View Full Version : electric boat, proper rpm and propeller


bairachtn
10-28-2007, 06:57 AM
Hello everybody, this is my first post, i am nikolas from greece and i would like your opinion on my project. I have a 2.6 meters g.r.p. boat and i am going to make it electric. After a few thoughts i am thinking to use a 2 hp inboard electric motor which will give about 6 knots to my boat. My problem is the correct selection of rpm(i am thinking about 1500 rpm) and the correct propeller diameter and pitch. Your help will be very useful to me...

Guest625101138
10-28-2007, 08:34 AM
Hi Nikolas
If you have a picture of your boat, main dimension and the intended total weight I can do a drag calculation and performance estimate.

Have you got a motor in mind? Have you considered a commercial electric outboard?

The most efficient propeller will have a high aspect. Do you have draft constraints? It is unlikely that you will get an efficient prop off-the-shelf for this application but it is not hard to make a good prop if you can weld stainless steel.

Rick W.

bairachtn
10-28-2007, 09:20 AM
Hi Nikolas
If you have a picture of your boat, main dimension and the intended total weight I can do a drag calculation and performance estimate.

Have you got a motor in mind? Have you considered a commercial electric outboard?

The most efficient propeller will have a high aspect. Do you have draft constraints? It is unlikely that you will get an efficient prop off-the-shelf for this application but it is not hard to make a good prop if you can weld stainless steel.

Rick W.

I do not have a picture at this time, but you can see a simple drawing of the boat at the attached file below, also i think that the total weight should be about 250 kgs with me and the other stuff inside(motor, batteries,etc). For the motor, i have attached another file, where you can see the motor i am thinking of(http://www.leeson.com the low voltage one(24V). Also, i am going to "builld" the dc controller alone so i do not want to use a commercial product. But as i told you i need your advice, and calculations for the proper rpm and propeller if it is possible because this project is my university diploma thesis. I am studying electrical and computer engineering at patras university, Greece, thats why i am going to make the controller alone and thats why i need the math calculations i told you, unfortunately we do not have a naval engineering dept at Patras to take advice:rolleyes: . I am looking forward to your response.

Guest625101138
10-28-2007, 04:29 PM
Nikolas
If it is a university project then you should be doing learning as much as you can about the design.

For a start you can Google JavaProp and run the prop design Applet. You have to set thw Options page for water. Density is 1000 and viscosity is 0.0000013.

You then go to the Airfoil page and set the foils to E193 at Re100000. Set the angle of attack at 0 degrees.

Now go to the design page and set some prop parameters. Start with a diameter of .3m", rpm 1000, spinner .03m, power 1500W, speed 3m/s (6knots). Then press design. You can play with the paremeters to find the combination that gives best efficiency.

I will do some numbers on the boat drag later today and send you a curve. This will show if 6kts is possible with 2HP.

Rick W.

Guest625101138
10-28-2007, 05:52 PM
Nikolas
I have attached an image of the hull and a chart showing drag versus speed. It is heavily loaded. The drag is very high for a small boat because of the shape of the stern and the load it is carrying. 250kg is a lot for a 2.6m boat.

The hull as you have drawn is made for planing so is not ideal for only 2HP. It would probably plane with this power level if it was much lighter.

Anyhow you will find it will almost do 6kts with the 2HP so it should meet your objective. I can modify the shape if you think it is not a good comparison. Send a photo if you can get one.

If you have trouble using JavaProp then make a post with your problem.

Rick W.

bairachtn
10-28-2007, 06:27 PM
Mr Rick thank you very much for your help...i am going to use the java applet you told me, and soon you'll have news from me...also i would like to tell you some things. I know that 2 hp is not enough for a planing boat, at 10 knots savitsky method gives me about 5 hp, so i decided to reduce the speed at 6 knots because more hp means more Ah which means more batteries and much more weight for my boat and you already told me it is heavy enough. About the weight maybe it will be a little lower about 200-220 kgs. Also my boat is about like you draw it, tomorrow i' ll probably send you a photo of my boat. Also when you say drag what exactly do you mean? I am going to post my news soon. Thank you very much again.

Guest625101138
10-28-2007, 07:02 PM
The drag on the hull is a result of water friction/turbulance at the surface of the boat and the wave energy required to move the hole in the water that supports the boat. The values on the chart provided are in Newtons. The drag is dominated by wave drag.

The data produced by Javaprop will have a thrust figure in Newtons. You have to iterate the result from JavaProp to match the drag for a given speed in the chart I have provided. Each iteration will require the velocity setting to be changed in Javaprop. Speed in knots is almost twice the value of m/s.

This hull is intended for planing so is not ideal for displacement mode. With reduced weight and adjusting the trim so it is down at the bow it might be possible to lower wave drag.

You should be able to get prop efficiencies around 80%. It is not practical to make blades that have a chord smaller than say 50mm to take the thrust loads. Also the Reynolds number is more like 300,000 so use the E193 300,000 data.

I have a more flexible and precise prop design method and if you want to actually make a prop then I will provide a design. However JavaProp will enable you to understand the variables and gives a reasonable result. These props are high efficiency for low loads not like a normal outboard propeller.

Rick W.

bairachtn
10-28-2007, 07:25 PM
The drag on the hull is a result of water friction/turbulance at the surface of the boat and the wave energy required to move the hole in the water that supports the boat. The values on the chart provided are in Newtons. The drag is dominated by wave drag.

The data produced by Javaprop will have a thrust figure in Newtons. You have to iterate the result from JavaProp to match the drag for a given speed in the chart I have provided. Each iteration will require the velocity setting to be changed in Javaprop. Speed in knots is almost twice the value of m/s.

This hull is intended for planing so is not ideal for displacement mode. With reduced weight and adjusting the trim so it is down at the bow it might be possible to lower wave drag.

You should be able to get prop efficiencies around 80%. It is not practical to make blades that have a chord smaller than say 50mm to take the thrust loads. Also the Reynolds number is more like 300,000 so use the E193 300,000 data.

I have a more flexible and precise prop design method and if you want to actually make a prop then I will provide a design. However JavaProp will enable you to understand the variables and gives a reasonable result. These props are high efficiency for low loads not like a normal outboard propeller.

Rick W.

thank you again, i will work on it and soon i'll inform you about my results...

bairachtn
10-28-2007, 08:06 PM
by the way mr rick, have you any way to calculate the displacement of the drag you send me if you know that the height of the red area is about 10cm?

Guest625101138
10-28-2007, 08:35 PM
by the way mr rick, have you any way to calculate the displacement of the drag you send me if you know that the height of the red area is about 10cm?

Yes.

To support 250kg the back of the hull is down 17cm if the keel is horizontal.

When it is at 10cm at the stern is the keel horizontal or inclined with the bow down.

