Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Submarines => Topic started by: webbo on February 06, 2017, 05:01:26 pm
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LA class now in the water, loads of probs but steerage is very very bad, not a lot of room for bow thrust , any ideas please
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Assuming maximum throw on rudders e.g. 35 degrees either way. Extended rudders, try and get as much mass as possible in the centre of the boat, move the c.g. aft slightly.
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Would a fishtail rudder work on a Sub?.
Len.
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CAN TRY EXTENDED RUDDERS, WONT LOOK NICE . AND WILL TRY TO MOVE CG AFT A BIT, NOT A LOT OF ROOM
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Finally got foto down to size
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You can extend just the lower rudder, that won't show when in the water.
But like I said, make sure you have the maximum deflection you can obtain.
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I have the ohio class and that has poor steering at low speeds . to do tight turns you need to go fast .
john
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An LA should be more nimble than a Ohio, as it has a lower aspect ratio. Control surfaces forward of the props tend to be a bit weak as they lack the flow from the prop.
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webbo ....that 689 looks great just sitting above the water.......you must accept that these vessels in real life were not designed to turn on the spot or have acute handling characteristics at low speed
Hence scale handling will be the same/or worse :-))
Large radius voyage motion is fine......it's all to do with launching and berthing O0.......
Derek
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Going back an awful lot of years to when I had my SLEC/Engel USS Patrick Henry, it was a pig of a thing to turn...I learnt that when sailing slowly on the surface, an application of full rudder and 'pulsing' the throttle helped a hell of a lot to get it to turn. Underwater, it was a different boat...it would turn without any trouble. The faster it was travelling, the better it would turn.
I haven't used the Akula enough yet to really know how it handles, but I hope next week will give me an opportunity to sail it for a couple of sessions.
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Finally got foto down to size
Just see the stern of my Springer, waiting to come
To the rescue a little bit later :-))
Ned
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Going back an awful lot of years to when I had my SLEC/Engel USS Patrick Henry, it was a pig of a thing to turn...I learnt that when sailing slowly on the surface, an application of full rudder and 'pulsing' the throttle helped a hell of a lot to get it to turn. Underwater, it was a different boat...it would turn without any trouble. The faster it was travelling, the better it would turn.
I haven't used the Akula enough yet to really know how it handles, but I hope next week will give me an opportunity to sail it for a couple of sessions.
I should have added that the Patrick Henry didn't have the top rudder operational, neither has the Akula.
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on my LA i had to extend the lower rudder as the turning circle was rubbish.
after doing this, it transformed it. did look silly out of the water but when in you couldn't see it.
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Not sure if the same principle on submarines - I will find out in a few weeks, but on surface ships a scale replica rudder on a warship will usually give something approaching a scale turning circle.
ie: The equivalent of half a mile. (at 1/96 that can be 25 feet).
In a lake environment you usually want a much tighter turn than that, so I have usually had to double the area of the rudder to get a more practical turning circle.
The K Class I am building has a small "scale" rudder, and the original boats were known for their poor turning circle. I will almost certainly have to greatly increase the rudder size.
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A perspex rudder extension should improve the turning rate , although not scale , it cant be seen , in the water that is , regards Pete
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Taking all this info in, had to extend rudder on HMS Rodney, worked a treat but did cheat a little and added a Bow thruster as well
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webbo,
I've heard that a bow thruster only works when the boat is not moving forward. Underway, there's almost no effect at all. Is that your experience?
Dan
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I am not sure if you are complaining about your sterring response SURFACED or submerged. If surfaced, then yes all nukes are dogs on the surface, but expect the turning response to improve markedly when submerged. The upper rudder makes a huge difference, all improvement. Being a prop driven boat you will also find a better response in one direction over the other due to the prop torque. if you build a pump-jet propelled boat you will find the surface response to be even worse that you are currently experiencing, while again, it will markedly improve when submerged.
Bow thrusters, as Skip Asay for years has explained, do almost nothing to improve turning, especially when underway. Don't waste your time.
I have found that by moving the center of mass, not gravity, forward, the boat will pivot around that center of mass and this will help your steering significantly. It can be difficult to due this if you are unable to compensate with foam for the mass forward.
Last word...now you know why boats always have tugs in attendance assisting at low speeds.
Hope some of this helps.
Jonathan
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I must say that I found your advice puzzling as the center of mass is the center of gravity.
I agree with the Skip Asay conclusion. I've talked to Skip a few times at the Carmel Indiana sub meets and he has a lot of very practical experience which he readily shares.
Cheers,
Dan
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Just a thought, if the centre of mass is behind the sticky-up finny-conning-tower-bit (is that the right phrase?), when submerged you should find that generates a lift aiding the turn.
Hmm. Another thought. Do subs lean in or out when turning?
Andy, not a submariner. Though me grandad was.
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Generally subs lean inboard. This, in turn, can lead to snap roll, an effect where by the rudders generate downward thrust due to the change in there angle relative to the axis of the boat. They effectively become dive planes positioned to dive.
The effect of the mass forward is to become the pivot point around which the boat rotates, in a turn. Move it further aft and the force required to pivot the hull increases as the forward and aft hull balance each other. I am probably not explaining this correctly, but remember that we are operating scale models in a non scale environment. This has to be factored in.
Jonathan
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I don't think that centre of gravity or mass has much relevance in turning model subs?
Aircraft - yes. They are moving and turning rapidly in a low density medium (air) so mass distributed to one end or the other really affects handling.
Subs are moving and turning relatively slowly in a very dense medium (water) so the main factor is the side area of the hull being presented to the water. (Moving the centre of gravity in a displacement hull WILL have an affect because it changes the side area presented to the water.)
So increased rudder size (and yes, throw) are the main factors useful to us.
David
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And I should have gone on to say that the rudder size and angle of throw produce a turning force.
I suspect that bow thrusters are not very effective while under way because they don't have much turning force compared with the dynamic forces generated by water flowing over the model.
David
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Rudder extension....I have seen this done by means of a “click on” acrylic piece. Very low profile in the water as it is transparent, and out of the water on the boat stand you remove it.
Another possibility is to make your propeller shaft pivot (gimbal the propeller), it has been done by David Merriman on a NAUTILUS.
As I’m not posting pictures of other people without their explicit permission, and I also strongly believe in referencing, so I hope moderators allow me to post a link to another forum were David’s “how to” was posted.
http://www.theassociationofmodelsubmariners.com/t1210-david-merriman-s-nautilus#7268 (http://www.theassociationofmodelsubmariners.com/t1210-david-merriman-s-nautilus#7268)
Grtz,
Bart