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Old 25-09-2007, 15:09   #61
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The drive legs are 1.10 meters long the size of the pods is 150 mm diameter and 390 mm long excluding prop the weight is 36.4 kilo including the 3 bladed alu prop.
We coppercoa the drives because these are also used for generating and people do forget to take them out of the water when in the harbor , it is just to prevent any growth. once we have many units in the water we might rethink this .
The hydraulic actuators are designed for 2100 NM and the totla weight of the pos , props , basalt fiber and epoxy wing is a total of 52 kilo,s so we have used a factor 4 for the hydraulic actuator. the system has safety valves in case if a huge wave to the side of the boat and than the pods can move 10 degrees in either direction to take the force, we will try out the system for 30.000 NM and if satisfactory go into production.
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Old 25-09-2007, 15:14   #62
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Originally Posted by Alan Wheeler View Post

I think one conclusion you should make from this discussion is, there are people out there that want to see an alternative propulsion system. Me included. Many looking for those alternatives tend to be very clever people. Maybe me not included. But what has been offered in the past has not fulfilled all the hype produced. If you really want to push a system like this, then publishing very solid specs I think is the real key. Especially for those of us that grumble when we order the McD's burger we see in the picture and get handed the very poor representation of that picture.
If he makes a couple and does the Atlantic a couple of times that would work for me!

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Hello Allen

If you want I can keep you posted.

Greetings and have a good day
Forget him. Keep me posted.

Also if you will bring me one to test.............or I can come over and bring it back myself for the lightening test...............
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Old 25-09-2007, 15:21   #63
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If you want the full info on the system send me your e mail adress and I can send drawings pictures etc
Greetings
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Old 25-09-2007, 15:25   #64
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African Cats standard install a lightning conductor on top of the mast that is connected straight down thru the bridge deck to a 14 mm dyform piece of halyard that hangs in the water ,
I don't think you are wrong in doing this, but from many instances, it is becoming clear that it is not necessarily right either. If you do a search here on some of the lightening discussions, you will see there is a lot of info regarding this subject. The sum of it all is, just when you think you have done somthing to lesson the chance, a strike somewhere in the world blows all theory up in smoke.
One thing I can assure you is, lightening certainly does not travel in a straight line. It will try and take the easiest path to earth most certianly, but when nature is trying to sink so much current and voltage to earth so quickly, we simply can not provide a good enough path.
This is exiting that you are posting here. I hope others here can add there knowledge and advice to your comments(if needed) and help you to master a very exciting product for the market.
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Old 26-09-2007, 14:22   #65
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Customer designed, manufactured and delivered. I will find out who makes the magic pouches. Induction genset made by e-cycle using beta marine 3 cylinder Kubota. Very light.
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Old 26-09-2007, 14:28   #66
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Customer designed, manufactured and delivered. I will find out who makes the magic pouches. Induction genset made by e-cycle using beta marine 3 cylinder Kubota. Very light.
I certainly appriecate your efforts
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Old 27-09-2007, 08:34   #67
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25. We work with power output at the props shaft while diesels do not take transmission losses into account .
with 2 x 9.6 Kw electric motors we reach the same speed as with the 2 lombardini 30 hp motors. This has to do with more efficient props etc.
Gideon

The props make a huge difference. If you can run a large 3 blade or 4 blade prop at low rpm to gain hull speed it can produce a much higher thrust for the energy put into it. Most boats lose greater than 50% of the energy put into the prop through slippage through the water. Slower bigger props don't lose as much energy. Electric motors are perfect for this as they produce 100% of their torque at all speeds unlike a diesel which is optimized for the engine rpm to have one most efficient speed. You dont have to match the engine to the prop with an electric motor as finely as you do with the diesel.

I you look at Calders article it shows diesels being more efficient only for the most modern engines (IE the most expensive ones.) once you start comparing older engines or new older style engines you start to get parity or advantage to diesel electric. If you are cruising and have wind generator and big solar panels with decent sized battery banks you will not even use the generator that much unless your lifestyle is power hungry. Most motoring around the docks or harbour you will do under battery power alone. Which will be recharged from solar or plugged into the dock.

Motors under water in sealed pods have a lot going for them in cooling, then being able to pull them out of the water on the boat easily is a bonus for sailing performance and longevity and maintenance. Not to mention getting rid of a prop shaft hole through the hull. I have thought up a real simple bulletproof method of mounting a couple of the Re-e-power pods on the stern of a boat that pull up out of the water. Easy to retrofit a electric drive system to an existing boat. admittedly their systems only go up to about 50hp or so per drive. so for large boats are not suitable. but anything under 45 feet or so would be doable.

