Star-Lord, Electric Trawler Conversion

[Cliff Meima]

I would like to suggest that you use the Toyota Prius entire drivetrain with engine as well as the electric motor. There certainly is ample room in the engine bay and it will give you both gas and electric propulsion at your demand. Oh yea, keep the rudders. Cool Fun project, I will be following your posts.

 

[twistedtree]

My uneducated gut feel is that PV efficiency and battery storage capacity are not going to make huge improvements from here out. Incremental improvements, yes. Just this nagging bit in physics that puts a wall up at certain numbers.

I might be wrong, but doubt it.

But the electrical tech is going to find apps where it fits well and the market will adapt in cool ways. It is coming for cars, certainly, and in some limited instances, boats.

In cars, the math works. In boats, not so much.

I think that's about right. LFP batteries are right around 99% efficient in terms of power put in vs power that can be drawn back out. It's hard to get much better than that. So the only improvements available are cost, and size. Cost improvements would of course be welcome. So would density. When you look at how much propulsion energy can be stored in some amount of space (like a fuel tank), a gallon of diesel contains about 10kwh of propulsion power. In contast, an LFP battery stores about 500Wh in the same volume. So batteries require 20x the space to store the same usable power. That's going to seriously limit application of electric propulsion. It doesn't mean it can't work in some cases, but they will be very limited. And then there is recharge. 1 hour recharge rates are plausible for batteries. But to "fill" a battery tank the size of a diesel tank - let's say 500 gal - in one hour would require a 5 megawatt charger. That's a real big hurdle too. The OPs recharge time with his solar is 5 days. That's just not going to be acceptable for the vast majority of applications.


As for solar, even if it becomes 100% efficient, that would transform the recharge time from 5 days to 1 day. That might start to make some inroads. I'll bet there are a lot of boats that move less than 40 miles per day, and can then sit for a day to recharge. But it's still not enough to support continuous operation over an extended time like any sort of longer passage.


I think the main stream application for solar and new batteries in boats is supplying, or at least supplementing house power loads. It can be very effective at that, and more and more people are doing it every day. Propulsion just has too high a power requirement in most applications. Not all, but most. If you are willing to limit your range, slow way down, and pause a long time to recharge, it works. There just aren't a lot of people willing to do all those things.


I've mentioned this in other threads, but will repeat so I'm not viewed as too much of a nay-sayer... I have an off-grid house that has been solar powered for over 20 years now, and it works great. And 5 out of 6 of my closest neighbors are off-grid too. So I'm an advocate. I just want to help others be realistic about what can be done and what can't, at least today.

 

[Miz Trom]

if fiberglass resin and my time were cheaper and more abundant, my curiosity in hull design could keep me endlessly entertained.

quote of the month, g_dave!

 

[koliver]

The real foothold in this emerging technology is Europe where there are electric tugs and ferries already operating. I understand some of the canal boats have also been converted to electric as their type cruising lends itself nicely to electric.

The first all electric commercial ferry to operate in the US is now operational in Alabama. With a very large infusion of support from EPA and DOT and some very shrewd and inspirational development using the original Gee's Bend Ferry as historical framework to support the project.

https://www.marinelog.com/news/seaspan-ferries-orders-two-lng-battery-hybrids/

Especially interesting as Seaspan also owns and operates the very shipyard that Prime Minister Justin announced last week would be building 16 new Coast guard vessels (none Hybrid) for $15 Billion over the next several years. Too bad they have to go to Rumania for their own ferries.

 

[Star-Lord]

I would like to suggest that you use the Toyota Prius entire drivetrain with engine as well as the electric motor. There certainly is ample room in the engine bay and it will give you both gas and electric propulsion at your demand. Oh yea, keep the rudders. Cool Fun project, I will be following your posts.

Good suggestion.

I probably will keep one of the Prius gas engines to act as the generator.
With counter rotating shafts and a welded differential I will need to flip one of the transmissions 180degree to keep the axle spinning in "forward" direction relative to the Prius driving. There is an oil pump in the transmission that I think is directional.

Against my better judgement I am putting the rudders back on.

 

[Star-Lord]

bigger props

I need new props. I would like to go bigger for better slow speed response and take some advantage of the low speed torque of the electric motor.

Not sure what size props are on the boat but they are dinged up really bad.

I think I have clearance for larger props.

