TOPIC: prop

Trying to figure out the right prop and dont want to buy 20 to do it...

Larson era G3
'75 Evinrude 70hp inline 3
currently running a 14x17 and PO said it would run mid 30's. To me, with a 70hp it should be running more like low 40's

dont see pulling any skiers etc, just cruising.

Should run mid 40's. 21" pitch.

Ask, How much more does a Larson g3 weigh than a Tritt and is power output at the crank or prop. Are you over reving with the 17? If power is at the crank 21 could be too much. I'd like to get a 17p as its a good all around size in many cases. 19" is very popular and should get you to 40-45mph depending...

www.go-fast.com/Prop_Slip_Calculator.htm

suppose the gear ratio is 2;1? and 17P prop at 5200rpm,with 10% slip I get 38mph as a approximate speed. Change the prop to 19P and you gain 4mph to 42.

Without a tachometer it's hard to tell if you are using the proper propeller.
I would think the 17" would be just fine. A 21" may be too big.
A lot of long shaft 3 cylinder OMC motors turn a 19" just fine.
As I remember it. A 13 1/4 X 17" propeller was standard (shipped with)
that motor. Your G-3 is a different boat than most on this site.
You have a nice boat but different than mine. There are a lot of used
OMC propellers that fit that motor. You should not have any trouble trying
various sizes. Dealers will not order new ones for you to try and then return.
However a lot of dealers will lend you used propellers.

Good luck

John

19-21 would be awful close, depending on the load you're hauling.

Do you have a tach in the boat(immensely helpful in picking a prop)??

There was a large seller of props I saw on the internet two years ago that allowed you to exchange there new prop if it were in same condition returned within a specified time, dont remember the company or brand of prop? or know if they still have that service.

Don't think a 14 by 17 is the correct prop for a G3. The diameter is too big - think that prop more suited to pushing heavy loads.
My guess is that you need to go to the props that are 13 or 13.25 in diameter and as for pitch think 19 will be your best bet. You really need to get a tach though otherwise you are purely guessing on what is right for you boat.

I need to research and see if a tach can be hooked to that motor (Im sure it can). There is a tach in the boat but, its broke so Ill need to get a new one. What you guys are saying is lining up with my thinking. I was figuring something around 13x19 would be closer.

Why do you think the Tachometer is broke?
If it's not hooked up it will not work.

Anyway. There should be a gray wire inside the control box
which is the tachometer lead. You also connect B+, a purple wire,
and Ground from inside the control box.

I once found that the ground needed to be cleaned to make
my tachometer work properly.

Without a tachometer finding the correct propeller is just guess work.

On OMC tachometers the selector switch on the back points to 6.

John

The no pointer was my first giveaway of a broken tach... I was hoping to find the same style to replace it with. Just havent found one.

That's a good sign it's broke.