Pros and Cons of Outboard Engines on South Pacific Cruise

[canadian cat]

Help me brainstorm some pros and cons of outboards on a fast cat (catana- gunboat speed) when sailing in the South Pacific with 800 watts of solar. The engines should not have too much cavitation issues as the engines are 10ft. forward of the transom.

I am trying to think of what type of sea conditions would create an issue over diesels when the boat sails very well on all points of sail.

[CruiserAD]

hi

In the South Pacific you might encounter very strong currents in the passes entering the lagoons. Normally they are too narrow to sail through. Preferably your engines should be powerful enough to handle this. I personally like the idea of outboards but I'm not sure if they can produce enough power for such situations?

cheers Jan


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[canadian cat]

The cat motors at 9 knots max in calm seas, which is as fast as other boats. It sails well in light air, but I wonder what sort of range you need to make it through the doldrums?

[BigBeakie]

Are you doing a milk run cruise or are you cruising extensively in the South Pacific? Are you staying in the S Pac over cyclone season, if so, where? If you cruise in the equatorial regions, I am advised you will motor more that you would expect. So range capability is important. You might be motoring for several days.

Lack of enough "push" would be my concern. Outboards are designed to spin a prop fast to get a (relatively) light boat with planing hull design up on the plane and keep it there. But we want to push heavier boats through the water (resistance) for long periods ie days at a time. Which implies lower RPMs spinning a bigger, higher pitched prop to give maximum thrust for moving against tides, currents, high wind etc. How does it perform in those conditions?

A question I have wondered about is does petrol/gasoline degrade if stored in jerrycans on deck? Do you need to protect it from sunlight?

[canadian cat]

My plan is to go from East coast of Aus. to Panama with maybe getting as high as Hawaii.

[BigBeakie]

Originally Posted by canadian cat

My plan is to go from East coast of Aus. to Panama with maybe getting as high as Hawaii.

Great! Someone else planning on doing the SPac the wrong way! We too will route west to east, from Sydney. Would you catch the westerlies to NZ and then hang a left at the Austral Group?

Have you found any information on the risk of lightning strike with petrol tanks onboard? Is it a real risk or an imagined risk? Would you use the 25 Litre outboard tanks & store jerry cans around the deck, or have built in internal tanks?

[Rapanui]

Several cats have circumnavigated with outboards so it seems eminently doable. If it is a quality engine like a Yamaha high thrust, then I can see few downsides and lots of upsides. Petrol is easily obtained everywhere and provided you filter the fuel before use then it should be trouble free, unlike diesel. We sailed for 30 years with outboards on our cats including long motors in calm conditions. If your boat sails well in light winds you will really only use the motors in calm conditions or close to shore.
One advantage is that you can dump an outboard into a dinghy and take it ashore to a shop for repair. Another is that outboards are used the world over so there will be expertise generally available. A comprehensive set of spares would not be too heavy or require much space.
Storage of spare fuel will need thought. Dont rely on the outboard for charging house batteries. Run the engines once a day at least on passage to ensure they are ready for use if required and dry out the electrics. And if all else fails, you can order a new one through a local agent.

[ozskipper]

Originally Posted by canadian cat

Help me brainstorm some pros and cons of outboards on a fast cat (catana- gunboat speed) when sailing in the South Pacific with 800 watts of solar. The engines should not have too much cavitation issues as the engines are 10ft. forward of the transom.

I am trying to think of what type of sea conditions would create an issue over diesels when the boat sails very well on all points of sail.

What no one has mentioned yet is fuel consumption. For the most part, outboards are a little thirstier than Diesels.

They are also a bit louder when trying to hear people on bow who are working with lines, anchors and moorings etc. So make sure you have good hand signals from helm to bow.

Parts shouldn't be a problem assuming you have a regular brand like Honda, Yamaha etc. If you buy cheap chinese OBs you may end up with a part problem.

Cavitation? Not sure what you mean there. Cavitation can happen anywhere underwater.

One huge advantage is that when you are sailing, the entire legs can be lifted out of the water.

All that being said, I would be just as happy to do the trip with two oversized OBs with high thrust props as a standard diesel.

[Jim Cate]

Petrol is easily obtained everywhere and provided you filter the fuel before use then it should be trouble free, unlike diesel.

Well, I've been to a few islands where diesel was available and petrol was not. And I surely don't know what you mean when you say that diesel is not trouble free, whereas petrol is. Is this the same universe where we have so many folks with outboards complaining about problems with "stale" petrol and alcohol related problems (no, not rum). Oh, also in my universe diesel has been used successfully after many years of casual storage.

I'm not adverse to folks using o/b engines on cats, but these baseless criticisms of diesel engines are just silly and do little to support your arguments.