Rick W.

bairachtn
10-29-2007, 05:59 AM
At 10 cm it is horizontal, but when it is about 10 cm in the sea, i have not put any batteries & motor, show the weight should be about 150 kgs. If you can make two calculations 1st with 250 kgs and 2nd with 150 kgs as i told you, you would help me very much...thank you again.

bairachtn
10-29-2007, 10:10 AM
Mr Rick here are some photos of my boat...maybe will help you for the better comparison you told me, but your comparison is very good too i think...

Man Overboard
10-29-2007, 05:19 PM
It should be noted that the bottom looks by the photos to be very ruff, which will effect the drag calculations. Spending a day or so sanding the bottom and painting it will produce better performance results. I just thought I would mention it before you loaded it up with batteries and mounted the motor. You are probably going to find that there is not going to be sufficient clearance for the diameter prop you need for maximum efficiency; at least not at an acceptable thrust angle. I am interested in hearing more about what prop you are going to use.

Guest625101138
10-29-2007, 05:30 PM
Nikolas
I have revised the hull shape slightly based on the photos and reduced the displacement to 150kg. It needs to have a draft of 115mm for this.

The predicted drag is much lower as you can observe in the attached chart.

Rick W.

Guest625101138
10-29-2007, 05:39 PM
Nikolas
I noted that the hull has an outboard bracket. You should consider making an electric outboard as this will be a lot easy to set up and do subsequent work with.

All you need is a small right angle gearbox. There are many manufacturers. The nest I know of are Mitrpak:
http://www.mitrpak.com/
You can get version with 2:1 reduction. This would allow running a big diameter prop to maximise efficiency. It also means you can just mount the outboard in position once you have water deep enough. Could make it tilt like a conventional outboard if you want to get more complicated.

The outboard also avoids the need for a rudder. Just swivel the outboard to direct thrust.

Rick W.

Pericles
10-29-2007, 06:23 PM
http://www.thameselectric.com/ for information.

Pericles

bairachtn
10-29-2007, 06:30 PM
@ Man Overboard in the bottom there is only g.r.p. box with very small weight...i'll let you know about my propeller.

Mr Rick i have thought about it, but putting and outboard motor, probably will give to much weight at the bottom of the boat, also i have something else in my mind, such us the attached photos below...From your experience,what you say about 1500 rpm, and a propeller about 20cm diameter. Tomorrow i am going to work with java prop and i will post my news...Thank you for your help, it is very useful for me.

Man Overboard
10-29-2007, 06:31 PM
Nikolas,
To add to what Rick has said about outboard motors, it might be easier (and cheaper) to convert an old outboard motor. I am sure you could find an old 2 or 5 horse with a shot motor in Greece, No?
Check out this site:

http://www.psnw.com/~jmrudholm/etekoutboard.html

bairachtn
10-29-2007, 06:50 PM
Nikolas,
To add to what Rick has said about outboard motors, it might be easier (and cheaper) to convert an old outboard motor. I am sure you could find an old 2 or 5 horse with a shot motor in Greece, No?
Check out this site:

http://www.psnw.com/~jmrudholm/etekoutboard.html

i will have this at my mind, but with this i change my first plan(inboard motor), and i have worked a little bit on this, anyway every thought from anybody is welcome here.

@ Pericles, thank you for the information...

Guest625101138
10-30-2007, 02:16 AM
@ Man Overboard in the bottom there is only g.r.p. box with very small weight...i'll let you know about my propeller.

Mr Rick i have thought about it, but putting and outboard motor, probably will give to much weight at the bottom of the boat, also i have something else in my mind, such us the attached photos below...From your experience,what you say about 1500 rpm, and a propeller about 20cm diameter. Tomorrow i am going to work with java prop and i will post my news...Thank you for your help, it is very useful for me.

Nikolas
The reason I suggested the outboard over an inboard system is the design flexibility it gives you. It will not present a stability isssue particularly if you have a couple of batteries in the bottom of the boat.

I think you will surprise people with the performance that can be achieved with the small boat and electric motor if you keep the weight down and make an efficient propeller. So if best performance is important then you need to design accordingly.

With high efficiency propellers you get high bending loads in the blades if they are run at an angle to the flow. This is because they operate it a very small angle of attack and having an inclined shaft results in the blades alternating between thrusting and braking as they rotate. This give high vibration and will flex blades and shafts to fatigue failure.

With an outboard there is no need to put a shaft through the hull and all the complexity of leaky shaft glands. Also you will see with JaveProp that a big diameter prop will be more efficient the a smaller diameter prop. With a large diameter, the prop will be on a severe angle, which will make the problems noted above worse.

Do you actually intend to build the drive unit or are you only required to submit a design?

Rick W.

bairachtn
10-30-2007, 05:44 AM
Nikolas

Do you actually intend to build the drive unit or are you only required to submit a design?

Rick W.

yes i am going to build the control system

Guest625101138
10-30-2007, 06:47 AM
yes i am going to build the control system

Do you intend to actually use the control system in an operating boat? Meaning will you need to acquaire a motor and propeller?

Rick W.

bairachtn
10-30-2007, 07:04 AM
Mr rick, the pictures of the boat i sent you, is the boat we are going to make electric, in a few days or weeks i am going to buy the motor, propeller, batteries and the other stuff to start building the boat, thats why i need your help, the control system is going to build after january, and we expect about june to be able to use the boat, i have a question for you, with savitsky method i have calculate Re about 5*10^6 to 6*10^6, is the Re values suitable for my application?

Guest625101138
10-30-2007, 07:24 AM
Nikolas
The Reynolds number is a function of speed and length. What you have for the boat at a given speed does not apply to the propeller.

When you use JavaProp you can find the Re# for different sections of the propeller in the "Analyse" page. You use this iteratively to select a suitable foil section. JavaProp has a limited range of foils loaded. I have many more and can help you when you get to this stage.

You need to be aware that you will have difficulty buying a propeller that will give best efficiency. You need to see what you can find commercially but it will be better if you can actually fabricate the propeller.

First see what you get from JavaProp and I will check. Then you can look for a commercial prop that comes close to your design. This is the best place to start because you then know what is possible and you can assess the compromise in getting something that is not ideal.

Rick W.

bairachtn
10-30-2007, 07:36 AM
shrouded rotor, square tip, what it means mr Rick?

Guest625101138
10-30-2007, 07:42 AM
Nikolas
I have attached some screen dumps from JavaProp to give you an idea of what to expect. You can see one of the columns in the Analysis page has Re for different positions on the blade.

If you spend some time adjusting the airfoil angle of attack and other parameters like speed you should be able to produce a propeller with better than 80% efficiency.

So see if you can get to that stage and then we can discuss options.

Rick W.

bairachtn
10-30-2007, 07:56 AM
shrouded rotor, square tip, what it means mr Rick?

because if i tick, shrouded the efficiency goes about 80%:)

Guest625101138
10-30-2007, 07:56 AM
shrouded rotor, square tip, what it means mr Rick?

You can alter the settings to see what affect they have. Most boat propellers operate unshrouded. Some are shrouded in what is referred to as a Kort Nozzle. This reduces edge losses from the blades and improves efficiency.

