fuel use comparson
 

Here is a scenario I'm sure has been beat to deth.two boats same day same water. 100 mile trip 3500 rpm.
Boat one. formula 271,502 completely stock
Boat two. donzi 28 ,twin 350 mag

App how much more fuel would boat 2 use?

The twin engine boat will be running much faster at 3500 than the single, 502 and 454 will burn very close to same amount of fuel. So approximately 80% more on twin? 502 is 415 hp the 454 mag is 385hp

wow almost double

I think he said the twin boat was running small blocks not 454 mags. But I agree that the twin will be cruising faster and you'll have alittle less strain on the motors.

I've heard that at wot a boat will burn 10 percent gph of the horsepower. So say a 502 mag 415 hp will burn 40 gph at wot and just say a solid 20 at 3500 rpm.

Now twin 350 mags are rated 320 hp? 350 hp? So say 65-70 gph wot for both motors and cruising like 28-30 gph. So 33 percent more ?


I could be wrong on my math any twin engine boat I've ever wrenched on or been on no one looks at the fuel consumption. Just chalk it up as a fun tax.

But you'll get there faster with the twins, I don't have twins but everyone loves them! Lol

Maybe someone more intelligent then myself will chime in.

You changed your story from 454 mags to 350's! ...Either way you would be surprised how little difference there will be in fuel burn. Sure the twin 454's will use a little more than the 502 per hour, but you will be going faster. I actually use less gas in a 30' boat with twin 425's than I burned in a single 24' boat with 575-600 HP. Not exactly the same scenario but you get the idea.

That being said, twins make life so much easier in so many other ways that I would not let that deter me if I was worried about cost. Gas and oil changes are the cheapest part of boating.

:drink:

-Artie

...However at WOT it will use DOUBLE the fuel. No way around that one! :evilb:

The difference will not be huge either way. Whats an extra $50 when you're spending around $300 on fuel.

$300 on fuel? Must be a rowboat. Lol. I have and love the twins and would never go single again. But with a 130 gallon tank $300 is only about half a tank. Lol. I don't have the exact figures yet as I haven't finished flo scan but best estimate so ft is somewhere around 1.5 mpg at cruise. Not horrible and not much different ten my old 20 sea ray with a single 350. Plus cruise for me is around 40. So your making better time anywhere you go.

His original post said 292 with 454 mags, then he changed it. And yes 80% more is nearly double

I was just trying to get some idea on how much a 27 with the 502 would burn compared to next step into small twins.the majority of ppl on here say they don't watch how much it cost them in gas so my question is on average how much does everyone burn in a weekend and what boat set up?

How much burnt in a weekend is too vague and varies greatly even from weekend to weekend. Mpg and Gph are what you need for comparison numbers. I have a 27 with twin 350s. She is very reasonable on fuel at cruise. I wouldn't go back to a single.

find some old boat tests of a 28zx and see what the actual numbers are, the burn will vary greatly depending on load and speed. I had an Eliminator 28 Daytona with twin 496 375HP motors. Wide open they burned 30 GPH each but I was going 90 so I got 1.5 mpg. At cruise they burned 16 GPH each (3500 rpm) and the boat was going 65 so I got 2 mpg, but if had a full load of fuel it would drop to 1.6 mpg at the same speed. Also with the cat it got the same fuel economy from 40 to 70.

With my new boat I spend about $5000 per year for 150 hrs of use, but its diesel and averages 2.5mpg.

If you are just wondering which will be cheaper to run the single engine boat without question but it isn't so much better that you should stay away from twins, if it is because the fuel cost will determine which you can afford then don't buy a boat because it will cost more than you think to own it.

With my old ride (33OL with 509`s) its pretty consistent fillup at $200-250 a weekend.

My apologies I did not see the original post, only the edited one.

Go for the twins, if fuel is that much of a deal breaker maybe a blow boat? Jk jk :daz:

+1....29 Outlaw, twin 454...pretty much 250 a weekend.....but on a weekend with a lot of running, or a trip to the lake, I'm gonna burn almost a tank (150 gallons). My buddy has a Baja 272 with a 502mpi. His fuel burn is less than mine for sure, but it is not half of mine...

Ya I guess my ??? Was to vague but I was just trying to get a feel for how ofter the guts that say don't worry about fuel cost actually use their boats and how much distance they travel. I would be on mine every weekend and most of the time my first tie up spot is 50 miles away. So I wasn't to concerned with an extra 50-100 on average to run twins. I just don't want to be dumping an extra 2-3 hundred a weekend. Thanks for all input

For the last 4 years we have been running an 01 28zx with the 350's and our friends have a baja 275 with a 502 we run the same places, the same speeds, side by side while we haven't pulled into the gas station at the same time to do a direct compare we have talked about this quite a bit. I would say that if he burns 15 gallons on a run i will burn 17-18. As i said we run side by side... there is a difference but not as much as you might think.

