propshaft driving an alternator , when sailing

[a64pilot]

Originally Posted by Wotname

Question for the engineers on the thread.
Is there any meaningful side load on the shaft with coupled to the alternator as described up thread and if so, is this an issue?

If the pulley was mounted to the shaft and the alternator above the shaft, it would quite likely help add to the life of the cutlass bearing as the whole weight of the shaft is normally bearing down on it, but the alternator would help hold some of the weight up.

Probably not enough to matter much though

[tdunlap]

I went down this road myself.
Consider using a PMA type alternator such as this one -

https://www.windbluepower.com/mobile...uctCode=DC-540

No brushes, and you don't need to supply excitation or field current to it. A standard alternator requires something as much as 2.5 amps for the field current, so you could end up using amps instead of making them at slow boat speeds.

You could also use a DC Motor, but I liked the PMA approach. These alternators are designed to produce power at low RPMs. You can find these for sale on the net in many places, eBay included. They are often used on wind generators.

You can end up spending a bit of money to do this. I was already installing a thrust bearing to the prop-shaft, so I just had a pulley made to fit between it and the engine. Then put brackets on the motor for the alternator.

To engage or disengage the system, I use Powertwist Linked V-Belt on the pulleys. These can easily be rolled off the pulleys when not in use, even when it's tensioned properly. I fell in love with these adjustable belts in my woodshop using them on my 3HP table saw. I get less vibration and better transfer of power with them, and so began using them elsewhere.

As mentioned, you need to make sure it's OK to freewheel the transmission.

When I purchased my engine, I went with a non-hydraulic, mechanical gearbox that was suitable to be freewheeled out of gear. Some transmission can overheat if you do this. So check with the manufacturer.

There are other considerations, such as noise, and wear and tear on your stuffing box, cutlass bearing, shaft, the transmission, and perhaps even your prop when using something like a Max. Set up properly, it's not difficult to make it all work.

I don't think you will notice any appreciable drop in speed over just having the prop free-wheeling. If you have something like a Max prop and go from feathered to locking it to rotate, well maybe you'll lose half a knot, but it's had to say due to many variables. A bigger boat with a long waterline is likely not to notice it much.

For the approach to work properly you need a clean hull, clean prop, no cutlass bearing play, and the right pulley ratio. The ratio depends on many boat variables and what you're using to produce the power, but something from 5:1 to 7:1 is in order. So the prop-shaft pulley needs to be pretty large. This may not be possible to fit on many boats.

So, you can see this may be difficult to get all set up on a small boat, but it comes into it's own on a larger boat.

My boat, at just over 60 feet, space is not a problem. The approach can generate a lot of power.

The WattandSea is a great bit of gear, but for me was much more expensive, puts the generating device underwater with seals that might leak, and takes up space on the transom. However, boats are nothing if not a bunch of compromises. You have to pick the ones you're happy with. No one approach fits all. I would not be afraid to experiment.

I'll attach a photo of my set up when we were fist installing the engine.

One last note, when adding things like this to an engine, you may need to change one or more of the motor mounts, as you are adding weight to the engine. Check your manual. I would also put everything on the motor and avoid attaching parts of it to the hull. I'm not good at explaining the reason, but it's the same thing as adding pumps, refrigeration compressors, and alternators to be engine driven. You want everything attached to the motor so it all vibrates the same, or you can have problems.

Cheers

[atoll]

Originally Posted by tdunlap

I went down this road myself.
Consider using a PMA type alternator such as this one -

https://www.windbluepower.com/mobile...uctCode=DC-540

No brushes, and you don't need to supply excitation or field current to it. A standard alternator requires something as much as 2.5 amps for the field current, so you could end up using amps instead of making them at slow boat speeds.

You could also use a DC Motor, but I liked the PMA approach. These alternators are designed to produce power at low RPMs. You can find these for sale on the net in many places, eBay included. They are often used on wind generators.

You can end up spending a bit of money to do this. I was already installing a thrust bearing to the prop-shaft, so I just had a pulley made to fit between it and the engine. Then put brackets on the motor for the alternator.

To engage or disengage the system, I use Powertwist Linked V-Belt on the pulleys. These can easily be rolled off the pulleys when not in use, even when it's tensioned properly. I fell in love with these adjustable belts in my woodshop using them on my 3HP table saw. I get less vibration and better transfer of power with them, and so began using them elsewhere.

As mentioned, you need to make sure it's OK to freewheel the transmission.

When I purchased my engine, I went with a non-hydraulic, mechanical gearbox that was suitable to be freewheeled out of gear. Some transmission can overheat if you do this. So check with the manufacturer.

There are other considerations, such as noise, and wear and tear on your stuffing box, cutlass bearing, shaft, the transmission, and perhaps even your prop when using something like a Max. Set up properly, it's not difficult to make it all work.

