Re: Found an interesting site
Some very interesting information here. Things we discuss daily concerning current engines have their roots way back to the '50's as shown in these catalogs.
Couple of pointers.
Noticed that OMC power was OBC certified "Brake HP". That means that originally these engines were not prop rated as a lot had thought. Brake HP is defined as the output of the engine with nothing else considered.
Amazed that their 25 hp engine (up to '55) had 35 cubic inch displacement. No wonder it could push big boats. Today's engines are around 25 cu in. ('94 Mariner Catalog),
HP was rated at 4000 rpm's. Nice low rpm for quiet operation. Today's is 5000-6000.
One of the smacks Merc got in those days was all the noise it made and as I recall they were rated at a much higher rpm; I know their cubes were more like 1 cu in per hp.
Noticed totay's 25 is 2.25:1 gear ratio swinging the same sized prop as the old 25 with a 1.75:1. Guess all those cubes provided enough torque to allow the high gear ration.
3 pieves of the day were the gearbox, water intake, and shear pin.
Gearbox was always hanging up on weeds; Merc didn't.
Water intake was on the front of the exhaust port which put it right behind the prop. So you couldn't tilt the engine much and all the sand you drove through went right to the water pump. Merc, having theirs on the front of the skeg solved both problems.
Shear pin was always breaking at the worst times, like when on the windward side of rip-rap when you really needed your power. Merc solved that with the slip hub.
Noticed that back drag which we discussed a couple of days ago when we were talking about how to get more efficient operation when cruising. Go to full throttle and back off. They had it then. Huh!
And somewhere back there they quit using automotive 30 weight oil and went to marine oil with a 24:1 fuel-oil mix. I think early on they had it as high as 16:1. Boy, talk about smokers....phew.
The other biggie is that if you look carefully at the pics, the anti cavitation/ventilation plate was well below the bottom line of the boat. Talk about drag! Course with the props they were running then, anything higher probably would have been venting all the time; especially when they were trying to push those 24' cruisers around with 2 ea 25's.l
I have surely enjoyed the catalogs...........especially those cuties in those bating suits that look like a bathing suit.
Mark
