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01-06-2017, 18:53
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#46
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Registered User
Join Date: Nov 2015
Location: Fl
Boat: Wauquiez Hood 38
Posts: 1,187
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Re: Hydroelectric Generator
"run at night in bad weather" = wind genny. I have sailed across the Pacific with a shaft driven alternator and won my class in the Twostar Transatlantic race with a wind genny and two defective solar panels. I dont run a shaft driven generator as a result.
You seem quite intent on doing this and are resistant to opinions of those who have used them all. Build your system and let us know how it goes. I look forward to your thoughts once it is complete.
__________________
Keth
Boat Vinyl Lettering and Graphics
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01-06-2017, 19:42
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#47
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Registered User
Join Date: Sep 2009
Location: Houston
Boat: ‘01 Catana 401
Posts: 9,627
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Hydroelectric Generator
12volts @ 130 rpm.
I would be mighty surprised if you're getting 130 rpm out of a freewheeling prop shaft on a boat sailing at 4-5 knots.
And the 12 volts isn't going to charge batteries. It won't create any current until the voltage exceeds the resting state of the batteries. Ideally you'd want something that can pump out something like 30 volts at 50rpm. The. The batteries can drag down the voltage by making the shaft generator produce current.
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01-06-2017, 20:14
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#48
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Registered User
Join Date: Sep 2014
Posts: 321
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Re: Hydroelectric Generator
Quote:
Originally Posted by Bleemus
You seem quite intent on doing this and are resistant to opinions of those who have used them all.
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What does the OP say?
Does it say "is it possible to build a propshaft generator?"
Or, does it say "how many amps can be expected from a propshaft gen?"
Quote:
Originally Posted by Sailmonkey
12volts @ 130 rpm.
I would be mighty surprised if you're getting 130 rpm out of a freewheeling prop shaft on a boat sailing at 4-5 knots.
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I'd be mighty surprised if you didn't, considering that the $5k commercially available units claim at least one order of magnitude higher than that. But what do I know, I don't sell marine diesel engine alternators.
__________________
"If one does not know to which port one is sailing, no wind is favorable."
-- Seneca
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01-06-2017, 20:45
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#49
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Registered User
Join Date: Nov 2015
Location: Fl
Boat: Wauquiez Hood 38
Posts: 1,187
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Re: Hydroelectric Generator
How many amps can you expect from a typical cruising boat traveling at 5-6 knots? About 1.
__________________
Keth
Boat Vinyl Lettering and Graphics
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01-06-2017, 21:07
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#50
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Registered User
Join Date: Sep 2009
Location: Houston
Boat: ‘01 Catana 401
Posts: 9,627
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Re: Hydroelectric Generator
Quote:
Originally Posted by KISS
I'd be mighty surprised if you didn't, considering that the $5k commercially available units claim at least one order of magnitude higher than that. But what do I know, I don't sell marine diesel engine alternators.

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I'm going to need some help clarifying what you mean.
My point was that what you're suggesting to use makes 12 volts @ 130 rpm. You suggested coupling directly to the shaft with no step up gearing.
When I'm sailing @ 5 knots my prop 16x10 isn't spinning @ 130 rpm. I'd guess half of that.
And if your proposed gen only makes 12 volts there won't be any battery charging happening.
And I don't sell alternators either.
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15-08-2017, 03:47
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#51
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Registered User
Join Date: Aug 2017
Posts: 26
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Re: Hydroelectric Generator
First thing you will need is a digital laser photo tachometer. Found a few on eBay for around $20.00. Take readings at average knot readings, transmission in neutral and free spin of prop. End result is a automotive Alternator needs to spin at 3,000 rpm's to produce full amperage @13.8 Volts. Reading of 1,000 rpm of prop spin at 8 knots 3:1 Ratio with Pulley and Drive belt. I suggest using an electric clutch coupling between the transmission, and drive shaft. key on motor running engaged, key off free spinning and zero wear on transmission.
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15-08-2017, 04:50
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#52
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Registered User

