What is your Fuel Tank Size?

[Signal 20]

One of the things I have in the back of my head during my restoration project is what size tank I will put in the boat when the time comes. I have a 1981 Mercury 80hp Thunderbolt that will be going back on the boat eventually. What size tank are you running on your boat and how much use to you get out of it. I'm looking for something that will without a doubt let me run all day without a problem, however I also want the smallest tank possible as my boats only a 17ft center console. Just looking for some input

The only motor I have owned before this one was a 2008 9.9hp Yamaha that would run for 3 days on a 5 gallon tank so I'm looking for any help you can offer haha!!!

 

[j_martin]

Re: What is your Fuel Tank Size?

If yer driving somewhere and fishing, a 12 or 15 gallon tank. If yer going to sea and running WOT all day, you'll need 60 - 80 gallons.

In other words, there isn't anywhere near enough information in your post to figure it out.

It'll burn about 8 gallons per hour at WOT.

hope it helps
john

 

[Texasmark]

Re: What is your Fuel Tank Size?

I had a 17' Ranger with a 115 tower and a 10 gallon built in tank. Believe it or not I could play all day including the days water skiing was included in the agenda, on that 10 gallon tank. You did have to insure you had a full tank on the way to the water however.

Current 17' boat has the 3 cyl 90 and a 22 gallon tank. I usually use 5-6 gallons on an outing with this boat so I keep it at the 5-10 gallon level.

My usage is on inland lakes in an area of not more than 20,000 acres and I don't ski any more.

As Mr. Martin said, if you were considering off shore especially where you had a long run just to get to the open water, then a large tank would be necessary. Knowing your gph and usage habits helps a lot in making your decision.

I think the usage number people refer to (on this site) is like 10% of the hp of the engine rating at WOT. Obviously operating just above planing speed will significantly reduce the consumption for two reasons: Efficiency is much better there and you are not using your full engine rated hp. So, an 80 hp engine operated for a solid hour at WOT should consume about 8 gallons of fuel. But that same engine operated at say 25 mph when planing speed is roughly 20 would require say 40 hp so your consumption rate then may drop to 2.5-3 gph.

Mark

 

[j_martin]

Re: What is your Fuel Tank Size?

Don't count on a lot of gain in mileage by going slow in a boat. The faster you go, the less water friction there is, and the more air friction there is.

I find with my bass bote that will run WOT in the low 60's, that the most efficient fuel usage speed is about 50. Part of that is that it's set up to run 60 plus, so to run 30 I have to trim the nose down and plow a little or it'll hop like a frog.

Usually the best way to figure fuel usage is to figure the mileage you probably will run, and figure the fuel at WOT. You'll come out pretty close no matter what you do.

hope it helps
john

 

[BaDucK]

Re: What is your Fuel Tank Size?

i have a 16' starcraft and i am planning on something around the 30 gallon range......im running a '73 merc 850 so im looking at having about 4 hours at wot ...i usually just go out and play up and down the river....drown a few worms here and there, so in my case i think i am good for a "full days" use from a tank...

unless your going out into big water, or water skiing all day, how much are you actually at wide open throttle??

with my limited experience with small boats, i see a big difference in wot fuel usage vs cruising speed usage......

 

[BaDucK]

Re: What is your Fuel Tank Size?

Don't count on a lot of gain in mileage by going slow in a boat. The faster you go, the less water friction there is, and the more air friction there is.

I find with my bass bote that will run WOT in the low 60's, that the most efficient fuel usage speed is about 50. Part of that is that it's set up to run 60 plus, so to run 30 I have to trim the nose down and plow a little or it'll hop like a frog.

Usually the best way to figure fuel usage is to figure the mileage you probably will run, and figure the fuel at WOT. You'll come out pretty close no matter what you do.

hope it helps
john

im not sure i totally agree with you on that .....you neglected to factor in distance and time.......

if your just going in circles on a small lake, then wot will put alot of water under your butt, but youll be packing it in before the sunscreen is needed, same boat same water at cruising speeds, and you will be having lunch on the water......

same boat same water at displacement speed, and the wife is gonna be ticked you didnt come home until the next day.....

i guess my point is, if your sole purpose was to get on the water and run her until she is dry, you may actually get close to the same distance out of a tank of fuel, the difference would be how long it took you to do it....

but when you factor in grilling out, beaching with the buddies, sittin and fishin, pullin a tube, etc... theres more to effeciency then a strait chalked line in the sand of gallons per hour.....

lol, i have no idea where i meant to go with that, i hope my sometimes spacial reasoning and quantem outlooks dont confuse you guys as much as they do me sometimes

 

[trendsetter240]

Re: What is your Fuel Tank Size?

