The Dispatch Boat Appreciation Thread

SWM wrote:If it scaled, then larger ships would be able to have a higher maximum speed.

No, now you´re talking about something else.
Shipsize increase also means more that needs shielded.

I´m talking about the edge of where size of shielding goes beyond what is optimal or where it starts having severely diminishing returns.
The stuff noone builds because it´s so inefficient. Like supersonic passenger aircraft, it can be done but it´s seriously not worth the effort.


Because there´s just no reason for normal ships to go beyond that point of badly diminishing returns, improving max speeds by a few % if it means heavily cutting into the warload and doubling total cost and maintenance for the ship or something? Not gonna happen.

But if someone thinks it´s important enough, they might just consider it worth paying for a BC or maybe even BB sized d-boat just to get those extra few percent hyperspeed.
Especially if it´s combined with a streakdrive, allowing higher hyperbands to increase the gain further.

I have not seen anyone bring up the simple fact that DB's can "tack" into the grav waves with their oversized W-sails at greater angles than other ships and therefore are faster overall. Also maintained to higher tolerances. More than Honor I believe.(Appendix)

Relax wrote:I have not seen anyone bring up the simple fact that DB's can "tack" into the grav waves with their oversized W-sails at greater angles than other ships and therefore are faster overall. Also maintained to higher tolerances. More than Honor I believe.(Appendix)

You are mistaken. At one time, dispatch boats might have been able to tack at greater angles than heavier ships. But for quite some time, ships have been able to tack directly against the wave, at full speed. The direction of a grav wave is no longer a factor in ship speed. That is also mentioned in More than Honor, the Universe of Honor Harrington.

Here is the text:

By 1750 pd, however, sail tuners had been upgraded to a point which permitted the "grab factor" of a sail to be manipulated with far more sophistication than Dr. Warshawski's original technology had permitted. Indeed, it became possible to create a negative grab factor which, in effect, permitted a starship to sail directly "into the wind," although with a marginally greater danger of sail failure.

Other than being able to mount a Streak Drive on a Dispatch Boat (with whatever weight and other costs that entails) you current production Military Dispatch Boat give you the speed to move mostly data to where you need it. There is a little actual cargo or personal capacity but it is really small.

We really haven't see the small volume/high value commercial fast transports that would be running critical shipments and some people from point to point. I expect they exist but so far have not been relevent to the plot lines. "Small" commerical freighters are in the millions of tons range. The difference between current air-freight and moving stuff by containership is generaly you can get something overseas in a number of days by getting into the loading/shipment cycle of any of several commercial shipping organizations vs chartering something like a coupe of 747's or similar aircraft. At inter-stellar distances, just how badly do you need X amount of equipment or materials that are too big to stick into a private corporate (or news company) DB?

You start to get really specilized and in "interesting" market segments like stuff that is such a super expensive but small volume luxury or is actaully contraband and you are sneaking around really fast.
As the volume becomes of any significant size you start into the realm of Tea Clippers which were designed and optimized to essentilly haul one type of cargo really fast one-way and then had to drag themselves back with as much paying cargo as they could carry even if it slowed them down with more weight (vs the weight to volume ration of tea) because you also had to contend with production/delivery at the dock being tied to agricultural growing and processing realities.
You don't really have that with things like Montana Beef or Teran Wisky or all sorts of stuff because you really do need those really large freighters to be able to move enough general cargo (including things like beef) for efficienties of scale and make the ships profitable to run at some sizeable % of capacity.

Brigade XO wrote:We really haven't see the small volume/high value commercial fast transports that would be running critical shipments and some people from point to point. I expect they exist but so far have not been relevent to the plot lines.

Well, the Atlas-class liners we saw in Honor Among Enemies were sort of like this, though mostly geared to carry passengers. BC-sized, military-grade hyper generator. And I think Bachfish's "freighters" in War of Honor must have had military-grade hyper generators to shadow a Havenite destroyer being used as a dispatch boat. Granted, both of those were armed, but one imagines in a more settled region than Silesia, fast transports and freighters would still exist.

