The tides on Regina should average 80 meters high

[Peter Newman]

Much of Earths tides are caused by Luna. Assiniboia, Regina's primary is tens of thousands of times heavier than Luna is. Oh, sure Regina is about 38.3 times farther away than Luna is (55 diameters of a size 170 or so world is about 9.35 million miles, vs about 0.242 million miles between Earth and Luna) but that will only reduce the tides about 1,500 fold. (Inverse square law)

Since Assiniboia, as a large gas giant should have a mass over 1,000 times that of earth, while the moon has a mass of about 1/81st of earth. Therefore the "lunar" tides on Regina should be about 62.5 times higher than Earths lunar tides.

Since many parts of earth have tides of about six feet (30 feet here in Anchorage, but we're in a fjord) and earths tides are about one third solar and two thirds lunar than Luna must cause about four feet of tides on earth. Multiplying that by 62.5+ we get 250 feet of tides in average areas. Converting back to metric, as all Traveller measurements should be, we see that Regina should have tides of about 80 meters.Why would anyone ever live by the sea?

Also, what about erosion? Why haven't the continents been worn down into the sea by now? How new would they have to be to be as big as they are?

 

[Spinward Flow]

You are proceeding from a potentially false assumption.

Regina (moon orbit 55) may be tidally locked to Assiniboia (large gas giant in orbit 4) and if Regina is not tidally locked then it probably is not rotating anywhere near as quickly as Terra (terrestrial world in orbit 3) is relative to Luna (moon orbit 60). Slower rotation on Regina would mean that the tides still happen (from Lusor the stellar primary if nothing else) but they would rise and fall much more gradually, meaning less "violently" near any coastlines on Regina.

Extrapolating tidal forces and tide heights from Sol-Terra-Luna into expectations for Lusor-Assiniboia-Regina may not translate over in quite the way that you are assuming, for a variety of reasons.

 

[whartung]

Slower rotation on Regina would mean that the tides still happen (from Lusor the stellar primary if nothing else) but they would rise and fall much more gradually, meaning less "violently" near any coastlines on Regina.

Does that suggest that the size of the tide is more the "ripple" of the forces affecting the water?

I've seen figures (obviously exaggerated) about how there's this "bulge" of water following the moon, similar to iron filings following a magnet.

Is that whats really happening? Is the moon "holding" the water higher? Or is it, rather, simply stomping, like feet in mud puddles, and the tides are, essentially the large waves that result from this stomping. I honestly don't know.

If the water is being pulled, then Regina (or whatever) will have to cope with large tides, even if they slowly form. Consider, in San Felipe, in Baja California, it has both a large tide and shallow coast line. When the tide goes out, the shoreline falls back by, I think, several 100 yards. You would certainly not want to build anything on that space, as it'll be flooded the next day. Since this is a daily tide, obviously this is not an issue. But by the same token, there's no docks there either -- they don't make much sense. Instead there's a bunch of small, grounded fishing boats waiting for the water to return.

Regina would have to cope with, what, annual? Semi annual? Once every few years? massive water surge as the tide rolls in, in tune with the planets rotation.

If, however, it's "feet in a puddle" the water is just constantly being disrupted, then the wave systems may be quite different and routine even with a slow rotation.

 

[Enoki]

If Regina were tidally locked and not rotating with respect to Assiniboia, there would be very little change in the gravitational pull between the two. They'd be like two magnets with their north poles facing each other at some distance that varies little. The only change would be if Regina were not in a circular orbit. Then the change in gravity would be relatively slight resulting in smaller tides due to that small change in gravitational pull. The gravity of the star would still have an effect, but it too would be smaller, so I'd think the tides would be slow changing and not massive in terms of height.

 

[Spinward Flow]

I'd think the tides would be slow changing and not massive in terms of height.

The tides could be massive in terms of height (the proposed 80 meters variance), but if it takes a month or more for those tides to ebb and flow, that's hardly a tremendous hazard to life and limb like the tides on Terra can be if you're in the wrong place at the wrong time. The tidal changes over a month (which for a tidally locked moon would be "a day"), rather than twice every 24 hours, makes for some very different assumptions about tide heights, flow rates and timing.

To put it politely, we have nowhere NEAR enough detailed information about the Regina star system to start making definitive guesses as to what the ocean tides on the moon Regina ought to be like.