I don't think you will notice any appreciable drop in speed over just having the prop free-wheeling. If you have something like a Max prop and go from feathered to locking it to rotate, well maybe you'll lose half a knot, but it's had to say due to many variables. A bigger boat with a long waterline is likely not to notice it much.

For the approach to work properly you need a clean hull, clean prop, no cutlass bearing play, and the right pulley ratio. The ratio depends on many boat variables and what you're using to produce the power, but something from 5:1 to 7:1 is in order. So the prop-shaft pulley needs to be pretty large. This may not be possible to fit on many boats.

So, you can see this may be difficult to get all set up on a small boat, but it comes into it's own on a larger boat.

My boat, at just over 60 feet, space is not a problem. The approach can generate a lot of power.

The WattandSea is a great bit of gear, but for me was much more expensive, puts the generating device underwater with seals that might leak, and takes up space on the transom. However, boats are nothing if not a bunch of compromises. You have to pick the ones you're happy with. No one approach fits all. I would not be afraid to experiment.

I'll attach a photo of my set up when we were fist installing the engine.

One last note, when adding things like this to an engine, you may need to change one or more of the motor mounts, as you are adding weight to the engine. Check your manual. I would also put everything on the motor and avoid attaching parts of it to the hull. I'm not good at explaining the reason, but it's the same thing as adding pumps, refrigeration compressors, and alternators to be engine driven. You want everything attached to the motor so it all vibrates the same, or you can have problems.

Cheers

looks like a great setup ,and correct ratios,the shaft pulley appears to be about 30-35 cm to 5cm on the alternator ,ideal

[davegeorge44]

I have been reading these posts with some interest. Lots of good input, but not much actual experience. I did have a prop shaft alternator installed on my cruising boat (Roberts Offshore 44) for a period of time and it worked very well, with reservations. The boat had lots of room in the engine room, and we were running a big prop (22"). At the time there was a guy in Australia who was re-winding alternators so that they would put out at lower RPM than a standard automotive unit. A large pulley (10:1) was installed between the transmission and the prop shaft. This worked fine on the initial installation. I was getting up to 10 amps while sailing. Prior to circumnavigating - circa 1998 - I decided to re-engine and put in a smaller engine with more flexible mounts. I found the sideways pull on the back of the engine to be untenable and so abandoned the set up. By that time we had more / better solar panels and installed a wind generator. Probably should have just altered the set up and kept the prop shaft alternator as it always delivered plenty of good reliable charging while sailing - way better than the wind I replaced it with. By the way, I also tried a tow generator on a different boat, way back. Lots of noise and vibration so not good, but a properly set up prop shaft unit is good.

[Dave_S]

Sorry I didn't read it all so probably been covered but.

If you want 600W you need 1kW to drive it, how much slower will your boat go with 1kW less, if your happy with that you can do it......... No?

All you have to work out is ratio's.

[tdunlap]

Since the question of actual experience was raised, I googled to see if others are using this approach. I found the following using the same alternator as I'm using. So here is some more real world data. He has several post on his blog and covers setting up his system. Pretty good write up.

https://justalittlefurther.com/searc...ft%20generator

[rgleason]

A couple of good points made by others here:
1. Make sure the transmission can freewheel without damage.
2. Consider that solar panels can also have windage and slow the boat down too depending on installation.
3. Use of a perminent magnet alternator will improve output.
4. Use of external diodes will help wirh cable distances.
5. Consideration of max shaft speed under power is necessary so the shaft alt is not destroyed.
6. The stuffing box must be adjusted properly or salt water will get all over the shaft alt and damage it. Dripless stuffing box is probably best.
7. Excess power can be dumped to domestic hot water.
8. However the shaft alt should have overheat protective device and be shut down.
9. Best mounting is off the engine/transmission with a large pulley sandwiched between the prop shaft flanges. To get adequate power at lower rpms at the least 5:1 is required, but it should be calculated. Some smaller boats cannot accommodate the larger pulley size needed for the prop flanges.
10. Larger boats can accommodate shaft alts more easily.
11. Suitable for 3 blade fixed props or max-props.

[Cadence]

Originally Posted by tdunlap

I went down this road myself.
Consider using a PMA type alternator such as this one -

https://www.windbluepower.com/mobile...uctCode=DC-540

No brushes, and you don't need to supply excitation or field current to it. A standard alternator requires something as much as 2.5 amps for the field current, so you could end up using amps instead of making them at slow boat speeds.

You could also use a DC Motor, but I liked the PMA approach. These alternators are designed to produce power at low RPMs. You can find these for sale on the net in many places, eBay included. They are often used on wind generators.

You can end up spending a bit of money to do this. I was already installing a thrust bearing to the prop-shaft, so I just had a pulley made to fit between it and the engine. Then put brackets on the motor for the alternator.

