Seeking input re. plan to add electric pod drives to 39' catamaran

[CaptainPete222]

I am considering adding two 6kW electric pod drives to my 39' catamaran which already has two 29hp Yanmars. I am wondering if anyone has done something like this and, if so, what their experience has been. I am also interested in more general feedback about whether what I'm proposing will work.

My goal is twofold: (1) To be able to increase boat speed, especially when sailing to windward; and (2) hydrogeneration. In purchasing this boat, I compromised on the side of comfort as we live on the boat 6 mo of the year. The price of this compromise is that, to make headway upwind, especially if there is any decent sized chop, I end up running one engine. While I eventually get to my upwind destination under sail alone in most conditions, the time to get there is sometimes doubled (or more), which is hard on my wife, and the motion of the boat is far more uncomfortable than if I increase my headway by a knot or so with an engine running. The simplest and undoubtedly least expensive solution is to accept that under many (most?) conditions my boat is a motorsailer and just run one or two engines when I need to. (Or just get used to doubling the time it takes to beat upwind and accepting the increased discomfort--not an option for reasons I won't get into here.) The more expensive possible solution is to install two 6kW pod drives to provide that additional knot of speed that the boat seems to need to make reasonable progress upwind. (To be clear, I'm not considering removing the Yanmars; there are many situations when they will very useful.) That additional price is greatly outweighed by the satisfaction and benefits I will get from being able to power my boat only using wind and solar. For those who are interested, and without getting to deeply into the specifics of where the massive amount of power to run the engines will come from, I have 4kW of solar panels on the boat that generate 20-22kW on an average sunny day and 38kW in lithium battery storage. The pod drives run on 48W, just like my electric outboard, and will be powered by a cable to the dinghy when it is in the davits hooked up to the 12V charger to avoid adversely affecting my 12V house bank.

Given that both pod drives maxed out will consume 12kW/hr, they can obviously only be used wide open for short stints if I expect to be able to recharge the spent energy from my solar input. So, my plan is to run them at half power (6000W) during 4 hr upwind passages (my and my wife's preferred limit sailing upwind in moderate-sized ocean waves). Despite reading an considerable amount of technical literature from the companies, I haven't been able to determine whether a combined 6000W of electrical input into the pod drives (ePropulsion Navy 6.0 EVOs) will give me the same amount of propulsion as running one of my 29 hp Yanmars at 2200 rpm (max 3200 rpm), the rpm range that 90% of the time gives the the extra knot to a knot and a half I want and in many cases need. According my Yanmar owner's manual, I'm getting around 10 hp at 2200 rpm. According to ePropulsion's literature, 6kW of power input into their pod drives produce that same amount of hp. I've read a number of discussions on this forum about electric motor companies' claims about how much propulsion their various products provide, so I know this is a very difficult and confusing topic, at least for people with limited understanding about the subject like me. Thank you in advance for any input you can provide whether that amount of power put into the pod drives will give me the same propulsion as my Yanmar at 2200 rpm. Thanks also to anyone who has tried something similar and would be willing to share their experience.

[tkeithlu]

Quote: "The simplest and undoubtedly least expensive solution is to accept that under many (most?) conditions my boat is a motorsailer and just run one or two engines when I need to."

Yeah. I tried, and failed, to make it through your calculations of energy in v. out. Part of that was running into storage numbers in KW rather than KW times hours. While I'm suspicious of the numbers, let me approach the goal through areas in which i am on firmer ground.

One, you are adding a very complicated system to your boat for a very small advantage. Your advantage is only the different feeling about getting your upwind power from solar rather than diesel, and only for the times you are tacking upwind. You are gaining nothing in terms of performance.

You are adding considerable drag to your boat. The shafts and the propellers are down there all the time. You are already concerned about performance in this boat, and now want to add drag.

This is going to be expensive.

I'm not convinced that you own the right boat for you. Have you considered selling and starting over with a boat that performs better while still being comfortable? I have a suspicion that the admiral would support that move, and the money for the second propulsion system could go into the boat instead.

[Sailmonkey]

If this is really the route you are interested in going, these may be a better option.

https://www.hybrid-marine.co.uk/inde...ducts/retrofit

Assuming they can adapt to a sail drive.

[dougweibel]

This does not sound like a good plan to me, but...

Based on the roughest calculations and quickly Googled info, a Yanmar 3YM30 has a power output of roughly 6kW at 2200 RPM, so it appears the pods would give you the speed increase you desire. If you truly would run the pods at half power (6KW) to get the same speed increase as one Yanmar at 2200 RPM then why would you go to the extra expense of installing two pods? Just install one and run it at 100%. You could make the argument that with two you could use them for maneuvering and save some wear and tear on the Yanmars but would that result in a savings that would offset the cost, not to mention the additional drag?