One huge thing for me is the silence of a well designed electric system. That is something golden and I would even trade a little efficiency for it.
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Old 27-09-2007, 13:13   #68
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Slower bigger props don't lose as much energy.
Not quite correct. I think I know what you are trying to say though. Slower bigger props have less slip in the water. They are more efficient at turning rotary motion into forward motion. Not True about being more efficient though. They take a heck of a lot more energy to turn them. There is mass to take into account, but that part is not as important as surface area. The more surface area, the greater the friction the prop encounters in the water. Thus harder to turn. Slowing the speed down lowers the resistance, but it also means the pitch has to be increased to compensate. It is the pitch that governs the forward motion, not the prop size or blade No. of course.
So all in all, propelling a boat hull forward takes ruffly the same amount of energy, not matter what. It is why a rule of thumb exists of Hp/lb(Kg) of boat. All calculations should be worked backwards from that. Of which I find most alternative solutions do not do. It should be...energy required to propell boat of X weight at X speed, with X margin of reserve energy for safety factors. Then the propulsion system power requirements should be worked out from there. The industry seems to be going the opposite way. ie. smallest amount of power required to push boat along equalls enough.

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once you start comparing older engines or new older style engines you start to get parity or advantage to diesel electric.
There is a small advantage in newer engines. But it is not that big. There is a fact of diesel that a given amount of fuel produces a given amount of power. No matter what age the engine design. What is true is that polution has been greatly reduced, so we have cleaner burning. To obtain cleaner burning, better control of the fuel dose has been needed. So with better control, slightly less waste of fuel has been obtained. Slightly less weight equates to less fuel used.What the big advantages have been is better power control. Torque bands have been able to be produced over a wider range and flatter respons. This also equates to better efficiency. But the difference in fuel use over all is very small. Once again, the real big saving is in using the smallest motor you can get away with. But once again, I think this is false economy.
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Most motoring around the docks or harbour you will do under battery power alone.
True in some sense. But lets say you have a 10Hp electric motor. Lets say you take 1/2hr from marina to open water sailing. And 1/2hr from end of sailing to back to marina again. So a total of 2x1/2hr is 1hr and thus 7.5Kw of energy. That is going to take some recharging using solar and wind and one heck of a battery bank and Genset to keep up. So what is saved in fuel from the Diesel engine propulsion is taken up in generating.

I guess what I am trying to say is, yes there are savings of efficiency in electric drives. Yes there can be advantages with it. But the small savings are far outweighed by other factors, such as additional devices(solar panels, wind gennies etc), the huge weight and expense and short life of a very complex battery bank system, the comlexity of charging that bank, the shorter life span of electric drive and the so far greatly reduced power required to drive the boat.
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Old 27-09-2007, 16:33   #69
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So all in all, propelling a boat hull forward takes ruffly the same amount of energy, not matter what. It is why a rule of thumb exists of Hp/lb(Kg) of boat. All calculations should be worked backwards from that. Of which I find most alternative solutions do not do. It should be...energy required to propell boat of X weight at X speed, with X margin of reserve energy for safety factors. Then the propulsion system power requirements should be worked out from there. The industry seems to be going the opposite way. ie. smallest amount of power required to push boat along equalls enough.



I guess what I am trying to say is, yes there are savings of efficiency in electric drives. Yes there can be advantages with it. But the small savings are far outweighed by other factors, such as additional devices(solar panels, wind gennies etc), the huge weight and expense and short life of a very complex battery bank system, the comlexity of charging that bank, the shorter life span of electric drive and the so far greatly reduced power required to drive the boat.
First as to prop.... I am not an expert but am more knowledgeable than some. I have had questions with engines and props and what really worked. I looked at the theory and then tested it in the real world with different props on the same engine and boat with on the water tests and also with static thrust testing using equipment rated to 3000 lbs good from 1 lb to 3000 in 1 lb increments. In general in the tests I have conducted you can see as much as a 25% difference in thrust for a given rpm for each inch of change in pitch. You will also see a change in max rpm for a given amount of torque. The engine didn't change nor the output it was putting out. However the change in thrust with different props is flat out major. So in the end you can put so many ft/lbs of torque on a prop shaft and have major changes in boat performance for any given amount of torque depending on the prop. Electric motors are just flat better for max torque at any rpm. while a diesel generator running at max efficiency single rpm all the time will be over all more efficient.

This is not to say that a modern diesel engine run at top efficiency wont out do a electric setup. Or that any diesel setup wouldn't be better than a bad electric setup. I think either system properly built will give good efficiency. I think the electric will do better over a wider range than the diesel alone. in the end it comes down to the whole system integration which ever way you go.

I have several serious dislikes with standard inboard diesel setups.
1. all the through hulls needed to support them and the prop shaft through the hull. All are high maintenance places looking for a problem to happen and let water in the boat. Not to mention all the places that water flows through inside the boat before going back out. I understand that this is mostly reliable and has been standard setup for many years. But it is a point of failure with potential to sink boats in the wrong circumstances.
2. having a prop dragging along under your boat while under sail. this is one of the reasons sailboats are so inefficient under power. They use folding and 2 blade props that flat out give up huge amounts of efficiency. compared to a much larger 3 blade fixed prop. Or spend lots of money for a mechanically complex very expensive feathering prop. Your sailing performance is also degraded with a prop and shaft and all the other stuff supporting it under the boat. Ideal is to pull it out of the water when not in use. electric makes this much more doable.


at the end of the day you are correct in that it takes so much force to move the boat through the water. But the old rule of thumb hp per ton of displacement is a very very rough guide. It can vary widely depending on the shape of the hull. I also agree that you shouldn't power a boat for just getting it to hull speed in calm water. you should have a large margin of extra power for wind and waves for when the situation gets out of hand. Both standard diesel setup and electric can be designed to accommodate this.