Best friend has a 28 donzi with 350 Mags. I had a 252 with a single 454mag. He burned BARLEY more gas then i did, but he also crused around faster as well.

Now with the 342, I burn more then him, 496mags, but I also cruse same speed as him, and have WAY more boat to stay one when we get there.

I'm torn on this subject. When I was looking to buy another boat this past fall I thought about going with a twin big block boat, but I run my boat every weekend and we don't pull up at the sand bar and sit all day. We will stop at 4-6 places on a regular day of boating. That being said, my last boat (Baja 235 force 468bbc) had a 62 gallon tank and I would burn at least 50 gallons on Saturday and 50 on Sunday.

My second dilemma is I always want to modify my engines and if I had two it would be double the cost on cash for builds and I'm sure fuel bill would suffer too. I knew I wanted a blower motor for my second boat. I ended up buying a 280 velocity and pulled the motor to build a 509 blower motor. From what I understand the velocity is pretty fast and efficient hull so I think the faster cruise speed will cut down on the fuel a bit. I just think if I had a twin blown bbc boat I would be hitting the gas station hard with as much as I run. My next boat will be a 35-38 lightning, so at some point I'm going to have to bite the bullet, but I figured I would stay single engine for another year or two.

My offshore fishing boat has a 150 gallon tank and we use 120 of it a day and its not fun spending almost 600 a day for fuel. If I had some buddies to split it with then it wouldn't be so bad, but I got into boats about 4 years ago and haven't had any of my friends show much interest so my wife and I do it alone so I'm stuck with the bill. 3-4 day fishing trips get expensive when you add up bait, tackle, hotel and diesel for the truck. When we got into speed boats two years ago I felt like I was saving money only having a 62 gallon tank and only being 20 minutes from the boat launch.

Saving money and speed boats in the same sentence....funny, but in my case its been true.

Fuel
 

+1 If you you are looking at getting into the performance boat world, fuel expense will the least of your worries!!! :daz:

The way I boat, I could get by with 50-75 bucks worth of fuel (20 gallons) for the weekend. boating Friday night after work, saturday, and sunday. but we do alot of sitting and partying and short runs to where we are going to be.

Now i have the Twin BB. and if you where running that kind of gas out in a single, your twins are going to EAT your wallet haha. but totally worth it.

Fuel use comparison: most V hull boats 20'-35' with a inboard outboard configuration get around 2 mpg. +/- 1/2 mpg. at 3000 rpm. with 1 or 2 engines. Average cruse ship uses about 200 gal. a nautical mile or about 50 feet a gal. If anyone is getting any different please reply with your boat info. (mpg. size boat and engine info.) Thanks.

There is so many other things to consider when it comes to the cost. especially when you consider weight of people in the boat, gas and speed of travel. I like to consider the other cost that so many look past. Like the fact that twin 350's can run bravo drives with no issue and a single 502 put a lot of stress on the drive with only one. In the end it's extremely cheap to maintain a 350 compared to a 502 when it comes to re-building motors drives and so on.

I personally burn about $250 a weekend with twin 502 and like many have said "What's $50 when spending $600 to fill a tank

Simple solution just get a single 575 and say screw it!

glad i dont spend 250 a weekend in fuel, I would not be able to afford this habbit.

100 -150 bucks will last me all weekend.

My current boat (27' Hallett) has twin Scorpions (377" small blocks) and is really easy on gas. I would say it uses no more and possibly less gas than the same boat would use with a single Big block. I usually cruise at 2600-3100 rpm and burn from 8.5-12 gph. I check it against the hobbs on every fill up.
My 35' Fountain that I used to have had twin 500efi's and it consistently used 22-25 gph. It was much heavier than the Hallett 270T.

We ran from Sturgeon Bay to Fayette Michigan on a day run (most expensive Subway sandwich ever, $455 footlong), I figure that's about 130 miles round trip. Ran a boring 3400rpm max up there to get a sense for fuel burn, used ~3/8ths tank and ran 4000+ the whole way home, the last 35+ miles around 4500rpm. I think we burned 115ish gallons total with the ride home being much faster. Twin 496HOs 26p merc 4 blades 31 Sonic

I try not to figure the costs, but average about $1000 month in season running all over green bay and around door county. Maybe winter isn't so bad:daz: save all winter, spend all summer. I don't run slow to save money, but would slow down to save gas to get to a pump, I run what feels good and that usually is 3800+

As others have said if fuel $ is a concern, it gets much worse the bigger the boat and engines. I also read here on OSO the most true thing about boats ever: It's not how fast you want to go, it's how fast you want to spend!