[CaptainPete222]

After dusting off some of my math skills not used since high school and recalculating, you're absolutely right; it doesn't add up. I've come up with an easier and far less expensive solution that will give me at least some added propulsion when I need/want it: install and outboard bracket on one of the cat's transoms and move the dinghy's epropulsion 6kW outboard to the bracket when we're making a passage. Obviously need a longer cable from the dinghy's 8kW battery, but that should work out pretty slick without adding weight or significant complexity. Put outboard brackets on both transoms and I get a bit of redundancy if one of my Yanmar's has problems.

As to whether I have the right boat, like everyone who loves performance, it was a big compromise to go with what I have. But there really wasn't much choice. I wanted the smallest cat I could get that could take me where I wanted to go safely and reasonably comfortably. I almost bought an old school Outremer 40/43, so that should give you an idea how important performance is to me. But I couldn't stand up straight in the boat anywhere but a 9 square foot area just inside the saloon. At a minimum, I wanted to be able to stand up straight in the head/shower, as well as the rest of the areas of the boat. Getting that kind of headroom on a performance cat would have required me to go up to a considerably bigger boat with the associated bigger headaches and financial burden. I also looked at trimarans, such as the Neil 43, but they are beasts and it's already hard enough to find a berth in a marina for my 22' beam cat. I offset the compromise a bit by trading in my Corsair Sprint 750 tri that I keep here in Maine for a F31, which, as you may know, is about as comfortable as a VW camper bus (had one of those too way back). :-) Thanks for your comments.

[Ifitsworthdoing]

Was just about to ask you if you had considered drafting in your existing electric outboard for extra duty - seems much the most sensible idea. BTW I have it from the horse’s mouth that Hybridmarine sadly only work with shaft drives. I’m currently in the market for a 6kW outboard and May end up going with the French start-up Hy-generation (not least because the above-the-waterline elements of their novel rim driven thruster look rather DIY and hence are extremely unlikely to attract thieves).

[tomsnrg]

Originally Posted by CaptainPete222

I am considering adding two 6kW electric pod drives to my 39' catamaran which already has two 29hp Yanmars. I am wondering if anyone has done something like this and, if so, what their experience has been. I am also interested in more general feedback about whether what I'm proposing will work.

My goal is twofold: (1) To be able to increase boat speed, especially when sailing to windward; and (2) hydrogeneration. In purchasing this boat, I compromised on the side of comfort as we live on the boat 6 mo of the year. The price of this compromise is that, to make headway upwind, especially if there is any decent sized chop, I end up running one engine. While I eventually get to my upwind destination under sail alone in most conditions, the time to get there is sometimes doubled (or more), which is hard on my wife, and the motion of the boat is far more uncomfortable than if I increase my headway by a knot or so with an engine running. The simplest and undoubtedly least expensive solution is to accept that under many (most?) conditions my boat is a motorsailer and just run one or two engines when I need to. (Or just get used to doubling the time it takes to beat upwind and accepting the increased discomfort--not an option for reasons I won't get into here.) The more expensive possible solution is to install two 6kW pod drives to provide that additional knot of speed that the boat seems to need to make reasonable progress upwind. (To be clear, I'm not considering removing the Yanmars; there are many situations when they will very useful.) That additional price is greatly outweighed by the satisfaction and benefits I will get from being able to power my boat only using wind and solar. For those who are interested, and without getting to deeply into the specifics of where the massive amount of power to run the engines will come from, I have 4kW of solar panels on the boat that generate 20-22kW on an average sunny day and 38kW in lithium battery storage. The pod drives run on 48W, just like my electric outboard, and will be powered by a cable to the dinghy when it is in the davits hooked up to the 12V charger to avoid adversely affecting my 12V house bank.

Given that both pod drives maxed out will consume 12kW/hr, they can obviously only be used wide open for short stints if I expect to be able to recharge the spent energy from my solar input. So, my plan is to run them at half power (6000W) during 4 hr upwind passages (my and my wife's preferred limit sailing upwind in moderate-sized ocean waves). Despite reading an considerable amount of technical literature from the companies, I haven't been able to determine whether a combined 6000W of electrical input into the pod drives (ePropulsion Navy 6.0 EVOs) will give me the same amount of propulsion as running one of my 29 hp Yanmars at 2200 rpm (max 3200 rpm), the rpm range that 90% of the time gives the the extra knot to a knot and a half I want and in many cases need. According my Yanmar owner's manual, I'm getting around 10 hp at 2200 rpm. According to ePropulsion's literature, 6kW of power input into their pod drives produce that same amount of hp. I've read a number of discussions on this forum about electric motor companies' claims about how much propulsion their various products provide, so I know this is a very difficult and confusing topic, at least for people with limited understanding about the subject like me. Thank you in advance for any input you can provide whether that amount of power put into the pod drives will give me the same propulsion as my Yanmar at 2200 rpm. Thanks also to anyone who has tried something similar and would be willing to share their experience.

