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[jaymac]

Can someone please clarify if this is accurate when props are OFF the boat lay the prop flat one blade at 12 o clock the  if the edge of the  blades are touching the  left then its LH and vicy vercy

[cdsc123]

In the real boat world, in the UK, yes, but the model props I have bought are from European suppliers and they consider this to be RH.

[SteamboatPhil]

Thats how I understand it   

[jaymac]

Thanks guys  Ithink I got it

[derekwarner]

 .....why not ask missyd  .....she is an expert on getting the port prop on the stdb side  ....but only on Tuesdays & Fridays..........the other days of the week the props are on the workshop bench  .....Derek

[bubbletop409]

Well here in the good ole US of A on model boats and real boats we look at the prop from the stern of the boat. Props rotating clockwise are referred to as "right hand", and props rotating counter-clockwise as "left hand". On a dual engine/propeller installation it is normal for the port prop to rotate left and the starboard prop to rotate right when viewed from  viewed from the stern.
Two props rotating in the same direction cause steering issues as speed increases.

[Neil]

great to hear that, bubbletop..that's exactly how I describe prop rotation to anyone asking me..........to much of this European c*** in our every day life for them to try  confusing me with props the wrong way.
well done that man,.....

[jaymac]

  My question guys was when Off the boatI agree with the statement but thats only describing the rotation dont identify  if its in your hand . Bubbletop  that dont hold for 3 props in the same direction as on my Wiesel no steering probs I'm not saying it might be better using  split direction but would be marginal I think, and though my PT 596 has    2 Lh and 1Rh I believe the real ones all went the same way .

[NFMike]

My question guys was when Off the boatI agree with the statement but thats only describing the rotation dont identify  if its in your hand .

It's the same. If you lay it in your hand so you are looking at the back of prop (ie. if the shaft was fitted it would be through your hand) you can see which way it will need to turn to push the water toward you (or to screw itself into your hand). If that means it would be turning clockwise it's a RH prop (UK) or LH (EU).

[bubbletop409]

  I believe the real ones all went the same way .

You are quite right about the real PT's props all rotating in the same direction ( right hand US ), and as a result as much as 5 degrees of counter rudder was necessary at speed to correct for the torque of all three turning clockwise.

[rickles23]

Hi,


The German E or S Boat had a shaped stern to counteract the torque of the three props.


I believe that the Turbinia had triple shafts each with three screws.


Regards

[bubbletop409]

Hi,


The German E or S Boat had a shaped stern to counteract the torque of the three props.


I believe that the Turbinia had triple shafts each with three screws.


Regards

That boat does have counter rotating props on the outboard shafts, the prop mounted on the center line has much less torque effect than the wing props. And you are correct in that those boats hulls and underwater gear were carefully selected to help give the craft neutral steering which could be a life saver in a tactical maneuver under fire.

[rickles23]

Hi bubbletop,


In an earlier post I think the figure of 5 Degrees rudder offset was used.


That is a lot of drag and wasted speed, especially when someone is trying to shoot you...


Regards

[bubbletop409]

I agree, and have often wondered why neither of the US builders of PT's took torque effects into consideration when they were in the first phase of layout design. I understand the situation was worse on the Elco built boats due to their small rudders in comparison to the Higgins boats, which were known to turn better than the Elco.

[Perkasaman2]

I suspect they accepted the side thrust generated as acceptable and avoid having to redesign one of the outboard veedrives to spin a prop in the opposite direction. The centre prop was direct drive. The German E or S boat had a trim wedge fitted at the stern to help keep the bow down at speed. The trim wedge generated lift at the stern to effect this aim. I think all the props on these E boats were direct drive. 

[jaymac]

I would think it very likely  the crews learned to use the  Bias at times to advantage as for the Makers and Powers that Be   to them  after all '' They Were Expendable'' 

[rickles23]

Hi,

On my racing Marblehead I use 7 degrees either side of central for normal racing.

But in a tacking dual I move a switch to give 11 degrees either side of central.

So 5 Degrees is a big drag.

Regards