propshaft driving an alternator , when sailing

[atoll]

Originally Posted by bailsout

What about a generator instead of an alternator. Less spin resistance and rpm need? Or more?

you would need to regulate voltage through a range of different rpm's.
generators generally work at a fixed rpm and rely on the torque of the engine to compensate for loads.

[onavegador]

My sailing club asked me to let install a prop shaft alternator on a Contest 42 by Conyplex in the Netherlands. That thing produced not much power and failed very often, as the engine bilge was very small and not deep. If water (salt water!) intruded through the stuffing box the huge pulley on the prop shaft sprayed the salty water around. What a mess! Better not to find out the price of the W produced. For me it is clear: never again.
Today there are several trailing systems available. Some of them good value for money some very pricey but very powerful (Wattandsea) and used during round the globe races.
My two cents but good luck
onavegador

[billknny]

Originally Posted by tml

Max Prop used to mention in their literature that it would work with a shaft driven alternator. If you stop the engine in reverse the Max Prop will spin in reverse driving the alternator with the engine off.
Stop the engine in forward the Max Prop feathers as normal and the shaft and prop don't turn.
Never saw one hooked up but always seemed an elegant solution.
Tom

This was actually quite a common arrangement on Amel boats before they shifted from MaxProp to Autoprop. The Autoprop worked fine with a propshaft alternator without fussing. All you did was NOT lock it from rotation when sailing.

The propshaft alternator was a very popular option on Amels delivered to European customers. More so than Americans for some reason.

Of course the Amel has a lot of room in the engine space for mounting, and there is no shaft packing gland to spray salt water around either. Kind of the ideal setup for this.

[jmschmidt]

As mentioned several time on this forum, a free-wheeling prop on a boat, or an airplane, creates parasite drag equal to a solid disk the size of the prop's diameter. Add a Mickey Mouse alternator lash-up to that and you are really sucking the power out of your sails. Wind generators do the same thing unless you are anchored or in the marina.

Solar? No drag, of course.

[Cadence]

Long story short it is folly!

[Seman]

I have had a small 25A car alternator connected via some idler pulleys ( to increase the RPM ) to the prop shaft. it worked reasonably well, except the noise was driving me nuts.
Chucked it all out, too noisy!

[Blue Reef Cafe]

Hi,


When I purchased my Moody, it came with a propshaft alternator, although not fitted. The couple I bought it from were Norwegian and he, a Rolls Royce marine engineer, had fitted it. Through some correspondence and Google translate, I learned that he had the alternator rewired in New Zealand to excite at a much lower speed due to the lower RPM produced. After a while he modified the field circuit to include a thermistor to drop excitation as the alternator was getting hot due to reduced air flow. I am yet to set it up so don't know how much power it will produce. I have just been given the generator off a trolling generator system and am thinking that may be an easier alternative.


Regards


Russ

[nhschneider]

We crossed several oceans with some friends on a Najad 39 that had a very simple system of a freewheeling prop shaft driving a small alternator. My friend, René, said that it developed enough power to run his autopilot.

Fair winds and calm seas.

[atoll]

Originally Posted by nhschneider

We crossed several oceans with some friends on a Najad 39 that had a very simple system of a freewheeling prop shaft driving a small alternator. My friend, René, said that it developed enough power to run his autopilot.

Fair winds and calm seas.

the system i built provided the constant 16 amp 24v draw 24/7 on the boat required for the auto pilot,radar , plotter and 3 fridges on their atlantic crossing

[Wotname]

Originally Posted by jmschmidt

As mentioned several time on this forum, a free-wheeling prop on a boat, or an airplane, creates parasite drag equal to a solid disk the size of the prop's diameter. Add a Mickey Mouse alternator lash-up to that and you are really sucking the power out of your sails. Wind generators do the same thing unless you are anchored or in the marina.

Solar? No drag, of course.

And discredited every time by posters who understand physics and by empirical data. Let's keep this thread on topic.

The power is sucked from the wind as you state but as others have posted, it would hardly be noticed. In most trade wind and passage sailing conditions, some sails are partly reefed so if you are slowed, add a little more sail area.

[Wotname]

Originally Posted by a64pilot

One question though, alternators have brushes correct?
It’s not usually good to turn a brushed component backwards as the brushes wear faster. It’s obviously done, look at a reversible drill, but I think I’d still look at a way to disengage when motor was running, cause the the alternator is turning backwards

This more of an issue with brushes on commutators rather than on slip rings; alternators use slip rings.

[Barney21]

Just an observation which may not be relevant. Harmonic vibrations at certain conditions will destroy 'Stators" in Alternators" in certain conditions. It is probably not worth the effort to remote mount the alternator away from the engine ie. on the engine bearers as the suspension of the alternator to prevent the transfer of vibration will require some allowance for belt flex. Which will only work with lots of experimentation?

[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?

[atoll]

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?

generally the pulley is on the output flange of the gearbox between the prop shaft coupling and gearbox coupling with the alternator supported by mounts on the engine and gearbox so no appreciable side preassure apart from on the output bearing of the gearbox.

the one i designed was directly above the thrust bearing and commected to the bearing mount of the flexible coupling mounts, so no side load on the shaft

[a64pilot]

Originally Posted by Wotname

This more of an issue with brushes on commutators rather than on slip rings; alternators use slip rings.

Yes, I was actually thinking of the admonishment of don’t turn a turbine engines starter / generator backwards as it will break off the sharp edge of the brushes, but as you said those are commutators, not slip rings.