Running a large outboard at low speeds for long periods

[crofty1984]

Hi All,
I'm looking at getting a boat with no engine, an 18 foot Hardy or similar.
I'm going to be using it mainly on the norfolk broads, but may do a little coastal work if the weather's nice, I'm wondering what engine to get.

If I bought a 40-50hp engine, would spending a lot of it's life at the low end of its performance band (speed limit on the broads is 6 knots max) be harmful? My engine budget is pretty low in the grand scheme of things at £500-750, so it'd probably be an older 2-stroke.

Or do you think I'd be better off getting something closer to 20 hp and accepting that I''ll always be at displacement speeds (no great worry, most of my boating's been on my dad's Cygnus GM32 which is a full-displacement hull) As long as I can see about 10-12knots flat out I'll be happy enough.

Also, assuming both engines are OK for it, would the economy be comparable between the 2 engines at cruising speed? I guess it takes x amount of power to push a boat through the water at 6knt regardless of what engine is producing it.

Thanks,
Dan

[danyeates]

I wouldn't run a two stroke at slow speeds forever, no. It will oil up. Four stroke engines won't mind, but the high thrust or sail drive engines have gearboxes designed for such tasks.

[brad.noble]

Why oww why oww why would you be looking at big 2 strokes for plotting around at 6 knots for?

Get a nice 4 stroke thats slightly to big for the job Dan!

[Simpo Two]

Get an inboard!

[rhinochopig]

Or thinking laterally get a smaller prop and run the engine at the speed it was designed for. Even better get one that will give you 2 knots at 12k rpm in a cloud of blue smoke. The disapproving glares from the canal boat owners would be worth penny of the frequent rebuilds.

[tr7v8]

My Dolphin 20 ran a Evinrude Speedtwin 25HP on the Thames so 25:1 premix, stone age two stroke from the 60's.
It never gave a moments trouble, new plugs every year as part of a service with new leg oil. Second year it had a decoke & new gaskets. So a 750kg boat, running at 6-8mph on the Thames it was fine. The mooring was a very narrow stream into Wargrave Marina so it was astern one way or another, very slowly again no probs. Two tank fulls used to more than cover a full weekend on the Thames.
So a more modern 2 stroke running either 50:1 or pumped will be fine.

[crofty1984]

Simpo Two said:

Get an inboard!

And what boat do you suggest I put around said inboard? I think I can guess.....

[Simpo Two]

crofty1984 said:

Simpo Two said:

Get an inboard!

And what boat do you suggest I put around said inboard? I think I can guess.....

Well, like cameras we're all biased towards whatever we have, but as far as river cruisers are concerned I always think outboards are (how can I put this nicely?) the 'cheap' option.

As it happens I happened to be looking at Shetlands last night - the 27i and 29i...





Omnomnom. But is all that cream flooring and seating really practical...? And do I care....?

[crofty1984]

Very pretty. May be looking at an inboard engined beastie on Saturday. Well, the hole where the engine should be is inboard.

[Simpo Two]

crofty1984 said:

Very pretty. May be looking at an inboard engined beastie on Saturday. Well, the hole where the engine should be is inboard.

Don't worry, the Shetland I linked to is pretty but at 6x the price of mine, poor value. I was thinking how different it would feel sitting in an almost-new spangly Shetland as opposed to my 1973 F23. And whilst the Shetland would be great for showing off and saying to friends 'Look at my shiny new boat', it doesn't have character. I can sit in my floating mahogany shed - as I intend to this weekend - having consumed a nice steak and plenty of red wine, and go 'Yes, this is nice'.

I'm rambling but what I suppose I mean is 'boats are more than simply money'. It's a lifstyle, an escape. What price freedom? So if you see a boat you really like that's a bit more than you planned to spend, heck, buy it. Because one day you will be dead, and shrouds don't have pockets.