electric boat, proper rpm and propeller

Chris
It is good to have objectives clear. I think the hull is good for intended purpose. The underwater lines will be similar shape to the launch just not as full. You would get a lighter boat with composite construction.

Start you own thread so you can post a good history of the project.

I don't think you will need to get too fancy with props. With two motors you should easily get your 5kts. So better props will just extend the range.

Make a post on a new thread and I will respond there. You could give me a bit of information on the existing props like diameter and blade chord. If the pitch is stated anywhere that would be useful as well.

Rick W.

 

Thanks Rick.

You have been a big help so far. I think I should proceed with some actual on-the-water tests with the two props I have, then afterward consider a new thread on optimization.

The 2-motor Launch is a new project which I hope to begin building late Spring/Summer in NY.

I am in FL until then. I have a small 13' AL Jon Boat which should be ready for use in our FL 'lakes' (ponds really) in a few weeks, with a single 34lb thrust 34A MK Endura motor and 0-24V 40A PWM drive, and the two props.

While the hull is different, I should at least see any relative differences between the two different props, and compare with my earlier Tank Tests - such as if the Kipawa will actually end up - at 34A - at higher than 10V.

I should also borrow - or maybe buy - a GPS for accurate kts figures (I was planning one for Lake George anyway)

More then. Until then, thanks again and Best Regards.

Chris

 

Chris
Keep in mind with your testing that hull speed will be like a brick wall in a wide hull. You need considerably more power to get it to plane than you have so it will bog down and extra power will not make much difference once you get to about 4kts.

Moving weight forward to push the bow down and stern up might gain a bit more speed. It will increase the waterline length and reduce the transom drag.

These are the sort of things to appreciate if you are trying to get the best from low power. The proposed 19' boat does well on these counts.

All the battery powered stuff being used in China is putting pressure on lead supply so battery costs are getting up. On the other hand the controllers and motors are good value because they are being made in big quantities.

Rick W.

 

Having read the last 5 pages with interest I would like to find out if a sharpie 'box hull' of the Bolger type is more efficient than the same hull with a 'box keel' attached under it. 'Duck Flats Wooden boats' has a Mundoo 3 series...craft about 34ft long and 8ft wide. The Mundoo Solar electric has a 'box keel/pod' and the outboard version does not. Which of these two boats are hydrodynamically superior?

 

Harry
The Mundoo box keel is not wide enough to give the full benefit of the design. I do not think there would be much in it without going to a lot of effort to work it out.

If you go to the style of an Atkins hull, which is really a canoe with stern extension then you get a real advantage over a dragging transom.

If you have a displacement in mind I can work out the optimum for your constraints. If you are thinking about solar power then you need to have an efficient hull to get decent speed.

Rick W.

 

Box Keel versus no box keel

I am refering to a displacement hull. The reason for my questioning is to discover whetther or not efficiencies can be made in wider beamed boats by adding a box beam underneath.
Some of the designs I'm partial to with regard to styling would be Jay Benford's Friday Harbour Ferry Yacht 24' & 26', and Mal Low's 21' Tug Yachts.
I was thinking of trying to get a plan like those to work in solar electric by adding the box keel. Am I dreaming?

 

Box Keel versus no box keel

I am refering to a displacement hull. The reason for my questioning is to discover whether or not efficiencies can be made in wider beamed boats by adding a box beam underneath.
Some of the designs I'm partial to with regard to styling would be Jay Benford's Friday Harbour Ferry Yacht 24' & 26', and Mal Low's 21' Tug Yachts.
I was thinking of trying to get a plan like those to work in solar electric by adding the box keel. Am I dreaming?

 

Harry
The box keel tends to work best on a narrow hull where you can make a canoe underwater and what you want above the waterline.

There is a clever program, called Godzilla, developed by Leo Lazauskas that works out the optimum hull shape for a design speed, design displacement and most other constraints you care to fix. It is reasonably accurate for most displacement hulls. It can do about 1000 iterations a second so can achieve millenia of boat development by a huge team in a matter of seconds.

