Surface piercing props???

[mr_bonkers]

Newbie question...

Whats the difference between surface piercing props and ..er .. normal props?

I just designed and build a tunnelhull thingie, but it will only plane when I give it a push from the bank..... using standard prop

[mbjunkie2001]

a surface piercing prop does exactly that, pierces the surface. by some hard to explain rule of hydrodynamics, props only make power during a small part aof their strok and are otherwise just being dragged through the water. by taking the prop out of the water,it isn't dragging through the water and has less resistance, hence more speed.

[FrankW]

Surface (surface piercing) and sub-surface props aren't really different at all. Infact most props are both. The difference is how the prop is set up in relation to the boat and the water.

A surface drive (surface piercing prop set up) usually only has the bottom half of the props rotational arch in the water. This reduces drag and allows the prop to reach higher RPMs, and thus a higher top speed for the boat.

A sub-surface drive puts the prop completely in the water. This set up is best for slow/heavy boats and boats that need more bite in the water for acceleration purposes.

-Frank

[mr_bonkers]

Ah right :)

Someone told me they cavitate less? Meaning they don't drag air under with them??

[mbjunkie2001]

logic would make it very easy to cavitate because they're so close to the surface. but this is not a logical world,so im not sure.

[Andrewg]

They dont cavitate they aerate - ie they drag air in with tem - this is good because it reduces their drag and allows them to turn at high speed

The disadvantage is they tend to slip a little on acceleration but they top out at a higher speed

Put it this way it doesnt seem to slow down hydros or drag boats