If your propeller has low efficiency to start with it could make a big improvement. If the unshrouded efficiency is high then the improvement from shrouding is not as great.

The gain in efficiency is offset to some degree by the extra drag from the nozzle so this needs to be taken into account if you want to shroud. Nozzles are most often used in high thrust, low speed applications where tip losses are high. At higher speed the gain in efficiency does not offset the extra drag.

If you load the boat to 250kg then you might benefit from a nozzle. With a load of 150kg the open prop should be better because you could expect to do better than 6kts.

Rick W.

bairachtn
10-30-2007, 08:15 AM
here are some results for Re# E193 300000, and 0 degrees,what you think?

Guest625101138
10-30-2007, 09:04 AM
Nikolas
Try some larger diameters and slower rpm.

You now have to tie in the thrust produced to balance the drag for the speed from those curves I supplied.

Do you want to design for the 150kg case or the 250kg case.

Have a play with it and see what you work out. If you tick the shroud then you have to think of making a nozzle for the prop to operate in. You can Google Kort Nozzle to see what they look like. This will allow you to get good efficiency from a small diameter prop.

Also you have to make allowance for any mechanical losses in you system. So rather than designing for 1500W maybe you should drop to 1400W.

I am going to bed no so will look for your next set of numbers. Also look around to see what propellers you can get.

Rick W.

bairachtn
10-31-2007, 06:56 PM
Mr Rick, i attached the files from javaprop, as you can understand i have many draft constraints because i have the boat, i am not going to get another one, i can not put very "big" in hp motor because it requires more batteries which means more weight and cost, so i have to find the best propeller and rpm selection with my requirements, with these requirements i tried to get an efficient enough propeller from javaprop. Also my propeller is a little big for me and the draft constraints i told you, so it my be about 3 cm less, also i have attack angle at 0 degrees and Re# 300000 E193, as you told me. The next thing i am going to see what propellers there are out in market and i am going to select the more efficient. I am waiting for your opinion for the propeller and the rpm. Good night from Greece...

Guest625101138
10-31-2007, 07:24 PM
Nikolas
I checked what you have done and it shows you have a good grasp of JavaProp. You might get a bit faster than 3.5m/s but what you have should be conservative if you keep the weight to 150kg

The prop with 0 degree AofA has blades with large chord so you will probablyy have trouble finding ones like this. I have increased the AofA to 2 degrees and the chord is more reasonable around 60mm. This increases slip so the pitch goes up to 207mm. Efficiency is slightly better as well.

So you should look around for a propeller with a diameter of 250mm(10 inchehes), pitch of 207mm (say 8 inches) and maximum chord around 60mm (say 2.5 inches). It does not matter much id it is 2 or 3 bladed. If three bladed the chord could be a bit less.

If you can find a propeller similar to this you can recalculate just to make sure based on exact measurements.

Do you have facilities to weld stainless steel flatbar that is 50mm wide and 4mm thick. If you do I can give you a procedure to fabricate the prop. This is backup if you cannot get the prop you want. However you should have no trouble getting a 10X8 prop that is very similar to what you need.

Rick W.

bairachtn
11-01-2007, 12:46 PM
Mr rick, i would like your opinion also if i get a smaller one propeller, about 22-23 cm with another pitch because of my draft constraints, would that be a big problem?

Guest625101138
11-01-2007, 05:20 PM
Once you find a propeller that will fit the you will need to recheck its performance. As you reduce the diameter you will find it harder to get a propeller and the efficiency will drop off. It will still wotk but thet boat will go slower than it would with a larger diameter prop.

Rick W.

bairachtn
11-01-2007, 05:51 PM
ok mr Rick, soon i will be back with my news for the propellers i found in market, also i would like your opinion for the rpm, about 1500 is ok, how can i be sure about this? is there any mathematical calculation for this?

Guest625101138
11-01-2007, 06:20 PM
If you can only fit a small diameter prop then 1500rpm is OK.

If you do trials using JavaProp you can easily assess the impact that variation makes.

I believe you have determined that you do not want to shroud the prop. In this case I think you will find a prop around 400mm diameter running at 700rpm will give the best efficiency at around 250N thrust and 3.5m/s. Experiment with JavaProp to test this. You then know how little power you need to meet these conditions. For example a 400mm diameter prop running at 700rpm would require 1090W.

As 400mm is too big you need to set the diameter to what you can fit in. If that is 220mm then set this in JavaProp and test different RPM to see what gives the least power. I have attached a screen dump from JavaProp with these conditions. You can see it will require 1330W and the pitch is just over 8 inches. The efficiency improves slightly if the prop is run at higher RPM but you start to get very small pitch and you will not be able to buy a suitable prop. You should be able to find a 9X8 prop. The chord does not matter too much. Also it will not make much difference if it is 3-bladed.

Once you find a propeller you then check with JavaProp to see where it will operate.

Rick W.

bairachtn
11-02-2007, 05:23 AM
Thank you very much mr Rick, about the start of the new week i wll inform you about the propellers i have found. have a nice day.

bairachtn
11-07-2007, 04:52 PM
Hello again...i am coming back with my news. Mr Rick, i got information from different marine stores, one of them also gave me for free a 9x10 3-bladed,used aluminium propeller, witch may be good for as. Also i can have whatever bronze propeller i want for different diameter and pitch(that i think is very good). But one of the technicians told me that it is possible the 2hp electric motor can not move the boat because of the big diameter(i mean the 8 or 9 or 10 inches, we have calculate), and told me to see for smaller one propeller(like the outboard 2-2.5 hp, but these have different rpm from mine). My opinion is that with a bigger propeller i can get better efficiency(java prop, am i wrong?These are my news from the stores, probably i will build a new propeller with my requirements in pitch and diameter. Is it possible to use the free one propeller i told you i got? Also i would like your opinion for the two cases, in the rpm selection for the 9x10, and also your opinion on rpm and pitch for a 8 inch bronze propeller for a total weight of my boat about 200-220 kgs, as i think it is.Good night from Greece.

Guest625101138
11-07-2007, 05:06 PM
You will get better results with the largest diameter you can fit providing it is not overpitched. The 9X10 might be too higher pitch but it is worth a try. You can determine how it will operate using JavaProp.

For the heavily loaded case you are still better off using a large diameter prop to the maximum you can fit but you need a smaller pitch. Use JavaProp to work out the pitch based on the initial drag curve provided. Will probably be a 9X7 if you can get one.

The smaller diameter props will reduce efficiency but will still work. See what you can get and use the software to check it out. If you have trouble doing this then let me know.

Rick W.

Guest625101138
11-08-2007, 02:44 AM
Nikolas
I have looked at the suitability of the 9X10 prop with the boat in heavy displacement at 250kg. You could expect around 4kts. This is on the basis that motor is current linited and you are running at 1.1kW at 1100rpm. This means you will be running at rated current if the motor is designed for 2HP (1.5kW) at 1500rpm. The prop efficiency is down to 48%.

