02 Johnson 40hp 2stroke prop help

[Luna Sea]

Hi,

I just picked up a 2002 Johnson 40 HP 2-stroke and it didn?t come with a prop. After looking around this site (and the classic whaler site) most of the morning I have figured out the prop will be approximately 12? in diameter but I haven?t a clue as to what pitch I need to order. From the order sheet I believe I need a ?Thru Hub Exaust & 13 Tooth Spline Small Gearcase? style.

It?s going on a 13?Achilles SGX (rollup model w/aluminum floorboards). The boat?s rated for a 40 HP up to 209 pounds, and the boat itself weighs a little under 200 pounds. I have a safe/stable 10' AB inflatable RIB with a 20 hp 4-stroke on it for normal/safe cruising. This new to me boat is supposed to be the ?speed? boat/toy. Any help as to what pitch will give me and the bikini girls the most entertainment/speed would be appreciated. Course I?d still like the thing to plane at a reasonable rpm, cruise normally, ect. as well. I?m guessing 15,16 or 17 pitch??

Thanks in advance,
Mike

 

[steelespike]

Re: 02 Johnson 40hp 2stroke prop help

I would guess a 16" pitch. With no base line performance it might pay to find a dealer that
will let you try props till you find one.You'll need make a deposit and be expected to buy a prop.
You'll also need a tach and gps for rpm and speed.The motor must operate within its rpm range no way to tell without the figures.If the prop is a little light you can still use it just watch the rpm.If too much prop you just shouldn't use it over an extended period.
Just because the boat is light doesn't mean it will be truely fast and easy to push.

 

[ditchen]

Re: 02 Johnson 40hp 2stroke prop help

I am running a mv1448(tin) with a modified johnson 50hp (twin) on a jack plate. I am running a 21" pitch heavily cupped. I still need more pitch, but with this small gear case they are very hard to find. I have a collection of 11 1/4 dia X 15, 17 19 OEM SST props

You may be able to start at a 17" pitch amin of 15". Availability may dictate where you will start at.

 

[steelespike]

Re: 02 Johnson 40hp 2stroke prop help

I'm running a 19 on my 88 stock 50 on a 18' 77 Crestliner utility 375lb dry weight.
I don't have rpm/speed figures but it has had the 19" since new and has performed well under all conditions.19" is the largest available here at iboats.
While a 19" is available for the 40 ,16 is not, a 17" has 4 types available.

 

[Luna Sea]

Re: 02 Johnson 40hp 2stroke prop help

Thanks guys,
I found a prop site that had a nice ?prop calculator? on there. I typed in the 40 2-stroke Johnson, ?3? passengers, ?100? lbs of gear, and ?12? gallons of gas. I was even able to find my exact brand/model inflatable on there! It recommended the 17 pitch for ?speed? and a 15 for ?watersports?. Guess I?ll go with a 17, less chance of overeving the engine right? And for the price of an aluminum prop here on iboats I think I?ll just order a standad aluminum one for $75 and see what happens. I can always have it reworked at the local prop shop if it's off.

The Piranah prop ?kit? is available with 15 and 17 pitch blades, anyone got good/bad reviews on them?

Seems "get a tach" on the prop forum is the equivalent of "get a manual" on the engine forum. Are you guys talking like an automotive one or a wired gauge type? Would I have to run with the cowling off then? Or maybe I could sneak a couple wires through there somewhere? Where to hook the wires would help me, manual has to wait till next month to order....

Thanks again,
Mike

 

[steelespike]

Re: 02 Johnson 40hp 2stroke prop help

That does sound like a really good prop calculator.A 17 seems a reasonable size.
The Tinytach is easy to install, it is the inductive type ,off a plug wire.One that fits yours will fit any 2 cylinder 2 stroke.. I think you could mount it anywhere you just need to be sure of the wire length as it can't be trimmed.I believe there are other brands as well.