Engines: 2 x 4.3GXi or 1 x 5.7Gxi

saaristo

Petty Officer 3rd Class
Joined
Sep 22, 2017
Messages
80
Looking for a new boat and the same boat is available either with two engines (4.3 GXi) or 1 engine 5.7Gxi. Everything else is exactly the same.
So what do you think - a 29 ft boat that weighs 8500 lbs - what would be the fuel consumption difference between those two in cruise, who would be the winner here?
Is it reasonable to expect that the one with two engines will be faster to plane and plane speed will be lower than on single engine?
Is it true that while the single engine will be doing say 4000 rpm the two smaller engines would be doing maybe 3500 at same speed?
 

alldodge

Supreme Mariner
Joined
Mar 8, 2009
Messages
31,869
IMO the single 5.7 will not preform very well, get the twin. If offered I would get twin 5.7's. The single 5.7 will be giving everything it has to keep it going. The twins will be running easier

My single 10K lb with 7.4 boat had a hard time getting on plane with just 2 people. Formula only made the model one year with that option, no one like it. All others had twin 5.7 motors. I installed a 415hp 502 and it helped, but wasn't until I repowered with a 530hp 502 that now it does pretty good.
 

BRICH1260

Lieutenant Junior Grade
Joined
Jul 6, 2011
Messages
1,122
The twin engines will give you better maneuverability around the dock. But you will have twice the maintenance and winterization expenses.
 

larson260

Seaman Apprentice
Joined
Dec 31, 2012
Messages
49
I have a four winns V-275 which has a hull lenght of 25'7" and weights in at 7,800 empty. Its powered with a Volvo 320 (5.7) with a bow thruster. The boat performs well and burns 7.9 gal per hr. average since 2015 new. I would not recommend going past these specs with the 5.7. A 29 ft. at 8500 is just over what you need for the 5.7. Personally I would look into twin V6-DPS or V8-DPS. You say this is a new boat. I did'nt know that Volvo is still offering the 4.3 or 5.7 g.x.i. With the twins you should expect around 25 gal.per.hr. on a 29' hull.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
34,063
Looking for a new boat and the same boat is available either with two engines (4.3 GXi) or 1 engine 5.7Gxi. Everything else is exactly the same.
So what do you think - a 29 ft boat that weighs 8500 lbs - what would be the fuel consumption difference between those two in cruise, who would be the winner here?
Is it reasonable to expect that the one with two engines will be faster to plane and plane speed will be lower than on single engine?
Is it true that while the single engine will be doing say 4000 rpm the two smaller engines would be doing maybe 3500 at same speed?
fuel consumption at cruise will be identical....... the maxed out 5.7 will burn the same fuel as two partially loaded 4.3's however getting out of the hole to get up to plane you will need the twin 4.3's

fuel consumption is 0.4# of fuel per hp per hour

speed is dependent on hull design, wind speed, wave height, load, drive trim, trim tabs, and how you place the throttle.......engine RPM is dependent on load, gearing and prop pitch. no way to know if the 5.7 would be spinning 4000 RPM or 5000 RPM or what the 4.3's would be doing.
 

Lou C

Admiral
Joined
Nov 10, 2002
Messages
7,103
A boat that large should have a big block but twin 5.7s would be a good package. The 4.3s max out at about 225 hp depending on how they are set up, while the 5.7s are not that much more powerful but have more torque.
 

H20Rat

Vice Admiral
Joined
Mar 8, 2009
Messages
5,053
Fuel consumption has very little to do with the engines. It will always take X amount of horsepower to push a boat at Y speed. Fuel to horsepower is relatively constant, and it doesn't matter much how you get that horsepower.

In other words, it is going to require say 200 horsepower to maintain cruise, and 200hp requires .4 lb of fuel. That might be .4 from one engine, or .1 from 4 engines.
 
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