Sk8man

Hey Jack, I think you might want to stay away from the deck chair idea...they are very" tippy" and ina 12 footer that could spell disaster. I guess I'd be looking for an inexpensive fold down seat that clamps to the cross piece.... a lot safer....

sandbags? can reposition and don't move

Jack, You should be OK with the 40 lb trolling motor on a 12 footer. I use a 55 lb thrust on my 18 ft powered by a heavy duty deep cycle battery.( Not familiar with the ones you mentioned) and it works fine (3,000 lbs plus boat).

Pap -I have the Mag 10's too and I'm, pretty sure the top recommended maximum weight for the older motors is about 10 lbs. As far as the depth finder goes the frequency (measured in Khz) of the unit (matched to the transducer) is a different factor than CONE ANGLE. Sometimes you have to check with the tech people to find out the cone angle because they don't always include it in the literature. The cone angle is usually greater (i.e. wider) the smaller the KHz (e.g.50 khz vs. 200) but cone angle can vary considerably with the function and type (e.g. through hull vs. transom mount) of transducer.

Sometimes returning to "basics" can be productive or helpful to understanding the basic problem here. If tracking your downrigger balls is the primary concern (rather than separating fish from the bottom for example) get a finder with the widest beam coverage (determined primarily by cone angle). The cone angle from any transducer will be significantly narrower at the top than bottom so as your boat speed increases your downrigger balls will be increasing their outward "journey" away from the cone center and as they get to the outside edges of it they may appear intermittently on screen or disappear. The weight of downrigger balls is a factor in this but only to a point as is resistance of downrigger wire itself. There will be a point reached no matter how heavy the ball is or how sensitive the fish finder is that the boat speed and perhaps current conditions will force the ball outside the edge of the cone. When you look carefully (and providing your sensitivity or "gain" is set properly for conditions) you will see the the lines on the screen made by the downrigger ball tracking getting fainter and fainter as the ball goes toward the cone edge. In most cases (depending on transducer location etc.) you will probably mark one downrigger much better than the other and the farthest one from the transducer will be going in and out of the cone edge especially at increased speed and on turns and generally the deeper the ball is set the more pronounced this is because of the relationship of the angle of the wire (and increased water resistance) to the cone angle. The "long and short" of this is that no matter what unit you buy it will not get around these limitations....you will still have to experiment with boat speed to see where your range of operation is best and transducer placement is optimal.