Fuel consumption and tank size questions

[F470]

I recently purchased a Zodiac FC-470 and I am new to boats. In general terms, what kind of fuel consumption can I expect from a 2-stroke versus a 4-stroke? Also what tank size in usually recommended? I am trying to decide between a 6 gallon tank and an 18 gallon tank and i would like to know advantages and disadvantages of each.

[Nos4r2]

There's a lot of variables there.

What size motor? What AGE motor?

[9D280]

Other thing to be very aware of when reading replies - Nautical vs Statute miles and UK vs US Gallons. (At least Litres & KM are such a different name it's obvious the numbers are different!)


To expand on Nos' question -

2/4 stroke is one thing, but how you use the engine will give a much varied consumption for any pair of engines you might be comparing.

For example - if you blast out for 10 mins, drop an anchor and spend the day fishing, you'll use next to nothing. and you could use a 1958 engine with planet destroying emmissions and still see no perceptible difference in consumption.

Next stage - you blast out to your favourte bay & start trolling. That is where the difference between 2 & 4 stroke will be most obvious. Old engines throw way too much fuel in at low RPM - it;s the nature of the beast. (Also don't forget that new DI 2- strokes are up there with the 4- strokes in the consumption world at low RPM)

If you head out & spend the day razzing up & down at wide open throttle, the 2/4 difference will be negligible. Yes, there wil lbe a small difference, but real world unless you are out all day every day I doubt it will make a big difference to the dent in your wallet.



Now, you have a Zodiac 470. I guess thatls 4.7m long, so on a par with mine. If you do a search for "fuel consumption", you'll find on a rolling average most ribs will do about 1L/mile. Mine clocks 0.83L/ Nautical mile on a 20/22Knot cruise, bizarrely regardless of sea state. I did one trip down a canal (Falkirk Wheel 10th Anniversary - I was the only RIb at the event!) - 14 miles at 4 (statute)mph and I was chiselling the soot off the plugs when I got home. 2 L/nautical mile recorded.

If nothing else it's a snapshot to show that a premix 2-stroke of 60s design is actually more efficient at speed & Illustrates Nos' point!

[ssobol]

I have a Zodiac 470 Pro II with a Yamaha 40 4 stroke. I have gotten ~10mpg with 2 adults on smooth water at about 18mph (~3600-4000rpm). My 6 gallon tank will give 60 miles range which is plenty for us. (Yes, I was surprised by that, 30 miles down river and 30 miles back.)

I usually take a 6 gallon main tank and a 3 gallon reserve when we go out. In the way we use the boat I have never had to use the reserve for that purpose. (I occasionally use the reserve tank to burn off the older gas.)

Having an 18 gallon tank would take up a fair amount of space. Also a full 18 gallon (US) tank will weigh about 115 pounds (just for the gas). This can be hard to move around.

[captnjack]

FYI you can get 3, 9 and 12 (US) gallon tanks too.

[F470]

Thanks everyone. Very helpful. I'm a European living in the US so yes I'm very familiar with the difference between gallons, miles, etc.

I'm planning a trip this year with a fully loaded boat (4-6 people plus gear) and I want to make sure I don't run out of gas.

I'm planning on getting the Zodiac Milpro fuel bladders. Does anyone have experience with them? I is possible to get two 6 gallon bladders and connect them so that they can be used individually? It seems that would be a better way to go over the really large 18 gallon bow bladder. I'm concerned about storing that much fuel in one place.

I haven't purchased an engine yet but I have access to a 10 HP 4-stroke Evinrude engine until I figure out my needs and preferences. In the spirit of keeping the boat original I am also looking at a 2-stroke 35hp Johnson Durajet engine but the only concern I have there is the emissions of the 2-stroke.

[Maximus]

Four to SIX!?? People.. +Pluss Thier Gear+ Pluss On deck Fuel Bladders!?
Not wishing to Pour Cold Water on your Plans but seems like ALOT of Loading for a Zodiac of that Size!!..Mine seldom went out with more than 3..and then was'nt exactly ''Spacious''.
Anywhere Near That!....I'd make sure it was Plenty Flaaat

[F470]

Probably 3-4 people with gear and make two trips to/from the destination then ( = more gas needed).

[captnjack]

As far as I can tell you can't find gasoline fuel bladders in this country. Only diesel ones and they are stupid expensive. I don't think the gas ones are approved fuel containers here. 18 gal is a shiit-load of fuel for a 10hp. Heck its 3x+ as much as most 35hp 2 strokes might carry around.

You mention all the people, but no mention of how far this trip might be...

[F470]

I will check with the inflatable boat store on this. To my knowledge MilPro gas bladders of various sizes are available from Zodiac.

I need to plot out the trip on a map or software. Does anyone have a recommendation for how to do this? is there an app for that?

Originally Posted by captnjack

As far as I can tell you can't find gasoline fuel bladders in this country. Only diesel ones and they are stupid expensive. I don't think the gas ones are approved fuel containers here. 18 gal is a shiit-load of fuel for a 10hp. Heck its 3x+ as much as most 35hp 2 strokes might carry around.

You mention all the people, but no mention of how far this trip might be...

[willk]

Originally Posted by F470

I need to plot out the trip on a map or software. Does anyone have a recommendation for how to do this? is there an app for that?

For quickly planning gas usage, Google Earth is as good as the next. Navionics app for iPad is good for actual navigation planning (Google doesn't know where the rocks and shallow bits are...)

