T-Pain Is On A Boat: Re: [Electric Boats] Torqeedo travel 1003

Ron, Mike and others

On the Zodiac it felt like it was climbing up out of the water on its flat bottom and close to planing - it wasn't sucking a mass of turbulent water along behind it.

The vee shape felt like it was going along in the water, rather than on top as did the Zodiac. And it it was dragging along behind it a turbulent patch of water.

And this idea of dragging along a patch of turbulent water is something that Francis Herreshoff talks about in his yacht design books. I kind of like his style of writing and explaining things in everyday terms. In his article he he was talking about clean hulls and a hull that has some fouling. And the example he mentioned was being on a big passenger ferry and walking from bow to stern and looking down at the water going past next to the hull.

Near the bow the water right next to the hull is going past very fast. At about the speed of the ferry. But as he walked back the fast water began to detach from the hull and there was a zone of water that was being carried along with the boat. The further back he went, the wider this zone of water being carried along. And right near the stern the turbulent patch of water being carried along was substantial.

So the boat was sucking along behind it a big patch of water. The cleaner and more streamlined the hull is, the less thickness is that area of turbulent water that has to be dragged along. And looking at a plan view of what is happening, if you drew a line around the boat where the water is clear of turbulence, you'd get a double-ender hull shape but longer and wider than the actual hull, and at the bow the shaped coincide. The effect is to make the boat bigger - that is, the thing that is being pushed through the still water is bigger as the bottom gets dirtier.

And getting back to the inflatable example, I think Mike is right, that its this extra patch of water being sucked along, making the boat appear bigger than it really is.

Cheers

Chris

On 15/08/2010, at 12:10 AM, Capt. Mike wrote:

Ron

I read somewhere that the reason for the limitation of speed on displacement hulls is that the V shaped bow pushes the water aside which then fills In behind the boat creating a vacuum like drag on the stern. Causing more and more energy to be used to make the boat go faster. Which makes sense to me. This may also be the reason why barges are flat bottomed. More efficient at low speeds?

Capt. Mike
Sent from on board BIANKA
http://biankablog.blogspot.com
From: "Ron" <rlgravel@swbell.net>
Sender: electricboats@yahoogroups.com
Date: Sat, 14 Aug 2010 13:48:31 +0000
To: <electricboats@yahoogroups.com>
ReplyTo: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Torqeedo travel 1003

Hi Chris,
My thought on why the V did not do as well as the flat bottom, is that the displacment is lower and more force is needed to push aside and upward against the weight of water. Or more likely the flat is riding on a small chusion of air.

--- In electricboats@yahoogroups.com, Chris Baker <chris@...> wrote:
>
> Hi Matti et al,
>
> I have a 1003 for my dinghy and have been using that on a few other boats for testing. I've become a Torqeedo dealer and so have been testing the motor on various boats for prospective buyers to see how they go.
>
> On my Zodiac 2.7m inflatable with a flat bottom I can get 5 knots if I carefully position my weight to find the sweet spot for speed. But if I'm not careful about weight balance full speed is more usually around 4 knots. For most use though I go along slowly around 2 or 3 knots to conserve the battery.
>
> On another inflatable 2.6m long and with a vee shaped hull formed by a tube inflated in the bottom, and with two on board the best we could get was 4 knots. With just one on board the speed picked up to about 4.4 knots. I somehow expected more because if the vee shaped bottom. We didn't experiment much with it, and perhaps its just that I've got used the Zodiac and can balance it better.
>
> On a sailing keel boat called a Payne 7 which I'm told weighs about 600kg, we could get a top speed of 4 knots.
>
> On an Adams 10.6, a racing keel boat weighing around 1.5 tons and with a dirty bottom the best we saw was a disappointing 3 knots. I expect that the smoothness of the bottom has a substantial effect here, and we concluded though that it was a reasonable test because the bottom is going to be like this now and again, and that would be the worst case for battery life. The objective was to be able to motor to the start area for the race and then motor back later. On the return journey he expected to be able to resist the desire for full throttle, but the pressure of going to the start line and having to moderate the speed to conserve the battery would be too much to ask :) and so the only way it could be done would be to add more batteries. We plan to test again with a Cruise 2 and see if a useful speed is available at 2kw. (I'm actually going to use the Cruise 4 off my tri for this test, and just run it at 2kw - the Cruise 2 and 4 use the same prop)
>
> On a more streamlined boat, an inflatable catamaran kayak, the top speed was 11km/hr, which is close to 6 knots. This was done with two people on board on its first day of use and the motor had not been trimmed for best performance, so it may do better.
>
> I have also heard of a racing keelboat of about 600kg displacement reaching top speed of 6 knots under ideal conditions.
>
> As to the aluminium cover which gives the foil shape to the leg being loose, I have noticed that on my 1003, and on others. It is not a structural element so it seems not to be significant.
>
> My feeling is that the 1003 could be barely powerful enough for your boat, and would really depend a lot on your style of sailing and expectations. If you expect to sail the boat in most conditions and won't be wanting to rely totally on the motor it could do the job. I've found that motor-sailing gives good results from the point of view of not needing a lot of power from the motor to be able to help the boat tack. I have set my Cruise 4 running at a few hundred watts when sailing under jib alone. Because with just the jib she'll often stall when tacking, and not make it through the wind. But by adding that small amount of power from the motor it takes her through the tack nicely. Then when she speeds up a bit as she settles in to the tack, the power requirement drops right back to negligible (and even shows some regen at times - but you won't see this on the 1003). I should mention that I have the motor set up to steer parallel to the rudder and this is a major improvement over the previous setup where the motor was fixed, and this device helps a lot in the tacking manouvre because the thrust is directional.
>
> Motor-sailing helps both the motor, and the sailing. Helpful to the motor because it only uses power when the boat slows down, which is mostly when she's tacking, and so very little battery power is used. And helpful to the sailing because she tacks easily and also keeps her way better when the jib luffs - and this is also handy in fluky conditions such as when sailing in narrow fiord-like bays. (which I'm thinking you might encounter up your way)
>
> Cheers
>
> Chris
>
>
>
> On 10/08/2010, at 6:08 PM, MattiB wrote:
>
> > Hi Ed
> >
> > It would be interesting for me, and maybe for others also, if you could share your experience with the Torqeedo 1003 here on the forum? Some real world data would be interesting for me. This summer I "tested" a 1003 in a tank. It seemed ok though i didn't dare to go to full power fearing the tank wall might bend too much and the engine slip from the mountpoint which was a little bit too thick for the engine to fit correctly. The building quality seemed alright, at least superficially. The only negative thing I observed during the maybe 15 minutes I assembled it, tested it and disassembled it (the person who was responsible for Torqeedo products was on vacation so the shop owner said I would have to assemble it myself if I wanted to test it) was that the aluminum which gives the leg a foil shape, was a little bit loose. I don't know if that is a common problem or was only specific to the one motor I had in hands, since it was the only one. The battery had 33% charge when I started and still 30% when I stopped. I was running it for maybe 5 minutes between 50-500 Watts forward and backward. My conclusion was that it actually might be strong enough to push my 28 foot sailboat weighing about 2,4 tons, but that the battery capacity is simply too low for serious motoring at an assumed 3,5 knots and 1000 watts. As I understand Torqeedo does not plan to add a battery adapter for external batteries (which I see as a measure to assure noone is able to use the engine excessively within the waranty time without bying a lot of batteries or modifying the engine). However, if there was a battery adapter, the engine might also be interesting for me since I dont't think I need more than 1000 watts.
> >
> > Matti
> >
> >
>