SUPER SPORT 15: Moving Battery and Fuel Tank

[speedra421]

I have a 1986 SUPER SPORT with a Yamaha F70. I feel that there may be too much weight in the stern. A 12-gallon fuel tank and two batteries are behind the helm bench seat.

I plan to change to one battery under the helm console. This battery must be small to fit in there.

Give a recommendation for a small battery that could mount under the wood console.

Also, I would like to move the fuel tank forward and possibly under the front bench seat.

Q: Has a fuel tank to fit under the front bench seat ever been custom made?

The height under the bench seat is 7-inches—not a lot. The width available is about 30-inches between the two slanted non-skid areas of the deck. If [the custom made tank I might have made were] to extend wider than 30-inches then [the custom made tank I might have made would] need to get even fancier than a simple rectangular shape due to the angle of the floor.

The location of the fuel filler inlet, the fuel pick up, and the fuel gauge must also be considered.

I'm not looking to reinvent the wheel. I will appreciate advice from those that have gone before me.

[jimh]

Do you plan for a total of one battery, and that one battery will be the engine cranking battery?

If so, then my next question will be: what is the required CCA rating from Yamaha specifications to crank over the F70 engine?

[biggiefl]

I use a 275-CC lawn tractor battery for my Suzuki DF40. I also use a 3-gallon fuel tank; a 12-gallon fuel tank would last me several months

Q: why do you have two batteries for a 15-foot boat?
Q: why do you need 12-gallons of gasoline fuel?

If you do occasionally need 12-gallons of gasoline, then carry a 6-gallon Jerry Can with you and go down to a 6-gallon fuel tank.

[speedra421]

Re the battery: [the boat battery is currently used] to crank the engine, run a fishfinder, a GPS receiver, and [illuminate the navigation lanterns].

To be able to charge electronics like cellular telephones and bluetooth speaker from the [boat] battery would be nice, but only if there is a simple way to set this up.

I think only need one battery for such a small boat. The boat came with two batteries. I generally favor being extra cautious. I don't want to be in a situation where I can't start.

GIve me recommendations on [whether one battery or two batteries should be installed on a 15-foot open skiff boat].

From the Yamaha manual:

Minimum cold cranking amps (CCA/SAE):380.0 A
Minimum marine cranking amps (MCA/ABYC):502.0 A
Minimum reserve capacity (RC/SAE):124 minutes


Regarding the [fuel] tank, I agree that I do NOT routinely need 12-gallons routinely, and a smaller tank could work

Q: if the fuel tank turns out to be less than 12-gallon capacity, is moving the [less than 12-gallon capacity] fuel tank forward under front bench seat better [than not moving it]?

By my measurements, [a custom made fuel tank of dimension] 30 x 6.75 x 11-inches (as I am planning) will hold about 9 gallons. This involves custom fabrication; I was hoping [to avoid having a custom-made tank fabricated] IF someone already had a good solution for a ready made tank that I can install under the front bench seat.

[jimh]

I don't understand your explanation about the "single" battery, so I am assuming that you mean to convert to ONE battery under the helm console in the SUPER SPORT 15, and that ONE battery will be the only battery on the boat and will be used to crank-over the Yamaha F70, which needs a battery that can deliver 380 CCA.

Since you have not given any dimensions for the space, it will be impossible to know what battery case GROUP SIZE could fit. I recommend you measure the space available, and then look at the battery case GROUP SIZE listings to see what battery might fit that has a standard case group size.

Since I don't know the GROUP SIZE case that would fit the unknown space, about the only advice I can offer is very general advice. The most compact batteries in today's technology are no longer lead-acid batteries.. The Lithium-Ion battery technology delivers more power in a smaller volume and in a lighter weight than lead-acid battery technology. If no lead-acid technology battery will fit and meet the CCA required, you may have to go to a Lithium-Ion battery. The only drawback to Lithium-Ion technology is the cost; those batteries are about four to ten times more expensive than lead-acid batteries.

