Hi Jam (or is it Jade?)
Things haven't changed too much in the last two years, in my opinion, LiFePO4 batteries are more accepted then they were when I bought mine in 2010, but they're about the same price as they were back then. PMAC motors and controllers are still the most common drive systems for your size boat.
The general rule of thumb that has been confirmed in many different conversions done by various members here is 1kW of drive power for each ton of displacement. That amount of power typically can deliver 90-95% of theoretical hull speed.
All of the design data that I could find for Alden boats before WW2 leads me to believe that they are essentially custom boats, with only one or two boats being built from a given set of plans. Minor tweaks were constantly included in each subsequent boat, so I don't have enough data to accurately predict your performance, but I'll give it a shot.
A number of early Alden boats near your boat's size were built with LWL between 23' and 26' and the displacement was 8-9 tons. So I'm going to do some calcs under the assumption that your boat has 25' LWL and weighs 8.5 tons. My calcs for 25' LWL give a hull speed of 6.7kts. With 8.5 tons displacement, 8.5kw (11.4 hp) should drive the boat 6.4kts in calm conditions. If you choose a 72V system, full power would be 120A. 5kts should draw about 35A. Lithium cells like I mentioned above, in a 12kWh (160Ah - 75V) bank, would cost about $5-6k and weigh about 300 lbs. This bank would give you a usable range of about 16nm at 5kts. Slow down to 4kts and your range jumps to the neighborhood of 27nm. You could use AGM batteries or Flooded Lead Acid, but batteries that would deliver the same range will weigh 750-800 pounds.
All of these numbers are based on the assumptions that I mentioned. If you can provide more specifics about your boat, I could dial in my predictions, but these are probably closer than you think.
If you've got more questions, feel free to ask here on the list or you can contact me off list.
Welcome to the list.
Eric
1964 Cheoy Lee Bermuda 30, 5.5kW Propulsion Marine drive, 8kWh Lithium batteries
Marina del Rey, CA
--- In electricboats@yahoogroups.com, jam_jade <no_reply@...> wrote:
>
> Hello everyone,
>
> I just joined your group. I did look into electric power about 2 years ago so my knowledge is a bit dated. I was wondering if you can fill me in with respect to what is the current state of affairs for an electric propulsion for my vintage sailboat. I have a wooden 36 ft 1935 John Alden with full keel. My old volvo 3B2 is in need of a change soon. I did the calculations a while back with a repower company and it turned out that I needed about 35hp to achieve the hull speed of 7 knots.
>
> Of course with a cruiser sustained power is a consideration. I do have 2 85W solar panels that I'll be installing soon so I guess that's a start.
>
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