2 motors vs three
 

anybody got any idea about the fuel comsumption of three motors vs two?will the three motor boat use more gas all the time,vers a two motor boat with the same h/p rateings.a guy was trying to tell me that a 42-47 fountain will get better fuel comsumption w/three 502's vs the same boat w/twin 600's or 700's.any input?

Its possible. My 32 AT with twin 502mpi's get better mileage at cruise speeds than my single hopped up 525SC 28 Pantera did.

A hull design will take X amount of horesepower to power the boat forward at a given speed. Ideally that horsepower is devided between how many engines you have. But there is the increase amount of drag in the water from an additional drive an weight increase. Potentially 3 engines could deliver the needed horsepower lower in there RPM range at a point where they are more fuel efficient than the same boat with twins.

I like the idea of a 47'er having three 525's strictly for reliability sake if for no other.

If the 3rd engine can allow you to cruise under 3500 you will have a fuel saving

Fuel consumption is relative to how much horsepower you're making. There are conditions where you would use less TOTAL horsepower with the triples and get better fuel efficiency.

I love triple engine boats. I had a 40' Hustler w/3 502 Mag 415s.

There are other advantages to trips:

You can lose one engine and still get home on plane at a good speed. (I blew away Stu Jones when I ran most of a Poker Run on two engines)!

Instant planing. Never have that bow up situation that limits visibility until planing speed is met.

Boat flies level with the center engine so far forward.

The down-side is buying oil, filters, spark plugs and belts for three engines rather than two. Still worth it.

The downside is less efficiency. Running the output through two drivelines vs. 3 is an advantage. Plus the drag loss of the 3'rd drive and prop slip all have to be factored in. Plus, there's the fact that you're carrying around an additional 1,000 lbs (and that's conservative- allowing for additional hardware on the twins, like blowers.)

There are plusses & minuses- and mostly it's dependent on the individual boat. I think that a larger boat would be more forgiving of triples vs. a smaller one.

3vs2
 

so are you guys telling me you can use either 2 motors or three when running.i was under the impression that you have to use 3 motors all the time??

If you want to run on just two, you're going to have to jump in and yank the prop on that center drive.

You don't have to yank the center prop. Sure you could pull the prop to reduce drag but it is not necessary.

I have trip 496's and my boat it will plane on any combination of the two. I blew a drive on the port side halfway between Key West and Sanibel. I was actually on my way back to Tampa and continued on, but Sanibel was a fuel stop on the way back. I ran the port engine at idle and left it in neutral so the hydraulic steering worked properly. It is a little harder to get on plane but not a big issue and can still cruise about 40-45 on two. I have had trips for four years and find more positives than negatives to having them.

I remember my 38 with twins and when one went down, you better hope and pray you are not 40 miles from your destination as you are not going to get on plane.

I agree that maintenance costs are higher but since I do most of the maintenance myself, it is negligible.

I would definitely go trips on my next boat.

Are you tripp guys finding insurance OK?

My Hustler had a priority valve so I always had power assist as long as one of the rear engines was alive.

Ed,

That is something I need to check into. Who's steering system was on your boat?

Jason,

There was an increase when I went to trips vs twins even though there was not a big difference in speed. No problem getting insurance.

I had Mayfair which is now Marine Machine. The priority valve is an easy add-on as long as you have two belt-driven power steering pumps.

I wish I can test drive a triple someday, and really see the fuel consumption difference, apparently very little different... Still have a little doubt...

trips verses bigger twins? about the same from my last 2 boats.about the same hp about the same fuel useage but different octane cheaper, we spend most of the time in the 3000 to 3400 range now. what is this priority valve and who makes it, sounds like something i should add when the starboard pump goes out.

It's the $hit! You need power steering pumps on both engines both plummed to the priority valve and from the valve to the steering actuator. If one engine stops, the pressure comes from the running engine and you do not lose your power assist. I'm sure it's a MerCruiser part available from any MerCruiser parts house or from Latham. Jay Ross, when he was with Sonic, was the one who told me about it many years ago.

If I still had my Hustler I would invite you.

I once donated a day on a high performance boat for auction to the Wildlife Rescue down here. A guys wife bought it for him for his birthday. He still says it was one of the best birthday presents he ever received. I ran him, his wife and two of his friends from Port Everglades to Government Cut full blast. At first they were scared, but when they realized I wasn't going to kill them, they loved it.

Has anyone changed a 3 engine to use only the 2 and taken out the middle and plugging the transom?

Ed,

I have Latham steering and there is a "T"block that feeds the fluid from the two pumps for the steering. There is a definite difference in how the steering works without one of the motors running. I checked on Latham's site but did not see anything mentioned. I need one of these valves.

Keith

Call Mac at Doller Marine. (954) 463-9988 He has a good used valve or the complete kit new.

Thanks! I will call him Monday!

Another plus for 3 engines would be around the docks, at least compared to a staggered setup.