Don't count on a lot of gain in mileage by going slow in a boat. The faster you go, the less water friction there is, and the more air friction there is.

I find with my bass bote that will run WOT in the low 60's, that the most efficient fuel usage speed is about 50. Part of that is that it's set up to run 60 plus, so to run 30 I have to trim the nose down and plow a little or it'll hop like a frog.

Usually the best way to figure fuel usage is to figure the mileage you probably will run, and figure the fuel at WOT. You'll come out pretty close no matter what you do.

hope it helps
john

That is not correct. 99% of the time cruise speeds will have significantly better fuel economy compared to WOT. It will be different for every boat and motor combination. With your typical planing hull and a motor that is above 70% of the recommended capacity of that boat, you will achieve best fuel economy somewhere just above planing speed. (Not counting displacement speed fuel economy because nobody is going to run at idle 5 miles out to their fishing hole)

Also the best way to find out your ideal cruise speed on your particular boat is to get a fuel flow meter. Use the fuel flow meter to determine your ideal RPM based upon fuel flow, RPM and speed.

Cheers~!

 

[j_martin]

Re: What is your Fuel Tank Size?

If yer going point to point, it's rather amazing how little difference there'll be.

From the landing to my favorite spot in Voyagers National park used to take me an hour and 3/4, and 2 gallons of gas with the tinny and and a 10 horse.

With the bass bote and a XR4 mounted high and back, it takes about 14 minutes and 3 gallons.

And it's one heckofalot more fun.

john

 

[milehighboater]

Re: What is your Fuel Tank Size?

I have a 99 75hp 3cyl with a 20 gallon tank. This is normally enough for any of our colorado lakes. I make sure the tank is topped off if it is going to be a heavy driving day. For me though 20 gallons is enough to play all day, run around do some fishing and then get it back on the trailer. I wouldn't over analyze it. If you are inland a 20 gallon tank is enough.

 

[sschefer]

Re: What is your Fuel Tank Size?

On your boat at 17' a full 20 gal tank is just about the upper end of the limit for weight. Just follow the golden rule of 3's, use 1/3 to get you where your going so you have a 1/3 to get you back and 1/3 left over just to be safe.

 

[trendsetter240]

Re: What is your Fuel Tank Size?

If yer going point to point, it's rather amazing how little difference there'll be.

From the landing to my favorite spot in Voyagers National park used to take me an hour and 3/4, and 2 gallons of gas with the tinny and and a 10 horse.

With the bass bote and a XR4 mounted high and back, it takes about 14 minutes and 3 gallons.

And it's one heckofalot more fun.

john

True enough. Most of the time I have no concern for fuel and rip around at WOT. If I have a long run to make, 10 miles or more, then I start to think about it. On my boat, 4000RPM uses about 2/3 the gas of WOT (5700RPM). This means $$$ on a long trip. (even if it takes an extra half hour)

What I detailed above on fuel economy is fact and is based upon my experience and many test results I've read over the years. Check out evinrude.com, go to the motors section and click on performance reports. You will see dozens of engine test data reports. And like I said 99% of them will show best fuel economy just faster than planing speed.

Cheers~!

 

[j_martin]

Re: What is your Fuel Tank Size?

Well when I'm going WOT, I've got about a foot and a half of boat and about 2/3 of the propeller in the water. I can slow down to about 50 and keep the nose up. It rides real sweet there, and I'm sure uses less fuel per mile, but if I slow down much more, it'll porpoise and cut up, especially if I have some water in the fish's swimming pools so I have to pull the motor in and put the keel down in the water. Then it's using fuel to overcome drag.

It runs ok there. In fact, I take some real old timers fishing, and I sandbag the bow about 150 lbs just so I can run slow and smooth, and I can mush up onto plane without getting too excited and scaring the poor fellows. The XR4 don't really like it, though. It'd much rather truck donkeys.