Subs with twin props - alignment

The U class I am having a go at building is my first sub with twin screws.

Usual practice in submarines seems to be that the props are at right angles to the direction of motion. Does anyone have a feel for what happens if the props are angled slightly up or down? Is this important? Does it give you bows up/bows down operation?

The reason I'm asking is that experience tells me that it is very difficult with a new model to get the right combination of motor, gearing, prop diameter and prop pitch to get the right current draw, model speed etc.

Hence a bit of "wriggle room" with prop diameter is useful but twin screws don't give you much scope to increase the prop diameter before you start to foul the hull, rudder, stern planes etc (I'm thinking of the U Class.)

So a little bit of scope to change the angle of prop shaft relative to the subs axis would be useful. So I hope you are right. Because yes we are not talking racing models here.

I have spoken with Nigel about this who indicates that the alignment is important.
It is similar to the "thrust line" concept in model aircraft.
Probably less significant in model subs but Nigel suggests that if you imagined extending the prop shaft to the bow , the line would be close to the bow at the waterline/

Just adding to this, now that Dzik is complete.

The props in the end were fitted parallel horizontally but the shafts were inclined slightly upwards, vertically - if you see what I mean.

It doesn't seem to have created any problems - the bow does not dip when you throttle up etc. etc.

This is my first experience of running a sub with twin props so some videos of using twin channel mixing to aid stationery and under way turns:

https://www.youtube.com/watch?v=oy7Wxdo13bs

https://www.youtube.com/watch?v=CQfYg0AbKAU

Richard(Admin) wrote:That's very impressive David, although I'm not too sure what that yacht skipper thought of you chasing him through the turn in the second video...

Yacht Capt probably thinking Dave looking for a firing solution,bloody targets getting in the way.

nice video's David


Mark

Yes,I only just noticed that when I was looking at the videos. With the mixer I can now do the marine equivalent of Harrier "viffing" to avoid impacts!

Still Sunday morning at Barrow is as nothing compared with the "Free sailing session" at Alfold.