Towing a Dinghy: How much drag?

[dvideohd]

that is just really darned ingenious....

With a GOOD solar panel - actual use of a charging motor might even be a lot less....

I most WHOLE HEARTELDY recommend you go for a patent on this.. If you can.....

"Patent it Yourself" and "PP in 24 Hours" are two good books to have... If you meet the time lines - and it was your original idea, then SPEND $100 to get this filed - and then you can think about it over the year....

--jr

[Duane Dunn, Allegro]

I have two provisional patent applications under way, one for the integration of the electric propulsion system with the rudder, and the second for the design of my feathering propellers which use a simpler, unique design with only two moving parts that is great for smaller prop applications.

Once the basic electric propulsion system is designed and in production I will move on to my more advanced designs which provide joystick computer controlled docking.

[DaveB]

Duane,
I had both the 2.5 Suzuki and a 40 lb thrust elect. with a Lawn Mower Sears Gold deep Cycle battery in a 6 pack soft container bag.
Best performance was at the 5 setting and that would give me 4-4.5 knots and at half throttle 2.5-3 knots and it had a 3 blade under winds less than 4 knots.
it would go to about 1 hr at half throttle before it got down to 12.2 volts.
With the Suzuki I don't need a battery pack and do 5 knots at 1/2 throttle to last around 2 hrs.
I sold the Elect. motor to keep things simple.
There is great need for both powers and if in doubt it is best for the gas Guzzler .
It all depends if you want to do that long distance gunkholeing after anchoring to explore, or that long trip against wind and current to get back from dock or trip.
If one only needs to go to beach or dock up to 1/2 mile or so away than elect. is way to go.
If on a extended Cruise than the Gas Beater is the way to go, unless you have solar or gen. to recharge battery eash time you use it.
There are many ways to improve your system as you pointed out. Is it pratical or not is something the Skipper needs to understand their needs.
I will add: many fresh water lakes do not allow cumbustion engines and a Elect. outboard on a Dink is perfect.
Dave

I have two provisional patent applications under way, one for the integration of the electric propulsion system with the rudder, and the second for the design of my feathering propellers which use a simpler, unique design with only two moving parts that is great for smaller prop applications.

Once the basic electric propulsion system is designed and in production I will move on to my more advanced designs which provide joystick computer controlled docking.

[James V]

Never tow a soft bottom dinghy. It will fly.
Foldaboat does not tow well.
Most people do not take their dinghy motor off when towing for day hops.
Get a big 50 foot tow rope. The marine stores carry polly tow ropes for water toys. Get the biggest you can find. I use 5/8. The polly will float and will last about 1 year in the Florida sun.

Clean the bottom of the dinghy every week or so.

My rpm's did not suffer at 5 mph. That is the displacement speed of my dinghy. After that it slowed my boat.

Towing distance. With stuff close by you will want your dinghy as close as possible. In open waters, as far back as you can. One person I meet kept his 300 feet behind in open waters.

When docking, keep the dingy close to the side if comming to as wall or "T".

[Lvoight]

I'm hijacking this old discussion to ask why not just bring the nose of an inflatable up over the outboard so the back is in the water still floating? Seem like the easiest, but adds some windage.

[RobertB]

I have towed a canoe behind my with little or no drag. I made sure the bow of the canoe was riding just barely up on the top of the wake, it was stable at high speed and very little drag (none I could notice).

[Lvoight]

I have towed a canoe behind my with little or no drag. I made sure the bow of the canoe was riding just barely up on the top of the wake, it was stable at high speed and very little drag (none I could notice).

I mean like pull it out of the water and up on the back of the outboard with the stern dragging. Clearly just an an inflatable would work.

[DaveB]

Lvoight,
Since my last post here in March 2010 I have a Zodiac 8 ft. that use with twin bridal and keep it about 15ft. back with little or no drag. Close quarters I bring it up to about 3 ft. back from lines hitting outboard. I can keep it this way sailing but high windage may flip it. (42 lbs easy inflate,high pressure floor with inflatable keel)
I have a Suzuki 2.5 hp mounted on stearn to power it but I love to row this dink with one person.
Docking I bring it tight against the motor for ease .
So your ? works for me.
Remember Sea conditions make a huge difference in towing.
Dave

I'm hijacking this old discussion to ask why not just bring the nose of an inflatable up over the outboard so the back is in the water still floating? Seem like the easiest, but adds some windage.

