Have to Ask: Outboards on Sailboats?

[wannago]

Ignoring the gas vs. diesel argument, the biggest differences that I see between outboards and sail drive systems on a lot of newer boats is how they are mounted. The outboard being hung off the transom and the saildrive getting stuck through a hole in the hull.

The sail drives are used to allow the weight to be lower and more centered (near the keel). There is also the issue with the prop coming out of the water in waves.

On lighter boats outboards are more common, where the power requirements are smaller and there's little need to use the alternator for electricity. And I haven't seen any 15 HP or less sail drives that could be used in the smaller boats like mine.

The outboard does allow me to direct the thrust when maneuvering (My outboard is tied to rudder and turns with it) and tips up to center the weight more into the cockpit and get rid of the rudder drag when sailing. (I have a 9.9 hp 4 stroke Yamaha, a much larger outboard would become hard to tip up by hand)

For people more involved in racing it can be removed on race day to save weight and the rudder drag.

Interestingly though, I've never understood why the larger power boats use these 100+ HP outboards. It seems silly to engineer a system with the power and weight of those that has to be mounted on the brackets they require, and forces the weight of those engines to be up high, on top of the transom.

[slomotion]

Originally Posted by s/v 'Faith'

The conventional (or now common) method of mounting an outboard on a sailboat does have some 'issues'... Many will mount an outboard on a retractable bracket on the transom. Boats generally do not like this arrangement, especially if they lack the reserve buoyancy aft.

And some such installations are truly scary:

[RickD]

My boat lists to port without any other weight in the boat because the outboard is sitting on the port side of the transom (obviously because my rudder and tiller take up the middle of the boat!)

Since it's a small boat it works, but one day I want to try the boat without the motor attached because I think the extra 100 pounds or so causes me to have a lot of issues with sailing close to the wind off port. Seems to be much less responsive... (and yeah, I DO pull the motor up when sailing of course!)

[Bash]

Originally Posted by wannago

For people more involved in racing it can be removed on race day to save weight and the rudder drag.

Many boats ago I raced an Olson 30 with an outboard mounted on a stern bracket. We'd motor out of the harbor and then I'd have to pull the outboard and stow it on the keel bolts where its weight was least insidious (an Olson 30 being an ultra-light displacement boat.) Then, after the race, I'd have to trundle the doggone thing back to the transom, always fearful that I was going to drop it astern.

Nothing like that sort of experience to make a sailor appreciate the delights of an inboard diesel.

[Hud3]

Originally Posted by 2ndstar

The biggest issue I see is in waves, especially short steep waves where the prop spends a lot of time stirring the air. There's the weight in the ends issue and manufacturer's don't make extra long shaft motors above 10 hp.

Carl

Carl makes a point that's often overlooked or minimized. A friend of mine was sailing his boat (26 footer or so) from Cape May, NJ, up to New England. A storm blew in from the NE and he found himself on a lee shore. He wasn't able to make progress upwind due to the heavy chop. When he started his outboard to try to motorsail off the lee shore, he found it didn't help at all, because the prop spent so much time out of the water.

He ended up on the beach.

[Factor]

A lot of truisms and popular logic here. - I have an outboard powered boat 2 YAmaha 9.9 GEX motors.

Outboards aren't as efficient - I use less than a litre per hour at 5 knots (on one motor)
They cavitate in heavy seas - depends where you mount them, mine are fairly close to the pitch axis of the boat and any such cavitation/ventilation is very very rare. Indeed it hasnt happened for me yet.

Petrol is dangerous, - well yes it is, but the outboards are outside the human area of the boat as are the fuel tanks and all of them drain to the sea so in the event of a problem the fuel doesnt end uo in your boat. I note that most people have petrol powered outboards for their tender and still seem to be able to sleep at night.

They are unreliable - our coast guard flotilla uses a number of outboard powered rescue craft. And their history in seawind owners is one of virtually no dramas. Similarly in PDQs. I think they can b much more reliable because access is so good. maintenance is easy.

A real cruising boat needs diesels to power all the electrical crap. Mine doesn't - I have efficient systems and a great solar array that keeps the fridge / freezer and other systems functional without ever plugging in to the shore.

I love that the total wight of the motors is less than 100 kilo, 100 kilo in fuel gets me up to 600 nm range. I can get the prop out of the water to unwrap the crab pot lines that get caught on them, they are outside the habitation space and don't make cabins hot and smelly.

The props dont fold or feather - they are big meaty ones and when you stop motoring you pull them up out of the water - so no drag, and no dramas with performance in reverse etc.

Oh and a new prop is around $120 if you damage it - whats a folding Gori worth? And the prop is always clean - no growth etc, cause it spends so little time in the water, so its always more efficient than a prop with growth over it.

All in all - very happy with them.

I also like that I don't have two great holes in the bottom of my boat for sail drives.

Look diesels are fine, but really still suited to bigger boats than mine. They too have their issues, Modern Outboards, properly mounted and designed in are efficient quiet and highly reliable, and best of all they are a fair bit cheaper to buy and a lot cheaper to maintain.

There is a free podcast in the apple itunes store on a couple who circumnavigated on a cat with a single outboard - its worth a listen

BY HUD - He wasn't able to make progress upwind due to the heavy chop. When he started his outboard to try to motorsail off the lee shore, he found it didn't help at all, because the prop spent so much time out of the water.

Sounds like he has bigger issues with his boat than his motor. I dont think I would buy a boat that could not sail off a lee shore in horrid conditions, or if I did I would buy a couple of really big anchors.