I know you're talking small blocks, but gives some reference for spend if you not focused only on fuel costs like me. I think I'd still spend almost $800 with small blocks because they'd be near redline everywhere:lolhit:

BTW, it was one of the most memorable days of the summer. I got to share one of the coolest places in reach by water with my wife and had weather that must have been a gift from above, priceless...

Hey deemo, nice to see someone on the forum that boats the same area as we do. If you see a white and yellow donzi on the water say hi!
Do you ever get to Menominee? Maybe I have seen your boat.

Mostly because I like to go full throttle everywhere and always have a few people on the boat. I also make a three day weekend out of it. In the general scope of things around this forum $250 is peanuts!

It may be irrational considering the cost of performance boating but I am also concerned with Fuel efficiency

If you were to prop the boat for top speed and only run that prop(s) then the twins would burn about 20% more fuel at cruise and 80% more at WOT.

If you run the 502 and have a cruise prop with more blades and maybe a little more pitch....then the fuel difference is much greater. The twins already have enough blade in the water so more blades don't have the same fuel saving results.

You could switch back to a top speed prop to get the last few MPH back when you know you will be at WOT.

At higher HP the BBC needs forced induction and the twins may not. fuel consumption is alot closer.

At the power level you mentioned...maybe consider a more efficient single engine (less weight and less cid than the 502). ILMOR 7.4 LS 580HP. less expensive than twins, less fuel consumption than a single 502, more RPM range to run only one prop all of the time, and faster than both.

If you want a fast boat but still want good mpg get a Eliminator 30 daytona and put a pair of 370hp Yanmars or 350hp Cummins, you will have a 90 mph or close to it boat that gets 4 mpg at 60 mph and close to 3mpg wide open. 1.36 drives and 32 or 34 pitch props should get you there. Doesn't have a huge cabin but there is plenty of room to sleep in there. You won't save any money but you will get great fuel economy!

I also make a weekend out of my 100-150 bucks.. and run a genny.

But most of out stuff is 10-20 miles from the doc, and then we dont move really. maybe one trip to dinner and back to our spot.

I have though about the diesel thing, the problem is the cost to get set-up is so much more... you can buy a lot of for the difference in price... IMO. Also they just don't sound the same!

Fuel use comparison
 

Hi,

Its different as I have an outboard. 25 feet Phantom. Before twin Merc 2.5 Efi SS engines 280 hp each. 24 gallon per hrs on 4,000 rpms plus 0,75 gallon oil running 47 mph Total cost Usd 325 per hour on cruise. Now a single Verado 350 sci. 10,4 gallon at 4,000 rpm and 49 mph. No oil. Total cost per hour Usd 102. Top speed twins 86-87 mph. Top speed single 81-82 mph :)

Good luck!

Cheers Toffen

Last year at D.S. I put 12 hours on my 30 foot Hallett with 525s with lots of idling in the channel and wot when out on the water and burned 220 gallons so it worked out to just about 10gal per hr per motor average but we all know what we burn when it is all wot, all of it! It also usually works out to about 1.3 mpg and my old 24 foot Carrera with a 400hp 454 averaged about 2 mpg.All of us know we can make the fuel last a while or we can burn it up depending on how we run. Speed costs money, how fast do you want to go!

Agreed mine are in line 6's so they really don't have anything special sound wise. The newer Yanmar and Cummins are both V-8's so maybe they sound slightly better but nothing like a gas motor.

I think the only way to make it work money wise is to buy a boat that has good 525's and sell them and use the money to by the diesels.

I am really happy with mine my boat is a heavy center console with a big hardtop and loaded up for a weekend in Bimini with 6 people all the crap we need and 200 gals of fuel I still get 2.2mpg out in the ocean going 40mph! By myself in the bay I get 2.5mpg going 40. At 50 I am still getting 2mpg, boat tops out at 55 with 26p bravos and 57 with 28p, going to try some 30p for fun but they are worse on mpg even though the top end and cruise speeds are better they just make the motors work harder.

By comparison if you look at a similar boat with a pair of 300 verados, they might get 1.4mpg lightly loaded but real world is closer to 1.1mpg and the top end will be 60-62, I can run at 50mph forever you would be pushing the outboards pretty hard to do the same. On the same boat diesels are about twice as efficient as gas motors.