Author Topic: Propeller shaft alternator on our boat. (Read 12632 times)

la7qz · « **on:** May 25, 2009, 05:46:42 AM »

Hi

Not sure what section to put this in, but I suppose hydro is as close as I can get.

I'm thinking about installing a propeller shaft alternator on our 36 foot 10 ton Cheoy Lee Clipper Ketch, but have some questions.

A lot of people have tried installing a standard marine or automotive engine alternator as a shaft alternator and I already know this is doomed unless the alternator is rewound since the alternator never spins fast enough to really produce anything. However, we have a spare 400Watt three phase permanent magnet wind generator alternator (from a Duogen). We are flying an identical alternator as a wind turbine with blades from a Four Winds, and this works very well. Cutin is at around 300 RPM, producing (from memory) around 5 A at 400 RPM and maybe 10A at 500 RPM. (Not sure about these numbers, but pretty close). The most I've seen is 34A at 1170 RPM in a big gust. (I clamped the turbine and tied off the blades for hurricane Omar... My boss did not secure his Aerogen 6 and ended up with a totally toasted stator.)

Magic's engine is a Yanmar 3GM30F (24hp), and she normally cruises happily at 5 - 5.5 knots at 1500RPM under power. I believe the gearbox is 3-1?

My goal is for the shaft alternator to produce 5A when sailing at 6 knots. More will be welcome of course, but 5A would make me happy. In other words, the alternator needs to spin at around 400 RPM (or more). Does anyone have an educated guess what propshaft RPM I can expect at 6 knots with a load of 5A (approximately 65W) on the alternator? Sizing the pulleys right is probably more important with a permanent magnet alternator since I can not control the field.

BTW, the PV panels and wind turbine are regulated by a Tristar 60 configured as a dump load regulator with a 600W 12V heating element in the hot water tank. This works very well and we even sometimes produce hot water from wind and sun. Since the regulator is connected direct to the batteries with a set point of 14.4V, it will automatically take care of any excess energy from a shaft alternator, so overcharging is not an issue and any hot water produced would be most welcome.

Owen, Donna and Sparky

Yacht Magic

St Maarten

la7qz · « **Reply #1 on:** May 24, 2009, 11:53:51 PM »

Oh, and before anyone asks...

No, I don't know the diameter and pitch of the propeller and we don't have any way of finding out until we haul out some time later this year.

Owen, Donna and Sparky.

jondecker76 · « **Reply #2 on:** May 26, 2009, 12:18:25 AM »

Why are you going through the trouble of dragging a propeller through the water to generate electricity when you can just find a way to hook an alternator up to the engine? (Or is this a sailboat?)

I'm sure you understand this, but just to be sure... The extra load put on the engine by the drag of the propeller will be greater than the amount any alternator will recover from the propeller - which is why an alternator directly connected to the engine makes more sense.

Of course, maybe you have a specific reason for wanting to do it this way. Please describe more what you are trying to accomplish, that will let others give better advice

electrak · « **Reply #3 on:** May 26, 2009, 05:57:58 AM »

I'll give you what little I know, or think I know, 1500 rpm engine / 3:1 gear = 500 rpm drive, so your prop is going 500 rpm to push at your boat just over 500 feet per minute. So 1 foot per rev in push, you need to find out what it will turn in pull, I have seen sailboats that the shaft doesn't turn, and you have to make sure you do not have a feathering prop,

Things to check, when sailing: Does the shaft turn? how well does the boat handle in reverse, engine? how much space is there around the shaft?

Next how much power can you recove from the shaft? can you rig up some kind of proxy brake?

la7qz · « **Reply #4 on:** May 26, 2009, 01:02:00 PM »

Hi

The prop is a fixed three blade prop, no feathering. . Yes, the shaft turns when sailing unless I put the engine in gear and there is room to put a pulley on the shaft and room to install the permanent magnet three phase alternator above it.

I suppose I could put a revcounter on the shaft to check what the freewheeling revs are when sailing, but that doesn't answer what the revs would be if I put a load on it.

I know that others have successfully installed shaft alternators on sailboats. The ones that have been successful have either used a car/boat alternator rewound for the lower revs or a very large pulley on the shaft.

The question I need answered is really just what pulley ratio I need between the shaft and alternator to be able to take out somewhere between 50 - 70 Watts when sailing at 5-6 knots knowing that the alternator I intend to use produces around 60W at 400 rmp. I do not expect a three decimal point answer when there are so many variables (including pitch and diameter of the prop), but an educated guess would be useful.

