You've kind of covered the bases and are now at the point to make a decision. As you stated you want to find fish up to 200m then you will need a 1kw. Have you looked at the M260/M265 option for fitting an in-hull rather than through hull? The flush face through hulls don't get a very good report as they can still make their own disturbed water over the face. Better through hull transducers have a fairing block to create the best water over the face but the fairing block can affect the handling of smaller boats.

If you do some more research over on thehulltruth.com you will find posts about just about every kind of sounder setup as well as you have here some excellent ones from JohnF and Glen.Vit showing garmin and raymarine gear. There are also some excellent posts about Lowrance/Simrad setups as well and how people found the best setup works.

Could your rocking and rolling be creating bubbles as your transducer is dunked up and down on the transom? A good test would be to set the transducer up in a plastic water filled bag inside your hull and see what the difference is. This is an acceptable practice from the manufacturers and part of the doco on some of their transducers. By testing your transducer inside the boat you are eliminating noise across the surface of the transducer.

As far as I know there is no scrolling history on the Furuno gear, this seems like a feature of the Simrad/Lowrance gear.

Good luck, it's fun trying to work it all out!

I have the 628 which is the same as the 688 (differences being 1kW option and bigger screen on the 588).  Biggest gripe for me is the inability to shift the bottom lock.  It makes identifying ground really difficult, especially when crayfishing.  Add in bit of sea and swell and it's even harder.  I was fishing in a 2.5m swell and had a really hard time finding my lumps.  Bottom contour goes up and down with the swell and your lump is hidden in that.  With prior sounders where i had bottom lock and could shift it, i used to always be able to identify when the hardness of the ground changed from bottom lock, so sea and swell were never an issue.  I very rarely looked at the contour/profile, that was always secondary.  

Personally, i wouldn't buy another 628 (or a 588) until they fix this.  I would suspect that this is only a software thing too - so a potential easy fix.  Maybe the 295 addresses this issue. 

 Talk to cruisecraft they will be happy to talk to you about your specific model boat very helpful with anything after sales even if your not the first owner. Transducer technology has come a long way over the last 5 or 6 years. I made the mistake of purchasing a m260 shoot through hull transducer and then asked where I should best install it as it turned out it they didn't work well with my boat and not a easy install in my case. I ended up selling that transducer and installed the ss264 pair (equivalent to tm260 but split into 2 separate 50 & 200 kHz transducers)and they are unreal, work at all speeds and have found a lot more ground since installing them. Chirp technology would be nice but depends on budget. Start with cruisecraft anyway they have done a lot testing themselves 

 I run a 588 with a 1kw tranny and love it! They don't have a scroll back feature but if you have a decent plotter it's easy to turn around and follow your track. In my opinion furuno sound bottom really well making it easy to see hard bottom, corals, fish flares etc. mine picks up ledges and caves which is easy to see when zoomed in and handy when cray fishing. I can sound bottom clearly up to 24 knots on a calm day and normally sound around 10-15 knots in rougher weather. It seems like it's simpler technology compared to simrad and other chirp sounders but it definitely works! Hope this helps

 Look at a garmin 7410xsv. 1kw built in chirp, quick draw contours, very good sounder software and can also be used as a gps.

 Airmar 1kw in a wet box mate. Gives a super clear reading 

Gruntre, I have an NSS8 gen 1 and I love it.

The deteriorating sounder readings in less than ideal seas are not due to the sounder or transducer unit!

When a boat is stationary in calm waters the highest powered part of the echo is sent directly downwards in a straight line. It hits the bottom as is reflected straight back to the transducer like a mirror and gives you a clear image. If the boat is at 45 degrees, the highest power from the echo still travels in a straight line, but at 45 degrees. It hits the seafloor and bounces away from your boat (angle of incidence = angle of reflection). Since sound travels in waves you will still get a return signal from the weaker outer edge of the ‘cone’ that is still directly under your boat, or a blank column if if it is completely out of the ‘cone’. The sounder unit doesn’t keep up with this constantly changing return signal strength and will only show you the highest powered returns, ie when the boat is momentarily upright and the middle of the beam returns to your transducer, which means most of the image looks like shit/pixelated/poor resolution. I have read John Adams too and I do have a few disputes with it, one being (if my memory serves me correctly) his view on this particular section. John says your transducer will read the bottom in the direction the transducer is facing. It wont (well the bottom wont, but the fish will -advanced), a boat at an angle will still return the signal from almost directly under the boat as this is where the reflection comes back to the transducer, albeit at lower power. I can prove it by the fact that when your boat rocks side to side, the sounder reads a flat bottom as a flat bottom, if the book was correct then your sounder would read the depth getting deeper and shallower as it rocked side to side - im talking like from 40m to 50m then 40m then 50m (if the bottom actually is flat and there is no rise/fall from swell). He also seems to forget the reading is a combination of every part of your 3D cone squashed into a 2D image - ie, if your 'cone' under your boat includes a sandy bottom with a rocky bombie off to the side, it will show both on the 2D screen and the bombie is probably not directly under your boat - you have to be able to distinguish which side of the boat the bombie is on by a couple of neat tricks you may be able to figure out from what I talked about above. Full credit to John though, the book is a great introduction and well written, maybe he simplified some areas.but there are definielty ways to get more out of your sounder when you know the ins and outs. j

