Matt,
Yes the boat is very efficient. Craig Clos in Australia designed it. He's a retired guy whose hobby is hydrodynamics. He recently finished an 8 meter long cabin cruiser with all the amenities that makes 22 knots on two 30 hp gas engines. My dinghy is a slightly stretched version of this:
https://m.youtube.com/watch?v=SA6cDk2Imb0
These are pretty much full displacement boats that are designed for a specific speed range. The dinghy above does 14 knots on 3 hp gas. He later put a Yamaha 9.9 on it and got 15 knots. So the top end is very cliff like.
He sells plans through the gmail account. They are very good. He might take a while to respond while he's cruising. A lot of this has to do with keeping the weight down. 3/4 of way thru building I think my 12 foot divinylcell dinghy will be 120 lbs without motors and batteries.
Myles, thanks for the motor info. Explains a lot.
Jerry
On November 1, 2022, at 7:38 AM, Harry Michalowski <harrymichalowski@gmail.com> wrote:
Miles and F Neil,
Thanks for the info. For the 12 foot dinghy I have a 1.2 kw Hang Kai, which like the Elco is a gas lower end modification. Small prop. I've looked around St Thomas at what people have and there are a ton of inoperative Torqueedos and I do have a friend with an Epropulsion 3.0 which he likes. The Elco is too big for the boat. I consulted with a boat designer friend who's a drag expert and he said it should run at 10 knots on 700 watts. So I'm going to put it in the water and test it with the small motor and see if it's acceptable.I've noticed that 2 kw and under ebike and gocart motors are getting really cheap on Amazon. If one were to make an outboard leg out of these the most expensive part seems to be the right angle gearbox for the lower end. I found an industrial/farming type that would work but it's not water sealed. Anyone know of one? I agree with Myles that I don't want an underwater motor type unit. What I'd like to do is make a really lightweight leg out of mostly carbon that could swing big props and that is bulletproof. Then use the cheap motors and replace them as needed. It looks like the quality smaller motors like the Etek and Mars have almost disappeared.
I'll write back once I test the boat with the small motor, it might be enough power.
Thanks,
Jerry Barth
On October 31, 2022, at 1:46 PM, Myles Twete <matwete@comcast.net> wrote:I can't imagine that the drive efficiency loss thru the "90 degree turn from drive shaft to prop" amounts to much. The big loss is in using a small prop.
My outboard conversion has served me well now since converting a 25HP 2-stroke Tohatsu to electric in 2003. There are few with conversions or kits running today that predate this. Thunderstruck Motors had started not long before this and had not yet offered its boat kits yet---I bought my ETEK from them after watching them drag race motorcycles in Oregon in 2003. My telling them about my boat and buying the ETEK from them may have got them interested in targeting the boat market.
Initially, I was not super impressed with the performance of my conversion, yet I was sold. But then initially I was running with the stock 9.9" prop. It did not take long before I modified my lower unit to accommodate up to a 14" prop. I have been running with a 12" diameter 3-blade brass prop for about 18years now and have been quite pleased with the economy. The amount of efficiency gain possible in going to 14" might be worth the expense and hassle, but probably only a small percentage. Still, I may consider that one day.
One thing I will never do: Eliminate the lower unit gearing for some other drive or relocation of the motor to an underwater pod.
I do need to replace my original ETEK 8HP motor very soon. It's served me well for 19 years+ now, but with 3 sets of brushes nearly gone now and none available anywhere these days, I need to upgrade. I'm considering brush and brushless options.
-Myles Twete, Portland, Or.
The Reach of Tide: www.evalbum.com/492
From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of F. Neil
Sent: Monday, October 31, 2022 11:16 AM
To: electricboats@groups.io
Subject: [electricboats] Elco vs ePropulsion
I would recommend checking out the ePropulsion outboards. I first bought an Elco 9.9 and was not happy with the noise and low efficiency. I then bought an ePropulsion Navy 6.0, which is much quieter, and much more efficient with its' larger 3 bladed props. The Elco is basically built on the bottom unit of a small-propped gas outboard, and loses efficiency in the 90 degree turn from the drive shaft to the prop, whereas the ePropulsion is a more modern design, with direct drive motor underwater that the prop is directly attached to. There are lower kW units that would be cheaper than the 6.0 that would be appropriate for your smaller (displacement?) boat.
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