on the battery. And if youd get/add the solar charger, you can charge as your going or while your sitting on the beach... so range is not a problem really. BUT, speed is. The electric motors are VERY convenient, light weight, easy to mount, easy to transport, easy to store, no maintenance, no gas, no oil, no CARB! The only downfall is, speed. And this I suspect will be fixed very soon with some new models that will be 4hp or better.

Higher power models are already advertised from Torqueedo. However, given the current physics of electric power storage, the price does not scale well with increased power levels. It's around $2700 for a sort of standard 1.5-3 HP equivalent outboard with a battery integrated onto the unit. To go to their 5 HP equivalent model requires a 50 pound external battery and a heavier motor unit which combines to over $7,000 and still has a limited range at high power levels.

With gas it's easy to have fuel storage for sustained high power levels. There is so much power stored in liquid fuel, it's hard to conceive of just how little power batteries actually store compared to a liquid fuel. When you scale up electric, you require massive batteries to achieve what a small tank of fuel can do. Look at a Tesla battery, the entire bottom of the car is a very heavy battery with over 7,000 cells in it to achieve what a relatively small 15 gallon fuel tank can in gas powered cars.

While it is certainly technologically feasible to have a high powered, planing boat with electric power, for now the cost of doing so is prohibitive for most.

At this time, electric outboards are perfect for running dinghies at displacement speeds. Power to plane will remain the job of gasoline engines until there is a significant breakthrough in electric energy storage pricing and density.

 

[Sonchaser]

Like some of the others, I have never run out of battery and had to paddle back as the little "dash" on the motor tells me how much time I have left and changes depending on how much throttle I use. I pull the battery before I take the motor off the dinghy. It's just less cumbersome and it has a built in handle (believe it or not, the battery will float if you do drop it in). But, while in the dinghy I pull the battery, set it up on the dock, then pull the outdrive and hand it to my wife on the dock. If the battery is low, I just plug it in to either my solar panels (the unit comes with a connector and switch for solar) OR I plug it in to a plug on my aft deck and it charges when I run my generator OR, I take plug it in when we are at a dock and on shorepower. I thought that I would need or want an extra battery, but so far I have no need for one. Like I say, if you are used to an outboard that you can pull a skier behind, this won't make you happy. But if you want to cruise around, explore, go to shore when anchored out, we love this. We crossed the Ohio River and back recently, cruised around island for an hour or so, tied off the boat for the night, did it again the next morning, and still had half a battery left. I love it. BTW, my dink is aluminum hull. Pretty light.