Tank & Consol Location

[JohnC]

I have no deck in my project so I am starting from scratch as far as the location of the gas tank and the console. I am planning to put the back of a 52 Gal. Moeller tank at about 89" from transom at the deck. That's where the factory notch in the stringer is and the tank fill is at the aft end of the tank. I am also planning a custom console to be about 76" from the same point. I made a drawing for clarification.
Since I don't have the original deck I don't know if I am moving CG forward with this. Does anyone know the original locations? This is a 77 MA 20'.
Thanks, John

[uncleboo]

The experts will be along later, but, it's going to depend on the motor your gonna install, bracket weight, etc. good luck with the project.

[JohnC]

Sorry, I should have mentioned that. Motor weighs 365 lbs.

[72potter20]

I'm not sure where the tank originally was in relation to the transom, but i started from scratch as well and I moved my 50 gallon tank as far forward as i could before the height would interfere with the deck. My engine also weighs 365 lbs and is on a 24" setback fiberglass bracket. I'd put your tank as far forward as you can as well

[FishStretcher]

Moving the tank that far forward means trim will change as fuel level changes. Moving the console forward doesn't do that as much. I have a 1975 MA with the ginormous console from a 23 footer. With a bracket, if you fish it offshore, I'd push the console forward to get weight forward and omit any serious concession to a forward facing bench seat forward of the console. Then you will have some room back there to fish. Mine came with a leaning post and it was pretty tight between it and the transom. You will be a bit more forward, so heave or really the vertical acceleration from pitch will be a bit more noticeable, but the console and T-Top and people standing at the console while underway will help flatten out the boat a bit.
Then you can move the tank forward and the change in trim won't be quite as bad. It is a hassle, but consider two smaller tanks so that the free surface "slosh" doesn't put the fuel as far sternward when you try to climb on plane. You can even empty the middle tank and keep the forward one full until you need the last bit. I fish offshore. I think a notch and a splashwell gate or insert is a pretty viable alternative to a bracket, especially if you have to look at the powerhead or prop offshore. Like when you wind leader around the prop fighting a fish.

Composite deck and hatch cores might not be a bad idea. Especially sternward.

Or ditch the bracket. I presume you read Bushwacker's excellent treatise on brackets? It's a sticky.

[Old'sCool]

Are you sure the fill is at the rear of the tank? Or fill at front, pick-up in rear?

[JohnC]

Thanks for the help. The fill is at the back of the tank. I have not bought the tank so that detail is not written in stone but it seems my best options are Moeller FT5299 52 Gallon or a custom - not much else fits.
FishStretcher, I didn't consider 2 tanks as you suggest - I will look int that. That's about the only way to tweek the CG after the deck is on. I don't mind moving the tank(s) forward since I am moving the motor backwards; I just wish I had a reference as to what "forward" is. Without the original location its just a guess. I will push the console forward until the gunnels get too narrow. The most stable seat on a boat is on top of the cowling, everything gets bouncier from there as you go forward. I think your right about space behind the console though - it's worth slightly more bounce to gain some space.

[FishStretcher]

There is a thread or two on CG location on 20 footers and the MA. Chaser's thread on his build has some, but there is a deeper thread from a year back. If you don't find it, I can look.

If that doesn't work, then a place to start is where the 5 foot long ~50gallon tank starts. I'd have to measure. The 72 Gallon tank starts in the same place- perhaps a foot (?) forward of the rear fish boxes and splashwell, and ends, well, another 7 feet forward. I put a 20 gallon tank in the forward 18" of that space, inside the console. And I have two batteries under the console. I am putting another 22 gallon whaler bench seat tank forward of my console. My original tank location is full of buoyancy foam. As are the caps, to help prevent turtling.

[JohnC]

Thanks FishStretcher. I did a search and found "Center of Gravity" thread by Chaser; lots of good stuff there. That's the first time i have heard someone say they would not have moved the tank so far forward it they had it to do over again. I'll find the one from a year ago as soon as I have some browsing time. More and more I like the idea of moving the console forward as that is a fixed amount of weight and will transfer the CG forward permanently, not just when the tank is full. I plan to foam everything under the deck so it ain't movin once the deck is down. Thanks again!

[72potter20]

After moving my tank as far forward as i could, and spending time on my boat at varying tank fill levels and types of sea, I wish I would have found a way to move it even further forward. just my two cents