Is it wise to install outboards on pushboat?

This is a very rude generalization, which is mostly not true at all.

It is true, that most often diesel has "a lot of torque", but that is only due to much lower rpm. Power is "torque*rpm", thus for the same power you need more torque from a diesel. This has nothing to do with a propeller selection, since all that propeller sees is the rpm and torque of the propeller shaft. With the same power you can get the same propeller shaft rpm and torque from a 90 hp diesel running 3000 rpm and 90 hp gasoline running 5500 rpm.

The same applies also for two vs. four stroke.

Then there are differences in the power (and thus torque) curves, but these depend more on the details of the engine than on the type of the engine (diesel, two strore, four stroke).

This video between E-tec and Yamaha is really stupid and proves nothing. It all comes down to propeller size and selection and has very little to do with "torque" and real performance on a boat. I think acceleration tests including top speed tells much more about the real power (both maximum and curve) of the engine. From what I have seen two and four strokes are very equal in these and E-tec doesn't really show anything more than others. What is clearly seen is the very good acceleration of charged Verado's at lower speed. With a charger you can get much flatter power curve, even constant maximum power for wide rpm range.

 

Hello Joakim,

Yes, rude indeed.

It's the bloody 4 strokes that had outboard prices sky rocket Too heavy as well. There was a reason they used two strokes initially and remember that most things were already figgered out during ww2. There are very, very little new things coming along nowadays. You name it, it was done before.

All these guys are doing now is to abuse cerain worries like polution to give us less better under the flag of cleaner. The same is being done with two strokes low pressure fuel injection, also complies so there you go.

BTW, they did the same with lead free solder. Put up one hell of a thing re lead poisoning then come up with a more expensive lead free solder that is a lot more dangerous than lead can ever be. Hey, but WTF, they're making good money out of leading the illiterate by the nose. I'm still waiting for boat keels to go lead free - maybe it won't happen, they'll get the finger too often.

He he... personally I enjoyed the video (a lot !). My Yamaha's CDI packed up (poor soldering of components) and they wanted to rip me off more than what I can get another motor for (with a working CDI in it). So let them lose a bit on sales, maybe it will get Yamaha off their stiff upper lip attitude

 

A lead free keel would be worth its weight in gold - for a reason.

 

There used to be two strokes in cars as well...

I think the modern outboards are quite much better than the old two strokes. They are much more fuel efficient, don't stink and are quite noiseless at low rpm.

I use lead free solder. What makes it more dangerous?

 

lead free solder:
http://www.okinternational.com/binary/articles/Lead-free_Fume_Extraction.pdf

Quote: Many solders contain a rosin-based flux that produces colophony when heated, containing
harmful constituents ranging from acetone to carbon monoxide, and is recognized as one of the
most common causes of occupational asthma. Non-rosin solders contain alcohols and acids that
can be even more dangerous to health than colophony.

 

View attachment New-England_Mooring-work-barge.pdf
Joakim,
Thanks for clearing the air on entertaining videos posted on youTube. All this talk sounds like a good episode for Myth Busters.
This thread started with a question on push motors. High thrust, low speed.
I would always reccommend twin thrust for reliability.
Repeated heavy loads over long distances = diesel.
Light to medium loads over short to medium distances, well this is the boat builders preference. I chose twin 4-stroke outboards for reliability, easy maintenance, and easier to remove rope from the props. The props can be quickly changed to suit the job demands. I am not even going to try to do much in the math department on thrust but, here is my experience.
I have been pushing 220-ftL X 20-ftW X 6-tons of dock for a distance of 1.5 miles every year for 20 years.
200+ hp V8 Mercruiser IO on a large runabout took 45 minutes. 10+gallons of fuel. Unknown prop size.
Twin 50-hp, 4-stroke, outboards on 24-ft work pontoon boat took 30 minutes and less than 4 galllons of fuel. Props are 12.25" X 9", 3-blade.
Top speed with the twin 50s is a whopping 12mph. I did consult on props at our local Acutech shop and there will be 4-blade props next season.
Just like BigBuilder, my barge came out because of ice on Lake Champlain. I can wait for a warmer day to winterize the outboards.