Regards,

Owen, Donna and Sparky

Yacht "Magic"

St Maarten

Netherlands Antilles

la7qz · « **Reply #5 on:** May 26, 2009, 01:06:05 PM »

Hi

This is a sailboat. A ketch is a sailboat with two masts and this one is a heavy displacement 10 ton full keel boat built for crossing oceans which is what she'll be doing... and what she did to get me to this island.

Crossing oceans means hours, days and sometimes weeks spent at sea under sail with no running engine. We do not want the noise and pollution of the engine at sea, and the fuel in the tanks will be conserved as much as possible for emergencies. We do not run the engine for battery charging when we are at anchor, and wish to avoid doing so at sea.

We have 310W of solar power and a wind turbine, but at sea the wind turbine will not work because it is installed to face forwards and there is no room to make it yawing on this boat. At sea the sails will also be up so there will be more shade over the panels than when anchored. S shaft alternator which generates power from the propeller shaft is a tried and tested way for sailboats to generate electricity at sea. I'm just looking for a starting point for the best pulley arrangement for this particular combination of boat and alternator.

Owen, Donna and Sparky

Yacht "Magic"

St Maarten

Netherlands Antilles

TomW · « **Reply #6 on:** May 26, 2009, 02:01:59 PM »

Owen;

A sailor nor a mechanic am I but....

My initial thought was that maybe you could use a stepped pulley [or 2] in a sort of "transmission" like you see on pulley driven drill presses. Seems it would allow you to dial in your rpm?

If you knew the "no "load" speed under way then you could select main pulleys for that and adjust with stepped pulleys to get the power in that you need.

Usually more than one way to defur a feline.

Just a thought.

Tom

electrak · « **Reply #7 on:** May 26, 2009, 02:19:00 PM »

Once you get a rev count, 50-70 watts shouldn't slow it down much,

To crudely find out haw much torque you have, find a solid tyepiont close to the shaft, with the shaft stopped, repete with the shaft stopped, ie in gear, rap a rope around it, about 3 times, keep tension on the other end, disengage gear, slowly lessen the tension until the shaft spins, chech tension in the fixed side, if you have avalible a spring scale even better,

Warning don't do this until you understand it!!!!!!

As for pulley size, what size is the pulley on the alternator, I can throw numbers but without your numbers they won't work. I would go with the largest pulley I could get/fit/afford, then change the one on the alternator as it is likely the easiest,cheapest to change

la7qz · « **Reply #8 on:** May 26, 2009, 02:19:53 PM »

Hi Tom

My guess is that I will probably end up quite close to 1:1 or maybe have to gear the alternator up just a little bit. Something like 1:1.25 or at the most 1:1.5.

Owen

la7qz · « **Reply #9 on:** May 26, 2009, 02:22:58 PM »

Hi

Thanks for the suggestions.

This is a wind turbine alternator (identical to the one I am flying with a 5' two blade prop) so at the moment there is no pulley on it. The project here is to figure out a ratio between the propshaft pulley and alternator pulley and then have pulleys fabricated or adapted to fit both.

Owen, Donna and Sparky

Yacht Magic

St Maarten

Netherlands Antilles.

dnix71 · « **Reply #10 on:** May 26, 2009, 04:23:13 PM »

You might look at AmpAir and Ferris models for design clues. Both companies have made microhydro since the 1970's. Their tow behind models aren't cheap, but they claim to be able to provide all needed power for open ocean sail. Ferris has a model that converts to a wind gen for use at anchor (at port).

You might even experiment with a electric trolling motor. The following thread is about one converted to run in a stream for campside power. You will need a much bigger prop and flipped over so the motor is forced to spin backwards.

http://www.fieldlines.com/story/2005/6/27/41048/5123

wooferhound · « **Reply #11 on:** May 26, 2009, 08:31:55 PM »

I probably don't know what I'm talking about, but I'm sure going to tell you what I think...

It seems to me that a boat prop is too small to catch enough water to make it spin under load. I'm thinking that the water will just go around the water prop, and that what would work best is something like a small wind prop under water. Another note would be that the "airfoil" on the water prop will be reversed from what you really need.

-Warning-

This may or may not be right or not right !?

Simen · « **Reply #12 on:** May 27, 2009, 01:58:08 AM »

I would agree with la7qz; 1:1 to 1:1.5 with your 5' windgen alt, but a rpm estimate would help, even with unloaded shaft.

With the amount of displacement you have, i would guess there would be good torque from the water returning from around the boat towards the 3-bladed prop.

Also, take a look at Ozmarine's OzEcoDrive http://www.ozmarine.se/OZecoDrive/Eng/IndexOZecoDriveEng.html ; they estimate 7-12Amps at 6knots with their motor/generator with a lockable folding prop.

la7qz · « **Reply #13 on:** May 27, 2009, 08:33:13 AM »

Hi Woof

For once I'm glad to be able to tell you that you're wrong.

