How far forward to mount transducer in Trident 13?

If I had permanently mounted and routed wires through the Hull, I would definitely be using a foam block.  But since I use my FF on all three of my yaks, just haven't seen the need to do the foam block on all three yaks.  I wouldn't trust the duct seal or a foam block though for retaining water while my yak is upside down on my truck.  But for you Bill, it should work fine since you trailer yours.  Another 'experiment' you could try is filling your puck with vasoline instead of water. It apparently shoots through it just fine, from a friend of mine that tried it years ago.  However once his yak was upside down in the sun, it liquified and ran out, and all over the inside of his hull. 

I bought some vaseline to try ... in some elses yak

   Was a little messy & I could see it running out after getting hot.  Had to be cautious that I didn't lube the puck hole

Took my Lowrance Mark 4 out on my OK Trident 13 yesterday - SUCCESS!!

Photos and story coming soon!  (Maybe after TRWIII)