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Old 24-01-2023, 19:30   #1
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Sizing Twin Electric Pod Drive Motors for a 33ft Cat

Hello!

Hope someone can help break this down for me. I've got a Prout 33CS Quest thats in need of an refit. Mywife and I are very interested in going for a hybrid system and I've been looking over the Epropulsion line of Pod drives as a possible replacement for the 20HP Yanmar and replacement for the Sonic Drive these older boats have that they no longer manufacture.

We run the current single engine around 2600rpm and have motored along at a fine 5+knts. Comfortable in the ICW no big deal.

My question is.. When switching over to twin engines how does the power equate? Are two 9.9hp equivalent 6kw pod drives around the same thrust as a 20hp 2ym20?

Now in a perfect world I'd go for twin 6kW / 9.9HP with the two of the big E175 batteries.
but it turns out the space between my rutter and skeg.. bar, beaching plate? Not sure what you call that under the prouts hulls isn't large enough to fit the Pod Drive 6.0 without hull modification. Don't want the pod drive being lower than those! Looks like it sits about 4 inches lower. Hate to see us run aground and rip the drive off.

So the question... Can we push the boat along with twin 3kW / 6HP equivalent pods or will this cause us issue with power in those tight spots?
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Old 24-01-2023, 21:11   #2
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Re: Sizing Twin Electric Pod Drive Motors for a 33ft Cat

6kw ~ 8hp, so, that's around 16hp, so you are giving up some power. On the positive side, splitting it across two props is a small improvement but for most purposes, HP=HP.

In most conditions, that's plenty but in some conditions, it will be a bit light. We had a 25hp on our 34ft Gemini and a few times we needed all of it...such as motoring up a narrow channel directly into a 30kt wind doing around 2kt at full throttle. A fair number of folks run with 15hp outboards with Geminis. As long you accept the reduced power and capability, it should be fine.

Be careful of claims of "equivalent HP" most come from the automotive world. The reason a 100hp electric motor can match a 200hp ICE in a car is because, the electric motor has max torque from 0 RPM. An ICE typically has to build up RPM to reach max torque. HP = Torque * RPM, so the low end torque means at low RPM, the electric motor is producing more HP. In reality, your average ICE never puts out it's rated max HP in real world use. Cruising down the freeway a small car might be putting out 50-60hp electric or ICE.

With displacement cruising boats, acceleration isn't a big consideration. Plus since the prop can slip in the water, the ICE can quickly build RPM and get up into peak torque. As a result, HP to maintain cruising speed is the limiting criteria and at steady speeds with motors appropriately sized, electric or ICE are running at or near peak torque and HP=HP. Reality is you almost never see people using full throttle while docking...unless they don't know what they are doing or things are long since out of control.

If you can feed them, electric is a great option. The problem is storing the feed for electric motors is much more difficult if you want any significant range.
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Old 25-01-2023, 18:52   #3
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Re: Sizing Twin Electric Pod Drive Motors for a 33ft Cat

Thanks for the info. Seems the only drive that really fits would be twin 6kW drives. Issue with my cat is there slightly to long. They stick out past the hulls skeg.. bash plate... Whatever you call those. Pods Stick past about 4 inches. Would need to come up with a fix.

Thanks for the info on HP
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