11.5 inch radius with 5 inch clearance in the pictures.
1.5 inch shaft

 

[Star-Lord]

There is a guy here in the Vancouver area who did a conversion on a Tollycraft who has posted a series of videos about the experience. I think it shows both the good and bad. Interesting viewing if someone is looking at a do it yourself conversion.

https://www.youtube.com/user/WhoIsHayley

I watched their videos before. They really enjoy their conversion. In one of his videos "The Hull Truth" he wasn't quite happy with the transom of the semi-displacement hull creating eddy currents and drag at low speeds.

At first I was looking to unstep the mast on a sailboat but then I saw the Gulfstar trawlers that already have a very sailboat like hull shape.

I am hoping for efficient low speed cruising.

 

[Star-Lord]

There is no problem building an all electric boat. Electric boats have been around for over 100 years. Range is only limited by the number of batteries that can be fitted and how much money you can spend on batteries. The issue is recharging the batteries. As mentioned above a 4.5 kilowatt array can recharge 100 kilowatts of batteries in about 5 days IF those days are 100% cloud free AND the panels can be tilted toward the sun. In the real world with fixed horizontal panels, a percentage of cloudy or even rainy days and seasons other than summer, the solar recharge time is likely to average more like 10 days or even longer. Charging at a marina will most likely be limited to about 12 kilowatts for a standard 50 amp connection (or 3 kilowatts for a 30 amp connection), so you are looking at a minimum of 9 hours plugged in to a 50 amp connection to recharge and about a day and a half from a 30 amp connection.


Now what about range. From what I can find on line a Gulfstar displaces around 22,000 lbs and has about a 40' waterline length. The simple formulae for boat speed versus power at the prop suggest that such a boat will need about 4.5 kilowatts to go 4 knots, 9 kilowatts to go 5 knots, 15 kilowatts for 6 knots and 23 kilowatts for 7 knots. Given a 100 kilowatt battery bank that can be drawn down by 90%, that give the following approximate ranges: 4 kt - 81 nm, 5 kt - 50 nm, 6 kts - 36 nm and 7 kts - 27 nm. These numbers are for flat water and no wind. A bit of chop, a head wind or a foul current with drop the range significantly. This illustrates one of the big limitations of electric boats - they have to go slow to have acceptable range.


Note that I don't want to discourage you. I just want you to be aware of what to expect.


I have one additional comment. One of the benefits often touted for electric boat propulsion is the availability of lots of torque at low rpms. Unless you are dealing with a purpose built electric boat that can accommodate a LARGE propeller, you simply can't use that torque. That is particularly true for a diesel to electric conversion where the prop size will be quite limited - i.e., the amount of torque you can utilize is also severely limited by the prop(s). Consequently, the availability of lots of torque at low rpms is meaningless for a diesel to electric conversion of a trawler.

Very helpful post.
Thank you

I am hoping the sailboat like hull pays off with some added efficiency.
I would also like to fit a larger prop. I posted some picture of the running gear above.

 

[Star-Lord]

Hey Star-L:

Great project. I hope to read all about it here as your project moves forward.

We will be back to our home in St. Petersburg (Weedon Island area) in the winter and perhaps we can look you up and see how your Gulfstar electric project is coming along.


We have two 235-watt panels on our upper deck, six Fireflys for house bank, and Victron controller. Two 60-hp gas outboards for propulsion. Also owned a Volt.


You have some imaginative, great cost-saving ideas. And the Tampa Bay area is the perfect place for a solar electric cruiser. There was an electric boat-builder that used to be based in St. Petersburg, too; we knew one of the owners.


Have you studied hull forms and understand that full displacement hulls, in particular those with rounded sterns, are the most efficient hulls (i.e. sailboat hulls)? I imagine you have, but decided to go the trawler route for more roof space for panels.


Our friend and marine electrician, Charlie Johnson, is working locally right now on refitting a large catamaran with a Torqeedo inboards/batteries/genny project. Those Torqeedo drop-in systems are wicked expensive, though. I can see your E-Gulfstar becoming a star in the St. Petersburg electric fleet.


Cheers,
Mrs. Trombley

I am very interested in local electric boat activity.
Weedon Island is real close to me. I am down at 36th Ave NE
The boat is over in Gibsoton on the Alifia River.

I understand why the off the shelf components are so expensive. For example I am grinding and repairing blisters on this old boat. Nobody could afford me to do this to their boat.