Finally, all the talk about not needing much engine propulsion in a cruising cat may be true, but I see an awful lot of typical cruising cats motoring along the east coast of Australia. I don't think there is so much difference in how folks utilize their boats... number of hulls does not seem to change behavior very much in the real world.

IMO, if an outboard powered cat has sufficient power to move the boat against the wind in moderately strong conditions (30+ knots), and has sufficient fuel storage capacity to provide a few hundred miles of range then it matters little what sort of engines are involved. The o/bs will do just fine. I would prefer diesels myself, but wouldn't knock the o/b solution.

Jim

[canadian cat]

With a range 350-400 knots on internal tanks from 200L. How much more gas would one need? To go from Aus to New Cal. then east and then on up to Hawaii?

[ontherocks83]

Originally Posted by BigBeakie

Are you doing a milk run cruise or are you cruising extensively in the South Pacific? Are you staying in the S Pac over cyclone season, if so, where? If you cruise in the equatorial regions, I am advised you will motor more that you would expect. So range capability is important. You might be motoring for several days.

Lack of enough "push" would be my concern. Outboards are designed to spin a prop fast to get a (relatively) light boat with planing hull design up on the plane and keep it there. But we want to push heavier boats through the water (resistance) for long periods ie days at a time. Which implies lower RPMs spinning a bigger, higher pitched prop to give maximum thrust for moving against tides, currents, high wind etc. How does it perform in those conditions?

A question I have wondered about is does petrol/gasoline degrade if stored in jerrycans on deck? Do you need to protect it from sunlight?

Gasoline degrading has been discussed extensively but from my own tests and experience if you use stabil fuel additive religiously it keeps gas fresh for up to 2 years. Just follow the instructions on the bottle and it even states over treatment of gas does not harm operation and doubling the dose gives you the 2 years of protection.

[valhalla360]

Originally Posted by canadian cat

With a range 350-400 knots on internal tanks from 200L. How much more gas would one need? To go from Aus to New Cal. then east and then on up to Hawaii?

Unless you want to do the entire trip under power, you should be pretty good.

If we fill the tanks and a couple jerry cans, we have 60gal and that will take us around 350mile if we cruise at normal speed. Testing a slower 4kt speed showed, we could boost that to 500 miles. (gemini 3400 with 25hp 4stroke).

Assuming you have modern 4 stroke engines and don't go crazy big, I would expect a high performance cat to be able to do pretty good on fuel efficency and I would think you could get close to that range.

I would also agree that outboards are probably better for service (assuming you pick a common brand) as most of the little fishing boats will have an outboard. Your worst case senario, you could buy a new outboard and give the old one to a local for parts (might not be cheap on an isolated island but probably more practical than getting a new diesel).

If you get a workboat prop, the motor will be quite happy pushing you along at sub 10kt speeds and unless you go crazy small will have plenty of power to get you thru cuts.

[Factor]

Originally Posted by ozskipper

Cavitation? Not sure what you mean there. Cavitation can happen anywhere underwater.
.

Think he means ventilation.

[barnakiel]

IMHO outboards are fine in a well sailing boat under a skipper who can sail.

You will be disadvantaged in heavy seas.

b.

[Rapanui]

Don't get me wrong, I am not against diesels for propulsion, I have 2 on my current cat. However, given the right circumstances, petrol outboards can be a good option.
First, the boat must sail well to windward and in light winds. However, if the owner chooses to motor over sailing, then to me that tips the balance towards diesel. However, if sailing is the thing, lifting those outboards clear of the water is a big advantage.
Petrol is widely available, basically where there is powered road transport cars, scooters, motorbikes etc you will find petrol. Agreed it may not be at a refuelling berth.
Petrol may go stale when stored for a long while, but in 30 years of bring my spare 5 gallon containers ashore for a UK winter storing in my shed and then re-using them the following season, I never had a problem. Diesel can have the bug problem which does cause problems. The only problems I experienced with petrol was contamination with 'bits' which were easily filtered while filling the service tanks.
While most outboards are designed for lightweight relatively high speed boats, there are a number of outboards designed as sail auxiliaries. These have a larger, slower revving prop so are designed to give a high thrust at slower speed. They are usually 4 stroke and hence very fuel efficient compared to a 2 stroke although they will be slightly higher consumption compared to a diesel. I am only referring to these high thrust types.
Outboards are prone to cavitating due to ventilation when the prop is too close to the surface due to pitching. Extra long shafts and siting the o/b as far forward as possible or in a well will help.
Cost and weight are big factors in favour of an outboard. You get the whole propulsion system and even a tank for ~£2000 and 45Kg (Yamaha 9.9 High Thrust in UK used to power my previous 10m cat). Plus you can pick it up and put it in the car to take home to service. That's about the cost of a decent folding prop. (I know, as I am looking at buying 2 folders to mitigate towing 2 windmilling sea brakes through the water when sailing)