Big single vs twin engines fuel consumption comparison

[daddystoy]

This has probably been discussed before but I thought I would ask again.
What do you guys think the fuel consumption comparison would be say between a single 300 hp outboard and twin 150's
Would it be significantly different in favour one way or the other or not?
I get all the pros and cons of twins versus single engines. Just wondering about fuel.

 

[GGF]

In theory I think they would be very close. This chart would appear to bear that out:
https://www.boat-fuel-economy.com/yamaha-outboard-fuel-consumption-liters
with the twins burning a little more.

 

[fishin solo]

Pretty close but twice the maintenance owning twins.....

 

[Aces]

And twice the lift plus you double your handling accuracy

 

[Foxsea]

In the old days, when marine engines were much less reliable, twins made sense, even on a smaller boat. These days a single, as Fishin Solo says, makes great economic sense. Okay, at the dock twins are great but after you learn to run the boat a single works just fine, especially a duo-prop and overall costs substantially less to operate.

 

[trophywife]

i love burning 6.5gph at 25kts...
same set set up on a neighbours boats with twin 150's and add 3.5 gph

 

[daddystoy]

That is the sort of comparison I was looking for Trophy wife. That is a significant difference.

 

[macro]

Lifetimer has some interesting comparisons on their boats. Sometimes a larger motor will yield better fuel efficiency.

 

[seabeyond]

Really depends on the hull and where the boat will spend its tim. The aluminums we run on wcvi do much better with twins. Fuel burn is very similar between the motors. Seems to be better when the weather is snotty with the two screws down there than with a single. If your a yamaha guy, tandem 150s have a much better track record than the single 300 for longevity. My 2 cents anyhow.

 

[Sir Reel]

A Yamaha 300HP weighs 558 pounds and Twin 150hp weigh 485 pounds each. That's an extra 412 pounds hanging right off the back of your boat.
Even if you add a kicker your still 300 pounds less with a single 300hp
Its going to affect fuel consumption, performance, and trim
Went through this for a Campion 682. We figured 20 to 30% higher fuel burn and twice the maintenance plus higher initial cost for 2 engines and installation

 

[sly_karma]

Lifetimer has some interesting comparisons on their boats. Sometimes a larger motor will yield better fuel efficiency.

Is it safe to assume this is data from different motor configurations mounted on identical hulls? If so, it shows the 150 is underpowered and lugging whereas the 225 is breathing easy at cruise. Makes sense. It also shows that the twin setups are delivering the same fuel burn and speed results as their single counterpart.

 

[ericl]

Would it be significantly different in favour one way or the other or not?

Define significant.
If cost is the main concern, you should get another hobby IMO. Right now engines are priced pretty close to dollars/HP. With twins you will pay a premium but outside maint this gets payed once. Let's say it then gets down to fuel burn. I go fishing to catch fish & to not have to screw around with equipment while doing so. In my experience, mainly DR trolling WCVI kickers such as best - having to start-up & use the main for course changes when going into the wind, etc. So I burn an extra 2-3 GPH with twins, thats what $20 day? Lately my boat has been down, so I go guided. Spending $1K per day has put a new perspective on fishing; unless you don't have the money in the first place (in which case you don't fish or own a small boat & don't have the option for kickers/twins) like I used to, then safety & enjoyment become a higher priority (at least for me at 70 Y/O).

 

[uclueletcharters]

On cruise it will be pretty close when comparing a V6 300 to twin 150 I4's fuel burn wise . Performance wise the sheets don't give you the feedback you get from the boat when you run it. If you have a boat with twins and you drop to a big single it's not a straight across feeling when operating, feels like a loss of power and control in comparison. On the other end maintenance wise it's cheaper and so is re powering with a single.

 

[daddystoy]

Significant... say 30 percent or more.
This is just a question for curiosity sake.
No real simple answer unless you can compare like boats with the different power packages.

 

[Sharphooks]

I’m thinking hull design, boat weight and propeller application (three blade? Four blade? Pitched for speed? Pitched for cruise?) play a huge part in this discussion. I just transitioned from a 24 foot boat (Skagit Orca) with a Suzuki DF300 single engine to a 26 foot Seasport hung with twin DF200’s. All my previous boats were singles—-this is my first boat with twins.

The lean-burn Suzuki’s are very fuel efficient but I was leaning forward in my chair to see how the fuel burn of my Seasport (10,000 lbs) with twins would compare with the Orca (9,000 lbs) with the single.

This chart was taken from the Seasport brochure for the 26 foot Kodiak. The performance numbers were generated from my boat ( it was a SEasport demo boat before I purchased it) and I have since more or less duplicated those numbers running it myself (up to 4,000 RPMS; once I get more comfortable with the servo-motor actuated ZipWake tabs I might flirt with WOT but I haven’t done that yet)



So, I can say anecdotally that these performance numbers are VERY similar to the fuel burn I saw when running my Skagit Orca with the big single. The difference: with twins, the Seasport gets more speed at lower RPM for same fuel burn. (Really)

However......Most of my Orca experience was with a HUGE 4-blade (16” PowerTech) It was a great prop for cruise but the weight of that prop was significant. It was normal to run 3,700 at approx. 18 MPH with fuel burn at 10 GPH. Compare that to 3,500 RPM in the Seasport with twins—the same 10 GPH, but a bit higher speed...