If you could get a 9X7 prop then you can get full motor power and run at 1500rpm but speed only gets to about 4.5kts.

The message is to try to keep the boat as light as possible. There is a point of diminishing returns from the perspective of loading it up with big batteries. It is not an efficient hull for good performance with low power once weighted down.

If you can keep the total weight down to 150kg then you could expect to get 8.5kts with your 9X10 prop. Drag at this speed is 235N and the prop efficiency is 73%. So the 9X10 will be a very good match if you keep the weight down. 8.5kts is an impressive speed for a low power electric boat. You might have to adjust your position in the boat to get is to trim to gain this speed.

Rick W.

bairachtn
11-08-2007, 09:02 AM
thank you very much mr rick for your advice, tomorrow probably i am going to order the motor, for the propeller selection i will decide int he weekend and i will work with javaprop, i will let you know about my decision, have a nice day.

Robin Larsson
01-06-2008, 07:26 AM
Will,

You speak about building a stainless propeller as if it was pretty easy to get a good working high efficiency propeller, is it so? I would be very interested to know how:) I can most certainly weld stainless flatbar, I work in a metallworkshp, I running our digitalmachines like the abrasive waterjet and bending machines.
I´m also thinking about putting an electric motor in my boat, but its a bit lager then Bairachtn´s boat, its 13.5m*2.55 meters sailboat.

Would of course be better with a folding or pitchable propeller, but maybe a fixed is the only way to get good charging when sailing?
Maybe I could even build a pitchable propeller, maybe something like the Kiwiprop, but that could be locked.

Will, how do one shape massive stainless to the airfoilsection one want? Have any good advice? Would be very interesting to know more about this propellerbuilding technique you mention!

Best Regars
Robin Larsson

Guest625101138
01-06-2008, 03:29 PM
Robin
I weld stainless steel with stainless welding rods. It is not much different to welding mild steel. The props I make are lightly loaded. If you want a prop for a 13.5m sailing boat you should be able to buy a suitable prop.

For my solar-wind boat I have been looking at a Perm Motor PMG-132 motor running at 48V with a 2:1 reduction drive with a Sevcon 4- quadrant controller. The gearbox will be a ZP3 2:1 box running submerged but with a lubricating oil head. It will be able to be dropped in and out so is easily serviced and does not have to be in the water its entire life. I have operated smaller right angle drives submerged without any problems.

It would be possible to make a heavy stainless prop but finding a suitable hub could be difficult.

Rick W.

Robin Larsson
01-06-2008, 06:09 PM
Rick,
Thanks for your answer!
The workshop I work in weld alot of stainless, thats most of what we do, build primarily windows for yachts:) So that is no proplem. Could probably build the hub to, if I wanted to.
But as you say, shouldnt be to hard to find a suitable propp. I´m thinking that a Volvo Penta 3bladed folding could be nice. Maybe modify it so I can lock it in extended position.

The thing is that I really want to be able to charge good when sailing, with a regenerative controller. I´m thinking about using a Perm 132 with a Alltrax 7234 controller, or maybe that one doesnt have regen? Maybe a Millipak would be better? But I want a 72Volts system, to get as much power as I can, when I want to.

I was thinking that maybe I could use the bottompart of my Penta 110 Saildrive leg, just rebuild the top, and connect the motor verticaly, with just a reductiongear of some sort. But maybe it would be to unefficient when sailng+charging? It would be much easier to rebuild the saildrive, than to cut away alot of the skeg to get a good position on a shaftmounted propp...
Already have the hole and such for the saildrive.

I have more questions, and its hard to get good answers about electric drives here in Sweden, sailors here are extremely traditional... Should write I new thread about it, but not now, need to sleep, its midnight here:)

Regards Robin

Guest625101138
01-07-2008, 12:42 AM
Robin
The sail drive leg is a really good option. I had a look at the Yanmar legs:
http://www.yanmar.com.au/marine/sail_series/sail_series.htm

You will see the SD20 leg should be a good choice. I would be interested in the price if you get that information. The gear ratio of 2.6:1 should match the Perm PMG-132 reasonably well. It does 3480rpm on 72V so you would have 1340rpm at the prop. This would enable a fair 2-bladed prop - something around 70% efficiency would be possible. The prop would be 18 x 11 assuming the boat takes full power to do 4m/s (say 8kts). The motor has good overload capacity so you could run a bit harder into a head wind if you needed.

You could get prop eficiency up over 80% if you spin it slower. Something like 800rpm with a 2ft prop but you will waste some of the gain in the added gearing.

The Sevcon 4-quadrant controller should work well with the Perm PMG-132. I believe it will provide good charging once the boat is doing a few knots. You should be able to set the regeneration current limit to prevent stalling the prop. I am not sure if this controller can be set up to prevent overcharging the batteries. You may need some extra control.

I have a prop fabrication procedure if you wanted to have a go at making a prop but if you are going to buy a sail drive then you should be able to get a nice 2-bladed prop to suit. I am not sure if a folding prop would work with regen it might want to close up.
http://www.australpropeller.com.au/fixedyacht.htm

Rick W.

Robin Larsson
01-07-2008, 08:24 PM
Rick, You think it would work with a saildrive?
I already have an old dieselengine with a saildrive, its an Volvo Penta MD11C with the 110S Saildrive. Couldnt find a good site where ypu can see it, you can find some info on www.volvopenta.com and under older engines, couldnt link to it though. I would like to use that one, not buy one more:)

But I belive that the pros and cons are about the same in the Volvo Saildrive and the new Yanmar one, dont you think? I will rebuild the saildrive I have, all bearings and seals new. And I plan to take away the gearbox/reverse, dont need that. And the upper angle gears. And build new mounts, and put the motor verticaly, connected via an reductiongear.

Should be much lower losses compared to using a complete Saildrive with reversegear and all. Maybe not much more losses then an axel. And the prop would be in a much better position, so maybe the total effiency would be the same?
Some people on a swedish sailingforum didnt think it would work good with the saildrive leg, to much mechanical losses they think... I dont know, much better bearings and seals in the saildrive.

About folding and regen, theres a Swedish company, www.ozmarine.se that sells a system with folding propp and regen, and it seems to work, but of course, a fixed propp would propably be more efficent.
The best would be a prop like the Kiwiprop och Autoprop, that could be locked in pitched position when regensailing, and be allowed to feather when I dont want the regen. But maybe not to easy to fix..

Or just a standard pitchable prop, do anyone have a tip on where I could fin one? But then I wont be able to use a saildrive..

Regards Robin

Guest625101138
01-07-2008, 09:06 PM
Robin
What you propose will work perfectly well. The Perm PMG-132 on 72V should not be too far behind the old Volvo.

Check the reduction ratio in the drive leg. As you can see from earlier post, 2.6:1 in the Yanmar is still a bit high for the Perm. If you set up an input gear then you can swing as large a prop that physically fit.

