Gas or Diesel the age old question when buying a yacht?
Gas- Tan Canvas (Top) Diesel- Black Canvas (Bottom)
Boat Nut Media had a chance last fall to run identical 410 Silverton Sport Bridge Yachts one with twin big block gas motors and the other with a pair of cat diesels, so what were the differences? Does it make a difference when you are puttering along or cruising long distances, the answer is it does.
The gas boat is powered with two big block 454 ci low hour motors, and is set up virtually identical to the diesel boat. The only difference is a washer dryer in the gas boat, which is countered in the diesel boat with an automatic shore power cord system, So the weight difference is mainly in the motors themselves. However we will say the gas boat sits approximately two inches higher than the diesel boat at the water line.
Both boats were ran side by side down the lake for four hours on plain. The gas boat burnt $400.00 worth of fuel and the diesel burned approximately half of that $220.00. The boats were evenly matched for speed as a matter of fact the diesel boat could out run the gas boat if you pushed the throttle down and let the boats go. Why is this ? Well the gas boats props are at least 3 inches smaller in diameter, and the shafts on the diesel are a half an inch larger. This makes for a much smoother ride in the diesel as the running gear is larger you just do not feel like you are pushing the diesel hard at all. The diesel motors run at least 1700 RPM less at high speed than the gas motors.
I must say the extra weight of the diesel motors make the ride very stable overall, boat movement is reduced. The gas boat has more transom lift this would be due to weight and the extended RPM range this 1700 RPM is translated into more water at higher speed passing the props thus creating more transom lift. Transom lift creates more roll from front to back in the gas boat than the diesel boat. The diesel boat just punches a big hole through the water it provides the same bow rise it just squats in the water at the aft. Thus creating a much larger wake out the back
When departing the dock the diesel has substantially more push and more positive low speed control by the shifter's, this is directly related to the size of the props. Idle speed is also much faster with the diesel for the same reason, there is a larger volume of water passing the diesel boats props. The gas boat is also very manageable as well, but the reaction time from shift to movement is much tamer and slower. The gas boat will require more corrections for side wind or current. The first time you shift the diesel you may feel a little intimidated as it moves right away and quick. Neither one of these boats are equipped with thrusters so all docking moves must be made with the motors. When docking the gas boats gives you more reaction time to prepare for movement which can be a real plus for first time boaters, however this can bite you if you have an off the dock wind or current. At an idle at the dock the diesel can be dirty and smelly, as a matter of fact other boaters were not happy with long term idling . This though was partly due to the diesel motors requiring a general service. Although even with optimum fuel burn a diesel is a smelly proposition backed into the dock.
This becomes worse in a diesel if you have the generator running also. On this model boat running the generator would probably all but eliminate the ability of sitting in the back cockpit or keeping the large sliding door open. A real draw back while at anchor. The gas does not seem to have this same effect on the usage of the aft deck or cabin door.
When it comes to service these two boats are likely very close in maintenance costs, however if you had a starter or alternator go out the diesel, it would punch a hole in your wallet. Serious breakdowns will cost more with a diesel. Do not let this sway your decision making if a diesel receives regular run hours and correct maintenance then they will out last the gas motors two to one. The other upside to a diesel is there are less mechanical items to fail you there are no spark plugs no wires and no ignition system.
I believe that the choice between gas and diesel comes down to running hours and and what performance you are looking for in a larger boat. A gas boat is ideal if you are not putting on a lot of hours and not going far, in other words a floating cottage. If you had a diesel in these conditions it would cost you more to keep it running, diesels need to run they do not do well sitting around they are more difficult to get running if they do not see time then gas engines. If you are an avid traveler and cruise your boat all the time and like to go distances than buy a diesel the fuel burn rate will give you extended range and they love to run under load for days at a time. You have to take a look at how you are going to use the boat, access to fuel, the cost of fuel, can you get service on a reliable basis and how fast you want to get there, I must say a good diesel turbo set up will blow the doors of a gas boat the same size all day. The last benefit to a diesel is they do not seem to care what you load on your boat they seem to perform pretty much the same way with or without the tender and all your gear on board, where you will surely notice the difference with gas motors they just do not develop he same torque, and torque is push!
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