I should add, though—most of my fuel burn numbers with the Orca were when I was running very heavy—-multiple coolers of salt ice, 600 liters of gas, supplies for a 3 week trip. And speaking of propellers: I hit a rock in Shearwater last summer and punched the PowerTech in the nose. I took it off and replaced it with a Suzuki 16x18.5” spare. The first thing I noticed with the 3 blade ——approx. 8- - 10% better fuel economy! I was floored at the difference between a 3 blade and a 4 blade

So it’s not an exact science comparing singles to twins. I only bought a boat with twins because it is almost impossible to find 25 foot + boats with singles these days, at least in my neighborhood. I lurked for a year looking for the right boat; all I saw were twins, twins, and more twins. The closest I came to finding the right boat was a 27 foot Skagit Orca up in Prince George last October ....but...... it had a Yamaha F350 on it—-that was a deal breaker for me

If I’d decided to build a boat and hang a duo prop DF350 on it (which was my original plan) the wait time would have been 6 months to a year

So I grabbed a boat with twins because it was available and I didn’t want to wait. So far, with those fuel burn numbers, I’m happy I stuck with the Suzuki brand when going to twins, though I’ll admit, the 2.3 MPG mentioned in conjunction with the 4,000 RPM has been elusive for me.

Best I’ve done is 2.2 , though I’m running with approx. 40% more fuel in the tank then there was when this performance sheet was generated

 

[NDT]

Equal comparison of Yamaha 300 single vs twin 150 on same hull.

 

[daddystoy]

I'm glad you replied sharphooks. I started the thread with you in mind after reading about your new boat with the twin power compared to your previous boat.

 

[daddystoy]

I should also add I started the thread because I saw a 255 Monaro for sale on their website that has twin 150's and was just throwing it out there about fuel comparisons.

 

[ericl]

Significant... say 30 percent or more.
This is just a question for curiosity sake.
No real simple answer unless you can compare like boats with the different power packages.

Thanks for the answer.
Many boat & O/B mfgrs have "prop test info on their web sites. Most boat mfgrs bundle with Yamaha power, so info on Yamaha is the most widely available. I just repowered with twin 300 G2 ETEC's. The shop owner had twin 250's on his 28' well craft as a free promotional deal where he had to sell them every year. This deal ended when BRP stopped making OB's & he replaced them with twin 300 Yamaha. Dropped 5mph in top end & suffered a 20% drop in fuel consumption. I am going to venture that loss go torque (2 stroke versus 4 stroke) on a heavy boat is at play here, so a motor with larger displacement & longer piston stroke would win here (not all 150hp engines have equal power curves & good luck trying to get this info UNLESS it make that mfgr look better than the rest.
I have a 33' chriscraft that probably weighs 13000#, and before the OB's I was leaning towards twin diesels. I spent a lot of time using the prop calculator on www.boatdiesel.com where you can model boat speed/mpg/etc. The biggest factor is weight, followed by hull design (deep/shallow V). achieving the same HP with twins versus a single didn't matter a lot; more like 5%. If you run in rough water, having twin props will result in less RPM drop than a single prop, so economy with twins might be better. If you are considering a boat with around 300 HP which SHOULD be at least 25' long, twins with an autopilot & trolling on 1 (or 2) would be IMO the absolute best combo. My chris hits 40MPH & idles at 3 MPH in dead calm water on 2 engines; 7 MPG at 8mph on twins. Furuno makes auto pilots with a handheld remote & Sabiki mode (keeps you headed into the seas when in reverse still fishing).

 

[Rain City]

Thanks for the answer.
Many boat & O/B mfgrs have "prop test info on their web sites. Most boat mfgrs bundle with Yamaha power, so info on Yamaha is the most widely available. I just repowered with twin 300 G2 ETEC's. The shop owner had twin 250's on his 28' well craft as a free promotional deal where he had to sell them every year. This deal ended when BRP stopped making OB's & he replaced them with twin 300 Yamaha. Dropped 5mph in top end & suffered a 20% drop in fuel consumption. I am going to venture that loss go torque (2 stroke versus 4 stroke) on a heavy boat is at play here, so a motor with larger displacement & longer piston stroke would win here (not all 150hp engines have equal power curves & good luck trying to get this info UNLESS it make that mfgr look better than the rest.
I have a 33' chriscraft that probably weighs 13000#, and before the OB's I was leaning towards twin diesels. I spent a lot of time using the prop calculator on www.boatdiesel.com where you can model boat speed/mpg/etc. The biggest factor is weight, followed by hull design (deep/shallow V). achieving the same HP with twins versus a single didn't matter a lot; more like 5%. If you run in rough water, having twin props will result in less RPM drop than a single prop, so economy with twins might be better. If you are considering a boat with around 300 HP which SHOULD be at least 25' long, twins with an autopilot & trolling on 1 (or 2) would be IMO the absolute best combo. My chris hits 40MPH & idles at 3 MPH in dead calm water on 2 engines; 7 MPG at 8mph on twins. Furuno makes auto pilots with a handheld remote & Sabiki mode (keeps you headed into the seas when in reverse still fishing).

Is that a planing hull? What's your top speed and burn?