It is not that hard to make a prop to suit if you have the stainless steel. You could at least make one for an initial trial. Would take an hour or two to fabricate and about 4 hours of hand shapping with a grinder. I can give you a design based on 75mm by 6mm flatbar that will have the required strength. It will have efficiency around 84% if you gear correctly.

With the electric motor on the saildrive it will spin very freely so will not offer much drag unless you are regenerating. You could use lighter oil in the drive leg because the drive will be smoother than the diesel so gear loading will be better.

Take plenty of photos because I know there will be others interested in what you are doing.

Let me know if you want to have a go at making the prop and I will work out the blade geometry to suit the gearing you settle on. I will also need to know the speed you got at full throttle with the saildrive and some more detail on the yacht like displacement and basic style.

Rick W.

Robin Larsson
01-08-2008, 01:58 AM
Rick,
Thanks! Yes, I also think it should work great, but as I said, got mostly negative response here in Sweden:) But then again, none of them had used electric motors:)

I´m just a bit afraid that it would be to much losses on low speeds, when regenerating that is. That the gears will offer to much resistans at low rpm, especially since atleast the lower gear is in oil.
When motoring there shouldnt be any differens to using a straight axel, since it works with diesel engines.

Thanks! Yes, I also think it should work great, but as I said, got mostly negative response here in Sweden:) But then again, none of them had used electric motors:)

I will check the gear ratio, but since I will only leave the bottom anglegear, I think it will be 1:1, but not completly sure, will check next time I visit my parents, thats were some of the boat is:) But only the dieselmotor+saildrive, boom and the sails:) Had no where to put it at home:)

One downside I see with the saildrive, is that I will have to change oil every now and then. Volvo says 200hours in the manual, maybe I could do with more time in between. But even with 1000hours, it will be pretty often, if I use the regen, and are longdistans cruising. And when rebuilding the top-part of the leg, I will make it possible to change oil from the inside, or maybe even put a small pump and use a filter.

It is very important for me that the regen works good, I will probably use the regen about 10times more than the motor:) Is after all a sailboat! And I plan to circumnavigate so I will most likely visit Australia!

Yes, I would like to test to make a propeller like you suggest, your help is very much welcome:)
Sadly the boat has never been in the water, and the motor never installed, but I will check with other oners of the same boattype, see if I van get some info aboat speed. The boat is a Wasa 55, bit like a modern Skerrycruiser, and I plan to modernize it further, with a deeper, shorter cord bulbkeel and deeper spaderudder. Also I have a more modern rig for it, swept spreaders and no runners:) And kevlar racing sails...

Displacement will be around 5 tons, ~11meter Wl, 13.5*2.55 over deck, the keel will be something like 2.5meters deep. Pretty low freeboards, and a rather low coachroof. I will see if I can get up some pics later today.

Thank you very much for your help Rick, its been great!

Best regards Robin Larsson

Guest625101138
01-08-2008, 04:34 AM
Robin
I did a rough approximation of the WASA55 hull. See the attached image. It is a long slender hull and low displacement for its length so I consider it easily drive.

I used this to run Michlet on the hull. There is a pdf file of the drag curve. The pink trace is the Michlet output and the blue trace is the regression line. It is noted that Michlet does not allow for sinkage so it is likely that it is OVERESTIMATING the drag around 8kts because the wateline will increase with sinkage due to the overhang bow and stern.

It seems that a design point for 4m/s (7.8kts) is reasonable. This has a hull drag around 1300N without allowance for windage, rudder and keel.

I can design a prop that will give 84% efficiency running at 800rpm. This will require 6.2kW. I recommend that you gear for this speed at full motor rpm. This gives an allowance of 1kW for windage and other items like the drive leg itself and the rudder. So the required gearing for this prop is 4.35:1. This prop would be 550mm diameter and 275mm pitch. Plenty of traction so good capability in heavy weather.

This is an iterative process. You now have to determine if you can get gearing to suit and will have room to swing a 550mm prop.

I would not be too worried about the drive leg oil. The recommended frequency is more likely to do with oil contamination than actual breakdown through work. I had a small Bukh saildrive that had the bearings worn out in about 20 hours on the clock. Trouble was I left the boat moored in a creek with a strong current and it worked almost continuously for 6 months until I realsed I should leave it in gear when moored.

The point of this post is that I believe your application is suited to the Perm PMG-132 motor. Another recommendation is to get a spare set of brushes because these will wear a little even if not carrying current. They should give well over 1000hrs (say 7700nm) under light load but there does not seem to be good data on proven brush life.

Keep me informed on what you decide on the saildrive. It would be worthwhile determining the existing gearing as it may be satisfactory as-is.

Rick W.

Robin Larsson
01-08-2008, 05:51 AM
Rick,
Thats wonderful! Thank you very much! Actually I have made an drawing in Delftship on the boat, I´ll post it here, maybe you can use it? But the one you made is not that far from the truth:)
Yeah, she is long and slender, only abot 2m wide at Lwl. Lwl is more or less 10.7meters, but probably, as you say Rick, around a meter longer when att speed. Originally these boats had a penta engine of 11HP, and that seems to work pretty good, but more power is propably nicve to have when manuvering, and that I will get with the Perm motor.

This looks like it would work good, aslong as the friction in the saildrive leg dont screw with the regen to much.
Dont you think that the fixed prop will slow me down alot when sailing, I mean when not using the regen? A pithcable prop, that would be gold:) But to much hassle to build maybe, if I can´t rebuild a Jprop or Kiwiprop, but they cost alot! Specially if one will destroy the first thing one does...
Maybe I could buy blades from kiwiprop? But, as you say Rick, making the blades is not so difficult.

If the boat would do about 7.5 knots under "full" power I would be very happy! Then a can do 4knots at a fraction of the powerusage, and could backup the batteries succesfully with a 2 or 3Kw auxillaryengine, maybe just a small Honda on deck. That would be great.

Rick, if I ever get to Australia, I will take for a sail! And a few bears atleast, must thank you somehow for your help!

I will check the gearing in my saildrive as soon as I can. But as I remember it, the lower gears, that is between the vertical shaft and the propshaft, is more or less the same size, but I´m not very sure at all.

The drawings I´ve attached, one is complete with deck and so, but the other is more correct in the hull. I dont know the english word for it, but the grp "piece" that the original leadkeel is attached to, keelsole? is only included in one of the drawings, the keelsole also partialy extends to for the skeg för the rudder. It´s clear in the drawings. The rudder will probably be a freehanging spaderudder behind the skeg.

Regards Robin

Çemberci
01-08-2008, 03:11 PM
Mister
2 bhp 1500 rpm 1:1 Reduction
for 6 knots speed your propeller size is
Diameter 228 mm
2 bladed
Oktay Çemberci

cahudson42
01-13-2008, 05:34 PM
Nicholas,

Perhaps you are well along with your electrification project and everything is set, etc. But if not, here is an additional thought to go with Rick's Outboard idea and his comments on keeping weight down vs. adding batteries for more HP.