Brigade XO wrote:Other than being able to mount a Streak Drive on a Dispatch Boat (with whatever weight and other costs that entails) you current production Military Dispatch Boat give you the speed to move mostly data to where you need it. There is a little actual cargo or personal capacity but it is really small.

We really haven't see the small volume/high value commercial fast transports that would be running critical shipments and some people from point to point. I expect they exist but so far have not been relevent to the plot lines. "Small" commerical freighters are in the millions of tons range. The difference between current air-freight and moving stuff by containership is generaly you can get something overseas in a number of days by getting into the loading/shipment cycle of any of several commercial shipping organizations vs chartering something like a coupe of 747's or similar aircraft. At inter-stellar distances, just how badly do you need X amount of equipment or materials that are too big to stick into a private corporate (or news company) DB?

You start to get really specilized and in "interesting" market segments like stuff that is such a super expensive but small volume luxury or is actaully contraband and you are sneaking around really fast.

Especially interesting because on the timeline of interstellar transport the size of the ship has very little impact on the delivery time; its almost all whether you're willing to spring for mil-grade propulsion and shielding.

Let's contrast a 28,000 ton dispatch boat against a midsized 4 mton freighter - both presumed to have full mil-grade drives and shielding (and doing this all with pre-Grayson compensators - but the better the compensator the less the mass difference matters) and I'll assume Earth is a typical planet at about 12.8 LM inside the hyper limit.

The DB can accelerate at roughly 539g.
The 4mton freighter at roughly 450g.

The total trip time for a 20 ly one-way journey for the DB is 2.89 days (77.36% of which is spent cruising at top speed).
For the 4mton ship that same journey is 2.95 days (74.37% of which is cruising at top speed)
That's right about dead-on a 90 minute difference in transit time over a bit less than 3 days. And that transit difference won't vary with the trip length; since both ships cruise at exactly the same speed - they only differ on the acceleration portions of the journey.

Incidentally if you went up to something the size of a sphinx class (403.9g) the transit difference only goes up to about 2.5 hours. Though there's a question of whether any cargo is important enough to push even a medium sized freighter as hard as DBs tend to be - but that's harder to put numbers to.


I guess my overly detailed point is that there's no particular reason why small volume/high value have to be linked; you can be quite nearly as fast at high volume.

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I made some simplifying assumptions in my spreadsheet for this.
Ignored orbital velocity, time to reverse ship heading and the residual velocity upon entering n-space, assuming no grav waves, etc.
Despite that it should be pretty accurate, it does track time to reach the hyper limit, velocity drop from going from n-space to the Theta bands, time to accelerate from the residual speed to 0.6c, cruising time, then time to accel and decel to the planet on the far end.

Jonathan_S wrote:I made some simplifying assumptions in my spreadsheet for this.
Ignored orbital velocity, time to reverse ship heading and the residual velocity upon entering n-space, assuming no grav waves, etc.
Despite that it should be pretty accurate, it does track time to reach the hyper limit, velocity drop from going from n-space to the Theta bands, time to accelerate from the residual speed to 0.6c, cruising time, then time to accel and decel to the planet on the far end.

I'm pretty sure that you missed some relevant variables:

Cycle times of the Hyper generators. (IIRC smaller ships cycle hyperdrives faster and can thereby go up through a sequence of hyperbands faster than bigger ships.)

Wear and tear/stress at higher hyper bands. (DBs routinely run a level or two higher than bigger ships because smaller ships handle the stresses better.)

You're generally correct that DBs/smaller ships don't save that much time over larger ships if the captain is willing to push a bigger ship to the same degree as a DB operates routinely.

However, DBs routinely operate at least one hyperband higher than bigger ships because they're better able to handle the stresses. Commercial ships generally operate three to five bands lower than DBs, and that makes a huge difference in travel times.

Express Luxury Liners, like the Hauptman Atlas class, operate closer to DBs, but still seldom reach the highest hyperbands DBs use. The Atlas class could operate in the same bands as DBs, but don't because it apparently isn't economical.

Weird Harold wrote:

Jonathan_S wrote:I made some simplifying assumptions in my spreadsheet for this.
Ignored orbital velocity, time to reverse ship heading and the residual velocity upon entering n-space, assuming no grav waves, etc.
Despite that it should be pretty accurate, it does track time to reach the hyper limit, velocity drop from going from n-space to the Theta bands, time to accelerate from the residual speed to 0.6c, cruising time, then time to accel and decel to the planet on the far end.