To engage or disengage the system, I use Powertwist Linked V-Belt on the pulleys. These can easily be rolled off the pulleys when not in use, even when it's tensioned properly. I fell in love with these adjustable belts in my woodshop using them on my 3HP table saw. I get less vibration and better transfer of power with them, and so began using them elsewhere.

As mentioned, you need to make sure it's OK to freewheel the transmission.

When I purchased my engine, I went with a non-hydraulic, mechanical gearbox that was suitable to be freewheeled out of gear. Some transmission can overheat if you do this. So check with the manufacturer.

There are other considerations, such as noise, and wear and tear on your stuffing box, cutlass bearing, shaft, the transmission, and perhaps even your prop when using something like a Max. Set up properly, it's not difficult to make it all work.

I don't think you will notice any appreciable drop in speed over just having the prop free-wheeling. If you have something like a Max prop and go from feathered to locking it to rotate, well maybe you'll lose half a knot, but it's had to say due to many variables. A bigger boat with a long waterline is likely not to notice it much.

For the approach to work properly you need a clean hull, clean prop, no cutlass bearing play, and the right pulley ratio. The ratio depends on many boat variables and what you're using to produce the power, but something from 5:1 to 7:1 is in order. So the prop-shaft pulley needs to be pretty large. This may not be possible to fit on many boats.

So, you can see this may be difficult to get all set up on a small boat, but it comes into it's own on a larger boat.

My boat, at just over 60 feet, space is not a problem. The approach can generate a lot of power.

The WattandSea is a great bit of gear, but for me was much more expensive, puts the generating device underwater with seals that might leak, and takes up space on the transom. However, boats are nothing if not a bunch of compromises. You have to pick the ones you're happy with. No one approach fits all. I would not be afraid to experiment.

I'll attach a photo of my set up when we were fist installing the engine.

One last note, when adding things like this to an engine, you may need to change one or more of the motor mounts, as you are adding weight to the engine. Check your manual. I would also put everything on the motor and avoid attaching parts of it to the hull. I'm not good at explaining the reason, but it's the same thing as adding pumps, refrigeration compressors, and alternators to be engine driven. You want everything attached to the motor so it all vibrates the same, or you can have problems.

Cheers

I initially said folly. Yours is well thought out. I can envision people with a 30 boat swing a postage stamp wheel, slapping on a car alternator and expecting miraculous results. I would hope anyone considering this reads your post.

[a64pilot]

Word on RPM, average auto alternator is designed to operate between 6,000 and 18,000 RPM.
That would be real tough to gear to, and surely you couldn’t overspeed that, plus a significant amount of power is eaten up overcoming inertia and just spinning the thing that fast. Plus it may be noisy.
However at first glance it would seem that the PMA has good output at 1000 RPM. You can probably gear for that.

[Qayaq]

Had one on an 1980 Amel. Worked a treat could keep radar and autopilot running all the time.
However not very powerful. It ran a 15 amp car alternator. Alternator pulley was about 20 mm and shaft pulley about 180 mm using a multi belt. Not much output below 5 knots but 10 amps above. It was an Amel factory fit. We were running a 3 blade fixed prop.
It was great.

[Fuss]

Mine is based on a 24v mastervolt ext regulated alternator, but a pma would probably be better if it produced at lower revs. Mine starts producing at 5 kts, at 5.5 kts 10 Amps and 40 amps at 8 kts.
You need room and a dry area and the right ratio, I think mines around 6:1, Hydraulic gb that takes side load,
The benefit also is that under engine it produces 80 ah at 24v. So you end up with an extra charging source.
Doesn’t slow the boat down at all. Doesn’t care which rotation.

Experts say it cannot produce 40 ah at 8 kts as that’s impossible.

To people with a pma....can you post performance figures at various kts.

[Ozifrog]

I did this in the 80's. Before solar panels and wind turbines. It's ok at 7 knots but noisy (rrr rrrr rrr) and you have to start the motor every hour or so to make sure the gearbox is well lubricated. Solar is sooo much better these days.

[Pieta]

We have a hydropump on the prop shaft. Drives the autopilot till 1.5 kts.

[Xwiredtva]

Treadmill motor.


You'll get some gain without a ton of drag.



They use these motors for small wind generators. You can buy them for pennies on ebay. Then just belt the shaft with a couple collars to the motor and with a small mount, done. Not a ton of power, 30-60w but won't drag and you'll get that prop to speed quickly.

[LifePart2]

It works provided:
a) you don't have folding props and
b) you don't have lithium batteries.
c) you sail fast enough (over 6 kts)

Then you get some useful output.

Here is my experience of doing the prop-shaft experiment: LIFE: Part 2: Prop-Shaft Driven Alternator