Remember at 2 HP you are going to need a Battery Bank able to supply about 1500w - at minimum, as that is at 100% efficiency. If you use a typical flooded deep cyle - say 12V 105A at about 25 Kg each - and draw 30A/hr from each (a lot) - you are going to need four of them weighing 100Kg total!
12v x 30A x 4 = 1440W)

Rick can calculate the drag of your Hull at various speeds (Delftship?) and he may find that dropping HP to 1 does not really effect the top speed that much - as typically when you start to go over 4 - 6 kn - particularly in a Planing Hull - resistance goes up dramatically.

At 1 HP you now have only 50Kg of batteries.

Plus, it is now practical to use 'submersible direct drive motors' - yes, trolling motors, mounted as an outboard would be.

For about $110, you can buy (here in US at least) a 'speed coil' low tech trolling motor capable of generating about 1/2 HP continuously - particularly if you couple it with your own a 24V PWM controller. (You can 'load it up' to its full 34A current rating by increasing the voltage above 12V as necessary).

2 of these motors coupled with a drag link for steering control gives you 1 HP. The motors only weigh about 10Kg each (No bevel gears, no long shafts, no 'stuffing boxes' etc. etc.).

You could continue with your JavaProp approach also - should you wish to maximize prop efficiency by fabricating your own props for the trolling motors.

Just another thought thrown into the pot:)

Regards,
Chris

Guest625101138
01-13-2008, 06:02 PM
Chris
What you say about the drag is correct. It comes down quite a lot if you reduce speed just a bit. So for normal motoring, range can be extended dramatically.

The little motors would need to be geared to be useful as auxiliury drives. Occassionally the auxiliary is called into service when the boat is in trouble. Under these circumstances you need to overcome significant forces from strong wind, flapping sails and decent waves while making progress against a strong current. The thrust is a function of the installed power, the propeller diameter and blade geometry. The Perm motor suggested can develop 15kW for a few minutes at twice rated torque throughout its rev range. It will also have a decent sized prop so plenty of traction.

On the batteries I would recommend sealed gel L-A batteries. I have two small sealed batteries for testing and one advantage is that you do not get corrosion around the terminals from the acid. Maybe different in the bottom of a boat having to contend with salt but having acid spills would add to the problem.

Rick W.

cahudson42
01-13-2008, 08:59 PM
Hi Rick,

Great! I'm learning as always. Did you mean 1.5Kw? My experience is the same - 200% - 400% - even 600% (6 HP for two motors) for a (very) short time.. Gets Nicholas over any short-term problem.. As long as the controller can deliver the volt-amps.. And at $110/motor - you carry a spare.

For Nicholas's boat - maybe 250 Kg - I was thinking the two 12V trolling motors at 1 HP nominal total would be OK for the primary propulsion. And I was thinking that they would not need to be 'geared' - as a 24V PWM controller sort of 'self gears' allowing the full current rating of the motors to be obtained (or exceeded) by slightly increasing the voltage (see: http://www.cfnet.net/tm.

In my own planning I thought the sealed (AGM?) batteries too expensive. Instead, I put the conventional flooded in plastic battery containers - and they seem fine.

I use WALMART (belive it or not) EverLast 12V 105 Ah Marine Deep Cycle made by Johnson Controls - and priced at $60 each. Unfortunately, I've yet to see them again at our local WALMART. Hopefully, they are still available (Comments anyone?)

I would be interested in exploring a prop redesign for the 'direct drive' trolling motor.

The trolling motor I refered to was the MinnKota Endura 34 lb (34A) thrust. In tank tests, the aftermarket Kipawa draws 34A at a lower voltage than the stock prop does at 34A. Meaning - the Kipawa draws 34A at LESS HP since the voltage is less. But this assumes equal efficiency and slippage for the two props - which is likely incorrect.

There is probably a definite opportunity to develop an optimized prop for the trolling motors - particularly given that with PWM - the revs of the prop can be precisely controlled.

Your thoughts?

Regards,
Chris

Guest625101138
01-13-2008, 09:36 PM
Chris
The 15kW was correct. Robin is planning on a 72V system and the PMG - 132 motors are usually current limited to around 200A. They get up around 90% efficiency. So these motors are very powerful for their 11kg weight.

Most electric motors will reliably develop around 2 times rated totque throughout their speed range so are much more flexible than combustion engine. However for a design point to get the most from the motor you aim to have rated current aligning with full voltage for the application. This becomes the design point for the motor.

Hence for the prop design you need to know the drag on the hull, the speed of the motor at full voltage and current, the rated output power and the drag v speed curve for the hull you are powering.

If you give me an idea of some of these things I can do a prop design that will maximise your speed at rated power. If you decide you would like to be able to utilse the full available power from your motor for a short time then the prop could be designed for this.

On batteries - I understand the sealed gel give better cycle life than sealed AGM. But both types are considerably more expensive than a flooded battery. Remember a yacht will be doing a lot of heeling. The WASA 55 is narrow so will probably sail well on its ear. Need to watch acid spillage.

Rick W.

cahudson42
01-14-2008, 02:16 AM
Hi Rick,

Thanks! Sorry I was still thinking of Nichlas' boat when thinking 1.5Kw..

My application will be something like the attached Delftship fbm - an 'Aluminum Electric Launch' - or 'Poor Boy ELCO'

I'm planning on 2X 12V MK Endura Trolling Motors - either 34 lb thrust (34A @12V) or possibly 46lb thust (46A @ 12V). These will be driven by PWM 24V 'scooter' controllers, so I am not limited to 12V. I can increase (decrease) the voltage so whatever prop used draws 34A

I'd read somewhere that the 12V Endura is about 1200 - 1400 rpm. But I've no tachometer, so have not actually measured it. So thats 100 rpm/V (Anyone know for sure?)

I got an aftermarket 'Kipawa' prop for a 34. It is advertized as giving 'more speed' at rated 12V. A three-blade rather than the stock 2-blade.

The Kipawa will draw 34A at less voltage than the stock - more like 11.5V rather than the stock at closer to 13V. This seems as expected with its higher advertized pitch. I could measure the dia. and pitch of both if it would help as a starting point.

As I understand it, brush arcing excluded, I am mainly limited by the 34A current rating as current is the determinant of heat losses in the motor..

So I'm wondering if I would 'get more watts to the water' by going the 'other direction' from the Kipawa - like a prop drawing 34A at 18V turning 1800 rpm?

Thoughts?

Regards,
Chris

Guest625101138
01-14-2008, 03:29 AM
Chris
The launch is not too bad as a hull. I trimmed it bow up by half a degree and sat it lower to extend the waterline. The displacement in this trim is 1030lb.

If you take the proposed motor at 34A, 24V with 75% efficiency it might deliver 612W. Now we should be able to get a prop better than 80% so power to move is 480W. This will give around 5.4kts on the hull.

This speed is getting you into serious wavemaking for the hull. For example halving the power gives 5kts. So you are gaining very little screwing the motor to the max on this hull.

