Down sizing gas tank
 

In preparation for the new 4 stroke I was thinking I would take out the 70 gallon tank and replace it with a new 50? gallon tank and install it all the way forward where the 70 is now to help any center of gravity issues that may happen with the newer heavier engine.
With the better gas mileage you get with the 4 stroke I may not need the larger tank and I don't plan on going anywhere that far on the 20 anything soon.

Any opinions?

50 should be more then enough...

Strick

Smaller Fuel Tank
 

I too have thought about a smaller fuel tank considering todays engines are not so thirsty. As far as cg changes, let me remind you of the cg change estimator you asked about a few years ago.

I still have my ole rude 150 and did the same thing.
54 useable. We are so lucky here to fish whilst looking at condos.

Seems like a lot of expense and effort for 130 - 140# less fuel @ a full tank.

I did that when we repowered our 23. Old engine was lucky to get 1.25 mpg on a good day, and the 75 gallon tank was deeply pitted where water was trapped by foam. I realized that the new motor should get 3+ mpg, so opted for building a new 40 gallon tanks, with all new hoses, and a foam free install. Actual consumption with the new motor turned out closer to 4 mpg, so we greatly increased range, reduced weight, and tank was about half the cost of duplicating the old one. Not for everybody I know, we do frequent short runs... it's worked out just fine for us.

I hear you on the not a lot of difference in weight but looking at a different thread and see the junk that was inside the tank made me start to think. New engine ...old dirty tank and all that could go wrong.

I mean its just more 🤑

If you have any doubts on the condition, try scoping it. My tank was so dirty it made sense to replace for present & future engines. I went from 120 to 100 gallons. Seems there’s a price advantage at that size, easier to get back into place and no need for the capacity with newer 4 strokes. Good luck.

I did just what you're thinking about doing. I had a 50 gallon tank built by RDS aluminum in Perry, FL exactly the same width and height as the old 70 gallon tank only shortened 23 or so inches and mounted it all the way forward where the original was placed. I mounted mine using 5200 on strips of PVC and fiberglassing bulkheads on top and opted not to foam it in.

I have a 39 gallon tank on my 20ft with a suzuki 4-stroke. Even carrying 15-20 extra gallons over the course of the season for every trip would be like carrying one more smallsih passenger on the bow for every single trip. I can feel the difference on my 20 ft in the handling and performance of the boat without the extra 100 pounds on the bow and the 4-stroke range with 39 gallons I would probably never touch. Thats was just my thought about it, the extra is nice but the way I use the boat I think the most I ever used on one run was 20 gallons or half the tank. Also, depending on how often you use the boat maybe turning in some fresh gas every trip or two is a good thing to keep fresh gas going through the engine.