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,891
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Re: Hydroelectric Generator
Quote:
Originally Posted by robmclennan
Reading of 1,000 rpm of prop spin at 8 knots 3:1 Ratio with Pulley and Drive belt. I suggest using an electric clutch coupling between the transmission, and drive shaft. key on motor running engaged, key off free spinning and zero wear on transmission.
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A typical sailboat's freewheeling prop will not be spinning at anywhere near 1000 rpm even at 8 knots. More like a couple of hundred rpm at best. And by the time you slow it down with your pulley, drive belt and alterator it will be a lot slower.
And you don't see many cruising boats going at 8 knots a lot of the time.
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15-08-2017, 06:06
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#53
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Registered User
Join Date: Aug 2017
Posts: 26
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Re: Hydroelectric Generator
StuM the 8 knots was just a reference it could just as well be 3 to 6 knots. Fluid dynamics is a positive drive! ie: Hydraulic drives. The prop will spin with sufficient force, and have adequate torque. I am designing this on the cheap. Utilizing junk yard automotive parts to keep the cost down. a 12 v generator from the 60's could be used as well as an alternator. An A/C Clutch new or used. Bearings mounted in Rubber will reduce Harmonic vibrations. Adding a bead of silicone will cut down shaft vibrations. Water is a great transmitter of sound! Short of adding acoustical foam not much else one can do. Turn up the stereo? It was a thought!
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15-08-2017, 11:24
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#54
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֍֎֍֎֍֎֍֎֍֎
Join Date: Apr 2006
Posts: 15,136
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Re: Hydroelectric Generator
"End result is a automotive Alternator needs to spin at 3,000 rpm's to produce full amperage @13.8 Volts. "
A good ballpark, but many will see much better output at twice that speed, and they'll make 14.4 volts not just 13.8. To design a system, really, you need to check out alternator specs and design the system with one particular alternator in mind. That simple change can literally double, of halve, the mount of power you'll see. Pulley ratios can always be changed, but in the confines of a boat, not always enough. And custom pulleys aren't cheap these days.
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15-08-2017, 15:40
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#55
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Registered User
Join Date: Jun 2013
Location: Up Qld Coast, near Yeppoon.
Boat: Passport 41, Custom Perry in steel.
Posts: 628
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Re: Hydroelectric Generator
Bit of negative speculation here, My shaft alternator frequently generates 5 amps and my boat is not quick.
So my shaft alternator is driven by a 9" Dia pulley on the shaft and 2" on the alternator.
Mind you thou it probably costs a amp or so for excitation.
I avoid using it, as, to replace the V belt is likely to be a ordeal.
My Engine obviously must have a gearbox that allows free wheeling. Extra wear on Stern tube bearing is a possibility. Think this idea better than a clutch.
Think this idea had more merit when solar wasn't so developed.
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11-09-2017, 11:01
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#56
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Registered User
Join Date: Jan 2017
Location: Irish Sea
Posts: 1,321
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Re: Hydroelectric Generator
Seems easy to implement: trolling motor as generator.
If I read it right, a 600W rated brushless trolling motor ( costs ~300$/pcs, ebay new) should provide ~250W with the right propeller in realistic conditions. Produced for salt water use, piece of cake?
I don't want everything for free, but to me this looks like the Watt & Sea 600 performance at 1/10 of the price - and I even allowed for some customization and mounting...
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Useful as a fireproof bottom paint...
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11-09-2017, 11:49
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#57
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Registered User
Join Date: Jan 2017
Location: Irish Sea
Posts: 1,321
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Re: Hydroelectric Generator
Quote:
Originally Posted by GTom
I don't want everything for free, but to me this looks like the Watt & Sea 600 performance at 1/10 of the price - and I even allowed for some customization and mounting...
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BTW checked a few "alternatives", all commercial "hydrogenerators for boat" cost 3k$+. Maybe I am missing something, or these really aren't more than ridiculously overpriced trolling motors?
__________________
Useful as a fireproof bottom paint...
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11-09-2017, 16:48
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#58
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Registered User

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,891
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Re: Hydroelectric Generator
Quote:
Originally Posted by GTom
Seems easy to implement: trolling motor as generator.
If I read it right, a 600W rated brushless trolling motor ( costs ~300$/pcs, ebay new) should provide ~250W with the right propeller in realistic conditions. Produced for salt water use, piece of cake?
I don't want everything for free, but to me this looks like the Watt & Sea 600 performance at 1/10 of the price - and I even allowed for some customization and mounting...
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From one post there "You will get approx. 80% of the nominal power of the trolling motor"
Quite simply, b*llsh*t!.
I agree with the comments made there by philSweet, including this:
I have yet to see a report of any trolling motor producing 2% of its rated amperage behind a smallish sailboat.(peak,yes- average over time,no)
But please, give it a try and let us know how it goes if it's not expensive. If it doesn't work, you can always use the trolling motor on your dinghy or sell it.
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12-09-2017, 01:27
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#59
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Registered User
Join Date: Jan 2017
Location: Irish Sea
Posts: 1,321
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Re: Hydroelectric Generator
Quote:
Originally Posted by StuM
From one post there "You will get approx. 80% of the nominal power of the trolling motor"
Quite simply, b*llsh*t!.
I agree with the comments made there by philSweet, including this:
I have yet to see a report of any trolling motor producing 2% of its rated amperage behind a smallish sailboat.(peak,yes- average over time,no)
But please, give it a try and let us know how it goes if it's not expensive. If it doesn't work, you can always use the trolling motor on your dinghy or sell it.
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I was also afraid, that the 80% is far optimistic.
I am also thinking on using a 48V wind turbine alternator like this one with an outboard gear. This is meant to be used as a generator but unfortunately not waterproof.
I see the sailgen does something similar.
As bonus, the alternator can be used with a wind turbine when anchored.
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