Oceanvolt Hybrid Motor

[valhalla360]

Originally Posted by mcarthur

According to OV's (ha!) guesstimates to us when we asked, they say our 16tonne 50' powercat can go near 4kn on 3kW of motor power (so ignoring prop losses),

We did some tests on our 5ton 34ft cat that has a mount for the 5hp dingy motor. The motor had good bite on the water with the mount...flat water, no wind, it eventually got up to just shy of 3kts with the motor running flat out and yes, the motor got up to decent RPM.

Now I know they are going to claim that long skinny hulls and ideal prop...but not buying that a drastically larger cat with less power will beat it by 33% with less HP 4hp (3kw).

[Tupaia]

Derek Kelsall uses the following formula to estimate the speed under power of a catamaran. It is reasonably accurate.

Speed in knots = SQRT [(LWL X HP)/Displacement]

LWL - metres
Displacement - Tons

So your 5 ton 34 ft cat with 5 hp will do about 3.2 knots.

[valhalla360]

Originally Posted by Tupaia

Derek Kelsall uses the following formula to estimate the speed under power of a catamaran. It is reasonably accurate.

Speed in knots = SQRT [(LWL X HP)/Displacement]

LWL - metres
Displacement - Tons

So your 5 ton 34 ft cat with 5 hp will do about 3.2 knots.

Assuming the formula is reasonably accurate (not sure if I buy it or not), for the 50ft 16 ton cat with 3kw output...works out to about 2kt as opposed to the oceanvolt suggested 4kt.

Below 25% of hull speed, power and speed tend to follow a much more linear pattern (as opposed to when you near hull speed and power demand curves quickly upward), so 1kt on 1kw seems a bit optimistic...probably more like 2/3kt. This also doesn't consider at extremely low speeds even cats tend to wander and require more steering input, so your actual ground covered may be even less.

And as others have said, this assumes you use electricity for nothing else...yet most EV fans tout electric galleys which can easily eat up a significant portion of daily solar production even with a very large solar array.

[StuM]

Originally Posted by Tupaia

Derek Kelsall uses the following formula to estimate the speed under power of a catamaran. It is reasonably accurate.

Speed in knots = SQRT [(LWL X HP)/Displacement]

LWL - metres
Displacement - Tons

So your 5 ton 34 ft cat with 5 hp will do about 3.2 knots.

I'd expect more than that.


I push my 12m LWL, approx 10 ton cat at just over 4 kt with 5HP (one engine at 2000 RPM), your formula says only 2.5 kt.

[svReality]

Originally Posted by SDChristian

I think i know the answer but, if an oceanvolt cat was out of fuel and trapped in the doldrums, could solar alone push her even at 1 knot during the day until the wind came back?

Hi
Sorry for the delay which has resulted in much theoretical hotair. Unfortunately being in NZ and not the doldrums it is hard to get nil wind conditions. See attached photo. We have 4x 325W solar panels and 6x100W flexible panels. We get a maximum of about 850W into each battery bank. The max we have had so far this summer is 10kW - 5 into each bank.

With low wind at mid tide and 600 to 700 W on each engine we managed 3knots. Next time I am in the doldrums and the generator has broken down I will record the days mileage.

[john61ct]

Does a ballpark of 3-5 hours runtime @ 3 knots

collected per good-insolation day sound about right?

Assumes not too much expended by other loads

[StuM]

Originally Posted by svReality

Hi
Sorry for the delay which has resulted in much theoretical hotair. Unfortunately being in NZ and not the doldrums it is hard to get nil wind conditions. See attached photo. We have 4x 325W solar panels and 6x100W flexible panels. We get a maximum of about 850W into each battery bank. The max we have had so far this summer is 10kW - 5 into each bank.

With low wind at mid tide and 600 to 700 W on each engine we managed 3knots. Next time I am in the doldrums and the generator has broken down I will record the days mileage.

If I understand you correctly, you've got two battery banks and 1.9kW of panels which give you up to 1700 watts peak and a maximum of 10 Wh per day?


So a reasonable average in the doldrums would be around 8 kWh per day.