Thanks
Jeff

 

[Gdavid]

I have one additional comment. One of the benefits often touted for electric boat propulsion is the availability of lots of torque at low rpms. Unless you are dealing with a purpose built electric boat that can accommodate a LARGE propeller, you simply can't use that torque. That is particularly true for a diesel to electric conversion where the prop size will be quite limited - i.e., the amount of torque you can utilize is also severely limited by the prop(s). Consequently, the availability of lots of torque at low rpms is meaningless for a diesel to electric conversion of a trawler.

Are you sure you mean diesel to electric and not gasoline to electric? Diesel props run larger than gas props and this causes challenges for boaters who wish to repower with diesel engines.


Also, in my last post, somehow I misspelled "drag" and it autocorrected to "draft" which makes me sound foolish. I was very bitter with my phone about this since I'm quite capable of sounding foolish without any help.

 

[Star-Lord]

Big Blisters

You guys got any experience with big blisters between the chopped mat glass layer and the woven glass structure in the hull. I cut some these open. The most nasty fermented syrup like substance spits out.

There are quite a lot of them but I am going to try and repair them the best I can. My plan is to cut out the delaminated layer and reapply glass mat with some type of epoxy resin.

I am not a boat builder but I can learn.

 

[Gdavid]

You guys got any experience with big blisters between the chopped mat glass layer and the woven glass structure in the hull. I cut some these open. The most nasty fermented syrup like substance spits out.

There are quite a lot of them but I am going to try and repair them the best I can. My plan is to cut out the delaminated layer and reapply glass mat with some type of epoxy resin.

I am not a boat builder but I can learn.

Those sound like very deep blisters, usually the blisters are between the outer layers of chopped mat. Cutting them out, giving the boat time to dry out and filling them back in with fiberglass is the standard approach. Use polyester or better yet vinyl ester resin rather than epoxy which will save time and money. Whenever practical, boats are left in storage with the blisters ground out for the off season to allow them to fully dry out and avoid trapping any remaining moisture upon repair. It may be wise to grind out all of your blisters at once and proceed with your propulsion conversion while the hull dies out before glassing it back up.
Check with your marina before you start grinding glass, I know that here in the people's republic of Maryland, you can't do any work without a dust collection setup on your tools. I'm sure your boat yard isn't as stringent but check on the rules and be sure to keep yourself protected.

 

[Star-Lord]

There is an entire Industry with a magazine, two trade shows a year, and infrastructure in place to build and support electric commercial vessels. The Magazine is "Electric and Hybrid Marine" and the Shows are in Amsterdam and Ft Lauderdale annually.

The real foothold in this emerging technology is Europe where there are electric tugs and ferries already operating. I understand some of the canal boats have also been converted to electric as their type cruising lends itself nicely to electric.

I have attended the Ft Lauderdale show a couple of years and sat in on some of the seminars and the consensus is that for recreational boats this is coming, and on the brink of being viable, almost. Greenline, Torquedo and of course Elco are already out there. I am familiar with and have collaborated with several hybrid projects and the industry is just waiting for a breakthrough to really expand offerings.

As with almost all things marine, it will be an evolution from the auto industry when it does come, just as the OP is cannibalizing cars for his drive and battery components.

l:

Right on the money

I have followed a company in Amsterdam for several years now doing electric boat conversions, "New Electric". I met the owner of that start up back in 2012 at a DIY electric car conversion convention in the US.

BTW
May dog is named Elon.

 

[RT Firefly]

Greetings,
Mr. SL. Mr. Gd's post is right on. The blistered areas must be allowed to dry after being ground out.



Almost ten years ago we had our vessel "peeled" and affected areas were pressure washed a number of times over a period of two months. The pressure washing, evidently, was to remove any residual "fermented syrup" absorbed into the little nooks and crannies of the exposed glass or so I was told. After moisture readings were within acceptable levels she was re-glassed to original thickness and barrier coated. When hauled earlier this season for anti-foul paint there was no sign of blistering.


Hope this helps...

 

[TDunn]

A couple of answers to questions about prop size.


In response to Gdavid - The issue with prop size is not the original engine type (gas or diesel). It is the design of the hull which limits prop size.



