5-Meter Power Cat with 6kW Outboard

Interesting exercise with the 6kw electric. Displacement hulls at high speeds is a really tricky feat. In my dinghy design I tried to optimise the hulls to run at 12 knots yet maintain efficiency at lower speeds and we can achieve 10 knots two up with a 3hp outboard and 12 knots one up. What was really interesting is that with an 8hp we achieved high 14s and when almost doubling the power to 15hp we only achieved half a knot higher speed, low 15s, due to the hull shape. This was expected and suits our purpose however many builders try to increase the power and are disappointed at the results.

 

I finally got my act together and am back on YouTube. I hadn’t used the platform in years and post most of my build and design stuff on Instagram, but realize there are a lot of people who don’t use IG, plus you can’t easily embed a video like you can with YouTube, so I figured my first new video would be a highlight reel of my solar electric sailing catamaran SolGato.

Near the end I have included footage of the wake my boat puts out for comparison with dual 1.5kW motors at about 8MpH. Most of the water disturbance is from my trim/kick up struts and the corners of my transom motor mount plates which use the factory rudder mount threaded inserts so no extra holes had to be drilled.

Anyway, the hull shape of the Hobie Getaway hulls I’m using are very similar to your hulls except they have a more pronounced low aspect keel and more streamlines sterns. My boat is setup to be able to handle a forward trampoline full of passengers, so it’s a little light in the bow and stern draggy when I’m cruising solo.

I have considered adding a water ballast bag in front of the forward crossbeam to aid in trimming the boat as I have found the boat handles better with more weight when in ocean swell, but I just place my coolers there instead which keeps the bow planted pretty well provided I haven’t drank all the beer!

 

Very Cool! Love the articulating drive pods and power canopy. For a while I thought you had no rudder, and were maneuvering with just thrust differential between the two drive pods. Then I saw the picture that showed the retracted rudder.

I see six of what I think are 100Wp panels, then a pair of charge controllers. Wondering what your battery voltage and amp-hour capacity is.

 

Thanks!

Your assumption was correct, I do use independent forward and reverse thrust instead of a rudder and tiller. I never liked having to baby sit a tiller and wanted to reduce weight as much as possible (so no helm), plus having a wired remote allows me to pilot the boat from any position on deck which really comes in handy when navigating shallow water and approaching and docking alongside other boats.

Honestly, it would be hard to ever go back to traditional steering and controls. Operating this boat is more like piloting a spacecraft with thrusters in outer space. I can do 360’s without loosing ground and easily turn around up narrow rivers, even make a controlled stops. It’s less efficient, but so much more enjoyable.

The rudder shown is kept onboard in case of a motor failure and is also used with the sail rig (Crab Claw Lateen Hybrid). I found out the hard way one night as I set out for a full moon cruise around the mooring field just as the wind picked up, that losing a motor just creates a highly efficient donut machine! I had to hang onto a friends 40’ sailboat while I rewired a motor because I was drifting off shore. That was before I designed and installed my onboard anchor system. So now I have an anchor and a rudder.

Anyway, the motors are brushless 24V and about 68% efficient for about 1kW of propulsive power each. With the more aggressive props I’m running, they will pull a max of about 60A each.

Right now I’m only running a pair of 12V 100Ah LifePo4 batteries in Series for 24V that have been configured for a 120A continuous max discharge which I occasionally hit in the shade under full throttle.

The solar system is split into two paralleled arrays comprised of 3x100W panels in Series feeding each MPPT which are networked with the BMS and Shunt and paralleled to the battery bank. It’s good for about 25A which gives me a 4MPH cruising speed on good sun only.

I use this boat all the time and have built it around my typical use which is not long distance, but getting to my favorites spots up river or out to my Trimaran on morning in the Bay, then dropping anchor or tying up and hanging out. The batteries recover very quickly, and I live in Hawaii where we have consistent sun, so it is all designed to suit my needs. I can always increase capacity if need be (I have left room for additional batteries in each box which are located low in the hatches of each hull), and/or add a few more panels, but I am hoping to scale this build up to something much bigger (likely around EPropulsion Navy motors) so I probably won’t do a whole lot more to it except refine a few things.

I do however plan to add linear actuators to my motor mount trim setup so I can tilt and trim via the remote. This boat has made me lazy, and I do a lot of beaching and obstacle avoidance of things like Sea Turtles (they don’t even hear me coming) and water logged coconuts (plastic prop destroyers!).

I tell people cruising SolGato is like floating on a pool lounge chair next to a tricking water fall.

It’s pretty much my lazy boat.

 

Nice . . . thanks for sharing!

