Replace inboard engine with two outboards?

[Jammer]

So, I have an 8hp outboard on my 25' Morgan 250. The Morgan 250s were available with an optional inboard engine (probably an Atomic 4) but most buyers did not order them this way. Mine has never had an inboard. I have a moveable bracket on the port side of the transom that allows me to pull the outboard fully up and out of the water while sailing, even on a deep heel.


The Yamaha 8hp that I have is an extra-long shaft (25"), electric trim, electric tilt, high torque, 4 stroke, electric start motor. Essentially the perfect outboard for a 25' sailboat. Nonetheless, there are a number of important drawbacks compared to an inboard. At the same time, some of the theoretical problems listed upthread are not serious problems in my installation.


- The main problem is that manipulating the engine is extremely awkward, particularly in tight quarters where the engine tiller and the rudder tiller have to be used together to control the vessel. The throttle and other controls are difficult to reach. On boats with a transom-hung rudder, it is possible to attach a linkage between the rudder and the outboard, but this cannot be done with my boat as it has a spade rudder well forward of the transom. Remote throttle and shift controls are available for these engines but would not be especially useful without a rudder linkage or some other form of remote steering.



- The 5.75" pitch prop is substantially (1.5x) overpitched even though it is the lowest-pitch prop Yamaha makes that will fit this engine. There are aftermarket props available that are 5" pitch but it is not clear to me that they would make enough of a difference to matter.



- The outboard is more vulnerable to inundation in following seas than the rest of the boat, because the cowl vents that lead to the air intake are well below the gunwales.


- Noise and vibration are a factor, but not a huge one. Noise is particularly an irritation at higher power settings as when motoring upwind.



I generally find that when motoring at 5 kts I burn a little more than a quart of fuel per hour.


I have never had any sort of failure with my outboard, but have only had it for one season. I would not necessarily agree that diesel inboards are inherently more reliable.


Outboards do require annual maintenance and clean fuel to work reliably but so do diesels.


The cost of a new high quality outboard suitable for a sailboat approaches $3000. While cheaper than repowering with an inboard the cost is still substantial.


Keeping the prop under water in chop is mainly a matter of being sure you have an extra-long shaft engine and mounting it low enough.

[Jammer]

Originally Posted by Pete7

Plus storing large quantities of petrol inboard isn't a great idea. Petrol vapour is heavier than air and will sink down into the bilges and remain there presenting quite a hazard.

The question is how much fuel do you really need.


I use 6 gallon, steel, fuel tanks. They are readily available here used since they were ubiquitous on 12-16' fishing boats for decades. I get the Johnson/Evenrude ones because parts are still available, then make up a fuel hose to match them to my engine (which is Yamaha). I have two tanks. Ordinarily I just have one in the cockpit, and leave the other one at home. Having two allows me to fuel up one of the tanks and put it in the back of my truck on the way to the marina and save the hassle and expense of filling at the gas dock, I can just exchange tanks.


On rare occasions I bring both tanks, and keep them both abovedecks somewhere.



I also have a 2 gallon steel safety can, the kind with a flame arrestor and self closing cap, that I sometimes bring on board, mainly because it's lighter and less to handle than the 6 gallon tanks.



At typical motoring speeds on the Mississippi, around 5 kts, my fuel burn is just over a quart per hour so I can run the engine for maybe 20 hours on a tank of gasoline during which time I'll cover 100 nm. Two tanks would give me as much practical range as many inboard installations and two tanks plus the 2 gallon safety can would be enough to cover the longest distance between fuel stops on the Great Loop.


My fuel system is tight and does not leak. The steel tanks are non-permeable and I use the new non-permeable hoses. There is no lingering aroma of gasoline as was the case of olden time. I don't see a safety problem, at all. There are 100s of thousands of boats that use outboards with 6 gallon external fuel tanks above decks and I've never found a single report of a fire in boats so equipped. In contrast we get an average of one explosion a year in Minnesota alone in boats with inboard or stern drive gasoline engines.

[captstu]

Gemini sailboats - a 34 foot cat for those not familiar - are offered with a Westerbeke diesel coupled with a sillette sail drive. A few lucky owners have older versions with a place to install an outboard. I was one of the lucky ones.

My Gemini 3400 was originally fitted with a Honda (the second engine) when I purchased her. On a 1000+ mile trip, the old Hinda blew - pieces came thru the block. No matter, it was heavily used, old and had questionable maintenance from the previous owner.

For $4,000, I fork lifted it into the recycle pile and had a new 15 HP merc long shaft installed in its place.

