Diesel vs Petrol engines?

[zaqzaq]

Hey all,
I'm looking at buying a large speedboat boat and have come across many types that interest me. As I'm new to boating can anybody help me out with the pros and cons of a diesel vs petrol motor?
Apart from the oblivious fuel economy I'm interested in maintenance costs, horse power, engine hours, engine life etc.
Comparison between something like the Volvo KADs vs the Mercury 454.
Also is there any method of knowing the minimum vs maximum horse power for a particular boat outside the original manufactured models as I'm looking at older boats (pre 2000) and may look at re powering it?

Also looking for info on drives Bravo 1, 2 & 3's. What to look for and avoid.

Thanks in advance,
Zaq.

 

[Texasmark]

Re: Diesel vs Petrol engines?

In heavy equipment, farm tractors, and big over the road trucks, where there is real work to be done, diesels are head and shoulders ahead, in lugging ability and fuel efficiency......owner of many large diesels over the years.

In a boat, diesel will stay a lot longer in the tank than gasoline without degrading usually.

Diesel is not the fire hazard that gasoline (petrol) is.

They are usually heavier and cost more.

Sometimes diesel is messy and if reasonable hygiene isn't maintained you can have some diesel fuel odor present that MAY be slightly undesirable.

Personally, I have less maintenance with a diesel than a gas engine. The newer gas engines with fuel injection and electronic ignitions help a lot, but still diesels have the upper hand; at least the ones I've had.

There are some high performance engines out there that can compete pretty well with gasoline in the weight performance arena.

That's my view on the subject.

Mark

 

[tazrig]

Re: Diesel vs Petrol engines?

Hey all,
I'm looking at buying a large speedboat boat and have come across many types that interest me. As I'm new to boating can anybody help me out with the pros and cons of a diesel vs petrol motor?
Apart from the oblivious fuel economy I'm interested in maintenance costs, horse power, engine hours, engine life etc.
Comparison between something like the Volvo KADs vs the Mercury 454.
Also is there any method of knowing the minimum vs maximum horse power for a particular boat outside the original manufactured models as I'm looking at older boats (pre 2000) and may look at re powering it?

Also looking for info on drives Bravo 1, 2 & 3's. What to look for and avoid.

Thanks in advance,
Zaq.

Zaq, Diesels are bigger, heavier duty, more durable and reliable than petrol engines by basic design. They are also much more expensive to buy and when they break they break big and are almost always more expensive to fix. Also diesels have way more torque at lower RPM's, are slower to accelerate and usually slower than there petrol counter parts. Diesels also require much less maintenance as they don't need the conventional tune ups that the petrol motors need. Usually people buy diesels because they get up into a certain size boat and a petrol engine just isn't powerful enough and can't push the boat at the desired speed or they are going to run and run and run and run the motor and need absolute reliability. For example if you're buying a pleasure boat that you're just going to use summers for relatively short trips and trade it in a few years a diesel probably wouldn't make sense because of cost. If you were powering a commercial boat and or planned to have it until the engines died than it would.

As far as the min and max horsepower a boat can take you would have to check with the manufacture as each boat (even ones of the same size) can vary widely. I currently have a 37 year old 23 foot boat that I am re-powering with twin 300 hp petrol engines. It is perfectly safe because the transom is extra beefy and in perfect shape. Putting those engines in another brand of the same vintage might tear the transom right off the boat.

As far as the bravo 1,2 and 3 drives go they are all purpose built and the only thing they all have in common is that they are heavier duty then the Alpha drives and have a cone clutch so they shift smoother than the Alpha's. For instance the Bravo 1 is built for speed, (can go over 100 mph.) and can handle up to a 600 hp. petrol engine. Bravo 2's are made for bigger cruisers can go up to 55 mph. and can handle petrol engines up to 450 hp. The Bravo 3 has 2 counter rotating props (like the Volvo Duoprop) can go up to 65 mph and can handle up to a 525 hp. petrol engine. You can find out more about them here:

MerCruiser | Mercury Marine

Mercury also makes diesel sterndrives:

Diesel | Mercury Marine

Another option for you might be the Yanmar diesel. They have just come out with their own sterndrive design with a hydraulic clutch and counter rotating props.

Yanmar Marine Diesel Engines for pleasure and commercial boating; sailing and powerboats - Yanmar Marine

 

[emilsr]

Re: Diesel vs Petrol engines?

The answer unfortunately is "it depends"...

What is your definition of a "large speedboat"? Where are you boating?

As for Bravo drives, the B1 is built for speed, the B2 is built for large, heavy slower boats, and the BIII is twin prop; good for accelleration but runs into a wall at higher speeds. None of them will handle the higher power engines available today. The venerable 454 is on the low end of big block power (300-385hp); that's about half what is available "off the shelf" without power adders.

 

[Frank Acampora]

Re: Diesel vs Petrol engines?

A while back one of the big boating magazines did a comparison of gasoline versus diesel power in boats from about 28-40 feeet.. Gasoline was cheaper to install and repair, and when time came to replace, it was cheaper to replace. Diesel engines lasted on average longer but were much more expensive to install, repair, or replace. Diesels get better fuel economy but the fuel costs more.

Their conclusion was that if you intend to keep the boat for a long time it doeasn't matter which power you choose: Ultimate cost will average about the same.

 

[zaqzaq]

Re: Diesel vs Petrol engines?

Guys, A huge thanks, great info for me.
To answer a few queries,
The boat I'm looking at is something along the line of a Formula 31, or Sea Ray 380SS. If I go ahead I will be operating it in the Middle East. Hot temperatures and in Sea Water.
Top Seed is not really what Im looking for. Just cruising about at 25 - 30 MpH would do fine!
Alos is it practical to keep such a boat out of the water on a trailer? I had a 20 ft boat in the past and had no bother dropping her in and out but I'm not sure about a much larger boat. 2 reasons for this is the mooring is very expensive and the sea water here is very salty and corrosive?

 

[tazrig]

Re: Diesel vs Petrol engines?

Guys, A huge thanks, great info for me.
To answer a few queries,
The boat I'm looking at is something along the line of a Formula 31, or Sea Ray 380SS. If I go ahead I will be operating it in the Middle East. Hot temperatures and in Sea Water.
Top Seed is not really what Im looking for. Just cruising about at 25 - 30 MpH would do fine!
Alos is it practical to keep such a boat out of the water on a trailer? I had a 20 ft boat in the past and had no bother dropping her in and out but I'm not sure about a much larger boat. 2 reasons for this is the mooring is very expensive and the sea water here is very salty and corrosive?

It would depend on several things. Which boat you ended up with for instance. A 31' cruiser you might be able to handle yourself getting it onto a trailer but it would be a bear. (and really hard in any kind of wind) You would also need a whole different class of trailer than you're used to (big and expensive) and a fairly beefy truck to tow it. Also when you get into that size or bigger there may be legal considerations. Here in MA for example you need a special permit and drivers license to tow anything with a beam 10' feet or wider. How tall is the boat on the trailer? will you need to stop at every drooping power line and have someone with a wooden 2X4 lifting them up and over the boat etc. etc.? With warm salty water you will need to have a "full" closed cooling system to prevent corrosion and flush the motors for at least 10 minutes (at running temperature) with fresh water if you do trailer it because even with a "full" closed cooling system there are still parts of the motor that will be exposed to salt such as exhaust elbows and oil and power steering coolers. You might even want to think about installing something like this for each engine to help combat the salt:


http://www.marinepartsexpress.com/prodbull/NS_engine_flushing_kit.pdf