Tm260 or Tm185m

Im looking at going 1kw transducer for the boat, keen to fish bottom in Kaikoura so could be up to 400m +
Any advice or experiences would be much appreciated.

I run 260 but it ain't tm , thru hull. On a furuno. Easily spot Hapuka and 5 bar cod in 400- 600m. Spot at 50 hz then go 200 to pinpoint. Problem is u gotta be so accurate with the drop and drift to.not miss the fish. BTW round sinkers works better than std snapper style, the snapper style will " torpedo" and don't go down straight, round jobs just go straight down.

got a tm256 dual 50/200 with furuno slide bracket 10 pin plug a bit big for my 4mtr pontoon ucan have for 800 delivered the bracket alone costs 400 .

Of the two mentioned the TM260 is the one I would go for in 400m depths. The 185 is a shallow water unit, fixed transducer beam angle of 25deg which equates to a footprint of 100m at 400m - not very precise. On the other hand, the wider beam angle in shallow water is a lot more useful and the 260's 200Khz beam angle of 6deg is a bit like writing with a pencil vs spraying with a hose. Frequency isn't a problem as you are well within the envelope for 200Khz (or higher) - I was getting bottom lock in 1100m with 200Khz and a SS270W transducer in a thru-hull application. That's at the extreme end of what you can get out of a 1Kw rated transducer and that was used as a sales tool as well as a fishing tool but it does show what the things can achieve when correctly installed and set up. I'll add the edit there that the 270w has dual 25deg beams and the level of precision was the only thing that annoyed me about it in use - it was bloody hard to position the boat over the top of deeper structure although I did get better over time by looking at the thickness of the traceline and estimating how far off I was and checking with a cross-pass before setting up.

Never used the 256, although it seems to be narrow beam on both frequencies - I'd go for wide on 50Khz and narrow on 200 if selecting one nowadays???

What plotter/fishfinder/s are you running?

The chirp transducers like the TM265 will have better target separation but cost more too. And chirp may not be compatible with an older model fishfinder.

Are you only targeting the deep water or will you fish shallow and other game fish?

Are you running an existing transducer setup and wish to add a 1kw along side this?

Alloy or fiberglass hull?

I run a fibreglass hull with a thru hull M265LH that reads very well on the plane. Placement of the transducer and interference like air bubbles from planing strakes can impact the quality of your sounder returns/picture.

It's to be fitted on a 5m surtees with Simrad go9 and 3in1 active imaging transducer. I would like to use it on the go9 till funds can supply a separate s2009 fishfinder unit for the 1kw. I'm aware that the go9 dont have the full out put power for a 1kw but from lots of reading online they work pretty well.
So most of my research said the tm185m with chirp work a treat on the go9 with good bottom definition and separation at 400m+
I want to keep the go9 fitted in the dash as a plotter plus it has the outboard connected to it for tacho ect.
Any users with the S2009 and a tm260 fitted?

Two is always better than one unit - that would be a very good setup. From the people I have worked with, the general thought has been that the 1Kw units will work fine but you won't get full power/depth performance from them. What you will be doing is running in the mid to upper range of the transducer's output which is pretty good for resolution. What will offset any performance limitations to some extent is heavily oversizing your supply cables to the units to reduce voltage losses and having minimal connections or switches between the battery and the unit, with good separation of the cables positive and negative to minimise any chance of magnetic field interference. That was one of the things I did when I set up the ss270 in my boat after the initial install produced pretty poor performance (among other tweaks).

To be fair, while the chirp is good and you do get better definition (have used it fairly extensively on work sites looking for objects, obstructions and the like) it isn't what I would call a revolution. It's more of an evolution or a small step forwards. In conjunction with downscan, sidescan and multi-beam it's a part of a good package of tools but!

Nautic Electronics is your man, based in Rangiora

https://www.nauticelectronics.co.nz/