5-Meter Power Cat with 6kW Outboard

[bobkart]

Thanks for documenting and sharing your work. Perhaps a video more focused on the technical details of your electric cat would be nice? It would be good if those details reach a wider audience.

Thanks for the suggestion. I'd be up for that, if I thought I had enough material to fill such a video. Because the boat and motor are off-the-shelf items, there are only a couple of areas where it gets interesting. One is the DIY battery, and I've made a video covering that to a fair degree. The other area where I've gone past just bolting together boat/motor is the fairly long list of refinements I've made to the boat from its as-received configuration. Not all of those refinements are worth covering (imo), but possibly a video covering the more significant of those could be worth doing. Note that I'm still making refinements, so any video along those lines would only be part of a series of them, i.e. I'd probably break the refinements into groups of, say, five, to both keep the video lengths down and allow for ongoing developments.

 

[fallguy]

Anecdotal and useless, but that SKB box is the same one I use for my tackle box. Do they get warm in there? Technically, the box is required to be vented. But I am really only curious if they get warm when they are dumping current to the engines.

I enjoy the videos. But am more curious about the vessel than the shore as @Flotation suggests. Are they canoe hulls like Wood's Skootas?

 

[bobkart]

To confirm, that's the SKB iSeries Model 3i-1717-10BE. And I do wish they came in a lighter color, like silver as many Pelican cases come in. I use an inexpensive indoor/outdoor thermometer, with the remote sender inside the battery box, and have seen over 110F there on a hot/sunny day under high draw conditions. The black color definitely contributes to the heat issue, as I've observed temperatures over 90F just sitting in my driveway (~70F ambient). I've drilled roughly 3/4" holes in the bottom at the corners, then similar holes at the top on the sides. My next move will likely be to add an 80mm fan to either top or rear side. Another potential move I could make is some kind of shade easily attachable to the top of the box.

A separate-but-related issue on battery heat is that the positive terminal gets much hotter than the negative terminal, so my theory is that the fuse gets warm due to high constant current. I've increased the fuse size to 400A, and beefed up the size of the aluminum parts that move current from the cell terminals to the final output terminals. Those changes seem to have helped, but it's hard to compare one day's results to the next, as ambient and load conditions can be quite different.

I get that the videos are less interesting to someone not familiar with the area. My bad for assuming everyone has read all of this thread, where details of the boat/motor are covered. To start over on that, the hulls are from the RS Sailing CAT16:

RS CAT 16 – the most stylish, easy, exciting for clubs and families https://www.rssailing.com/project/rs-cat-16/

Then those are assembled by Rowing Solutions into a power-cat configuration:

rowing-solutions – My WordPress Blog https://www.rowingsolutions.com/

The last off-the-shelf piece is the ePropulsion Navy 6.0 Evo motor (in long shaft):

Navy Series Electric Outboard Motor https://www.epropulsion.com/navy/

I added the 10kWh battery and have made a couple dozen refinements to the boat, probably the most important of which is upgrading the seats and allowing the old seats to be used as a second seating row, increasing the seating capacity to four.

 

[fallguy]

I am using the coolerguys enclosure controllers. They could use a manual, but I hack my way through.

For you, the probe would go inside the box and the display whereever u like.

I have two, one is just an enclosure fan as the enclosure narrows at the top. The other is for the battery box. That one has two fans, one air in and one air out. Kinda nice, set for 100F and it turns on to protect the electronics. Yesterday or Monday it was 107F at the probe up top of the console. The stuff was off; that was ambient. When it kicks in, I generally leave, but tried to power thru some.

 

[fallguy]

Does the cat hull exit above the water? Curious about how those hulls exit the water is all.

 

[bobkart]

Does the cat hull exit above the water? Curious about how those hulls exit the water is all.

Not sure what you mean. Here's a video showing the boat running from various angles; maybe it will help.

 

[fallguy]

Curious hull design for electric. I see some inefficiencies in the design, but I am not expert enough to comment greatly and probably wouldn't change much, but the hull wakes seem rather deep. They would probably be better a bit wider aft..with a sharp exit and my guess is 10% efficiency improvement. But all in all a good rig for off the shelf.

Your system seems like it is very portable from one boat to another.

Wood's Skoota 18 hulls would perform a bit better I'd say..if u plan to ever change it.

I had planned to move to Puget Sound, but I got priced out of the market a bit, so I enjoy your videos and learning about Lake U n W on wikipedia.

Have you determined a power/speed to range chart? Betting the boat does best at hull speed, but curious if I'm wrong.

 

[bobkart]

The fan I added to the battery box made a world of difference. I was able to run at full power for close to an hour, with air temperatures inside the case maxing out in the mid-90s (mid-70s ambient). Without the fan I would have been over 110F. And the positive terminal is now cool enough to touch, compared to before where it would be too hot to touch after only 15 minutes of full power.

On the hulls, there are more efficient shapes for sure (Wintech, Stillwater, ...). One of the nice features of the RS hulls is their toughness. Hitting a rock at speed is not as likely to damage them, compared to a fiberglass hull. I sacrificed some efficiency for toughness:

Note that these hulls are considered as 'semi-displacement'. So 'hull speed' limits are less applicable. From Rowing Solutions I was told that speed is related to power by square root (p = Cv^2). This matches my observations well.

Difficulties in obtaining a power-to-speed table include variability of weather/water conditions, and different loading levels. It turns out that this style of hull is more sensitive to loading levels, compared to a monohull style.

What I can report, from my most recent outing (Shilshole to Edmonds, 22-mile round trip), is that 2/3 power easily yielded 10mph, and that's with a fairly full loading level (backup transom/motor/seat installed, for example). By solving for C with those numbers substituted, I get this 'theoretical' table (C = 40):

1kW = 5mph
2kW = 7mph
3kW = 8.7mph
4kW = 10mph
5kW = 11.2mph
6kW = 12.2mph

I've been in the 20.x km/h range on a good day (smooth water, light loading), so that's close to 13mph. And I've seen 19.9 km/h with more typical loading/water conditions (right at 12.5mph). So the above table seems close to reality, at least regarding the 4kW and 6kW lines.

 

[bobkart]

 

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