Yeah, another couple of 12V x 100Ah batteries will help your range a lot, and not cost that much (prices are dropping).

I see you use the same framing system I've been considering for my solar panel canopy (T-slot rails). I don't suppose you shop at McMaster's?

Always good to see other setups . . . yours definitely gives me ideas.

Speaking of no-wheel steering, I once had an Electric Hydrobike prototype set up to steer with the swivel of the seat. This is an earlier setup, but the same hull:





(I'm going to be putting the Electric Hydrobike up for sale soon in case anyone lives nearby and is interested.)

 

Thanks for sharing and putting it on youtube! And thanks to all the other people sharing information on electric drives in threads like these. On Instagram i would definitely have never found it.

About the sound it makes, among others I seem to hear a lower pitched, sort of rumbling, sound you do not usually associate with electric drives. Do you have an explanation on where it comes from?

 

Great build Bob!

I haven't read through all the posts but she could be a wee-bit lower in the bow
OR
Higher in the stern, which would bring the bow down.
She might go a bit faster and throw a smaller wake.

Enjoy your ride.

 

Thanks BlueBell!

I'll try with the battery pack further forward next time.

 

@bobkart I like the Hydrobike and see you used unistrut street sign type material for your cross beams. That’s also one of my favorite materials to use, especially after I found our local supplier who supplies the County. For many years I would pull sticks of it out of the scrap pile at the dump. The sign posts rot out at the ground, but the rest is usually good. I use to joke that the best time to “find it” in the “wild” was to drive around the most popular bars on a Saturday morning. Being galvanized and full of mounting holes with telescoping sections readily available, it also works great for adjustable cross supports on small boat trailers. A couple of roller brackets and rollers, and you can drape a catamaran over the axle keeping it low for easy launching, retrieval and towing.

Anyway, yes another favorite is T-Stot. I buy most of it and accessories for it from 80/20 Inc directly. Hard anodized, lightweight (thanks to the slotting and extrusion), with linear and end mounting points, it works great if you need to build and leave enough adjustment to dial things in. It holds up well here in the tropics provided you take steps to prevent galvanic corrosion, and it’s reusable of course. I also use a lot of standard stainless marine handrail/Bimini fittings in combination with the T-slot.

While on the topic of materials, the top on SolGato is made from multi-wall polycarbonate. Very strong, lightweight, and UV stable. It’s available in different tints and thicknesses, and is popular for use in greenhouse construction and storm protection. I like that it lets a bit of diffused light through and that it doesn’t require a finish and can just be pressure washed. It also handles the heat back contact flexible panels are known to give off. If it was easier to get here, I’d probably use an extra thick extra ridged piece for my Trimarans hard Bimini instead of ThermoLite. Check out PolyGal for more info.

BTW, did you purchase your Electra hulls second hand, buy just the hulls new, or buy a complete boat new?

@Flotation Thanks, ya I have so much video footage of boats, cars, bikes, projects, builds, etc.. it was time to get back on the Tube.

Regarding operating noise it’s funny, just like the EV industry learned when you eliminate most of the noise, a bunch of others become more noticeable. Imagine driving a car from the 80’s that has been converted to an EV, all that plastic in the interior would be quite the symphony!

The low pitch noise you hear in my videos is actually from vibration that then gets transmitted and amplified by the plastic hollow hulls. One of the reasons I built my motor plates out of Ipe as opposed to say aluminum was to try to absorb some vibration. I even rubber mounted them at one point, but with the motors hanging off the back and not being completely ridged mounted (they use a hinge and will kick up on impact) they produce a slight vibration that gets picked up and sounds more pronounced by the phone mic, and I’ve noticed it has increased a bit with the larger diameter more aggressively pitched 2 blade props I’m running versus the smaller stock 3 blade I previously ran. At slower speeds you can feel the bigger props biting through the water a bit more. This is all knit picking of course compared to an ICE outboard, but it’s a slippery slope and funny how eliminating one noise brings others to your attention. Mostly what you hear when under way is water blurbling which is great, so long as you don’t need to use the restroom!

Also keep in mind there are quite a few electric motor designs out there (first generation Torqeedo, some Haswing to name a few) that use gears versus direct drive. These motors tend to have a high pitched whine like a power drill. You hear it a lot in videos, and personally it would drive me nuts. The one major advantage to the gearing is that it allows for use of a more aggressive prop giving better performance, but it comes at a cost in reduced efficiency and increased noise (also early Torqeedos had a nasty habit of shearing prop pins), so if you want quiet motor, stick with a brushless direct drive motor that uses good bearings.

