Did a search as I was curious...did not find the answer.

I know lots of folks who use fish finders shoot through their Kevlar hulls.

Anyone know if that works with a carbon fiber hull?

That is an interesting question. I do not know the answer, but I think you should try it and let us know. Carbon Fiber seems very similar to fiberglass and kevlar composites, so initially I would think it would work just as well.

Then again, perhaps it works like stealth technology and the CF absorbs the signal.

Google came up with a negative response from a Raymarine forum, for what that is worth:
https://forum.raymarine.com/showthread.php?tid=7247

Thanks - I would try it but do not own a fish finder. May or may not get one at some point.

I don't have an answer for you. But having once tried an external mount on a canoe I will only say that the drag and attendant rippling sound while paddling are annoying. Shooting through the hull is the only option I would choose. If a transducer doesn't shoot through CF my advice would be to not get one.

Having said that, I wouldn't include one on a canoe trip anyway so I have my bias.

We have no problem getting a good signal through the floor of a CF canoe.

sns: "Thanks - I would try it but do not own a fish finder. May or may not get one at some point."

One thing to keep in mind when considering a fish finder is that not all transducer signals can shoot through a hull. Only traditional (2D) frequencies can successfully be passed through a hull. Downscan (3D) sonar cannot be shot through a composite hull. Sidescan and Forward Facing, it's probably obvious that these are not options for thru hull operation.

I have an ice fishing transducer for mine and a Northstar blacklite layup, so kevlar and carbon. I get a signal just fine as long as the transducer is in a little bit of water.

Nice; thanks all. My Blackwater is carbon fiber over kevlar. Sounds likely to work if I go that route. Which I may, or may not.

Let us know how it works out if you go that route.

If you go with a Lowrance unit, I designed a simple 3D printed transducer well which can be siliconed in place semi-permanently. It securely holds two models of the most commonly used 83/200khz (2D) transducers. I posted details in the DIY gear forum.