Outboard as auxiliary for small cruiser

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andrewbartlett

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I am looking for an outboard engine to serve as an auxiliary for my one ton 18 ft, mariner's mate motor sailer. The inboard is a YanmarYSE8 diesel. I want an outboard with an integral fuel tank. I have an adjustable bracket on the stern of the boat. I think 5 hp would be ideal but 4 hp would probably be ok. I want an second hand 2 stroke as 4 strokes seem to be a bit heavy and expensive(budget £750 max.). Does anyone have experience of aircooled outboards, I have seen one or two on e-bay quite reasonably priced. I live near Chichester so hope to find one (not necessarily air cooled of course) near here. Any help welcomed.:)
 
No experience whatsoever of air cooled outboards, but given that you will be pushing a relatively heavy boat (cf a tender) and travelling quite slowly (3-5kts) would you get the airflow needed?

Don't forget you will probably need a long shaft too, unless the engine is mounted really low - in which case it could be at risk of swamping if mounted on the stern.

Hmm, lots of "ifs" in that lot, but I hope you see what I am getting at. I had a 9.9 Johnson as main engine on the stern of my W25, & in overfalls or short steep wind over tide conditions it would alternately go very deep & then rise & cavitate. Mostly not a problem, but in severe conditions, I had to be quick on the throttle to stop it racing or stalling.
 
I am not sure why you would want an outboard on a motor sailer with a Yanmar inboard, but I do sympathise with the belt-and-braces approach.

I used a side-mounted Seagull 102+ longshaft on my 32 foot ex-6 metre (sailing only, no inboard at all) and it gave 4 knots in most conditions. That engine is optimised for high thrust and low speed, so it would cope with strong headwinds without much reduction in boat speed. I got through the Crinan Canal on several occasions but bringing the boat to rest without any astern gear and starting off (with a 30 degree sswing to port as it gathered way) were interesting!

When I got my next keel boat (two children and a decade later) I got a present of a Force 3 outboard. It was mainly used on the tender (and I could get about 10 knots out of it with only me on board) but I did need it to pull the 28 ft Commando motor sailer on one occasion. It towed at 3 knots but that was in calm conditions. The Force 3 is a Tohatsu-based unit of about 3 bhp.

I have used it as an exercise to tow my current Westerly Renown with the dinghy lashed alongside. In calm waters I got about 3 knots again.

So you will not need a large (in bhp) outboard for occasional use. More important than the power is whether you can get a prop that will optimise its performance for low hull speeds. That would probably be of finer pitch and slightly larger diameter (or have more blades) than the standard one.
 
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5 hp would be fine. 4 hp adequate provided you wont be wanting to get anywhere against strong winds and steep seas.
2 strokes larger than 5 Hp will almost certainly have a remote fuel tank but larger 4 strokes do come with integral tanks.

A long shaft will enable you to mount it a little deeper than "correct" to prevent the prop keep lifting from the water in a bit of a chop.

I know no suitable air cooled ones. ( Unless you want to buy my old 5 hp Volvo Penta 51 but is a standard shaft and has a remote fuel tank)

A high thrust prop would be preferable to a standard one to match the power to a low hull speed

An old Seagull Century or Silver Century longshaft might be worth considering or even one of the later QB models
( watch what you buy ... there was recently a Seagull ( Century ?) advertised on ebay as air cooled ... Seagulls are water cooled!)

IMHO it would be more sensible spending the money on the inboard diesel than buying an old outboard and spending extra money on that.
I wish I had an inboard diesel engine!
 
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Like others I would question the value of a dedicated second engine. Almost certainly you will need a long shaft, which are both rare and useless for any other activity. You will need a min 5hp to get any usable speed. Better to spend the money on ensuring the Yanmar maintains its reliability.
 
I had several Sonatas (23 ft, 1.1 tonnes) that used 5HP engines. Those were quite adequate for main propulsion but when one of them got nicked I replaced it with a 4HP that did the job just as well.

If you want a second engine to get you home if the main engine fails and there is a flat calm, all you really need is an egg whisk. I would suggest the ubiquitous Mercury/Mariner/Tohatsu 3.3. If there's too much weather for that to cope, hoist the sails.

Meanwhile you can use it to push a tender and it's light enough to toss in a locker when not required.

