Casting deck with gas tank underneath

[73GMC1500]

1987 1648 monark jon boat. Bought with a 9.9 4 stroke Mercury. Great little motor but as I got more comfortable on the water I got the need for speed. I have 2 motors I will be playing with now, Yamaha 20 4 stroke and Mercury 25 2 stroke. The boat currently has a 3 gallon tank and lawn tractor sized battery in the back by the motor. There isn’t any extra room back there either. The 9.9 would run for days on the little tank.

Now that I’m running bigger motors would like to go to a bigger tank (6 looks to be a common size) and larger marine battery. And probably put them in the front to help balance the weight out when I’m by myself.

No idea how I want to do it. It has a factory casting deck of sorts up front. Probably have to cut that out and build a taller one to get a 6 gallon tank under it.

Looking to bounce some ideas around this is my first go with modifying jon boats. Only pic I have right now, boat is outside covered up buried in the snow currently.
https://www.flickr.com/gp/138149315@N02/4L0715

 

[Weldorthemagnificent]

I have a 16’ boat with a 35hp 2 stroke. I can run 3 guys and gear up the French river and camp for 3 days fishing every day and then back to the truck on a 6 gallon tank. I like the security of the big tank on those trips but my point is, how much fuel are you using? My rule of 2 stroke thumb is 1gal per hour per 10hp at wide open. So hypothetically a 25 will use 2.5 gallon an hour a wide open throttle. Sounds like a lot of fuel but how often do you go farther than 10 miles from a boat launch? At 30mph that’s 20 minutes. 20 minutes out, 20 back and another 20 minutes worth running from spot to spot. Still leaves half a gallon in reserve in the small tank.
My advice is to see how much you use before hacking into the boat for more fuel storage.
I extended the hose on my tank and place it up front when I’m alone and in the middle when I’m not.


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[gatorglenn]

That six gallon tank should be more than enough. I took a 22 gal out of my boat , and using a 6 gal now. With a 60 hp, I can go 3 trips or more.


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[73GMC1500]

I have not ran the 25 Mercury yet as I got it over the winter. The Yamaha I had hooked to a 7 gallon tank testing it before I bought it. It burned that dry in 2 afternoons but the first day was a lot of wide open running on the Mississippi. Second day was maybe 1/4 of the time wide open on a local river. I guess I could try the 3, if it would get me a day I would be ok. Throw a gallon backup can in with me or something

 

[LDUBS]

It sounds like you want to move the 6 gallon tank forward because it won't fit back by the transom. IMO, if it will fit, leave the larger tank back there as you are adding less than 20 pounds. I currently use a 3 gallon tank with my 25 HP four stroke. I carry a gas can "just in case". I also want to move to a 6 gallon tank and have the same space issue. I found a 6 gallon Scepter tank that I think will fit in my transom area with maybe 1/4" to spare.

Anyway, other than knowing someone is in the same boat as you (pun intended), I guess the above isn't really going to be much help. :|

 

[gatorglenn]

I’d say it’s really good info above. At least people are trying to keep him from having to pour the old gas in his towed vehicle. So he can keep fresh gas for the outboard LOL.


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