Could someone please explain to me where the division lies between "short" and "tall" transoms? I am trying to rebuild my dad's '83 Alumacraft 1648 and replace the 50 Johnson outboard with a (22-30hp) longtail. The boat is a mod-V and has a pretty "tall" transom. Haven't measured exactly but attached a picture for scale. Looks to be well over 20".

First bit of advice, measure it.

20" is a tall transom

That’s probably a tall transom. Most longtails that you find used are usually short transom models. If you go that route you can cut the transom down to 16 inches. If your buying new, get a tall transom model.

Are there any red flags or considerations I should be making with a transom that is that tall?

Yeah, don’t buy a short transom model with a tall transom. It will run like shit.

What about the reverse? Saw on another post where the fellow is using 2 shims and the shaft still wants to dive. Anybody had success with the Backwater LS on a short transom? Because that's what I've got, I just haven't run it yet.

Ideally, you want a motor that matches your transom. These things are so slow and temperamental, I want everything to be dialed in - where the prop runs, RPM range, Etc. I’ve had to cut down a tall transom before, but it would probably be easier to fabricate a transom “up” instead of cutting down and rebracing.

I guess my thinking is while the extra weight of the longer shaft is not desirable, the forward component of thrust is increased due to the shallower angle and should only help performance.

Could be wishful thinking, might be okay though. The additional weight is negligible. If I remember correctly, the BW’s long shaft versions were shorter than some of the other brands tall transom models. Just out of curiosity, did you buy the long shaft for that specific boat?

Yes and no. I had a 23 BW Swomp (not the lite) SS to go on a 1542 short transom. I went out and ran it empty and was bumping 20 mph. I honestly do not care what my speed is, but I do want to get up on plane with a hunt load (2-3 guys, dog, decoys). Without having tried it, I had the feeling the 23 wouldn't do it. So I told myself I'd just keep an eye out for a 27 at fair price but keep on the current course if not.

27 came along via PM on this site, but it was a LS. It was newer though, and the frame was in better shape. Figured I'd give it a shot. I'm winging it here, I get that. But swapping these motors out is kind of fun in and of itself.

1648 with MM is more of a 2 man machine....

Especially if they are 200 lbs each...

An 1848 will do 3 men better....

My 1648 with 23LT ran 20 solo - 16 with 2 man and load - would not plane with 3 and load...

Yeahhhhhh, I'm probably going against hope with this 15'.

Honestly what's caught my eye now are these gator trax marsh series boats. Short, low profile, 3 guys and gear, and 23-26mph