I eventually sold it about 2000 miles later - still running fine.

Some observations:

1. Outboard had less charging, but the boat had lots of solar cells and ran a fridge 24/7 with no apparent electrical problems.

2. Outboards don't make domestic hot water - again no problem. I have a very small tankless propane heater in a storage locker - ran of 2 size D batteries and produced all the water you might ever want, even when running on dockside water.

3. Repairs are bounded by the $4,000 purchase price - I just put $10,000 into my Yanmar Diesel on my current boat - and I'd junk it in a minute if I could find an outboard replacement.

4. Simple - the outboard steers with the rudders, tilts on a power trim tilt switch and maneuvers better than the inboard Geminis could ever hope for

5. Fuel economy - my outboard burned about 1/2 gallon per hour at full speed. We won't debate if Diesels are better or worse - but . . . 1/2 gallon per hour - good enough for my pocketbook.

6. Noise - I don't know if this is good or bad - the outboard is so quiet at idle that I have left it running overnight on occasion - much quieter than the Diesel at cruise RPM.

7. Service - anyone can tell you where to get an outboard fixed. Yamaha, Honda, Merc and others have readily available parts and qualified service people. Diesels with electronic control are hard to fix - maybe impossible in some cases.

[hellosailor]

Hugo-
Consider this. If it really was a good viable idea? You think perhaps all the builders have been too dumb to offer it for sale by now? Or perhaps, the inboard engine cartel has prevented them from doing that?
It would be handy to have a full sized kitchen in my car, but somehow, no one offers that.

[Jammer]

Originally Posted by hellosailor

Hugo-
Consider this. If it really was a good viable idea? You think perhaps all the builders have been too dumb to offer it for sale by now? Or perhaps, the inboard engine cartel has prevented them from doing that?
It would be handy to have a full sized kitchen in my car, but somehow, no one offers that.

Well, they do.


Here's a 26.5' hunter: https://www.yachtworld.com/boats/198...s#.W6K0YPZOkuU


And a 27' Chrysler. They had a well for the outboard: https://www.yachtworld.com/boats/197...s#.W6K0Y_ZOkuU


Never heard of a Burr: https://www.yachtworld.com/boats/196...s#.W6K0YfZOkuU


And a Pearson: https://www.yachtworld.com/boats/197...s#.W6K1LvZOkuU


And a Cal: https://www.yachtworld.com/boats/197...s#.W6K1ivZOkuU

[hellosailor]

And how many of those were BUILT with TWO outboard engines? Not just one engine, and not just modified by some PO, but built with two?

And that's ignoring the question of what percent of successful market share that represents.

[Jammer]

Never seen one with two engines.


Typically the way it works, boats up to 25' are made narrow enough of beam to be trailerable, and are set up for outboards. Boats 29' and over are usually quite a bit wider and have inboards. In between varies.


The situation with a new boat is different than the situation with a repower. A boat manufacturer is selling new boats at a much higher price and the difference in cost between an outboard and an inboard is a small percentage of the overall purchase. It is also cheaper for the manufacturer to install an inboard on a new boat, than it is for an owner to repower an existing inboard.


There are many boats out there where an owner decided to install outboard propulsion and either remove the existing inboard or abandon it in place. Sometimes it makes sense. It depends on the specifics of the boat and the goals of the owner.

[Compass790]

I've had small yachts with transom hung outboards & in a well. In a well is much better as you dont plunge the engine underwater in a storm so easily ( believe me it can happen) But I much prefer an inboard diesel anyday. Outboard ok for daysailer. You can fix up an old diesel for much less than the price of a new outboard IF you can do the work yourself. Inboard diesel much better for charging batteries too. Agree with others you wanna get outboard with small pitch, probly not availiable in 6hp

[hamburking]

Originally Posted by Pete7

However, don't make any decisions until you have bought the yacht. Yes you may find an old diesel engine on board, but it might continue to run for another decade completely eliminating the problem. Our Volvo 2003 is 30 years old.

Only 30....why thats practically brand new!

[MickB]

I had a Bruce Roberts 28 that had a 9hp long shaft outboard mounted on the transom by the previous owner when I bought it. It was disastrous, even in a small swell the prop was out of the water and cavitating. Reaching the outboard to start and stop it or adjust the revs in a swell was quite dangerous. I retro fitted a diesel and sail-drive, expensive but necessary. However having said that your vessel may not react like a rocking horse in a small sea and your transom may not be as high.