[Russ]

Sounds like it might work. Give it a try and let us know.
Once while towing my inflatable dink a wind caught it and took it aloft. Like a kite. Scary to think this otherwise heavy thing could get lifted so easily.
Another time I was fool enough to leave the 2.5 suzi (like Dave's) attached when towing and wind lifted it straight up. The thing was pointing vertical with the motor probably being dunked. Yeah, these things take a lot of wind.

[March]

Yes, I do not doubt that high winds can flip the dinghy, regardless of the engine. I did experience the kite-flying dinghy in the Bahamas, @ 20 + kts winds. It was a large one (4 people) with two pairs of oars and proved to be a royal PITA. Mercifully, it started losing air at the end of the expedition so we deflated it and put it away on the last leg. In case of shipwreck across the GulfStream, we decided to trust the ever-floating mac, or go down with the ship. That didn't happen

Now we have a smaller Zodiac with a 2.5 HP engine. I plan to keep the engine on a starboard bracket when the weather gets bad and either allow the dinghy to flip at its heart's content, or even roll it up and store it below deck: it can be inflates with the electric pump in 5 minutes, if need be. Of course, mounting the engine in a storm is something else, too.

When the weather is good, having the dinghy intow would pose no problems. besides, there aren't many other options: storing the dinghy crosswise, under the boom, between the starboard/port stanchions while motoring is one. Cuts the visibility though

[Russ]

... when the weather gets bad and either allow the dinghy to flip at its heart's content

Been there, done that. It's weird to see this thing flipping around like a flag. It's so heavy to lift aboard and stow on the foredeck, but let a heavy wind take it and it goes.
We also store the motor on the aft pulpit bracket. If push comes to shove, we'll row the thing to safety.
Honestly, the 8' inflatable doesn't offer that much drag. We've towed it without noticing anything.

So, lately I've changed my tender to this..

Lightweight and tows super easy. It's extremely stable and easy to board from the Mac. "Only" goes 45mph, but is a great exploring vehicle.

And also this other one.

Doesn't tow as easy (heavy) but has 215HP and can haul (68mph). Plus it gets the teenager to eagerly agree to a weekend on the lake.

--Russ

[mastreb]

We have a 9 foot inflatable Zodiac that rolls up and stores in the v-berth. It's easy to inflate in the cockpit when we need it, and it fits on the foredeck upside down when we want to keep it inflated.

The whole family barely fits in it, so I just drop everyone off at a public dock or beach before going back to mooring or anchorage and then I row back myself. Have yet to be in a situation where that doesn't work. Here in SoCal everything you can reach by boat is already "improved" with docks and facilities, or the boat can be beached.

[mastreb]

We have a 9 foot inflatable Zodiac that rolls up and stores in the v-berth. It's easy to inflate in the cockpit when we need it, and it fits on the foredeck upside down when we want to keep it inflated.

The whole family barely fits in it, so I just drop everyone off at a public dock or beach before going back to mooring or anchorage and then I row back myself. Have yet to be in a situation where that doesn't work. Here in SoCal everything you can reach by boat is already "improved" with docks and facilities, or the boat can be beached.

[Catigale]

I see you dropped off your post before you returned with it, too...

Just for giggles, the 4 knots reported with the 4HP in a nearby (for now) thread was with a 100# plastic Watertender 9.4 in tow - the drag is very, very small IMHO.

And now that my CRJS medicine has kicked in, I was actually towing

Watertender 9.4
Optimist sailing Dinghy
Tohatsu 2.5 lashed down

Total weight 200# estimated

[Hugh]

We have purchased a 12' SOAR inflatable hypalon canoe for a tender.
We come from a wilderness canoe tripping background so this option still allows us to go for a paddle yet functions as as tender.
It has 3 chambers.Inflatable floor and two side chambers
http://soar1.com/soar_12.htm




I glued two D rings onto the hull to make tow points for a bridle.
The boat tended to rear up when under power(higher speed) but towed quite well while sailing.
I tried different lengths of floating tow line and found that riding on the front side(closest side to boat) of the second wave seemed to work best.
I'm adding handles to the tubes on the side and will try other attachment points for the bridle.
The SOAR weighs in at 52# and due to a narrow width might be wind affected more than a trad inflatable Zodiac style
Here is a pic of us towing the SOAR the link to dropbox doesn't want to work.....