I'm pretty sure that you missed some relevant variables:

Cycle times of the Hyper generators. (IIRC smaller ships cycle hyperdrives faster and can thereby go up through a sequence of hyperbands faster than bigger ships.)

Wear and tear/stress at higher hyper bands. (DBs routinely run a level or two higher than bigger ships because smaller ships handle the stresses better.)

You're generally correct that DBs/smaller ships don't save that much time over larger ships if the captain is willing to push a bigger ship to the same degree as a DB operates routinely.

However, DBs routinely operate at least one hyperband higher than bigger ships because they're better able to handle the stresses. Commercial ships generally operate three to five bands lower than DBs, and that makes a huge difference in travel times.

Express Luxury Liners, like the Hauptman Atlas class, operate closer to DBs, but still seldom reach the highest hyperbands DBs use. The Atlas class could operate in the same bands as DBs, but don't because it apparently isn't economical.

I did skip hyper generator cycle times; good point. RFC did tell us that smaller ships can cycle faster. An hypergenerator for an SD sized ship takes 4 minutes (240 seconds) to go from standby readiness to actual transition; go down to BC sized and that value is 75 seconds, and a DB has 30 seconds.

However RFC's old post (from 12-Jun-2012 in the "SPOILER – finding the torch wormhole’s destination" thread) goes on to say that "Under normal circumstances, cycle times apply only to translations into hyper-space. Generally speaking, any hyper-capable ship's hyper generator remains engaged the entire time it is in hyper, and the ship may move freely up or down the hyper bands." So for a given one way trip we're only talking about a single hyperspace entry, and a max additional time difference of 210 seconds. But even that is misleading because the cycle times for the hyper generators are know and (AFAIK) you can start the cycle before you cross the hyper limit as long as the jump doesn't happen until you're outside. So with any sized ship I think you could just time the jump for, say, 5 seconds past the limit.

So you're right that I totally overlooked and failed to consider the impact of mass on hyper generator cycle times; but upon further investigation it appears to have little to no effect on the kind of trip being evaluation.


As to the second part of your post as far as I recall DBs run in higher bands only because their hypergenerators and other drive components are more closely mointored, and maintianed more frequently (and because they're will to run a little more risk). I can't recall any inherent safety factor that their small size confers.

Obviously most commercial ships don't mount mil-grade propultion or hyper generators, and are happy poking along no higher than the Delta bands. But I was specifically looking at a fast freighter design and how much advantage a smaller ship would confer over a larger one - assuming they were pushed equally hard (but did note that people are less willing to push bigger more valuable ships as hard as DBs)

Jonathan_S wrote:As to the second part of your post as far as I recall DBs run in higher bands only because their hypergenerators and other drive components are more closely mointored, and maintianed more frequently (and because they're will to run a little more risk). I can't recall any inherent safety factor that their small size confers.

Obviously most commercial ships don't mount mil-grade propultion or hyper generators, and are happy poking along no higher than the Delta bands.

Even warships and miltary transports/supply ships routinely run at least a hyperband lower than dispatch boats -- even though they are capable of reaching the same "heights" as dispatch boats. Alice Truman's run from Yeltsin in HotQ was exceptional because she pushed her ship as high as it (or any known ships) could go; she was gently reprimanded for risking her ship at those levels.

For warships, there is no obvious reason they couldn't routinely operate at the same "heights" as DBs, but they don't -- and "stress" and/or "excessive wear and tear" is given as the reason they don't. That suggests that there is more than "better maintenance" involved in keeping larger ships away from the highest Hyperbands.

Getting back to Jonathan's actual point...

Jonathan did his calculation basically to show that smaller freighters don't actually go noticeably faster than larger freighters. He was calling into question the proposal earlier in the thread that small fast freighters might have a niche that larger freighters could not fill. Basically, he was saying that a large freighter with mil-grade gear would go just as fast as a small freighter with mil-grade gear; they would take the same time in transit, within a few hours.