Diesel Vs Gas Engines

[tkeithlu]

I see your point. Strange, because trouble shooting a diesel that doesn't start is much easier than trouble shooting a gas engine: 1. is it getting clean fuel without air mixed in?, and 2: is it getting air? No electrical problems, the very frequent reason for a gas engine to fail. My wife amazed me recently - the engine started to lose RPM and she immediately, with no mechanical background, said "fuel starvation," and she was right - a clogged primary filter from sludge in the bottom of the tanks getting stirred up in a storm.

[jeremiason]

Originally Posted by mikeling

With all the good things I hear about diesel engines, why are most Cruisers build with Gas engines ?

We are pretty much done with sailing and will convert to a Cruising Powerboat when the sailboat sells. I guess in SW Florida it becomes inevitable to own a power boat :-D

We plan on doing the Circle Loop and so gas mileage will be a consideration.

Also since we will be on the ICW and some of the canals, I believe the boat should be no bigger than 35-37 feet.

So far we have looked at a number of power boats and found that there are very few Power Boats under 40 feet with with diesel engines. When you do find diesels, the POwerboats are priced much higher (20-30%) more than gas Powerboats.

Gas Engines also have other problems besides worse gas mileage.

Gas engines don't like salt water... Around here owners of Mercruiser Engines are replacing their Exhaust Risers every 4-5 years (About $4000 each engine). Also if you get an I/O Drive, you will need to replace seals more often and again fight rust.

An option to this is looking at the new Power Cruising Boats with Out Board Engines.... The outboards are more fuel efficient and last longer than inboard gas engines.

There are several brands making boats over 30 feet with outboards, including Sea Ray's 37' Venture, which is powered by twin outboards

[tkeithlu]

Initial price is the primary reason. In the longer term, diesels are far more durable and get twice the miles per gallon. That's a matter of chemistry - breaking the bonds on diesel fuel molecules is more difficult (high compression, heavier and more extensive engine) but supply twice the energy when broken. Diesels are also more expensive because the fuel does not vaporize as readily and must be sprayed into the cylinder in a very fine mist at high pressure, hence expensive injectors/pumps. Do the calculation on fuel cost and repair cost if you are planning something as long as the loop, and use thereafter; diesel becomes more attractive as well as safer. If you go with gasoline, I agree - the new four cycle outboards, such as Tohatsu, are no heavier nor expensive and more fuel efficient than their two cycle predecessors. They are also bunches safer than gasoline inboards. Length is not the problem on the ICW - height is. We're 28' 1" in height, and between Palm Beach and Miami on the ICW there are 29 lift bridges we would have to wait for if we didn't go off shore.

[exMaggieDrum]

Originally Posted by wooden head

I know the objections mentioned are not real issues so much as perceptions. But as a boat owner that spent thousands not getting my first diesel running it's a common perception. Had I got the right mechanic in the first place it would have been different but my wife still refuses to consider another diesel boat. Perception becomes reallity

I feel your pain sir. I would note that some people have gone through exactly the same process with gas engines. The blame for the issue was perhaps incorrectly placed.

[exMaggieDrum]

In my experience, gas outboards are very reliable and appropriate for the right boat and situation. Unfortunately, they are also fairly expensive for the better ones. They do have other advantages over diesels, and also inboard gas motors. Replacing them is relatively very easy.

[SV THIRD DAY]

There also is a perceived safety factor of gas over diesel.
But i think that is over-hyped. An analysis of insurance claims would say for sure, but my gut thinks that operating hour per hour, there isn't an increased rate of fire or kaBooms with gas over diesel.

[pcmm]

Originally Posted by mikeling

With all the good things I hear about diesel engines, why are most Cruisers build with Gas engines ?

because they're not! I haven't seen a new cruiser built in the last 30+ years that came with a gas engine! Where would you buy one even if you wanted one! no one makes gas engines for boats any longer.

[tkeithlu]

Without having any statistic at hand... There is bound to be a difference in Kaboom rates, because it's just about impossible to go Kaboom with diesel oil. It's flashpoint (temperature at which it releases a flammable gas, not the temperature at which it auto-ignites) is in the 125-150 degree F range, while gasoline's flashpoint is in the -30 to -40 degree F. range. You always have flammable gas above a pool of gasoline, ready to make an explosive mixture with air, while you only have that situation with diesel if you pour it on your exhaust manifold. Diesel just doesn't go Kaboom. That's also why full tanks of gasoline are safer than nearly empty ones - there's more space for an explosive air/gas mixture in a nearly empty tank, while a full one will have too rich a gas/air mixture in it. Aircraft carriers, which used to have to carry gasoline because they had piston aircraft, filled the airspace in their tanks with non-flammable gasses to keep the air out.

[SV THIRD DAY]

How many gas cars, trucks, and gas power equipment explode per year?
This is why I don't buy the fear...accident stats matter and we just don't see cars and trucks in good condition exploding as they are running down the road. Now would I rip out my Diesel engine for gas? No...but I'm also not going to panic when on one of the millions of gas powered ski boats around the Country.

[tkeithlu]

And you shouldn't. This thread started at relative merits of gasoline and diesel in cruisers, with my throwing in safety as one (of many) considerations. For the record, the USCG reported 66 fuel/fire accidents in 2012, with 50 injuries and 1 fatality. If I read it correctly, that fatality was while fueling a boat. People do insist on pouring gasoline down fishing rod holders...... The important difference between boats and automobiles is that inboard engines (but not outboards) are usually in enclosed spaces where fumes can accumulate, while cars and outboards are well ventilated.

[StuM]

Originally Posted by tkeithlu

The important difference between boats and automobiles is that inboard engines (but not outboards) are usually in enclosed spaces where fumes can accumulate, while cars and outboards are well ventilated.

As are the fuel tanks and fuel lines.

[tkeithlu]

Gentlemen, and gentleladies, could we, without too much attention to the pun, agree that we have exhausted this topic?

[CC45]

I have a 45' CC Connie, 1960, being reworked, as far as it goes, its equipt for either fuels. Now would like to know what type, hp, of diesels did you put in yours? was thinking of 200hp. not sure if thats ok or go down to a 185hp
.

[pcmm]

Originally Posted by CC45

I have a 45' CC Connie, 1960, being reworked, as far as it goes, its equipt for either fuels. Now would like to know what type, hp, of diesels did you put in yours? was thinking of 200hp. not sure if thats ok or go down to a 185hp
.

Thats a crazy amount of hp for a CC typically you'd be around 75hp not 200!!

[CC45]

my literature says that it also comes in diesel at 185hp with paragon trans and reduction gears 1.51:1 P44. the fuel lines original are about 1\2 " so it looks like. so i was going to go with the 185x2 Detroit diesels. .
in the gas config, it should top out at 28kts.
i only need to top out with diesels at 20kts