[speedra421]

Q; is there a company called ODYSSEY that makes smaller AGM lead acid batteries?

Q: what is the smallest lead acid battery group size that I can use?

The space dimensions are 23-wide, 9- deep, 6.5 to 8-inches high, depending on what side of the console I’m under. I don’t think width is a problem so height will be biggest [limitation]. If I can mount sideways that would help.

[jimh]

Q; is there a company called ODYSSEY that makes smaller AGM lead acid batteries?

There is a company that markets batteries under the name ODYSSEY. I don't know if they actually manufacture batteries.

I recommend you visit their website to see what GROUP SIZE cases they have available.

[jimh]

Q: what is the smallest lead acid battery group size that I can use?

I think you probably want the BIGGEST battery case group size that will fit, not the smallest.

As I mentioned already, take the space available and then go to a battery website that lists all the GROUP SIZE case dimensions. Then compare the dimensions you need to find which GROUP case sizes will fit. Then pick the biggest GROUP case size. Then look at batteries made in that GROUP case size and see if any meet the CCA required. I am not inclined to do all that research, as I don't have the problem you have. You need to do the research.

[jimh]

Q: if the fuel tank turns out to be less than 12-gallon capacity, is moving the [less than 12-gallon capacity] fuel tank forward under front bench seat better [than not moving it]?

To get a real answer, the center of the boat's fore-and-aft trim movement would have to be determined. Then you could calculate the effect of moving a certain amount of weight from the stern to be closer to the center of fore-and-aft trim movement, and you could perhaps predict how much movement would occur at the stern for the movement of a certain weight a certain distance.

You could approach this empirically by adding a significant weight, say 50-lbs, at the transom, and measuring how much lower the transom was immersed and how much higher the bow was raised. Then move the 50-lbs weight forward one foot, and measure the transom immersion and bow height. Repeat this until you find a point where the bow goes down and the transom goes up. Now you have moved the weight forward of the boat's fore-and-aft trim center of movement. Then you could predict how much effect moving a certain amount of weight to a new position from a starting position will have on the fore-and-aft trim on the boat.

If not really interested, then either move the tank forward or don't move it. You can always move it forward if you didn't and always move it back if you did.

If you are really interested, perform the experiment and post your measurements.

[jimh]

GIve me recommendations on [whether one battery or two batteries should be installed on a 15-foot open skiff boat].

I used to have a SPORT 15. The engine was a 50-HP, and it was electric starting. I had only one battery. The engine had an option to use pull-starting with a rope cord. My memory is a bit hazy, but I don't recall ever actually having to use the pull-start. I do remember one morning I went to start the boat and the battery was dead. The boat engine's permanent magnet alternator's rectifier had failed, and there was no charing current. I had come back from a long day of boating the day before with the engine running, but it was pulling all electrical power from the battery; the permanent magnet alternator was providing no current. The next day the battery was so low in charge it could not crank over the engine. I was lucky I never shut off the engine the day before on the long cruise. I could have been stranded 20-miles away from my dock. I was also lucky because that was the last day of a week vacation, and all I needed to do was haul out the boat.

The inference from my narrative: if the engine cannot be started without electrical start, you should keep the electrical system under close watch, keep the battery at full charge, and carry one of those little Lithium-Ion jumper packs to get the engine cranked over in case of a dead battery.

If the engine CAN be started without electrical start, ask yourself if the engine CAN run without a battery. Many of these modern four-stroke-power-cycle engines do NOT have a permanent magnet alternator and they will need a battery with some charge in it to provide the field current to their alternators to generate power to run the engine.

On my larger boat, I ALWAYS have two batteries because there is no way I could pull start the 225-HP engine.

If your engine CAN be pull-started and if your engine CAN run without a battery providing some current, then you can operate with one battery. If you cannot meet those criteria, then you need a PLAN-B in case your battery dies.

On my SPORT 15 we always carried a paddle with us, and sometimes we carried two paddles.