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    Subs with twin props - alignment

    david f
    david f
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    Subs with twin props - alignment Empty Subs with twin props - alignment

    Post  david f on Wed Nov 17, 2010 4:28 pm

    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?
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    Post  Tom(ADMIN) on Wed Nov 17, 2010 4:35 pm

    I wouldn't have thought it would make a great deal of difference to a relatively low powered sub, David...I do recall back in my multi-racing days prop shaft angles were important when using a high revving, high speed motor like a .65 glo motor, and even more so in the world of hydro racing, but I don't think you'd notice much difference in a sub.

    I stand to be corrected though...
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    Post  david f on Thu Nov 18, 2010 12:39 pm

    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.
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    Post  Tom(ADMIN) on Thu Nov 18, 2010 12:41 pm

    That's one reason why I like boats with single props...
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    Post  david f on Fri Nov 26, 2010 4:21 pm

    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/
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    Post  Tom(ADMIN) on Fri Nov 26, 2010 4:52 pm

    I guess you could align the props and shafts correctly and then use flexible couplings to hook the shafts to the motors? I always use high quality silicone tubing now for connecting prop shafts to motors...easy to use, easy to replace and very adaptable to differing angles between motor and prop shaft.
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    Post  david f on Mon Jul 04, 2011 1:01 pm

    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
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    Post  Tom(ADMIN) on Mon Jul 04, 2011 1:14 pm

    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...
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    Post  thegrimreaper on Mon Jul 04, 2011 3:36 pm

    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


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    david f
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    Post  david f on Tue Jul 05, 2011 8:20 am

    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.

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