[GrowleyMonster]

It is certainly not a crazy idea. The only problem is getting a pair, one right hand and one left hand, in such small power level. I don't think they make them but I might be wrong. Also if you get badly pooped while the outboard is running, you could suck water into the cylinder and possibly cause a great deal of damage to the power head.


You do NOT want two outboards turning the same direction. Yes, you can correct for the crabbing but that is inefficient. You may as well have a single outboard big enough to push the boat. Two 6HP outboards cost more than one 12HP. If possible, go with a single 9.9 which being less than 10HP is in a completely different regulatory category. A single outboard will be more fuel efficient, too. Bigger prop, and only one of them, is more efficient than two smaller ones. You can tweak efficiency a bit more with the appropriate aftermarket prop. Most outboards are designed to push a small planing type hull and speed through the water is higher, calling for a higher pitch prop for proper loading and less cavitation at top end power levels. Just my two centavos. Outboards are notorious fuel wasters as it is, compared to an inboard diesel. Every improvement you can make that will not overly tax the engine is worthwhile. The only benefit to having two outboards where they don't turn in opposite directions is if one dies you still have mechanical propulsion capability with the sole running engine.


With a transom hung rudder there is a stronger incentive to have twin outboards, maybe, but most folks just mount the single outboard bracket off center. Not perfect but it works.

[Don C L]

It would help to know which 28 footer we are talking about. As someone who lives with an outboard, I have a few thoughts. In my case it works ok. My transom is low enough and my engine hoist is designed well enough that I have no problems with the engine coming out in swells. So I am ok with my outboard, which is a good thing since my boat has no accommodation for an inboard. BUT, I don't like your idea for a few reasons:
Weight. It's just too much in the wrong place, way too far aft. I have a 2-stroke and I am hesitating to upgrading to 4-stroke because I don't want another 30 or 40 pounds back there, but eventually I will get there, and it will necessitate more weight shifted forward.
Efficiency. You are (probably) going to burn more gas, and gas, even in a 4-stroke, is not very efficient compared to diesel. You'll need more gas which is even more weight in the wrong place. AND, importantly, do you have a safe lazarrette to store the gas tanks in? Remember also that once you have the boat up to hull speed, the fuel needed to go past that increases quite a bit without much benefit. It is not a planing hull. 12hp vs. 8 or 9.9 isn't much advantage I'd bet, but I don't have the math to back that up.
Portability. A long shaft outboard is not a good power source for a dinghy. It puts a lot of strain on the transom because it is trying to rotate it down with the prop, and its thrust so deep. I've tried it. It did work. And then it did damage the transom.
One 8 hp or 9.9hp, with a "high-power" prop and gear ratio, with a good hoist, is the only real solution, IMO. As far as I know, no one makes a hoist like mine commercially, but mine can lift the engine well clear of the surface without the need to tilt the engine which is really nice. You might do well to design and build your own for that reason. But again, which boat is this and how high is the transom off the surface?

[valhalla360]

Originally Posted by captstu

Gemini sailboats - a 34 foot cat for those not familiar - are offered with a Westerbeke diesel coupled with a sillette sail drive. A few lucky owners have older versions with a place to install an outboard. I was one of the lucky ones.....

Hey Stu.

We also had a 3400 outboard and it was a great option.

We had around 1200hr/7000miles on our 25hp when we sold it. I know the new owner made it at least down to Texas from Michigan after buying it before we lost touch.

The one comment I will make, the Gemini was designed for outboard power. Just strapping an outboard on the back of most mono's will not do nearly as well. But there are mono's designed for outboard, so I would consider one of those.

Also for a 20'something mono, a single 15hp would be plenty of power and still could do double duty as dingy motor for less money and more simplicity. As mentioned, you have sails as a backup and with a new motor, you should be pretty reliable if you make a reasonable effort at maintenance.

[calin1967]

I've had a 22 footer with an 4.5 outboard fixed aft. Perfect for harbour maneuvres and flat sea, pushed the boat with hull speed at half the power, but when there were 0.5 meter waves it was a nightmare - half of the time the propeller was in the air (bzzzzz), the other half the whole engine was underwater (blblbl). IMHO, having an inboard is a great value, on heavy weather. And should not be so expensive to repair an old diesel, especially if you have some tech skills (or find a relative or neighbor which will be paid in sailing hours). But if you plan to sail weekends on good weather, having an small outboard and transforming the engine space into locker, could be a comfortable option. Having two is definitely an eye-catcher and you will be a star on facebook, especially when you will turn in no space. You might even think about 4...

[markpierce]

More than one outboard to propel a small sailboat makes no sense. If you anticipated use of the boat is to motor, acquire a motorboat.