How is the bowthruster's power reduced by the boats speed?

[Michael Donning]

On 1.1.2018 at 15:08, Paul C said:

Are you using a physics model in the game?

Yes, I use a (quite limited) physics model in the game. There's a basic phyics engine which handles weight/gravity, inertia and forces. On top of that I add a simple 4-area buoyancy calculation and a multi-point approximated lift/draft calculation. Multi-point because opposed to an aircraft wing profile a narrowboat often moves in different directions on different positions of the boat.

My much simplified model therefore wouldn't cover the effect of speed on the bowthruster. For now, I just degrade the applied force depending on the forward speed... and I added an overheating turn-off after 10secs of use.

The attached image shows the draft/lift vectors of my model while turning.

 

[Paul C]

Instead of artificially degrading the bowthruster's effectiveness with increasing speed, you could introduce a "directional stability" force instead, which simply applies an opposite force to any sideways force on the bow, proportional to the speed. This would also have the advantage that it models the way a narrowboat can turn at various speeds, much more closely. Of course, its still possible to turn at speed, because the propellor is spinning faster and the rudder is able to change the direction of a greater volume of water, thus its able to apply a greater turning force anyway (ie it counteracts the directional stability, more-or-less in proportion). Most people know that the faster a narrowboat goes, the greater the push is needed on the tiller to deflect it the same amount - due to the greater amount of water being redirected by it. And that during reversing, there's actually very little force needed on the tiller - and also very little steerage from it. 

You might also want to think about propwalk and bank effect, since these are not insignificant either. 

[Michael Donning]

Thank you, Paul. I'll try the directional stability force (might take a time). But I fear that it will just interfere in a bad way with my lift/draft force model. I am aware that the latter is just a very rough approximation to the real thing. The implementation of propwalk is planned. Bank effect, not planned, yet.

By the way:

I've read that the Coandă-effect  is one of the factors which is responsible for bowthrusters becoming pretty much useless on speeds above 5kts (= ca. 5.8mph). But narrowboats don't travel at this speed (at least on canals).

[Irob]

On 01/01/2018 at 17:50, Jen-in-Wellies said:

Could it be a Bernoulli effect thing that causes this? The speed of the water rushing past the ends of the bow thruster tube as the boat moves decreases the pressure in the tube. The bow thruster has to use so much effort to overcome the pressure drop that the force of water coming out the end drops and eventually ceases? Dunno. My brain isn't working too well this New Years Day morning for some reason .

Jen

I like this one, it would seem to have a significant effect on the BT efficiency.

[Irob]

On 02/01/2018 at 22:46, Michael Donning said:

Yes, I use a (quite limited) physics model in the game. There's a basic phyics engine which handles weight/gravity, inertia and forces. On top of that I add a simple 4-area buoyancy calculation and a multi-point approximated lift/draft calculation. Multi-point because opposed to an aircraft wing profile a narrowboat often moves in different directions on different positions of the boat.

My much simplified model therefore wouldn't cover the effect of speed on the bowthruster. For now, I just degrade the applied force depending on the forward speed... and I added an overheating turn-off after 10secs of use.

The attached image shows the draft/lift vectors of my model while turning.

 

Wow very impressive !    Now if you could include a camera drone management system and a hydraulic autopilot to my tillerarm, i could cruise in inclement weather, sitting in my armchair watching the rugby on tv ! The future of narrowboating knows no limits. Keep up the good work !

[Ray T]

On 1/1/2018 at 09:50, Jen-in-Wellies said:

Could it be a Bernoulli effect thing that causes this? The speed of the water rushing past the ends of the bow thruster tube as the boat moves decreases the pressure in the tube. The bow thruster has to use so much effort to overcome the pressure drop that the force of water coming out the end drops and eventually ceases? Dunno. My brain isn't working too well this New Years Day morning for some reason .

Jen

In a similar way to how an Elvestrom bailer works in a sailing Dinghy?

With the bailer in the down position as depicted here a low pressure area is developed at the back of the bailer causing water to be sucked out of the inside of the dinghy hull.

"Elvstrøm was also noted as a developer of sails and sailing equipment. One of his most successful innovations was a new type of self-bailer. The design is still in production under the Andersen brand and has been widely copied. The new features were a wedge shaped venturi that closes automatically if the boat grounds or hits an obstruction, and a flap that acts as a non return valve to minimise water coming in if the boat is stationary or moving too slowly for the device to work. Previous automatic bailers would be damaged or destroyed if they met an obstruction, and would let considerable amounts of water in if the boat was moving too slowly."

https://en.wikipedia.org/wiki/Paul_Elvstrøm

Edited January 6, 2018 by Ray T