Back in the 70s when I started cruising the rule of thumb was 1 hp per ton for auxiliaries, 3 hp per ton for motor sailers. My 6 ton gaffer managed just fine with a 6 hp side valve engine and I got through the season on maybe 2 fill-ups of the 5 litre petrol tank.
 
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I had an Etap 22i with 6hp outboard fixed in a well. I also had a 4hp Johnson on a bracket on the transom. I liked to practise using the spare engine a couple of times a year. I could easily get 4kts. The only problem was that, being quite fat, if I went to the bow the prop would come out of the water.
Allan
 
I had a 4hp stroker on the back of a GK24 and that was quite ok. If you can get a 4 or 5hp with the high-thrust prop then all the better.

I once motored most of the way across the english channel with one of these at around 5kts.

Cheers, G
 
I p/ex some stuff and got a non running Yamaha 3.5hp. On inspection it was air cooled. Cleaned out the carb and it has been running fine for the last 7yrs. Built in 1980. A bit noisier than my 5hp water cooled Johnson. But good as a back up. No water pump or associated corrosion to worry about. There is a bit of pipe that faces the prop and sprays a somef water up the leg to cool/quieten the exaust. F-N gear too.
Does anybody make bigger a/cooled engines than the Honda 2.3? Briggs & Stratton do one but only for fresh water, 4hp IIRR.
A
 
Don't go on the rated horsepower too much.
I have a Tohatsu 3.5hp 2-stroke (like the Mariner/Mercury/Yamaha) that pushes my 17 ft yacht at 4.3 knots at less than half throttle.
My 4hp 4-stroke Mariner pushes the boat at 4.1 knots at just a bit above tickover.
An Evinrude 4hp 2-stroke I had struggled to reach 4 knots at well over half throttle (ear-splittingly loud as well).

These speeds achieved are those at which the motor seems least stressed. Opening the throttle invariably increases the noise and vibration out of proportion to the increase in speed. My hull speed is about 5.3 knots max.

The prop is very important. All these had their standard prop but the difference was marked.
 
I had an ancient 5HP Johnston on my old Seawych with a standard shaft and remote controls. It was great and if anything overpowered for the boat.

Equally I had the 4 HP outboard for my dinghy on a drop down bracket on my Maxi77 and that gave a decen 4 knots into a head wind.

All in all I would suggest 4HP as being adequate, and probably lighter, the 4 HP was portable whilst the 5 was a bit heavy for easy handling
 
Tohatsu made an excellent aircooled 5hp 2 stroke which gave me good service for 1 1/2 seasons after I fryed my Seagull. I bought it for £90 in 2008 but at that time I was told they stopped making them 15-20yrs ago so parts are definitely a problem. Questions: it is worth considering that a 2 stroke motor, especially one that old is not likely to be any more reliable than your main engine and by the way we replaced above engine with a new Toharsu 4 stroke because, among other things 2 stroke aircooled engines are VERY noisy.
Regards David
 
Aux outboard

andrewbartlett said:
I am looking for an outboard engine to serve as an auxiliary for my one ton 18 ft, mariner's mate motor sailer. The inboard is a YanmarYSE8 diesel. I want an outboard with an integral fuel tank. I have an adjustable bracket on the stern of the boat. I think 5 hp would be ideal but 4 hp would probably be ok. I want an second hand 2 stroke as 4 strokes seem to be a bit heavy and expensive(budget £750 max.). Does anyone have experience of aircooled outboards, I have seen one or two on e-bay quite reasonably priced. I live near Chichester so hope to find one (not necessarily air cooled of course) near here. Any help welcomed.:)
Click to expand...

The size of your outboard doesn't really matter as long as it is enough to push against any tide or current that is against you and as long as you have time. I suspect that it will only be for conditions in which you cannot use the sails ie. flat calm.
I once pushed - with the outboard mounted on the dinghy, lashed alongside, - a 12 ton motor sailer for 10 miles. The outboard was only 2hp and fortunately I had plenty of fuel. Took a few hours but made it.
As for aircooled outboards - 'cracking' bit of kit as long as they are in the open and not enclosed. No worries about water flow and can take a fair bit of hard use. The Yam 5 aircooled would be the best for your situation. Look after it properly and it will start 1st time, every time, anytime.
 
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