Running a larger outboard at low revs

[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 it's 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 can take 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

 

[Firefly625]

Hi & Welcome to the forum,

as you mentioned Hardy I thought I would respond..

My advice is go small, I have had 50hp and 80hp 2 stroke merc's and both ticked over ok at low rev's but certainly the 80hp would stall if you had been on tickover for a prolonged time and then expected it to go in reverse, but the bigger you go the older you go and I think I would want smaller and newer, also a Hardy is no lightweight, it still might not actually plane with a 40hp, and maybe not with a 50hp on it, especially if there is more that one of you on board (there have been various posts on here from Hardy owners who were struggling to get there boats to plane even with larger engines, I will try and find the post..)

I would go for something like this:

http://www.ebay.co.uk/itm/Tohatsu-18HP-4-Stroke-Engine-Outboard-/160621662006?pt=UK_CarsParts_Vehicles_Boat_Engines_EngineParts_SM&hash=item2565cc0f36

or a bit older, & cheaper

http://www.ebay.co.uk/itm/Mariner-15-HP-outboard-engine-/140582365781?pt=UK_CarsParts_Vehicles_Boat_Engines_EngineParts_SM&hash=item20bb5caa55

Fuel economy would be far better and parts easier to get hold of than something bigger and older like my Merc engines which were circa 1980 and parts were becoming rare, in some cases not available so then you have to search for second hand parts... all gets time consuming...

Here's one of the old posts I just found.. may put you off getting a bigger engine..

http://www.ybw.com/forums/showthread.php?t=194810&highlight=hardy+pilot