[roger.waite]

Lot of good points above. There are plusses and minusses, but the short answer is you generally see outboards only on smaller boats. There are good reasons for this. I have a 15 HP o/b on a 30' racer, and it is fine in benign conditions. Then you have to have a boat and a crew that can sail its way out of trouble.

1. Weight is not a particularly big issue. Horsepower for horsepower, smallish outboards on small yachts are light vs. diesels, paricularly once you factor in all the weight hanging off a plumbed in diesel. If weight in the stern was the real issue, relative to diesels, you would not see so many lightweight racers using them.
2. But smaller outboards generally have small props that cannot use their nominal HP to drive the boat into wind and waves. I generally have to motor sail under a small jib to get much progress against winds over 25 knots. Going through the engine calculations, I need a 10" diameter prop and lower revs to get good use of my 15 HP.
3. Above 25-30 knots in a seaway I get two problems. First, stern lift with power loss and over-revving. My o/b is in a well; this would be worse with stern hung o/b. Second, prop lift when heeling (note need to use sail to get upwind above ~25 kts w/s). My o/b is central. A side monted o/b would lift more on a particular tack.
4. Fuel: safety. Petrol is volatile, highly explosive (in tanks and as vapour), and goes stale reasonably quickly. ~60% of my lifeboats rescues in spring relate to o/b fuel problems, typically stale fuel or oiling (2 strokes). O/b fuel is also commonly stored in platic tanks in locations where accidents can happen more easily (vs. bilge tanks).
5. Fuel: range. O/b driven boats simply don't go as far, HP for HP, on a litre of fuel. So on long trips you carry a lot of it, largely nullifying the lower engine weight of an o/b. And tote tanks are generally small, increasing the likelihood that you have to refuel at sea. My 20 litre tote tank will get me 20, maybe 30 nm in flat seas. The 10hp diesel on a sister ship will take her well over 100 nm on 20L of diesel.
6. I have not found reliability is a major issue. I know some diesel-powered boats that have had outrageously expensive problems that I could fix at a fraction of the price by getting a new engine. I know diesel powered boats that have so many silly little (engine killing) problems they are always slowing a group of yachts down. And I know some people who have lots of problems with dingy o/b. Good outboards are pretty reliable if you keep the fuel fresh, maintain the engine well, and keep the plugs clean. And as for any engine, carry essential spares.

IMHO outboards are a good option on small boats (well below 30'), particularly those that sail in sheltered waters, or sail conservatively in coastal areas. But they are not designed for slow speed yachts, and will always be out-performed by a good diesel. They are an uncomfortable compromise on any cruising yacht, and potentially hazardous on boats that cannot sail upwind in a big sea.

FWIW.

[Ita]

I got a 25HP outboard on my 29', lots of power but lot of weight.
I can't take it out of the water on heavy seas because it's too much stress on the mount.
outboards must be lightweight!!!!!

[johnar]

wow was a simple question that I thought was kinds stupid to ask but without knowing why I had to ask. My first thought was it would help to be able to pull up while under sail but I thought the reason they didnt use them was the lower HP at the prop. didnt think of the weight displacement.

My last boat was a 21' with a inboard/out 302 with 260hp lowerend and it never blew up. But it was a ski boat, very open to the wind.


thanks all.

Dutch

[Bash]

I stand 1.9 meters and weigh 100 kilos. Back in our Santana 22 days, if I would go forward to hank on the jib while my wife minded the tiller, my weight would cause the prop to cavitate.

Her solution: We should hank the jib in the slip.
My solution: You should hank the jib, my love.
Our solution: A bigger boat.

[Heikki]

Originally Posted by 2ndstar

The biggest issue I see is in waves, especially short steep waves where the prop spends a lot of time stirring the air.

I agree with that. In short steep waves the engine will have rough time not reaching to water at all times. It also sounds really scarry with the rews going up and down and it makes you wonder for how long the engine can take that.

On tight marinas it is nice. We have an outboard and a torpedo keel on our smaller racing boat. With that setup we can literally spin around our keel.

[roger.waite]

Just want to acknowledge Factor's points. I found your experience with catamarans interesting. Is it centrally (pod mounted)? I.e. lifting issues are minimised.

Thread drift on the next point, but I found a really easy way to clean oiled plugs (on a two stroke) the other day. Just remove plug as usual, and squirt inside the base with lighter gas from a refill can. (Away from sparks and flames!)

[imagine2frolic]

Just do the right thing, and fix that deisel. You will never regret it..........i2f

[Sailor Doug]

OBs are great if they are close to center of pitch. Generally mine where stolen ever 3 to five years so that reliability was never a issue. Long shaft 9.9 have a great black market. One time I motor 115kt none stop.
I have had some tough situations trying to motor into the wind in a narrow channel with a prop fanning the air.

[Fiveslide]

Originally Posted by Heikki

...It also sounds really scarry with the rews going up and down and it makes you wonder for how long the engine can take that...

It wouldn't scare me with a two stroke engine. They aren't as complex as a four stroke, compared to a four stroke there are very few moving parts in a two stroke engine. Because of that 2 strokes generally won't turn enough rpms to hurt themselves. Four stroke engines, without a rev limiting system, will.

I love my 2 stroke outboard. It helps that I grew up racing 2 stroke dirtbikes so I can diagnose and repair my own engine. If you ever learn to work on a 2 stroke yourself you'd never want another engine for a small boat.