airmar chirp in 1 kw M135M which is an in hull, firing through the hull.  It works great but I am using a Simrad Evo3 with it, so it is working at 1kw.  The interesting part is I use an Elite Ti with a Lowrance 200/50 skimmer transducer siliconed inside the hull next to the 1 Kw transducer, and I get great readings from this as well.  As an experiment, you might want to get a 200/50 transducer and do the same and see how it works, mine has been working fine for 10 years.  I assume you have outboard/stern drive as the transom mount works, so position it in the middle as far towards the back as you can.  Make a pyramid of silicone, and wiggle the tranducer into it to avoid air bubbles and let is set.  You should clean the area first with acetone to help the silicone stick.  If your hull is solid glass, it should work fine.  Foam layed hulls have air pockets in the foam, so don't work well.  If this works at depth, mine does, then you may want to go for the in hull 1kw to avoid a hull penetration. 

Good luck

with your Elite Ti so you should be able to view that on the flybridge

With a boat that size I would be going a fairing block mount.

You will get the best picture possible that way.

Its always about transducer placement to get the best reading

fishwrecked.com/forum/ss164-thruhull-transducer-sale

you might be interested in this which just popped up

I originally siliconed mine in after reading about it in a forum, and I though that if the transducer stuffed up because of heat I have only lost $300.  In actual fact, as the hull sits in the water and is cooled by the water, the face of the transducer is cooled as well I guess, but anyway, it works.  It has been in place now for 10 years, and I hate to say it but works just about as good as the 1kw chirp.  I have them next to each other, about 100mm apart, and was concerned about interference, but there isn't any.  I guess because they operate on different frequencies, the 1 kw 85 to 135, the 600w at a fixed 200 or 50.  I have had a lot of problems in the past with transom mounts and this solves the issues.  Hope this helps.

I did try and silicone in my 3 in 1 chirp transom mount transducer that came with the Elite Ti and it did not work well at all.

has downscan but I never use it anyway, I do know that the 3 in 1 transducer that came with the Elite Ti is a piece of s**t on my boat.  I have a piece of cutting board on the transom that this is mounted to, it looks like swiss cheese from all the positions I have tried to get it working well.  Lowrance have replaced it once, but there was little improvement.  I run my units as 2 standalone units so if one is stuffed the other works.  I use the Elite Ti as a GPS and sounder, the Simrad I use for engine readings and sounder, I backup my waypoints by card every so often, as the Elite Ti is used to mark the new spots, I just backup on a card and to the Simrad.