Assume you keep your consumption down to 1 kWh for everything else, that leaves you with 7kWh for propulsion per day.


You use about 1.2 to 1.4 kW to make 3 knots. Which means your 7kWh is good for a little over 5 hours running per day or 15 miles at that speed



At a guess, if you take it slower, you may get around 20 miles over 10 hours.

[svReality]

I would hope that being closer to the equator the doldrums would improve the daily solar kW compared to what I am getting at 36S and I am assuming no wind usually equates to not much cloud so my guess based on this single test is 20-24nm. I had a look at the hourly solar prod on victronenergy.com VRM on a sunny day and I was getting between 1kW and 1.7kW for 8hours with 2hours of much lower production on both ends. I don't know if I will ever be able to do a real test as the temptation to run the generator and motor at 7knots (speed at 7.5kW on both from 15kW gen) in ideal conditions would be too strong!

[transmitterdan]

Your numbers sound about right. Have you tried to make electricity from the props when sailing in a brisk wind?

[StuM]

Originally Posted by svReality

I would hope that being closer to the equator the doldrums would improve the daily solar kW compared to what I am getting at 36S

You'd be surprised. Lots of cloud and thunderstorms in the ITCZ because of rising warm air and in summer the sun is more overhead at your location than it is at the equator.

[svReality]

Originally Posted by transmitterdan

Your numbers sound about right. Have you tried to make electricity from the props when sailing in a brisk wind?

Yes regen works as expected. about 1kW each side at 9+knots but that for a Leopard 46 is ideal sailing conditions in strong winds. When I crossed pacific (before OV conversion) I was averaging approx. 150nm a day motor sailing and 7knots sailing and at these speeds less drag regen only about 400W each side. Regen is best suited to a lighter cat which regularly sails at 10-13knots but having said that it means I get about 10kW during the night and 10 plus 10 during the day so that should keep the batteries well charged and provide some power for motor sailing when the winds are light. The Galapagos to Marquesas leg in 2012 took 18 days 6 of which were motorsailing.

[yvest]

Originally Posted by svReality

Yes regen works as expected. about 1kW each side at 9+knots but that for a Leopard 46 is ideal sailing conditions in strong winds. When I crossed pacific (before OV conversion) I was averaging approx. 150nm a day motor sailing and 7knots sailing and at these speeds less drag regen only about 400W each side. Regen is best suited to a lighter cat which regularly sails at 10-13knots but having said that it means I get about 10kW during the night and 10 plus 10 during the day so that should keep the batteries well charged and provide some power for motor sailing when the winds are light. The Galapagos to Marquesas leg in 2012 took 18 days 6 of which were motorsailing.

Are they the "servoprops" version of the OV SD15 or "standard" ones ?

[BigBeakie]

I was wondering the same thing. I thought you had the new Servoprops which would have an expectation of about double your result of 1 kW output at 9 knots?

What boatspeed reduction do you get on regen compared to no regen?


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[StuM]

Originally Posted by BigBeakie

I was wondering the same thing. I thought you had the new Servoprops which would have an expectation of about double your result of 1 kW output at 9 knots?

What boatspeed reduction do you get on regen compared to no regen?


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How's your build going? When do you think you will be able to post your performance figures?


(I thought you were hoping to launch this year?)

[BigBeakie]

Stu,

Our build is going painfully, and disappointingly, slowly here in Thailand. Past builder problems mostly re QA and productivity issues put us way behind , but now have new facilities, new and better worker crew so things are now going better. Yes, should have been launched by now, well and truly. As it's New Years eve already, obviously it will be launched now in 2020.......sigh🙄

Everything in our experience has been duly noted, and one day will be written up as an object lesson of what to look out for when building a custom performance cat in Thailand ( and rest of Asia from what I hear) but right now as a somewhat new and overwhelmed owner-builder, there are about a million higher priorities.

However, pertinent to this thread, our OV AXC20 shaft drive install went well. Now we just have to get the Flexofold props wet and give it a spin. I did hear a report from another AXC project though, and their numbers were right on the money as per predicted values, so that's encouraging. The quietness of the AXC motors is apparently amazing.


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