Putting a Sturmey Archer 3speed on a Schwinn Comfort Bike
 

Good Morning, I have a Schwinn Voyager Comfort Bike 7speed and I would like to put a Sturmey Archer 3 speed hub on it. Is that possible? Thanks, Mike
https://cimg3.ibsrv.net/gimg/bikefor...ff08ca75b4.jpg
Schwinn Voyager Comfort Bike 7 speed

If the hub has an over lock nut distance that matches your frame spacing it shouldn't be a problem other than due to vertical drop out having a way to get the chain length correct. .

Instead of the derailleur, to go from a 7-speed to a 3-speed? Yes, it can be done. Are you building the wheel yourself? Using a vintage hub, or modern hub? If so, be aware that older SA rear hubs may use 40 spokes, and 40 hole rims are now a specialty item. The rear frame spacing can also be an issue. Many older hubs are spaced at 114mm, considerably narrower than most frames designed for derailleur drivetrains. Modern Sturmey-Archer production uses longer axles, and shouldn't be a problem. The vertical dropouts on the frame in your picture may require use of a chain tensioner.

The front chain ring looks small, not a big deal if you don't want much speed, I can not tell from the photo if it can be changed.

Yes, it can be done, but there are a few challenges. You have an aluminum frame which means the dropout width cannot be altered. It is almost certainly 135mm, but confirm this before moving ahead.
Since you have vertical dropouts, you will also most likely need a tensioner of some sort. Your derailleur could serve in this role. There is an outside chance that the chain will run within acceptable tension without a tensioner. I have two bikes with IGHs in vertical dropouts without tensioners, and have done other builds where it worked out this way, so it can happen.
Many Sturmey Archer hubs are flexible when it comes to over locknut dimension if the axle is long enough, you can stack spacers and nuts to space it out as required, but the best and easiest way to ensure correct chainline is to start with a hub already spaced correctly. In your case, I would recommend this model. https://www.sturmey-archer.com/en/products/detail/s-rk3
It is the disc brake version, but it can be used in a rim brake application, and it comes only in 135mm width, so it should fit right out of the box, and dialing in the chainline should be a simple matter of flipping the dished cog to the most suitable line.

Thanks for the info, Guess I've got some measuring to do and some more research. I've never built a wheel but I'd like to try (maybe). Thanks again, Mike

Thanks Dan, great info, I've got some more research to do. Thanks again, Mike