Hi there,
I have been obsessing over buying a somewhat cheap but otherwise good-condition boat and converting it into an electrically powered boat by repurposing car parts. This has been done before, and I have done so much research by now that I have most of the plan laid out, as well as the support of skilled engineers and technicians. The boat would be retrofitted with about 240–320 kW of batteries (at around 1.6 metric tons / 3,500 lbs), with two efficient motors offering 320 Nm, 160 kW at a wide RPM range, most likely reduced with a 2:1 Gates Poly Chain GT Carbon to keep the efficiency at a peak around 200-700 propeller rpm and double the torque. They would be paired with two two four DC gensets, effectively forming a serial hybrid, based on partially marinized 1.9 TDI or 1.6 Multijet engines, coupled with the same EV motors (for simplicity and redundancy, as the motor with inverter weighs only ~60 kg and costs ~600–800 euro). All this would be relatively cheap and somewhat easy to do, so that part is not really a concern here.
The concern is which boat to use for this conversion project. A trawler would be ideal, given its very low power demand, but trawlers are too expensive and just not really my style. I do love, however, the design of the 1970s–1980s Vee planing and semi-displacement hulls, especially those made in Italy. Not only are they typically in good condition, they have beautiful interiors, are typically made of aluminum and are cheap — 70–100 k euro, likely even less after negotiation.
Specifically, I have my eye on the 1980s-era Baglietto Ischia 80, three of which are now on the market. They are 55–60 ft, ~20 kts cruising speed, ~30 kts max speed, typically 2 × Detroit Diesel 8V-71 650 hp, 55 k lbs.
The problem is, these are Vee / modified Vee / warping planing hulls, while I would naturally be aiming at cruising at lower speeds most of the time (7–10 kts) to take advantage of those ~240 kW of batteries — planing would likely drain them in a matter of 2–3 hours (a guesstimate).
It’s obvious these boats were not designed for displacement speeds. However, most people I talk to immediately reduce the conversation about efficiency to their big 600+ hp, high-RPM diesel engines, whereas what I am after is understanding and estimating the actual hull behavior and efficiency at those lower speeds. For example, theoretically speaking, if you downgraded the engines and the propeller pitch to aim at these ~8–10 kts cruising speeds and lower RPM, what effect would that have on the fuel consumption and boat behavior? It confuses me even more since I did find other boats with similar specs and hulls with same engines and slightly less hp that quote almost impossible fuel consumption numbers at much lower cruising speeds, like this Chris-Craft here at 3.5 gals/hour and 8mph(!): 1974 Chris-Craft Roamer Flush Deck MY in Englewood, Florida https://www.popsells.com/boat-for-sale/1974-chris-craft-roamer-flush-deck-my-302608?showfull
Which brings me to this set of questions:
Some photos of the Ischia 80 hull below:
I have been obsessing over buying a somewhat cheap but otherwise good-condition boat and converting it into an electrically powered boat by repurposing car parts. This has been done before, and I have done so much research by now that I have most of the plan laid out, as well as the support of skilled engineers and technicians. The boat would be retrofitted with about 240–320 kW of batteries (at around 1.6 metric tons / 3,500 lbs), with two efficient motors offering 320 Nm, 160 kW at a wide RPM range, most likely reduced with a 2:1 Gates Poly Chain GT Carbon to keep the efficiency at a peak around 200-700 propeller rpm and double the torque. They would be paired with two two four DC gensets, effectively forming a serial hybrid, based on partially marinized 1.9 TDI or 1.6 Multijet engines, coupled with the same EV motors (for simplicity and redundancy, as the motor with inverter weighs only ~60 kg and costs ~600–800 euro). All this would be relatively cheap and somewhat easy to do, so that part is not really a concern here.
The concern is which boat to use for this conversion project. A trawler would be ideal, given its very low power demand, but trawlers are too expensive and just not really my style. I do love, however, the design of the 1970s–1980s Vee planing and semi-displacement hulls, especially those made in Italy. Not only are they typically in good condition, they have beautiful interiors, are typically made of aluminum and are cheap — 70–100 k euro, likely even less after negotiation.
Specifically, I have my eye on the 1980s-era Baglietto Ischia 80, three of which are now on the market. They are 55–60 ft, ~20 kts cruising speed, ~30 kts max speed, typically 2 × Detroit Diesel 8V-71 650 hp, 55 k lbs.
The problem is, these are Vee / modified Vee / warping planing hulls, while I would naturally be aiming at cruising at lower speeds most of the time (7–10 kts) to take advantage of those ~240 kW of batteries — planing would likely drain them in a matter of 2–3 hours (a guesstimate).
It’s obvious these boats were not designed for displacement speeds. However, most people I talk to immediately reduce the conversation about efficiency to their big 600+ hp, high-RPM diesel engines, whereas what I am after is understanding and estimating the actual hull behavior and efficiency at those lower speeds. For example, theoretically speaking, if you downgraded the engines and the propeller pitch to aim at these ~8–10 kts cruising speeds and lower RPM, what effect would that have on the fuel consumption and boat behavior? It confuses me even more since I did find other boats with similar specs and hulls with same engines and slightly less hp that quote almost impossible fuel consumption numbers at much lower cruising speeds, like this Chris-Craft here at 3.5 gals/hour and 8mph(!): 1974 Chris-Craft Roamer Flush Deck MY in Englewood, Florida https://www.popsells.com/boat-for-sale/1974-chris-craft-roamer-flush-deck-my-302608?showfull
Which brings me to this set of questions:
- What would actually be a realistic fuel consumption at those 7–9 kts displacement speeds, assuming the most efficient engine and RPM/propeller pitch for them? What would be its estimated power demand, in kW?
- (nevermind)
- How uncomfortable would it be to use such a boat at these speeds most of the time?
- How do those hulls behave at low speeds, seafaring-wise?
- Is that Chris-Craft example above a complete outlier, or are the numbers stated actually in the expected range for this boat or similar ones?
- Would adding an aft extension plug to reduce wave-making resistance and drag help in any significant way?
- Bonus question: would adding skeg/guard for propeller protection effectively kill planing performance?
Some photos of the Ischia 80 hull below:
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