Huge side rant sorry, this was a longwinded way of saying that all transducers and sounders will suffer in less than ideal seas. A higher powered unit will give you a slightly better return as it has stronger signal to pick up but the trick is to manoeuvre the boat to limit the slapping about, as well as air under the transducer and transducer placement.
Is your resolution good when cruising through the harbour at 5 knots? All sounders resolution will become more pixelated as the return signal weakens. My bottom definition and resolution is great and I can pick out fish above bottom cruising at 20 knots in 12 knot winds.
I imagine your interference issues will persist with any unit if the wiring is in the same place.
Agree with you on the scroll back, best fish hunting feature!
 

I just installed the Markfish and she works a treat between the HDS7 and the 627. I had them hooked up via NMEA0183 previously and you can easily plug in your spots into the HDS manually from the Furuno whilst sounding ground but I dont like to do it whilst on the move and end up plugging a bunch in when I get home which is a PITA.

I wasn't going to fork out the coin but I cancelled my son's 7th birthday party due to disciplinary reasons at school in the week of so instead he came down with me to watch me spend the money on the Markfish. He has drastically improved so it's a win/win.

 Definitely go the in hull 1kw in your outsider.

I have a 6.85 and the space is tight to get it into the plane but worth the effort, I get clear bottom at cruising speed in calm water and I tried everything on the transom without success.

i run the nss12 evo2 and love it

 Hi Mate got a gruisgraft 625 Explorer with a 585 and through hull transducer perfect readings at 25 knots without any interference.

 Mate got same size boat as you although a different make boat

i have a simrad nss9 evo2 running a wet box 1kw tranny - maybe take a pic of it for ya if ya want?

happy as a pig in shit, easy to use, gets real good depth clarity, although must admit still learning how to tune it in for really deep water - I just can't get out often enough to the real deep stuff in Perth - suspect after my next trip to Exmouth I'll be all over it. 

its prob not as good by all reports as a similar furuno set up but suspect it didn't cost as much either...who knows who cares it's what I could afford.

when I bought the sounder it came with a structure scan transom mount and a 600w chirp transom mount...structure scan is shit and its only still on my boat cause I don't want four unused holes left behind....the 600w chirp was okay but only okay not great. Because my boat is so small I get lots of water movement and bubbles from the prop and the hull passing thru the area where the transom mount transducer was installed and if travelling at anything over 10kts I had a real bad picture. So.....I bought a 600w wet box transducer 50/200 non-chirp and happy days I loved it, able to tune it in easy, I could mark fish at a reasonable speed and could mark bottom structure no fish (at drift speed) in 200m (picture posted on FW somewhere to prove it if have any doubts). The only reason upgraded to 1kw wet box was I wanted to mark fish in deeper water and now I can.

For me: Wet box equals reduced issues with water movement/bubbles etc which equals clearer picture. I don't get much of an issue if any with rock and roll of boat with my set up and me and my most regular fishing mate are both pretty big blokes and we go out in some shit sea - my wet box is very close to centre line of boat so this prob helps.  People reckon you loose a far bit of power shooting thru the fibreglass and this is prob true but in yours (and my) size boat how deep do you want to fish...last weekend we were marking fish on drifts along the drop offs at northern end of trench in 250-400m and we're marking clear bottom  to about 550m and could still see bottom and depth to 700-750m although its was a shit picture over 550m.

scroll back with simrad and lowrance is underrated! I think it's awesome especially when you mark good ground at 15-20kts on your way to another spot and by the time you stop you're already a few hundred yards past it. With scroll back you can come straight back to it and check it out.

do with the no chirp 600w wet box?

 Still in my boat at the moment - not plugged in

 pM me your mobile number mate and I'll send thru

cant post pictures on here from phone - don't know how!

Furuno 628 + 1kw Airmar installed for $2500 locally
I couldn't be happier with the unit and I am sure I haven't used a third of its capabilities but looking to giving it a real work out in Exxie next week