Outboard Discussions

[ebb]

What a great and rare find.
I'm wondering if there is an apples to oranges comparison here?

Really! I don't know.

But there is a differnce between a standard prop and a high thrust prop.
Also that lower units can be standard or more robust. Is this important?
I understand that our boats are small enough to use a standard OB.
Was this taken into account? Is it important?
Certain that a 2stroke has MORE vibration than a 4stroke. Right?

google> prop size for sailboat outboard
boat design forums

The thread begins with 'liz' asking what to power a 24' 6000LB disp
with a 9.9 4stroke long shaft Yamaha behind the boat's rudder. [Could be an Alberg....]

last poster on thread, alan white:
"Your ratio is 2.92 : 1\The engine RPM is about 5500
Your motor appears to take a max diameter of 10" or so.
The most efficient prop would be too large to fit as a three blade,
so a four blade is recpmmended.
The recommended pitch is 8.5."

He's talking about a Yamaha 9.9 here, not the one you found, Craig.
A decade ago and still unused, I choose an 8HP Yamaha (said to be a choked down 9.9) that weighs in at 110LBS.

That is utterly rediculous, and it is utterly rediculous I customed litlgull's rear end to fit this monster. I know I will want and NEED a motor HALF the weight.
SOON I will also be looking for a 2-stroke, when I finally get on the boat.

We pointed this out befor:
If you can't get the 4stroke to run, it has to go back to the dealer.

With a 2stroke, you can do regular maintenance and tinker to keep it going.
And a 6 or even 8HP 2stroke won't require a crane to lift it out of the well.


Some people have all the luck!

[c_amos]

Dunno ebb,

My old Yamaha 6 hp worked well with the stock (7x8 IIRC) prop, when I switched to the 'high thrust' (also 6x8) mickey mouse ear prop the rpm did not change, but the backing was improved.

When I bought the tohatsu, I tried it with the stock prop which was something like 7x8, I was underwhenmed with this, it did not seem to want to turn up, so I poped for the expensive 5.99 x 8 'high thrust' prop (you can see the details earlier in this thread)... it was not much better.

I suspect I might have been happy with the tohatsu, had I not been spoiled by the Yamaha. I really think your answer of the 8hp (2 cyl) Yamaha with the high thrust arrangement is probably going to prove to be a wonderful motor for Lil Gull. I am glad many others find the 4 stroke Merc/Nissan/Tohatsu solution to work out for them... I am not happy with it myself.

I will do some testing with both motors though, I expect to conduct some rather scientific experiments where I force myself to motor a standard course with both (one at a time of course) to prove out the fuel use issue.

It is interesting to note, the 4 stroke has to work well higher in the RPM range to acheive hull speed then the 2 stroke did... I suspect this will negate some of the fuel savings. I KNOW from experience that the (2 cyl) 2 stroke is smoother then the (1 cyl) 4 stroke... and frankly I doubt that it is any louder (maybe I can barrow a db meter to see for sure). The Yamaha always reminded me of a cyl diesel with it's mechanical drone... not un unpleasant sound to me.

We will see, stay tuned for further updates... if nothing else, I do tend to go on (and sometimes on and on) about what ever I find.