Fat Shaft

[FlowMaxx]

What exactly is the difference between small and large shaft? are the splines the same and the shaft just larger?

Thanks

[FlowMaxx]

Anyone?

[catfish123]

The splines are different..........and the fat shaft is a bigger diameter...........no need for thrust washers on the fat shaft.

[Michael J Giesler]

hi Mark i have one on my grandsport with the 280 stronger than the small shaft but finding props sucks is getting better now in my opinion you only need a fat shaft if your running offshore or have big time horsepower :thumbsup:

[FlowMaxx]

Thanks Guys, I have a chopper that has 15 spline, but the area in the hub forward of the splines is much larger than the shaft. I have a thrust washer that fits the base of the prop well, but it still doesn't seem right. Can anyone explain this?

Thanks

[catfish123]

I believe the fat shaft has 19 splines.

[tj309]

Fat shaft has 19 splines and the small shaft 15. If you are running a surface piercing prop you need the fat shaft. Merc came out with the fat shaft for a reason.

[ddipert]

Flowmaxx.
Can you post a picture of what your talking about?
All of the Fat Shaft props I have seen the spline part of the shaft does not stick all the way through the prop hub like a small shaft does. The only part that sticks out of the fat shaft hub is the threads.

I would agree that Mercury came out with the Fat Shaft for a reason but most drag racers are still using small shafts for the prop selection.

[tj309]

Drag racing is all about lightweight boats spinning surface props for a short distance. Like the drag race cars with an engine that may last 60 seconds. I don't think most of us here want our stuff to break that quick. We want to go fast but need a bit more reliability. I will pay that small weight penalty for reliability. Just because a racing boat does it one way does not mean your personal rocket boat should do it the same way because in the raceing world they pay thousands of $'s for that last ounce of advantage. A smallshaft has less drag in the water than a fatshaft but also less strength. Unless you are a racer for the $'s I would go with the fatshaft.

I believe Merc came out with the CLE gearcase which had the smallshaft and it just did not cut it with the serious racers and so then went to the Sportmaster with the fatshaft.

You can buy a smallshaft prop and put it on a fatshaft with the proper insert. I am doing this now. There will be some venting of exhaust over the hub as opposed to thru the hub but that is the same as running a cleaver.

[FlowMaxx]

Flowmaxx.
Can you post a picture of what your talking about?
All of the Fat Shaft props I have seen the spline part of the shaft does not stick all the way through the prop hub like a small shaft does. The only part that sticks out of the fat shaft hub is the threads.

I would agree that Mercury came out with the Fat Shaft for a reason but most drag racers are still using small shafts for the prop selection.

I will need to dig it out and take some pics. It fits fine with the right thrust washer that has the lip with the OD to match the ID if the metal part of the prop. So it is resting on that and the splines. The rest of the shaft has a 1/8" or so gap all the way around it and is not snug to the shaft like every other one I have ever seen.