What is a "bow lifting" prop?

Richard Selman · 07 May 2008, 12:30

What do the prop manufacturers mean when they say a prop is "bow lifting"? Are they trying to describe a certain general characteristic of the rpm verses thrust curve?

Richard

jwalker · 07 May 2008, 13:21

It's a prop with a characteristic which causes it to pull the stern down into the water and therefore lever the bow upwards.

Chris · 07 May 2008, 15:12

The idea of a bowlifting prop is to give better hole shot, 4 bladed props for example generally lift the bow more.

Richard Selman · 07 May 2008, 19:17

Do they mean that there is more thrust at lower rotational speed (i.e. more efficient low down) to pop it out of the hole - and does this automatically mean that there is a trade off at the high end?

Richard

jwalker · 07 May 2008, 19:44

Nope. Normal use is to get the bow lifted at high speed and so reduce the wetted area of the hull in order to reduce drag. It is more common not to require bow lift for getting onto the plane. In some prop/hull combinations using a bow lifting prop requires trimming the drive in to prevent the stern bogging down while the boat is lifting onto the plane.

fred bolton · 07 May 2008, 20:04

one of these should lift the bow http://www.letsgoseeit.com/index/cou...e37_8in_30.jpg

sorry too obvious to miss that one, I'm sure that we will have some more "big ones"

Limey Linda · 07 May 2008, 20:37

Quote:

Originally Posted by jwalker

Nope. Normal use is to get the bow lifted at high speed and so reduce the wetted area of the hull in order to reduce drag. It is more common not to require bow lift for getting onto the plane. In some prop/hull combinations using a bow lifting prop requires trimming the drive in to prevent the stern bogging down while the boat is lifting onto the plane.

I agree with JW. I was getting a little confused with earlier posts relating to grip/holeshot. I have a Merc. Mirage ss prop. which they claim is bow lifting.
My limited experience is trim right in for hole shot and then trim out a little. As I get to about 4000rpm the bow lifts further and the boat starts to balance on the planing pad. The change is very noticable; vibration goes to almost zero and engine changes sound to a purr rather than a roar. Only testing I have done is in smooth conditions and I need more practice to get it right every time including adjusting my trim sensor so the gauge is more meaningful. I think it is going to take a few 100 dollars of petrol to learn how to drive the boat properly.

Bigmuz7 · 07 May 2008, 20:48

Quote:

Originally Posted by Limey Linda

I need more practice to get it right every time including adjusting my trim sensor so the gauge is more meaningful. I think it is going to take a few 100 dollars of petrol to learn how to drive the boat properly.

No guage ever works for me, the best ones are my eyes and ears

oh and yes .. my thumb on the button

Limey Linda · 07 May 2008, 20:54

Quote:

Originally Posted by Bigmuz7

No guage ever works for me, the best ones are my eyes and ears

oh and yes .. my thumb on the button

I am sure you are right. however my gauge at present barely moves off the down postion so a little adjustment might help me get a useful reference/starting point.

Limey Linda · 07 May 2008, 21:04

Quote:

Originally Posted by Bigmuz7

No guage ever works for me, the best ones are my eyes and ears

oh and yes .. my thumb on the button

I am sure you are right. however my gauge at present barely moves off the down postion so a little adjustment might help me get a useful reference/starting point.

Cookee · 08 May 2008, 13:47

Quote:

Originally Posted by Chris

The idea of a bowlifting prop is to give better hole shot, 4 bladed props for example generally lift the bow more.

Sorry Chris I have to agree with JW!

Chris · 09 May 2008, 00:14

Quote:

Originally Posted by Cookee

Sorry Chris I have to agree with JW!

Don't be sorry ! I am only going by what I was told when looking into four bladed props the guy I spoke to made reference to the fact they would lift the bow so I assumed that's what they are for.

If anyone is going to know it will be you lot !

Cookee · 09 May 2008, 11:47

Quote:

Originally Posted by Chris

Don't be sorry ! I am only going by what I was told when looking into four bladed props the guy I spoke to made reference to the fact they would lift the bow so I assumed that's what they are for.

If anyone is going to know it will be you lot !

Actually a four blader won't necessarily lift the bow - it's in the blade design that affects the handling rather than the number of blades. A four blade prop will generally give a better holeshot but have a lower top end in terms of revs and speed for the same design and pitch/diameter than a 3 blader. It is unlikely ever to be faster unless the three blade prop is inappropriate in the first place!

Hope that clears it up a bit?