[captnjack]

Originally Posted by F470

I will check with the inflatable boat store on this. To my knowledge MilPro gas bladders of various sizes are available from Zodiac.

Never seen one in this country. Its my understanding that they are neither USCG nor DOT approved for gasoline which is probably why they aren't imported despite being in the Zodiac catalog. The diesel ones are made by Vetus I think, they are available from West Marine and other vendors.

18 gallons is still rediculous. I can get 2+ typical trips out of my 12 gallon tank with a Yam F60 and a whole lotta scuba gear.

Have you been boating before? In an inflatable or otherwise?

[simsy]

Miles? What's the differene?

General rule of thumb for fuel usage on any petrol engine..... 10% of your horse power x us gallons an hour

E.g. 100 hp engine will burn 37 litres an hour.... At full power....


Very general, but often correct.....

[jyasaki]

This discussion is kind of odd.

OP has a trip planned (though no solid evidence of knowledge of distance or conditions), in a boat with insufficient space for pax+cargo, with no idea of how the boat performs in terms of handling or comsumables, and no engine to do tests on (or prior knowledge of the setup.)

Kind of sounds like a recipe for disaster.

My suggestion would be to obtain a motor, and get some experience on the water while amassing performance data so you at least have an idea of what might happen.

Then take 1/3 to 1/2 of expected fuel needed as a reserve, along with the more consumable (and easily replaceable) parts, just in case.

jky

[F470]

I have kayaked to this particular destination for several years. I am planning a trip 4 months from now and the fall back plan is to kayak there if this plan is deemed unsafe or unreasonable closer to the target date. The boat is currently being serviced and I plan to do several test runs before the trip. As I said before I do have an engine that I will install and test as soon as the boat is back from service.

I was under the assumption that a boat rated for 10 people/2,205 lbs would at least be able to carry 4 persons and some gear. Compared to a kayak its pretty damn roomy if you ask me.

The destination is a 7 nautical mile round trip with around 7-10 miles added to that if we choose to explore the area.

[F470]

The discussion may be odd but the original question is not. I just wanted to know if there were some general guidelines in terms of fuel consumption which would drive the need for tank size. I wasn't aware that I had to present "solid evidence" in order to get this question answered.

Originally Posted by jyasaki

This discussion is kind of odd.

[Nos4r2]

Originally Posted by F470

The discussion may be odd but the original question is not. I just wanted to know if there were some general guidelines in terms of fuel consumption which would drive the need for tank size. I wasn't aware that I had to present "solid evidence" in order to get this question answered.

It'd help if

A) You had a motor to calculate gas usage for

B) You could say roughly how many hours/how far you'll be travelling on a regular basis.

The question is impossible to answer otherwise.

<edit> Just saw the 7-10 miles figure. I'd carry a pair of 5 gallon or 6 US gallon tanks.

[captnjack]

Originally Posted by F470

I was under the assumption that a boat rated for 10 people/2,205 lbs would at least be able to carry 4 persons and some gear. Compared to a kayak its pretty damn roomy if you ask me.

The destination is a 7 nautical mile round trip with around 7-10 miles added to that if we choose to explore the area.

The boat will be fine. I'd carry 3 or 4 divers (with tanks and weight belts etc) so at least as much as you'll have. You might have a "2200 lb" capacity but you'll never plane that kind of load. If you're not planing your consumption will be stupidly high. And if the water gets a little rough you run the risk of swamping the boat, which won't sink it but you won't be moving much like that.

The 10hp will struggle to plane this much. Minimum 25hp or the 35hp you mentioned before is pretty much a requirement. For ~25miles of total travel, I would carry 6+3 gallons of fuel to have ample reserves. 18 gallons is just more fuel weight that you don't need.

[jyasaki]

Originally Posted by F470

I have kayaked to this particular destination for several years. I am planning a trip 4 months from now and the fall back plan is to kayak there if this plan is deemed unsafe or unreasonable closer to the target date. The boat is currently being serviced and I plan to do several test runs before the trip. As I said before I do have an engine that I will install and test as soon as the boat is back from service.

Well, that sounds more hopeful. Still, plan on what you're going to do if things don't go the way you plan.

I was under the assumption that a boat rated for 10 people/2,205 lbs would at least be able to carry 4 persons and some gear.

The 10 person thing is for weight only. While you *may* be able to get 10 people sitting somewhat safely on the boat, you 1) will find it's pretty damn tight and uncomfortable, and b) won't go anywhere quickly. Bottom line: the boat will float safely with that number of people, but I certainly wouldn't call it "usable" in that state.

The destination is a 7 nautical mile round trip with around 7-10 miles added to that if we choose to explore the area.

14 miles, plus sightseeing fuel. Shouldn't be an issue. A 6 gallon tank should do the entire thing, even if you go a little nuts on sightseeing. You should think about carrying a small (2-3 gallon) backup tank of fuel in case you get water or dirt or something that renders the main tank unusable.

The reason for details is that, much like cars, the boat and motor have a lot to do with what your burn rate is going to be. 4mpg is about "normal, but it may be higher or lower depending on a lot of factors, and that discounts weather and swell, which will affect it to some degree as well. Hence the need to take your combination out and see what kind of performance you get before you take off into the sticks.

How remote is the destination? Other boats around? Other land based stuff? Make sure you can contact someone in case of problems (VHF, cell phone.)

7 miles is a long way to row.

jky