To get the best result you should match the hull to your specific requirements unless you can get the hull cheap or you like some other aspect.

To go faster you need to go longer and reduce beam. The reduction in beam does not necessarily mean a reduction in stability. This hull has very good form stability. The KMt is 9ft. Do you need it to have such good form stability. Remember you can set the batteries down low in the middle of the boat. This will get the CoG low.

I had a look at a longer boat with a lower KMt to see what might be possible from optimisation. The attached shows a hull. The above water part is only there to show the waterline. It could be reshaped how you like. This hull should do 6.5kts with the motor flat out. Speed dropd to about 5.2kts with half power. The downside is that this boat is over 22ft long.

So if you want to rethink your design constraints along these lines before you settle on the design conditions let me know.

I have read that the 12V motors will run on 24V but not unless loaded. I think they will throw windings unloaded. So you might not like running it on the full 24V. My controller drops less than 1V at 10A and batteries fully charged are above 24V.

Have you looked at scooter motors? These are low cost. These are rated for higher voltage but not suited for submerged operation. I have a 300W motor that pushes a light catamaran at 5kts.

Rick W.

cahudson42
01-14-2008, 08:42 AM
Thanks again Rick.

I would be very happy with 5 kts at half power. What I'm trying to get to is a lightweight version of something like the ELCO Electric Launch:

http://elcoelectriclaunch.com/19%20ft%20launch.htm

- without all that wood, glass, and weight by doing it in Al. The ELCO 19' top speed is 5 kts - with 3 HP. If I get that with a small trolling motor I will be very, very happy:)

The beam is there for several reasons, 1. a wide enough floor so a wicker chair (or two) can be placed for 'full size' wife, 2. Stability - so she can get in and out easily, and 3. lower draft requirement as our Dock Space is maybe 12" late Summer.

The boat will be used on Lake George, NY for leisurely evening cruises with wife in calm water, and for fishing (by me).

I was thinking of using 2x 34lb motors on the transom - one starboard and one port. I have two 4-quadrant electrically reversible PWM controllers, and was hoping to get away with 'differential' (tank) steering - eliminating any rudder or need to rig up something to reorient the motor(s).

If I am reading your Post correctly, it seems I shouldn't need to 'stress out' the 2 motors at all - as I should easily get 300W/motor (34A @12V = 408W 'nameplate rating') - and 5 kts.

I briefly considered scooter motors - then abandoned the idea when I looked at the trolling motor economics. $110 for a 'fully submersible direct drive' is hard to beat in my opinion. I can treat them as 'disposable' and even replace them at the end of the season or 200 hrs - and still have $1/hr cruising cost. Plus they are light enough and cheap enough I can even carry a spare..

Thanks for the tip on 'unwinding' at higher RPM. Sounds like I should stay well away from 24V to the motors.. (I have been running them at 12V - 14V anyway because of the 34A current max.)

Any further thoughts or suggestions greatly appreciated!

Regards,
Chris

bairachtn
01-14-2008, 11:11 AM
Mr Chris(cahudson42) thank you very much for your advice...but at this time i have started my project and it is on another way different from yours( i am going to put an inboard motor), i appreciate very much your interest on me.

Mr Rick...hello again...i would like to ask you a favour...is it possible to send me the .fbm file from Delftship program which results the first drawing of my boat in the 1st page(in case i am wrong and this drawing was not a result of Delftship) ...i want to "play" with this a little...

cahudson42
01-14-2008, 02:29 PM
Thanks for reply Nicholas. Best Wishes for your Project!

Rick,

FWIW, I tried to get the pitch of the two trolling motor props. The stock 2-bladed has an angle of 16 degrees, and the prop is 9" in dia. If I multiplied/divided right, I get about 8 kts theoretical, then divide by 2 for slippage = 4 kts at 1200 rpm (approx).

The Kipawa '314' aftermarket 3-blade has an angle of 20 degrees. Also 9". So theoretical about 10 kts - divided by 2 = 5 kts at 1200 rpm.

The blades of the stock are quite flexible compared to the Kipawa. I remember reading elsewhere posts claiming the stock blade tips 'straighten out' at full RPM - and also reading that the stock prop top speed was about 3.5 kts.

I probably should plan 'on the boat' tests with both - but I'll likely start with the Kipawa and its theoretical 5 kts/1200 RPM. With the Kipawa, I ran static Tank Tests and got a 33A draw with only 10V going into the motor. I would think that with 'water going past the prop' at speed, the Kipawa 34A max draw should occur at a voltage higher than 10V. We shall see..

A custom prop may or may not be worth it (?) but a larger diameter prop is doable. No 'cavitation plate' to worry about, and the skeg is well behind the prop.

Comments suggestions appreciated as always!

Chris

P.S. - perhaps this discussion should be moved to its own thread? I don't want to impact/confuse your other two discussions...

Guest625101138
01-14-2008, 03:40 PM
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.

cahudson42
01-15-2008, 08:15 AM
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

Guest625101138
01-15-2008, 03:38 PM
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.

harry tams
01-21-2008, 01:32 AM
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?

Guest625101138
01-21-2008, 02:37 AM
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.

harry tams
01-21-2008, 03:07 AM
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?

harry tams
01-21-2008, 03:08 AM
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?

Guest625101138
01-21-2008, 05:38 AM
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.

harry tams
01-23-2008, 03:01 AM
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.

redu
06-26-2008, 03:04 PM
PMG-132 efficiency curves:
For instance here:
http://www.perm-motor.de/site/pdf/Gleichstrommotoren_PMG/Massbaetter_PMG_080_132/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

Guest625101138
06-27-2008, 03:44 AM
PMG-132 efficiency curves:
For instance here:
http://www.perm-motor.de/site/pdf/Gleichstrommotoren_PMG/Massbaetter_PMG_080_132/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.

kistinie
03-02-2009, 12:11 PM
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 ?

8430017
03-04-2009, 11:57 PM
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.

Guest625101138
03-05-2009, 12:09 AM
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

8430017
04-12-2009, 12:47 AM
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

Guest625101138
04-12-2009, 01:53 AM
Displacement?

Is the transom submerged at 10 knots?

What area have you got to mount solar panels?

Rick W

8430017
04-12-2009, 02:16 AM
displacement=2.65ton
yes
area=13.9875 m^2
thank you for helping

Guest625101138
04-12-2009, 06:13 AM
I have done the attached sketch of the boat you describe. You will have to advise if I am close to the mark.

The boat drawn will require 17kW to do 10knots if the propulsion can achieve an efficiency of 75%.

Good solar panels can produce up to 160W/sq.m in strong sunlight directly overhead. So the required area of panels is:
Area = 17000/160 = 106sq.m

With your available 13sq.m you could produce 2080W. This will achieve a speed of 3.5kts for the boat I have drawn.

The transom drag is significant. If I have shown it deeper than it is in your boat then this should be modified to get a more accurate calculation of performance. A photograph of the boat would help.