To give you an idea of why I would say that, in the 19th century, you needed to combine 10 influence factors to determine local tides ... and by 1944 and the D-Day invasion, 26 influence factors(!) ... in order to reliably predict ocean tides at specific locations on Terra. LBB6 simply doesn't provide anywhere NEAR that level of detail to be able to model similar outputs.

 

[Peter Newman]

You are proceeding from a potentially false assumption.

Regina (moon orbit 55) may be tidally locked to Assiniboia (large gas giant in orbit 4) and if Regina is not tidally locked then it probably is not rotating anywhere near as quickly as Terra (terrestrial world in orbit 3) is relative to Luna (moon orbit 60). Slower rotation on Regina would mean that the tides still happen (from Lusor the stellar primary if nothing else) but they would rise and fall much more gradually, meaning less "violently" near any coastlines on Regina.

Extrapolating tidal forces and tide heights from Sol-Terra-Luna into expectations for Lusor-Assiniboia-Regina may not translate over in quite the way that you are assuming, for a variety of reasons.

No, we know that Regina is not tide locked because that canonical map does not feature a hot face and a cold face. Regina must rotate.

Checking the details from DGP's Grand Survey page 35-36, which shows the original creation of this map of Regina, we see that it is not Tide locked. Then go to page 43 for this completed map and we see that (in CT at least) [1] Regina has a rotation period of 25 hours, 31 minutes and 31 seconds. The extra 91.52 minutes will not make up for the 65 times higher tides.

On the other hand, since each map hex is 1074 kilometers we would be fine if all those mega-cities were 25 kilometers from the coast, and at an altitude of 250+ meters.

[1] MegaTraveller uses the same map in World Builders Handbook but the table listing Regina's length of day is absent.

 

[BackworldTraveller]

Hot-Face/Cold-Face is a feature of items tidally locked to a star. Not an issue on Regina as the star is looked at by both faces each time it rotates about Assiniboia.
Assuming the moon is tidally locked, it will be lit on each face (from 2 directions) as it is turned on its way about the giant - although planetary eclipses could make a significant difference to the received daylight from Lusor/Speck (depending upon orbital tilt of Regina that could be daily or seasonal) and Darida's contribution is tiny and mostly infra-red (also eclipsed regularly).
All this does suggest that the Amindii would be keen astronomers in their early history.

I'm not sure I agree with your calculation of the gravity effect exactly - the force from the moon of (1/81)/(238855^2) is nearly 4300 times stronger from the gas giant (81000/(9350000^2))...There may be an extra square-root in your version, or you could be right and I'm missing one. Anyway - the "locked to the giant" option seems quite likely just due to tidal friction in either model - which suggests no tides to speak of!
OK that was rubbish: The tidal effect is the difference between the moons gravity on the near side of earth (238855-6000) and the far side (238855+6000). For assiniboya, it's the difference between the near side of Regina (9350000-5600) and the far side (9350000+5600). The ratio of these is about a factor of 101. This still suggests we a re looking at a long period rotation if not locked.

n.b. Also recall that tidal forces work on rock as well as water. Regina will still have a molten core, so that will also slosh if the moon rotates its face relative to Assiniboia. Cue: Volcanoes. e.g. The ground moves by more on Io (OK much closer than Regina and pinned by Europa) than the water does on Earth!

The exact height of the tidal range at a given point would be impossible to check, but if Regina isn't locked, it would probably be large (see "Bay of Fundy" for the lower end of the lower-range).

If there is a huge tide, Large tidal ranges make great food resources for wildlife. They can provide tidal power options in early settlement scenarios and make gated docks a requirement for any harbours for ships brave enough to head out. They make good tidal currents for those Seafarer rolls and some spectacular whirlpools and periodic waterfalls (as the tide goes over a ledge/ridge) for characters to get caught in. Maybe not on Regina - but useful ideas for somewhere.

 

[tjoneslo]

There are several things wrong with the math. Tidal forces is an inverse cube relationship, and depends on the size of the world.

https://keisan.casio.com/exec/system/1360312100#! => Tidal force calculator

Tides are cause by the fact that worlds are real objects. Objects in different orbits travel at different velocities. An object 1000km in diameter orbiting another object (of any size), the inner side and outer side of the object should travel at different velocities. But can't because they are bound together by gravity. There is a "tidal" force that wants to pull the object apart, both toward and away from the other object. Water moves more than rock, so you get two tides a day. The tides are trying to pull the water off both sides of the object.

There is a "roche limit" where the tidal forces will tear the orbiting object apart.