As to all the extra systems on the boat such as wind and solar generators. I would plan on having them anyways along with a moderate battery bank as I like my computer and other electrical gadgets and gadgets.

for someone that use lamps and no electrical then it might not be lifestyle effective to invest in all the electrical systems needed for electric drives. Modern life on a boat is trended though to be a good mesh with the systems needed for a electric driven boat.

oh battery banks.. as a add on to an existing boat depending on how much capacity you add it can be to much weight to add. However on purpose built boats, especially monohulls, it makes a lot of sense. You can replace a significant chunk of your ballast with batteries. No weight penalty at all.

I think the great successes will tend to be purpose built but even retrofits can find a good home on some boats.
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Old 28-09-2007, 08:15   #70
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Alan the comment that larger props are more efficient, while is not true in general, is usually true for sailboats.

If one uses the Taylor Propeller Characteristics from the Handbook of Ocean and Underwater Enginneering mcgraw hill 1969 to calculate the most efficient prop sailboats would have props 20 to 30 % larger in diameter than they are normally equiped with.
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Old 28-09-2007, 10:05   #71
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I suppose I should have stated that larger props are more efficient in general for displacement vessels. It would be inaccurate for planning hulls. I sometimes forget that planning hulls are more common than displacement. Most my experience is with displacement vessels so I tend to focus on them.
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Old 28-09-2007, 12:53   #72
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I am not disputing the fact that a larger diameter is more efficient at turning rotational energy into forward momentum. What I am trying to say is, while increasing efficiency of forward propulsion against slippage in the water, friction also increases. So the actual "power to forward movement" ratio tends to remain close to the same. However, this ratio is also closely linked with actual speed as well. Some fishing boats (in say the 40-50ft range) that towed nets, often had 5 blade props fitted. That was so they could get a good "Bite" in the water and have the power to pull the net through the water. But they had poor top end speed performance due to the large surface area of prop in the water. Surface drive props came about because of that very fact. They could have large surface area blades cutting the water, but with the rest of the prop out of the water, they still had little friction and drag.
So in a nut shell, it takes X power to push and object forward at X speed. You can connect X power to a variation of drives coupling that power to the water. But the final result is, no matter what type of drive you have, it still takes X power to get the hull to X speed.
Otherwise (to put a different perspective on it), we would all be putting larger tires on our cars because it makes them more efficient and will use less fuel because they have a greater surface area on the road. Sadly it doesn't work that way.
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Old 28-09-2007, 13:31   #73
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No, for any one boat and any one speed there is a prop design (pitch divided by diameter) which gives the best efficiency. The efficiency is defined as energy required to move the boat at that speed divided by the energy consumed by the prop.

The energy that goes into the prop, that does not contribute to boat speed, contributes to the wake swirling water, and the "jet of water" behind the prop.

A prop with 100% energy efficiency would have to leave the water behind the boat flat, calm and still, and have 0 friction with the water.

So, since most sail boats run a prop with about the right pitch but just small on the diameter, (to help reduce sailing drag), a bigger diameter prop will reduce the shaft energy consumed.

Prop efficiencies can exceed 80% on larger ships. but are more like 60% on sail boats.
The perfect prop on a sail boat might get 70% efficiency. This alone would be a 15% savings in energy. (This advantage would vary with the speed vs design speed).
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Old 28-09-2007, 13:33   #74
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The discussion about prop drag in thread In gear or out... references an article that plots prop efficiencies, against the advance coefficient and the speed.
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Old 28-09-2007, 23:38   #75
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js, your forgetting one very important point. Friction. If there was no friction imposed on the rotation of the prop, then your statment would be true. 100% efficinecy is always good and all boats would be designed for the most efficient prop as the No1 design criteria and the rest of the boat and it's mechanics would be based around that. But unfortunately we have to deal with friction. This is also a good thing as Friction is what also allows the prop to "screw" it's way through the water. It is simple physics. The resistance to rotation of the prop is the same resistance that allows the prop to move forward. I don't know how to make this any more clear. The simple point is, it takes the same(x) energy to move a hull forward at a specific(x) speed. No matter what you have in the water propelling it. You can not get around that simple law. Yes every hull design and weight will be different. But we are still using the same theoretical X hull for our arguments. Thus wether you have a small prop turning at high speed or a big prop turning at low speed, it will still take the same power to move the hull forward at X speed.
Yes I agree that as the propellor decreases in size, the efficiency of rotation to forward movement decreases with it. But so does the energy required to rotate it.
The original statement was about a big slow moving prop meant it required less Hp to propell the boat along, thus the ability to use less Hp electric drives as against big Hp diesel engines. Well if it didn't say that, it certainly alluded to that.
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