I'm not re-inventing the wheel here. Propeller shaft driven alternators have been in use on ocean cruising sailboats for a long time. Some are successful, some are not.

The sucessfull ones are the ones that use an alternator wound for slow RPM like you would see on the shaft of a sailboat under sail and to a lesser degree the ones who use a huge pulley on the propshaft. I already have a slow RPM three phase PMA, so that seems the logical thing to use.

If I leave the engine in neutral when sailing, the propshaft spins. That's energy, and I want some of it in my batteries.

Owen

DanG · « **Reply #14 on:** May 27, 2009, 08:55:07 AM »

Heyas Owen! I'm curious...

1) what the propeller shaft diameter is;
2) what the alternator shaft diameter is;
3) if considering endless loop belt, how installed & if field replaceable;
4) is the compartment a harsh environment chemical wise;
5) is static and/or heat build up absolutely to be avoided;

A photo of the area could be put to good use too!

hydrosun · « **Reply #15 on:** May 27, 2009, 09:48:57 AM »

You said you could get a rev counter to see how fast the shaft is turning when the propellor is free wheeling. If you could get that number I would then set up the pulley to get the generator to hit it's generating speed at half that number. In hydro systems you try to get the turbine to operate at half the speed of the unloaded speed. That gives the maximum transfer of energy from the water to the turbine. I'm assuming the propellor would work in a similar fashion.

This should give you a place to start. You know that other people have made this work so it should get you close.

Chris

pepa · « **Reply #16 on:** May 29, 2009, 05:54:23 AM »

my son lives on a sailboat and we are always trying to

come up with different ideas to make power. this is one sorse

i haven't heard about. will the shaft speed be to high when the

motor is driving the boat?

if the motor over rivs it will be bad for the windings unless

you use a spring or gravity contact type to pull power from the boat

shaft, some way to pull the mill back when the boat motor is used.

also keep it as close to motor as you can to to keep any vibtation

out of the shaft. just my thoughts, pepa

zeusmorg · « **Reply #17 on:** May 29, 2009, 09:08:11 AM »

Owen, given what you've stated a good starting place would be a 1.5 to 2 ratio on your setup. the 2:1 ratio may give you more available energy given your shaft RPM. I'm assuming a few WAG's here considering the drag of the alternator will slow down your prop speed, and the fact that it isn't as efficient in "sail mode".

I would guess that the alternator would most likely reduce the prop speed to about 300 rpm. and then a 2:1 ratio would give you 600 RPM on the alternator, near your target speed. I would look into the cost of a stepped pulley setup since they're generally not that much more expensive than a single diameter pulley.

la7qz · « **Reply #18 on:** June 05, 2009, 06:21:07 AM »

Hi

Shaft speed when motoring shouldn't be a problem. In most installations the problem is rather to get the alternator spinning fast enough when sailing.

A permanent magnet alternator can be run unloaded withouth when you don't need the power (or when you need all available power to move the boat). Unlike a wind turbine instalation where an unloaded alternator will run away and quite possibly self destruct, an unloaded shaft alternator should not be a problem. A regular alternator with a regulated field can also be left freewheling by disconnecting the field.

You could also install some sort of clutch to disengage the shaft alternator when not in use.

Owen

Airstream · « **Reply #19 on:** June 05, 2009, 07:14:46 AM »

I would like to see you try an o-ring conveyor belt on three idler pulleys with a small rotor plate attached to two of them, the image shows an effortless RPM doubler. If one could cam the air gap open the system could be taken offline while motoring, or stretch the belt off the prop shaft, etc...

The 'motoring' driven speed at 500 rpm off a 1" shaft is just above their high-speed belt foot per minute threshold, you could use it w/o the shaft pulley if all you want is 50w while under sail and have no worries when motoring.

Look at the ratings on these 3/8", 7/16" and 1/2" belts - all you need is 15-25 pounds ptension, they can last for 10 years, have good oil resistance (until they see a bath and they hydroplane) and their pulleys are molded resins with sealed bearings cast in.

I have three 17mm shaft 6" idler pulleys extra here, I got a lot of 10 to try the rpm doubler idea on a lawn-art wind turbine that hasn't happened (yet)...

Have to run, just a quickee idea sketch for your review.

http://www.durabelt.com/roundoringinfo.php

http://www.fennerdrives.com/pulleys_and_idlers/powermax_idler_pulleys.asp

News:

Author Topic: Propeller shaft alternator on our boat. (Read 12632 times)