As an aside, I built or bought 10 boats before I found Godzilla. It was a waste of 4 years apart from the fact that it makes me appreciate the real value of Godzilla better than most.

Usually you will find the optimum hull length for a design speed is somewhat below the length that aligns with the "hull speed" matching the design speed.
Hull Speed = (g * L / 2 / pi) ^ 0.5

So I usually start with a completely unconstrained hull for the design speed and displacement. Once I have this I start to apply constraints to see what each constraint costs in terms of power. For example, do I want it shorter, do I want more stability, do I need more beam, do I want easily developable etc.

There are many drivers for a boat and it gets down to what suits your purposes. Godzilla can reduce years of trial, error and speculation to a few seconds of computer time. So it is a powerful tool and easy to use.

If you have an idea of what you want with a boat then I can give you a good idea of what the optimum underwater shape will look like using Godzilla.

Rick W.

 

Thank you Rick. I'll begin a new thread under boat design as soon as I have have a concise set of criteria and allow this thread to continue as intended.

 

PMG-132 efficiency

PMG-132 efficiency curves:
For instance here:
http://www.perm-motor.de/site/pdf/G...2/PMG132_Massblatt_Deutsch_mit_Diagrammen.pdf

Confused1:
No curves given for 12V (580 r/min)? What would be the efficiency? Poor? In an el-boat with PMG-132, 15" prop, and 2.08 gear ratio I found that at a slow speed of 2.5kn, motor losses were as high as all the rest of losses around including hull drag, prop loss, etc. Perhaps, alternatively, no gear ratio or even an inverted gear ratio should be used, if long ranges at slow speeds are of interest too?

Confused2:
I measured PMG-132 power consumption with no load. Curve included. For instance: According to manufacturer at 72V * 20A = 1440W and efficiency = 84%. That makes a lost power of 230W. My measured LessLoadCurve gives 880W at 72V? Does the motor waste less if loaded? Really strange!

redu

 

redu
This does not make sense. Can you explain more about the tests you conducted?

I have a Mars PMAC motor that is nominally slightly less efficient than the PMG-132 and it has no load losses of 120W at full speed on 24V. It turns over with only 6W.

The motor will have higher losses if it is loaded but your figures do not look correct.

The efficiency will be similar throughout the voltage range. Maybe slightly better at lower rpm because windage is less.

Rick W.

 

Direct drive by OZ

OZ from sweeden does direct drive on PERM132
But carefull they use a modified version
With additionnal bearing and longer shaft for coupling two motors, and maybe other hidden mods ?
Propeller they use are flexoprop 13x9 to 15x9, that seem a good compromise.

For my trimaran, 3 tons 40 Ft very small wet aera, i have the same problem choosing motor and reduction...

About brush life, i heard everything from 3000 to 5000 Hrs ! Good luck !
After looking at all the solutions, a belt drive reduction is nice as you can modify the ratio if it appears to be maladapted... Of course with a saildrive it is a little more difficult.
try this
http://www.sillette.co.uk/elect_saildrives.pdf
http://www.bellmann.nu/?nr=10
http://www.kraeutler.at
This last one does a 180° turning SD...But price may also turn your head in the same way


About the mars motor, do you use it in a boat ?
And what is your opinion about it ?
Do you know where i can get parts for a belt reduction ?

 

hi.
i want to convert the propulsion system of a fishing boat from disel engin to solar.how can i do this work?
thank you for any help.

 

What size and type is the boat?

What speed do you want to achieve at peak and long range?

Where will you operate the boat?

Will you only use solar power or will you aim to have significant battery capacity?

What is your budget?

Rick W

 

type: fishing vessel
size:
l:8.24 meter B=1.95m H=1.30 T=0.37m
speed= over than 10knot
just use of solar power.
my budget is low
thank you for your helping