You already have the big battery bank and the solar, just put in electric saildrives instead of the Yanmars, 2 Kraeutler SDKH 11,0 AC should do the job. Add a moderately sized generator for longer motoring stints and you have an extremely enjoyable propulsion. As added benefit you get rid of quite some maintenance.

[CaptainPete222]

Originally Posted by tomsnrg

You already have the big battery bank and the solar, just put in electric saildrives instead of the Yanmars, 2 Kraeutler SDKH 11,0 AC should do the job. Add a moderately sized generator for longer motoring stints and you have an extremely enjoyable propulsion. As added benefit you get rid of quite some maintenance.

I've been thinking about doing exactly that for the reasons you mention. I haven't heard anything about the Kraeutler electric sail drives, but I will definitely look into them. Thanks.

[Searles]

Just run the diesels at 3000 ,make sure you are correctly propped ,bugger all more cost and better for the diesels .⛵️⚓️

[valhalla360]

Originally Posted by Searles

Just run the diesels at 3000 ,make sure you are correctly propped ,bugger all more cost and better for the diesels .⛵️⚓️

Other than feeling good about something that has little or no impact (possibly worse when you consider the overall system), this is a heck of a lot cheaper and easier solution.

[CaptainPete222]

Originally Posted by Searles

Just run the diesels at 3000 ,make sure you are correctly propped ,bugger all more cost and better for the diesels .⛵️⚓️

That is definitely the less expensive solution and thanks for reminding me that diesels are happier when they are run up closer to max.

[CaptainPete222]

Originally Posted by valhalla360

Other than feeling good about something that has little or no impact (possibly worse when you consider the overall system), this is a heck of a lot cheaper and easier solution.

Yup, I agree. The primary benefit is that it's very interesting to me to see if I can figure out a way to move the boat around with just wind and solar power (and, obviously, a lot of associated, very expensive, technology). We all need challenges to keep ourselves sane; this is one of mine (for the moment). :-) I will admit that I do enjoy having other boaters come up to me to discuss my solar system. It's a great conversation starter on a subject that is definitely of interest to many, many boaters. So, there's that too. And probably I just like pretending I'm one of the cool kids with the latest bike to show off... Some things never change.

[valhalla360]

Originally Posted by CaptainPete222

Yup, I agree. The primary benefit is that it's very interesting to me to see if I can figure out a way to move the boat around with just wind and solar power (and, obviously, a lot of associated, very expensive, technology). We all need challenges to keep ourselves sane; this is one of mine (for the moment). :-) I will admit that I do enjoy having other boaters come up to me to discuss my solar system. It's a great conversation starter on a subject that is definitely of interest to many, many boaters. So, there's that too. And probably I just like pretending I'm one of the cool kids with the latest bike to show off... Some things never change.

As long as you understand, it's essentially a science project...go for it.

[Nicholson58]

Easier calculation.

For the cost of your mods and annual maintenance costs, how much diesel can you buy?

We are 58 feet, mono, 40 tons, 115 HP. I use less than 100 gallons per year and we motor sail upwind a lot.

Another consideration, sails. We replaced our OK main last season with a North 3DI. (North in Antigua). Pointing ability up 4 degrees, speed up 1/2 knot. Fun quotient up a bunch. Can’t wait to replace the jib. We’ve noticed the 3DI on many boats of all types and size.

[CaptainPete222]

Originally Posted by valhalla360

As long as you understand, it's essentially a science project...go for it.

In essence, it is. But there are definitely some benefits that go beyond it being an interesting science project that are appealing. (1) At the risk of stating the obvious, electric engines really, really quiet. I have one on my dinghy now and its pretty amazing the difference. I'm not a big fan of noise. Granted, my Yanmars are pretty quiet, so it's not a huge difference, but you definitely know when they are on and it's a bit of a relief when conditions are right and I can turn them off. (2) Even when I'm sailing to windward and am running an engine, small amounts of exhaust finds a way into the cockpit. Not much, but you notice it and it's definitely something I could do without. (3) There is also a small comfort in some added redundancy. (4)I'm hoping to enjoy spending less time in a marina in the Bahamas/Caribbean fueling up on what is sometimes questionable quality fuel. Even if the fuel quality is great, I tend to worry about that and I can always use one less thing to worry about. (5) For $2,880, plus tax, I can store away a spare 60 lb electric 6kW engine to have as a spare if one dies on me while I'm in a place that it's hard to find someone to fix the engine (or any engine, including diesels). From what I've heard from other cruisers who inquired about my solar system, these are factors on their minds as well. So, it's not just about having a challenging experiment to make my days go by better; there are some worthwhile functional benefits.