R21 Electic Engine Investigation

[JayandEileen]

I did a lot of investigation this summer on possible ways to add an electric motor to my R21.
These are the two solutions that seemed most promising:
1. Create a hybrid by adding an electric outboard like the one from Stealth Outboards.
The batteries would hopefully fit in the back lazerettes.
2. The other choice is to replace the diesel engine with an electric motor. There are many
interesting electric motor manufactures but the one that was my favorite was a company
in Port Townsend called Powerflow.
Tariffs have messed up pricing on LiFePO4 batteries but hopefully prices will go down.
It would be great if Solid State batteries showed up in the consumer market but that is probably
5 years off.

Interesting aside that came up during this investigation. It was brought up that the diesel engine
might be quieter if the engine mounts were connected directly to the hull with the water on the
other side of the hull dissipating some of the sound. The current design with the engine mounts
on fiberglass above the hull probably acts like a speaker cone and amplifys the sound. Probably
a great problem for an acoustic engineer.

Hope somebody finds this useful !! Questions are appreciated.

 

[Newf]

A comment on your thoughts about mounting the engine directly to the hull. I’m not an acoustic engineer but I doubt very much that it would do anything to lessen the noise. It would almost definitely add more vibration through the hull IMO. I replaced the original mounts with ones that were a little stiffer and can feel increased vibration through the hull. Mounting it solid would probably rattle your teeth.

 

[JayandEileen]

A comment on your thoughts about mounting the engine directly to the hull. I’m not an acoustic engineer but I doubt very much that it would do anything to lessen the noise. It would almost definitely add more vibration through the hull IMO. I replaced the original mounts with ones that were a little stiffer and can feel increased vibration through the hull. Mounting it solid would probably rattle your teeth.

I race on a Frers 38 sailboat that has the exact same engine mounted directly to the hull and you can barely hear the engine when it is being used. I realize this is a stupid comparison because the sailboat is 15,000 lbs and our Ranger Tug 21EC's are around 3000 libs. I was thinking of approaching someone in acoustics at the UW and see if quieting down my Ranger Tug would be an interesting class project. I did replace the sound proofing material on the inside of the engine box with a higher tech product and it did help.

 

[Newf]

I race on a Frers 38 sailboat that has the exact same engine mounted directly to the hull and you can barely hear the engine when it is being used. I realize this is a stupid comparison because the sailboat is 15,000 lbs and our Ranger Tug 21EC's are around 3000 libs. I was thinking of approaching someone in acoustics at the UW and see if quieting down my Ranger Tug would be an interesting class project. I did replace the sound proofing material on the inside of the engine box with a higher tech product and it did help.

It would be interesting to measure the decibels right at the engine on both boats. That would be a direct comparison.

 

[ohioan55]

Two thoughts I'll share. One is that replacing the diesel with an electric motor will hurt the resell value of your boat. One of the reasons is that you will greatly reduce the range of your boat. Second, I found that noise on our boat was somewhat reduced after I treated the prop and rudder with PropSpeed. I also gained about a knot or so in speed.

 

[bob daily]

The problem with vibration and noise from these boats is mostly due to the three cylinder engines. If I was worried about the noise I would consider replacing the engine with something like the Beta-35 four cylinder engine! They are quite and lack the vibration of 3 cylinder engines used in our boats. Bob