In response to Star-Lord - You currently have 23" diameter props with 5" tip clearance or about 16.5" from the shaft center line to the hull. The minimum prop tip clearance to the hull is about 15% of prop diameter or 30% of radius. So if 1.3 x radius = 16.5, you can fit up to about a 25.5" diameter prop. Since you will be running at slow speeds, you may be able to get away with a 26" prop. I haven't done the calculations, but I suspect you would have to up your shaft size to go up that much in prop size. Even if you maintain the prop diameter, but go to a higher blade count for more disc area, the additional torque at the prop may require a larger shaft. Changing shaft diameter will be expensive. You can also increase prop pitch, but the same considerations apply. Any prop shop can increase the pitch of your prop up to about 2". Note that the 15% number comes from Michigan Wheel. They also state that 20% is ideal. In that case your boat already has maximum diameter props.

 

[Gdavid]

A couple of answers to questions about prop size.


In response to Gdavid - The issue with prop size is not the original engine type (gas or diesel). It is the design of the hull which limits prop size.

I understand this, what I was questioning is that your post seemed to be emphasizing converting from diesel to electric "That is particularly true for a diesel to electric" where the problem would be even worse when converting from a gas engine to electric as gas propellers are usually smaller in diameter than diesel driven boats.

 

[Nomad Willy]

TDunn, Gdavid,
The notion that for max efficiency one should fit the biggest prop possible. Not so.

If you could find props w skinny blades yes. But since prop manufacturers make props that people need for their boats only certain proportions will be found for sale. My Willard has clearance for a 20 to perhaps 22” prop but I’ve never seen one over 18” dia. Having a slow boat w low power one would want a large dia but any prop you’d be likely to find will have way too much blade area as each individual blade is wide enough to handle much more power. Only way you can do it is to cut a 3 blade down .. trimming off the leading edge and trailing edge (but not off the end (blade tip). Hard to do too. Lots of grinding and careful measuring.

The trap most fall into w this need is to get a prop the large diameter they want and w a very low pitch. Then in practice rated rpm will still be low so the prop man will need to take more pitch out. Then w such a low pitch and big blade area the parasitic drag (just the friction of the water passing over the blade surface) will eat up the power and thrust one was looking for in the first place. Many trawlers have such a prop to a lesser degree. Too much blade area.

For every application there is an ideal pitch/dia ratio and one needs to be within the ideal range. I think the pitch needs to be about .75 the dia. Example 20” dia X 15 pitch. You’ll need to look it up as my numbers is just a guess.

 

[Gdavid]

TDunn, Gdavid,
The notion that for max efficiency one should fit the biggest prop possible. Not so.

Certainly true but early in the design process is a good time to consider what the largest practical prop diameter allowed by the hull shape, shaft angle etc. is so that it is included as a design constraint. Assuming that he will be wanting make adjustments and optimize the system at a later date, it is a good time to consider what will fit and whether the existing shaft diameter will support his plans.

In college I participated in the International Submarine Races where we designed and build flooded human powered submarines. We ran a counter-rotating, high aspect propeller system which was really wild. It was driven by a single shaft and aft prop hub contained a planetary gear system which drove the forward prop in the opposite direction. The forward prop hub rode on bearings on the prop shaft. I wish I had the drawings for it.

 

[Nomad Willy]

In college I took the girls to submarine races but your sub races may have been safer.

I think you’ve got it basically. Consider though that the right pitch/dia ratio will get you thrust more effectively than just max dia. I had a 60” prop on a 45hp ultralight aircraft that didn’t perform very well. An old boat prop man told me to crank in a good dollop of pitch and cut the dia down. It was awhile before I did it as one can’t stick the cut off ends back on. HUGE difference. I went to 1000fpm climb to 1450. Almost scary the angle of attack. The old prop guy knew his stuff. I,ve been keen on pitch/dia ratio ever since. With the original UL prop I was making mostly noise w the flatish blades and 60” dia.

My Willard w her 40hp engine may be somewhat close to your application. Somewhat.
18” dia and 13 pitch w 2.57-1 gear.
20” dia and 13 pitch would be too much dia or too little pitch. 16” dia and 16 pitch would be OK for a faster boat but for trawler speeds too much pitch or too little dia.

You can call Michigan Wheel and chat w somebody having your hp/speed numbers handy. I enjoyed talking to those guys more than once.

 

[hpogue123]

Hi all,
I have often wondered about doing a hybrid conversion every time I look at the empty ER space around my prop shafts and 40cu. ft of floor space on the keel for batteries. I don't want to claim I have researched it yet, so wonder what others think.
It would appear that a multi phase motor/alternator (maybe one of those salvaged Prius motors) could be coupled to the shaft and add an alternative power source. I understand that the transmission would still need to be cooled in neutral to avoid damage. Would still need the solar and power storage, but the main engines could be used for charging as well. I would assume the mains would be needed for higher speeds but electric at <1/2 hull speeds? I've seen some solar hybrids at boat shows and on the net but they were short ranged planning speedboats. Any engineers out there run the numbers? Thoughts?

