Inboard vs. Outboard Engine: Which is Best?
There is no denying that more and more boats are being powered with outboard engines as compared to inboards. But why? And what is the right fit for you?
For any number of reasons, todays boat buyer tends to favor outboard motors, with more manufacturing options and more trust for that style of propulsion. As such, boat manufacturers of larger boats, and even more traditional boats you might not expect like MJM, Hinckley, and Back Cove are utilizing the popular technology to engage with new buyers and provide new experiences for their owners.
Even these manufacturers and others give the boaters their choice with inboard power options and outboard power options on the same model - or they have an outboard lineup and an inboard lineup. That should lead you to think that one propulsion system is not the end-all be-all, instead they each serve different needs.
If having extra aft storage space is important to you, an inboard engine is probabaly not the right fit. Whereas, if having a clear swim platform to take a dip on a hot summer day is important to you, an outboard engine wouldn't be the best option. Here we will give you the advantages and disadvantages of both for you to decide which is the best for your on-the-water experience.
With outboard powered 50’ cruising boats and 60’+ super consoles adorned by 4,5,6 outboards – what are the advantages?
SPEED! - Outboard motors are getting more powerful every day and that allows boat designers and manufacturers to build faster boats. With the premier engines from the most common brands like the Yamaha 425, Mercury 450R, and Seven Marine 527/557/627 lineup, you can pack a lot of horsepower in a boat to push it to new limits. What does that mean to you? Cruising speeds are now easily in the upper 30mph range and it seems as though every boat must do at least 50mph at the top end.
Draft – If you have a shallow dock you keep your boat at, the ability to trim the outboards up and get to deeper water by way of 20” of draft might be critically necessary. Some bodies of water are shallow everywhere so the prudent choice is shallow outboards. And right or wrong, we all feel a bit more comfortable dragging a $500 stainless prop through the mud as opposed to many thousands of dollars of prop/shaft/strut on an inboard model.
Inboard Engine Advantages:
What advantages do the more traditional inboard offer? For the sake of this discussion we will stick with diesel inboards as opposed to gas.
Fuel Efficiency - Really gets your blood pumping doesn’t it? If not that’s OK, but it is an undeniable advantage of diesel inboards for many reasons. This means your cost of boating each trip is lower, and you will spend less time at the fuel dock. An added advantage of fuel efficiency is longer range of cruising. Many diesel inboard powered cruising boats can boast over 300 mile cruising range, which similar boats with outboards will likely get half that range. Of course outboard powered boats can add more fuel capacity to help increase range but that has its trade-offs.
Engine Longevity – While outboard motors have increased their lifespan with most expecting 2500-3000 hours, diesel inboards should at least double that if maintained to the same standards. That will certainly affect resale of any boat later in its life and if you put more than the standard of 150 hours a year on your outboards you may need to factor repowering into the equation during your ownership.
Now on to some of the grey areas in this choice between the two propulsion systems:
Service: If you ask the average person walking through a boat show which engines they would prefer to service, the common answer is outboard engines because things are easier to get to and the engines are thought to be more simple. In reality, both engines have similar service needs: fluid and filter changes, raw water cooling systems and pumps, zincs, and few other items depending on the number of hours. Since diesel motors of a comparable horsepower are larger they do require more fluids and bigger filters, but this is nominal in the consideration of the purchase on the whole.
As for ease of service, opening a deck hatch with varying access as compared to working over the water hanging off the back of a boat is a wash in my mind. Winterization costs will be higher per engine for diesel motors, but lets talk about that “per engine” comment. A 35’-40’ boat, for example, will almost certainly have 3 outboards on it. Any given 35’-40’ diesel powered boat will likely have two engines. That means your service costs will reflect having an extra motor, and some might say that’s one more thing to go wrong.
Price: Another common misconception is that given the same boat, powering with outboards will be less expensive for the purchase price. If we take into account the 2 diesel engines vs. 3 outboard example above, and push it to 4 outboards on boats over 40 feet, sometimes growing to 5, it is not a guarantee that there will be a price difference at all.
Engine Placement: Some boat buyers will refuse to have motors mounted to the back of their beautiful boat, so engine placement can be a critical part of a boat buying decision. Others may think it looks fast and cool and are proud to have their horsepower displayed like a badge of honor. Aside from aesthetics, engine placement can play a big role in the design of the boat.
Inboard diesel engines are commonly mounted lower in the boat, thereby lowering the vertical center of gravity and making the boat roll less and run better. Designers can often play with where the diesels are mounted fore and aft in the boat using jack shafts, or mount the motors to IPS pod systems where it is ideal for the boat as opposed to only being able to mount to the transom or onto a bracket for outboards.
Again, this gives the designers the ability to perfect the weight distribution and the propulsion point. However, with the outboards in the back of the boat, that allows lots of creative use of deck and storage space where the inboards would have been. Finally, if extra gasoline tankage has been added to the outboard model, this can increase the overall weight of the boat and affect its trim.
Noise: Both propulsion systems have improved their idling and running noise leaps and bounds over what memories you may have of your uncles lake boat in the 70’s. Diesel engines have gotten better at exhausting underwater which also cuts down on the smell and noise. Four stroke gas outboards can be so quiet you can forget they are on when you are at the dock.
At running speeds you will probably find that their noise levels are almost comparable decibel readings if the inboard engines are well insulated and the boat is of decent build quality(a lot of boat noise comes from the boat rattling). The primary difference is in the type of noise. Outboards can almost sound like supercar engines, and diesels have the low smooth rumble that’s hard not to love.
Where do you go from here? Think about which of these characteristics are most important to you. Do you have a need like draft restrictions that strongly urges you in one direction? Next, call your trusted yacht sales expert and have a conversation about what you are thinking.
By Grady Byus