 

Bobkart,

Would you consider hydrofoils?
You are a little heavy for them but it's certainly doable.
You may double your speed.

Maybe this will inspire, or not:
https://energyboatchallenge.com/en/home-english/

BB

 

Good Stuff @SolGato . I bought the boat without motor. So they added the deck, transom, windscreeen, helm, seats to those sailing hulls. So far I've replaced the seats and have the original front seats available for use as optional rear seats. And added the motor/controller/battery of course.

@BlueBell I found the Energy Boat Challenge last year as part of my 'research'. Those challenges are a good way to advance the state of the art. I briefly looked at trying to build something with hydrofoils, but it was out of reach at least for me. Decided instead to do the best I could without that. I agree it would significantly increase efficiency, and 'could' still be done on this boat, but so far it's still too much of a stretch for me.

Very briefly, here is the requirement list I landed on as I was exploring my options:

- boat length in the 3-5-meter range
- reasonably seaworthy as I won't be confined to just rivers and lakes (Puget Sound is calling)
- minimum two persons capacity, four is more likely what we want
- around 20mph top speed would be the target
- I'd like to get at least one hour of battery runtime at that top speed

I added a few more along the way:

- unsinkability in some form (a'la Boston Whaler)
- steering wheel
- windshield

The last two came from my other half, but I also agree with those requirements.

I feel like I've pretty well checked all of those boxes, with the exception of the top speed. It was recognized early on that there might need to be some tradeoffs.

15kW of power should be able to 'just' get to that 20mph, then I'd need to increase the battery pack size by 50%-75% to get back to that one hour of full-power runtime. It will get close on carrying capacity at that point though. I think with that power/battery configuration, I'd be somewhat over the maximum weight capacity of the hull with four people onboard. The weight capacity is right around 1,000 pounds, and four people at 180# each is 720#, so that just leaves 280# for motor and batteries. A 15kW motor will be at least 100#, and 15kWh of batteries is about 240#, which is 60# over. It remains to be seen what affect that degree of loading has on performance and safety. What I really need is lighter batteries, but that's every electric vehicle's challenge.

Solar panels will help, as would a small/light generator (with propane fuel, for its much cleaner emissions). Fuel Cells were briefly on my list, until I found out how expensive they are. There are propane fuels cells, but so far I've only found either very small or very expensive models.

 

I'm selling last year's boat:

Electric Hydrobike Prototype - boats - by owner - marine sale https://seattle.craigslist.org/est/boa/d/mill-creek-electric-hydrobike-prototype/7462996169.html

 

How has your experience been this far with the EPropulsion product, and how many hours would you say it been used?

Any issues or design dislikes?

Any error codes?

I read of one user who experienced a remote connection issue with a Navy motor and the control system due to the mounting of the separate controller unit below deck on a sailboat application.

I believe in that case, a direct wired connection had to be made instead of wireless in order for it to be reliable.

 

I've put roughly six hours on the motor, totaling nearly forty miles travelled. Five outings so far. No error codes.

Initially I used the wired connection, but the last two outings used the wireless connection, with no problems. The cable that comes pre-attached to the motor is pretty much the right length to reach the control, and I have it rolled up and twist-tied to the end of power cable, only to be used if/when the wireless connection has problems.

Gripes so far include:
- could use more propeller pitch selection
- adjusting trim angle on the water is a bit cumbersome
- there's no propeller RPM readout on the top-mount control

Most likely the high-pitch prop I'm using is close enough to ideal, but it would be nice if I could try plus-or-minus half an inch to be more sure.

On the trim angle, trimming out is easy enough, but to trim it back in you have to come all the way up to 'beached', then all the way back down. That would likely not be as physically challenging in a more normal hull/transom configuration, as you'd be at a better angle to reach the release latch and pull on the motor at the same time.

The side-mount and dual-motor Navy controls have a separate display that includes propeller RPM, but the control I have doesn't. I could definitely use that to help find additional top-speed improvements.

 

Thanks for the feedback @bobkart

I’m one big step closer to scaling up my design now that I have acquired a pair of 30’ hulls to use as the foundation.

Still leaning toward using a pair of Navy motors for propulsion, along with one or two of their battery systems. I also have 2kw of flexible solar panels left over from my buy-in as a SunPower dealer.

Now I kinda wish I hadn’t sold a bunch to friends!

Anyway I think that all with be enough to get me started, at least until I feel the need to go farther faster.

The big question is do I go with a pair of 3’s or 6’s knowing that eventually I might retrofit much more powerful motors as some of the newer options that have been announced come to market.

Eventually I would like to be able to cross the channels and island hop with this new boat.