Hi Carter,
The general guideline is 1kW of motor for each ton of displacement. You can use much less in fair weather but for general safety, the 1 kW per ton is a good compromise. With 15kW, you should be able to hit 90-95% of hull speed at full throttle.
It's your boat and you can put in whatever you want, but our guidelines come from the combined experience of many installations.
I don't know where you sail, but if you're underpowered, you might run into problems if you need to motor against a current and a headwind when heading into a harbor.
A 12" prop sounds pretty small for a 45 boat, my 30', 5 ton ketch was running a 13" prop on the 12hp Yanmar diesel. I went up to 13.5 when I switched to electric.
Fair winds,
Eric
BTW, I think that a $6000 discount seems pretty generous. I wonder what a 40hp diesel installation costs...
--- In electricboats@yahoogroups.com, Carter Quillen <twowheelinguy@...> wrote:
>
> Alex,
>
> Thank you for your response. I'm not sure why you think the ST-72 would be too small. You said it is suppose to replace up to a 48hp diesel and the specs say boats up to 16 tons. Are the specification over optimistic? To answer your question about the prop, I'm not sure of the exact diameter but the old prop looked to be about 10-12" with three blades. However the boat was fitted with an autoprop designed specifically for it that somehow adjust the pitch of the blades for max thrust at any given rpm. It seems to work quite well although I get the sense I could get a lot more speed if I had a few more rpms on the shaft. There are gear reductions on both the transmission and the V-drive so the end result is more like a high torque mixer. It will kick out some serious volumes of water though and makes an excellent dredge when your slip is silting in but won't get the boat much past hull speed.
>
> The boat is 45' at 15 tons and has an 40hp diesel that will push it to hull speed at less than 1/4 trottle. I'm wild guessing that I should be able to reach hull speed in calm conditions with about 8 hp but I could be wrong. I'm trying to come up with a design to leave the old diesel in place for use in heavy weather or if I go offshore but this really complicates things and it would be a lot easier to scrap the diesel and go all electric. Since my cruising plans for the next few years are for just inland waterways along the great loop I think a nominal 10 hp motor should be sufficient and maybe all electric would be best.
>
> What type of controller comes with the motor? Where would it be shipped from? What else besides batteries and a means of chargeing them would I need for a complete installation? What, if any warrantee would come with the system? And, is that the best price you can do on the package?
>
> I'm looking at several options and I'll be getting something soon. Your system seems to be packaged a little better for the marine environment and reliability is bigg criterion but we all have to work within budgets too.
>
> I'm hoping you can sharpen your pencil a little bit.
>
> Thanks again.
>
> Carter
>
>
> ________________________________
> From: A <alecotech@...>
> To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
> Sent: Monday, October 24, 2011 9:55 AM
> Subject: Re: [Electric Boats] 6HP and 12 HP Solomon Technologies Motors for Sale
>
>
>
>
>
> Hello,
>
> Sorry for the delayed response. 45' Steel bilge keel cruiser seems to be a bit big for the ST-74. The ST-74 is a 9kW (12HP) electric motor that replaces up to a 48HP diesel. I would suspect that the boat of your size would probably required a 60 HP diesel; this would require at least a 20 or electric motor. What is the maximum size prop that is allowed on the vessel?
>
>
> The ST-74 system run off of 144VDC. The voltage is 144VDC in order to keep the current lower and manageable at high power. The motor is a Brushless DC permanent Magnet Motor (BLDC). The ST-74 is essentially 2 4.5kW motors aligned on the same shaft. This provides redundancy in motors and controllers for the system. The motor controller is included in the price.
>
>
>
> The RETAIL pricing for motor, motor controller(s), throttle, breaker are as shown:
> ST-74 system Retail: $18,778
>
> I currently have a demo unit of the ST-74 motor that were used for boat show
> displays. The system will be discounted at 35%. Customer is
> responsible for shipping and handling to their location.
>
> The Demo Unit Pricing at 35% discount:
> ST-74 system 35%: $12,205
>
>
> Let me know if you have any questions.
>
> Thanks,
>
> Alex
>
>
> ________________________________
> From: Carter Quillen <twowheelinguy@...>
> To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
> Sent: Sunday, October 23, 2011 12:08 PM
> Subject: Re: [Electric Boats] 6HP and 12 HP Solomon Technologies Motors for Sale
>
>
>
> I'm in the process of converting a 45' (15 ton) bilge keel cruiser into a solar electric hybrid to cruise the eastern seaboard and great loop in. I have the boat built with the solar canopy installed,(approx. 2 kW now to be expanded to 4.5kW soon). I've been looking a wide variety of motor and controller options and frankly am still a bit confused in spite of what has become some very extensive research on my part.
>
> I went to the website and looked at the specs for the ST-37 and ST-34. What voltage does ST-72 run at? What type of controller is recommended? How much do you want for the one you have?
>
> Thanks,
>
> Carter
>
>
>
>
> ________________________________
> From: alecotech <alecotech@...>
> To: electricboats@yahoogroups.com
> Sent: Thursday, October 20, 2011 1:06 PM
> Subject: [Electric Boats] 6HP and 12 HP Solomon Technologies Motors for Sale
>
> Hello,
>
> I am selling one ST-74 12HP electric motor system and one ST-37 electric motor system. Both are demo units; ST-37 never installed, and the ST-74 installed for a season as a demo. I can sell the motors as motor only or systems with as much or as little of the components required.
>
> Other stuff that I have to sell are Throttles, Chargers, Breakers, etc.
>
> Motor specifications can be seen on
> http://ikanostech.com/index.php/electric-motor-drives
>
> I can assist with any development and design aspects you may need.
>
> Thanks,
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
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