 

[twistedtree]

I think the best advice I could offer on this project would be to go take a class in mechanics. Not "mechanics" as in the guy who fixes your car, but "mechanics" as in physics and mechanical engineering 101. That will help you predict the outcome of various choices before you built something, rather that stumbling over it after you have built something.

 

[Star-Lord]

I think the best advice I could offer on this project would be to go take a class in mechanics. Not "mechanics" as in the guy who fixes your car, but "mechanics" as in physics and mechanical engineering 101. That will help you predict the outcome of various choices before you built something, rather that stumbling over it after you have built something.

If that is the best advice you got then I think your forum days are over. My physics background is not lacking. My boating and boat restoration experience may be. If you have something specific to add to the project it is appreciated.

BTW, I am an engineer with a proven track record of innovation and solving the hard problems.

 

[Nomad Willy]

I hear you my lord,
Hmmm
It looks like mr. Tree is saying look at the big picture before getting immersed in details. Foresight. But I didn’t even take physics. I like pictures though.

 

[Star-Lord]

A couple of answers to questions about prop size.


In response to Gdavid - The issue with prop size is not the original engine type (gas or diesel). It is the design of the hull which limits prop size.



In response to Star-Lord - You currently have 23" diameter props with 5" tip clearance or about 16.5" from the shaft center line to the hull. The minimum prop tip clearance to the hull is about 15% of prop diameter or 30% of radius. So if 1.3 x radius = 16.5, you can fit up to about a 25.5" diameter prop. Since you will be running at slow speeds, you may be able to get away with a 26" prop. I haven't done the calculations, but I suspect you would have to up your shaft size to go up that much in prop size. Even if you maintain the prop diameter, but go to a higher blade count for more disc area, the additional torque at the prop may require a larger shaft. Changing shaft diameter will be expensive. You can also increase prop pitch, but the same considerations apply. Any prop shop can increase the pitch of your prop up to about 2". Note that the 15% number comes from Michigan Wheel. They also state that 20% is ideal. In that case your boat already has maximum diameter props.

I will stick with 23" but may consider changing pitch. I could not read the number markings on the prop. I don't want to change the shaft diameter.

Thanks
Jeff

 

[Ski in NC]

You need to figure out the output shaft rpm from the Prius motor/transaxle and base prop pitch on that number.

 

[twistedtree]

You need to figure out the output shaft rpm from the Prius motor/transaxle and base prop pitch on that number.

And torque and/or hp. But I know you know that.

 

[Star-Lord]

And torque and/or hp. But I know you know that.

I really only have an idea of how must shaft torque and rpm I can produce with my electric drive. Shaft torque of 1200Nm up to 400rpm (50kW peak) then the torque will drop at higher shaft rpm. Can spin up to 1000rpm. I do not expect to have to produce this peak power for any length of time especially with limited battery.

The previous poster estimated 4.5kW@4kts and 9kW @5kts steady for my boat which is a helpful guideline for me. I am not sure how this was calculated.

simple math says 400rpm with 20" pitch is about 7.6mph (not including any slip)
I have no idea the pitch of the prop I currently have.

I don't really know how to get to thrust calculations for a given prop. Of course it will be a function of prop dimensions I do not have. I really haven't made much effort to make these predictions yet.

I have a very long list of to dos before selecting the prop which is why I appreciate the feedback I get from the forum. I think i am in the ball park with my setup.

Thanks

 

[Nomad Willy]

May be advantages to over prop w an electric motor.
Did I say that ???
I have no idea if applicable though.

 

[Mako]

* I am not sure how this was calculated.
* I have no idea the pitch of the prop I currently have.
* I don't really know how to get to thrust calculations for a given prop.
* I really haven't made much effort to make these predictions yet.
I think i am in the ball park with my setup.

Oh Lord, not to be flippant here, but perhaps you'd be better off getting some solid answers before proceeding further on a trial and failure basis. So here's a starter - go visit www.boatdesign.net/forums as those guys really know their stuff.

 

[Nomad Willy]

Is there any info and conversation on BoatDiesel?