Engine Question ?

[Luna Sea 5]

When I bought my boat, I was thinking about how I wanted it powered.  I decided to max it out to the 350hp max for the boat.  I had to do that with twin 175's. 

Now that they make a single 350hp, I was wondering what the difference would be to have a single or twin engines with the same hp. 

I know the basic.  Single = better gas milage, twin = more power and control, but HOW ABOUT TOP SPEEP and anything else.

[CapBob]

Nick

You'll get better control with the twins as well as better fuel efficiency

[Luna Sea 5]

better fuel with the twins?.. didn't know that.. how about top speed

[mboy]

Single 350 will be faster then twin 175. Twin 175 is not true 350 horsepower. Forget the exact formula, but should be closer to 280-300hp (equivelant). A single 350 will be lighter then tin 175's and the drag of the engine will be less with a single prop/lu in the water then duals.

[Luna Sea 5]

That makes sense, but giving all the pro's and con's between the 2 scenarios, which would most people prefer.

[IrishAyes]

For ANY off shore trips, most guys prefer the safety of twins.  If one engine fails you can always limp in with the other.
I do MOST of my fishing within ten miles from the shore and personally prefer the less costly single engine.  Less maintenance, winterizing, etc.

[mboy]

Good article on twins vs single in the Yammie world:
http://www.trailerboats.com/output.cfm?id=1255843&sectionid=313

Sea tow is MUCH cheaper (as is a kicker) then dual engines.

P.S. single engine is usally more fuel efficient then duals. Forgot to add that in my Original post.

[Luna Sea 5]

Good article on twins vs single in the Yammie world:
http://www.trailerboats.com/output.cfm?id=1255843&sectionid=313

Sea tow is MUCH cheaper (as is a kicker) then dual engines.

P.S. single engine is usally more fuel efficient then duals. Forgot to add that in my Original post.

Capt. Bob stated above that the better fuel efficient set up is with the dual engines. 

[IrishAyes]

This is true.  But when you are 35 or more miles off shore and can't reach out to sea tow and only slightly making headway with your kicker, you will be kicking youself in the a$$ for not going with the twins.  If you are into some bad seas, the kicker won't be much of a help either.  And that longggggggggggg wait for seatow...
But then again, if you are going that far off, best to do the buddy system and pair up with another boat if possible.  

Still, as I said before, I only prefer a single engine for my needs.

[Capt. Mike]

Better fuel efficiency with a single!!!

Faster out of the hole with the twins!

Better control with the twins!

MORE MONEY WITH THE TWINS!

I Still perfer the twins for offshore and peace of mind.

2008 gas prices will say other wise!!!

[Luna Sea 5]

Mike, great find... good info on that website..  I guess nothing is guaranteed as the statement below states..

Performance-wise, our testing over the years has generally shown that if horsepower is the same, a larger single engine will be faster than two smaller engines because the single-engine boat is lighter and, with only one prop, it has less drag. This is not always the case, however. Fuel economy is another area where a large single sometimes fares better — but, again, not always.

I noticed on the size boat I have, I don't loose any top speed if I drive by myself or I have 2 others with me, the the minor difference in weight between the twins or the big single shouldn't mean much. Then with the fuel, to get to the same speed, one engine helps the other so neither are being overworked..  I guess everything is a matter of preference.

[Luna Sea 5]

This is a very interesting topic since most people in the boat market want to power there boat to preference.  What I noticed with a single and a twin is...  With a single engine, the weight of equipment and weight of 3 guys on the boat will alter the speed lower quite a bit.  With the double, I don't seen any difference in top speed with a full load or by myself..

[CapBob]

The single vs twin propeller/engine propulsion question has several interesting ways to be considered. Let's look at them:

--Twin propellers (and lower units) have more drag than a single. It takes more horsepower to drag two propellers along than one. Efficiency favors a single.

--The propellers on twin engines operate in less aerated water (because it is not coming off the keel or deepest part of the hull) and may be more efficient.

--The crankshaft speed of twin engines at cruise is normally much lower than a single engine. For example, consider a pair of 150-HP engines compared to a single 225-HP engine. At cruise the twins are probably going to running about 3,000-RPM. The same boat with a single 225-HP engine is going to be turning about 4,000 RPM. This is very significant.

A 150-HP engine turning 3000-RPM is operating right at its "sweet spot" for fuel efficiency, while a 225-HP engine running faster at 4,000-RPM is beyond the "sweet spot" and is not running at optimum fuel economy. This is where all the difference in fuel efficiency probably comes from.

If you take engines of similar technology and run them at the same engine speed, they should all be operating at about the same fuel efficiency. But when you compare them at different engine speeds, they get different fuel efficiency.

Engine mounting is also a factor, mounting an engine on the Transum as opposed to mounting on an engine bracket, also the hull design, weight of boat, rise of hull, trim-tab position, diamiter and pitch of the propeller all come into play...........

I can only give an example, I run a 225 Yamaha 2 stroke on a 24' Grady, my budy has two 115 hp 2 stroke Yami's on a 24' Grady.....he is getting better fuel effeciancy than me.....the only differance in our boats is that he has an engine platform and I an transum mounted

I have talked about this a lot with my Yammi mechanic, have called Grady and Parker Boats, all concer that the twins are more fuel efficent than the single on the type of boat inquired about 24 or 26' Grady, 25' Parker


Just my Humble opinion......as with anything everybody will have their point of view.

 I can only say that the "Donna Marie II" will be a 25' Parker or 26' Grady with Twin  115/150 4 Stroke Yammi's

[Luna Sea 5]

I can only give an example, I run a 225 Yamaha 2 stroke on a 24' Grady, my budy has two 115 hp 2 stroke Yami's on a 24' Grady.....he is getting better fuel effeciancy than me.....

which boat has a higher top end speed, the single 225 or the twin 115's.

[CapBob]

single, but not by much

[Luna Sea 5]

very interesting and very good topic...  especially for people who are in the market with the boats show here...  If you in the market of buying a boat, make sure you get the facts about everything before you commit with the $$$$ factor..

[CapBob]

 

[ped579]

In todays used market especially.  Let the buyer beware, if something seems to good to be true there probably is something amiss, and time to move on.

[Bob]

Don't forget to factor in maintenance.  You double the cost with two engines although some of the larger singles may cost more than one single but certainly not double.  You also have to assume if you hit something two props and lower units are involved.  Sea Tow or Tow Boat are a lot cheaper than a second engine if you are looking for security and they will tow you to your home port.  Just some additional thoughts for consideration.

Bob

[ped579]

  Good food for thought...