Rick W

Defender130
04-17-2009, 04:43 AM
Hi,
I have been reading with great interest this topic on propeller design and electric outboard as I am looking at converting my aluminium dingy to electric propolusion.
I live in Perth, Western Australia so availabilty to your full range of products may be limited.
I currently have a 12ft aluminium dinghy with a 9hp Mariner(mercury) engine.
Can anyone suggest a suitable electric outboard?
Kind Regards.
George.

Guest625101138
04-17-2009, 06:11 AM
Hi,
I have been reading with great interest this topic on propeller design and electric outboard as I am looking at converting my aluminium dingy to electric propolusion.
I live in Perth, Western Australia so availabilty to your full range of products may be limited.
I currently have a 12ft aluminium dinghy with a 9hp Mariner(mercury) engine.
Can anyone suggest a suitable electric outboard?
Kind Regards.
George.

George
You really need a good reason to spend the money to replace a petrol outboard on a small dinghy intended for planing.

The only commercially available electric outboards are rated around 4HP. Something like these:
http://www.electricmotorsport.com/store/ems_marine_electric_outboard_motors.php

There are some others but most are more expensive. The ones shown are USD prices as well.

So you can get an outboard of considerably less power than the existing Mercury. The next step is the batteries. Lead are heavy. For a 4HP outboard you would ideally need about 240kg (three adults of weight) of batteries and they will set you back AUD3000. By the time you do this the boat will be way to heavy to plane. It will be like a barge.

For AUD3000 you could get lithium batteries that would weigh much less and enable full power for about 50 minutes. They might get you on the plane one-up but it would be borderline. You might need a special prop.

I expect by the time you have spent AUD6000 your little tiny will be overcapitalised. Its performance will also be considerably reduced. It will be a little quieter though.

If you are doing it simply to reduce noise with the intention of just mooching along then a Minn Kota or Torqueedo might be worth consideration:
http://www.minnkotamotors.com/
http://www.torqeedo.com/en/hn/home.html

Also be careful with things like static thrust on electric outboards compared with combustion engines. It has no meaning to moving a boat through the water. It only has meaning if you want to tie the boat to a pier and measure the force you can produce. I have no idea of the value in doing this exercise. None the less it seems to be something that helps sell electric outboards. It seems the makers get close to fisticuffs over this nonsense figure accusing each other of exaggerated claims.

You will find most of the developments with electric powered boats are in hull design where the designer starts with efficiency in mind at the outset. You can get impressive results from electric motors matched to an efficient hull and prop.

Rick W

Defender130
04-21-2009, 12:35 AM
Thanks for your valuable reply Rick.
Kind Regards.
George.

John.m
12-01-2009, 04:24 PM
Hi i'm John, i'm thinking of purchasing a wide beamed canal boat 57ft by 12 ft which will weigh somewhere in the region of 22 tonne.I would like to power it by electric motors , however i have no knowledge on the subject. I'd like to know what sized motors ,best type of propeller and drive system ?Also best type of batteries taking into consideration that i will be living on the boat and have all the electric amenities that you would have in a house. Would it be possible to link it all to a generator that would drive the motors when the batteries are low , charge them at the same time and run the electrics on the boat? Please note that i will be also incorporating solar panels on the roof of the boat. Can anyone help? Regards John M.

kistinie
12-01-2009, 09:25 PM
22 tonnes ...
Try anti gravitation solution before going electric ?
What about air drag ? Important ?

Power needed will depend of the way you will need to move, speed in heavy weather/water condition is expensive in energy. In lake use it can be low.
Power generator efficiency will count too as KWH to litre of oil ratio is wide !

Guest625101138
12-02-2009, 07:30 AM
Hi i'm John, i'm thinking of purchasing a wide beamed canal boat 57ft by 12 ft which will weigh somewhere in the region of 22 tonne.I would like to power it by electric motors , however i have no knowledge on the subject. I'd like to know what sized motors ,best type of propeller and drive system ?Also best type of batteries taking into consideration that i will be living on the boat and have all the electric amenities that you would have in a house. Would it be possible to link it all to a generator that would drive the motors when the batteries are low , charge them at the same time and run the electrics on the boat? Please note that i will be also incorporating solar panels on the roof of the boat. Can anyone help? Regards John M.

John
It will be an expensive method of propulsion. It can be done. I do not know of any system that you can buy so you are on a long and expensive learning curve. You need to have considerable engineering expertise. An electrical qualification and license would be handy or at least befriend someone this knowledge.

I can help with power and things like that. I expect the boat already has a prop so best to start with this to check its suitability.

Rick W

John.m
12-06-2009, 02:55 AM
Thanks Rick for your reply, may i point out that the boat will be used on the british canal and riverways system and i know that there are several boats of equivilent or larger size using quite a simple system driven by lynch motor. (Refererance magazine Waterways world and canal boat.) My problem is calculating propeller size ,motor size and batteries adequate to store power to give the most efficient drive and run all the systems on the boat . I would presume that any form of power drive would be inefficient and would relate to 1 or 2 HP being driven through the propeller. (Hey but these boats were pulled fully laden by one horse from the eighteenth to early twentieth century)
The maximum speed on the canal system which for the most part is still water is 4 m.p.h and the navigatable rivers would probably run up to 4 notts.
Regards John M

kistinie
12-07-2009, 08:08 AM
If you accept to run your boat only when wind and water stream is calm, energy need will be significantly lower.

redu
07-02-2010, 02:21 AM
using javaprop for finding props for electric boats. Great tool!

Some questions:
1.
To test efficiency penalty, if blade chord is increased, the "modify card" was used. However, running "desing" for modified chord fails? The "design" returns original optimum chord data, and omits modified chord data totally? Did I miss something?
2.
For water propellers, there are no typical foil profiles? Water prop profiles are in practice thin ones, and the entry is guite sharp. Actually entry and trail profiles may be about similar (symmetry). Used E193 and ARA D profiles in javaprop to approximate an actual water prop forms.

Great tool to play "what if",
redu

redu
07-03-2010, 01:59 PM
using javaprop for finding props for electric boats. Great tool!

Some questions:
1.
To test efficiency penalty, if blade chord is increased, the "modify card" was used. However, running "desing" for modified chord fails? The "design" returns original optimum chord data, and omits modified chord data totally? Did I miss something?
2.
For water propellers, there are no typical foil profiles? Water prop profiles are in practice thin ones, and the entry is guite sharp. Actually entry and trail profiles may be about similar (symmetry). Used E193 and ARA D profiles in javaprop to approximate an actual water prop forms.

Great tool to play "what if",
redu

O.K.
It was possible to compare e.g. blade cord increase beyond that optimizewd one. It could be done in the "analysis" section of Javaprop.

"Advance ratio" = v / (n*D) [v = boat speed m/s, n = revolutions per second, D = prop diameter] is something I do not understand? Why to use this "advance ratio" figure?

redu

View Full Version : electric boat, proper rpm and propeller