Does a stream lined prop dog work

[martin]

Any one know if this makes any difference to speeds as ive seen it mentioned a few times. Where the front face of the dog has a taper so you dont have the square shoulders of the strut & dog together with the gap between them causing drag. Thanks Martin.

[m4a1usr]

I dont think it would make any difference if the drive dog is smaller then your strut/ stinger diameter and the same diameter as the hub on your prop. When I size a drive system I go out of my way to ensure that the drive dog is approximate in diameter to the strut. Its sort of a tough job on small and mid size hulls. Thats why I no longer buy any flex shaft assy with the dog pinned or welded to the stubb shaft. I want to make the diameter choice based on my prop choice and what strut/stinger I plan on installing. Just my opinion.

John

[detox]

Grimracer once stated taper is needed on larger drive dogs to prevent lift.

[egneg]

Grimracer once stated taper is needed on larger drive dogs to prevent lift.

What is considered a large drive dog?

[detox]

What is considered a large drive dog?

Larger than strut diameter...or same size I guess.

[785boats]

Martin.
I think the idea of the angled front face of the dog was to reduce the shockwave of water from a vertical face that forces it's way past the strut bearings & up the shaft.

Cheers.
Paul.

[egneg]

Ok that makes sense but then what do you do when the prop hub is larger than the drive dog?

[785boats]

The outside diameter of the dog is not changed. Just the front face of the dog angled back say, 15 degrees or so. This leaves the rear half of the dog at the original diameter.
If the dog is a smaller diameter than the hub of the prop to start with, then I'd be getting a bigger dog to match the prop.
Cheers.
Paul.

[lomdel]

That refers to the dog, what about a streamlined prop nut? The one with the sharp pointy end at the back. Does that make a difference in the flow of water around the shaft/prop at speed?

[martin]

[QUOTE=785boats;321498]Martin.
I think the idea of the angled front face of the dog was to reduce the shockwave of water from a vertical face that forces it's way past the strut bearings & up the shaft.

Cheers.
Paul.
Thanks Paul, Yes i seem to remember hearing that as well.

Re pointed prop nuts i dont know whether it makes a difference but i do use them. Thanks Martin.

[tharmer]

I think a squared end is better. If it's goo for the sponson transoms, it's goo for the prop nut.

[Chris Harris]

Tapering the front of the drive dog even if it is the same diameter as the strut can make a difference. Because of the gap between the strut and the dog to allow for shaft wind up the water can not completely jump that gap and will reach the flat face of the dog. Any water hitting a blunt surface is going to cause drag.

I have seen tapering the the front of the dog make a 2mph difference in SAW boats.

As for coned prop nuts the only real benefit in my opinon would be on a subsurface drive. On a surface drive most of it is out of the water when the boat is at speed.

Chris

[Boaterguy]

Even with subsurface drives, there is so much turbulence behind the prop, a bullet nut is not required (thats the pointed one). Plus they come off so easily (Already lost some props that way) and the difference is so minimal (i haven't noticed a change) that it's not worth it. I don't know about the tapered drive dogs though.

[egneg]

The whole point I am trying to make is that there is quite a bit more turbulence from other areas. Unless you have access somewhere to test for turbulence caused by prop dog/shaft/prop interaction it's all speculation without the data.

[fatboyelectric]

Tapering the front of the drive dog even if it is the same diameter as the strut can make a difference. Because of the gap between the strut and the dog to allow for shaft wind up the water can not completely jump that gap and will reach the flat face of the dog. Any water hitting a blunt surface is going to cause drag.

I have seen tapering the the front of the dog make a 2mph difference in SAW boats.

As for coned prop nuts the only real benefit in my opinon would be on a subsurface drive. On a surface drive most of it is out of the water when the boat is at speed.

Chris

........but a conical prop nut does help me sleep at night...LOL