2 years Ive tried to answer this question.

This photo was taken from Shafts thru the transom thread and was posted by tom kane. I have always remembered this photo because of the closness of the prop to the transom. I do not know if it was succesfull or not maybe Tom could shed some light on it.

 

NICE! Never seen this picture, very interesting, the transom angle is 0°..and the propeller have traditional profile and works 50% in water...I'm curious....

What are the 2 things on the side? Do you have an idea?

 

I think the shaft length and angle has got something to do with the form of wave behind the boat.

 

..but the form of the wave behind the boat is related to speed...

 

I had a feeling that its wave length is a function of the boat length and its amplitude is a function of the boat speed.

 

At speeds over 40 knots the behind wake is near to flat...only spays due to the surface device skegs and propellers...

In the picture you don't see well the wake after the transom, but is near to flat. Both the boats are running at 50 knots.

If you have shafts on line + rudders + brackets + strut palms + bossings and speed of 30 knots abt. than you can observe the nice wave behind.

 

Syed..are you on board? I've found the picture in your gallery...

Where is the wave?

 

So you have found out that I am only a tiny boater. This is Usman, my son in the picture. I am making a shallow water propulsion system for this boat, therefore, I am interested to learn about this subject.

 

Thre are not tiny boater but only boater...!

Where is the boat in a lake? No waves at all...

If I'm not to curious, which kind of shallow water propulsion are you developping?

 

It is a river near Lahore with the name Ravi, the water depth is very uneven after every few minutes the outboard tilts. There are a lot of small heaps under water (I don't know the technical term for such things). I am working to have some thing like 'Gator tail outboard' if I find that it is mandatory to have a bit longer drive shaft. I shall be pleased to have any advice on this issue or any alternate solutions from all respected forumites.
There were waves, I shall find another picture showing some waves.

 

Thanks for the info, Syed!

 

You are welcome, RANCHI OTTO.

 

Seafury Marine's surface piercing drives seem to use shorter shafts than others. Their SF22, rated for up to 650 HP, has a standoff distance of only 14 inches/388 mm, and a shaft angle of 6 deg. They use a rudder behind the prop to steer. Leads one to wonder if the standoff distance is not as critical as Paul Kamen believes, provided there is a clean edge on the transom to leave water less disturbed, as jack frost suggested.

 

two years i hae tried to answer this question

A S/P (or any) propeller with rake will give a different thrust angle run in surface piercing mode.And still have an effect of pulling the rear of the boat down with an angled shaft.My trimmable drive when not locked down will stay at the lowest angle because the downward pull is greater in the decending blade than the accending blade and takes some pull to lift it up even with full power.It is surprising that just about any prop can be run in S/P mode.I/O`s and outboards are the only ones that realy can achieve a zero shaft angle and many of those often run with considerabe shaft angle because of boat plane angle or the need to trim for some reason.

 

Most of Hickman`s projects were very sussessful especially for that time.The boat shown ran close to 60 MPH.good for heavy machinery.