It's not a plothole. One of the key plot points of the book is that the Engineership Est-taun Zhiffir (portal-carrying) is traveling from a nearby star system to Ulubis to reconnect the system with the wider portal network. There's no mention of the specific tech used to hump a portal around, but it would seem that it's possible for a non-emplaced wormhole-end to be within a gravity field without exploding. It's only once it's emplaced that it needs to be in zero-g.

The Engineership Est-taun Zhiffir, portal-carrying, set out from Zenerre for Ulubis less than a year after the disaster, with a travel time initially given as 307 years, later reduced by increments to level out at 269 as the Eship upped its velocity even closer to light speed, the Engineers aboard fine-tuning the systems which insulated the hauled portal from the effects of its own and the ship's relativistic mass. - _{^{The Algebraist}}

Since we know that...

• The dwellers are perfectly capable of non-FTL travel
• Non-emplaced portals can be moved around, even within gravity fields.

...that would strongly suggest that they moved their portals in precisely the same way, by leaving them closed until they need to.

Speaking of plotholes, it might interest you to notice that based on the fact that the Eship can be communicated with at distance, a portal can apparently be opened (presumably wide enough to pass a radio signal) without going all explodey, even if it's within a gravity field.

It's not a plothole. One of the key plot points of the book is that the Engineership Est-taun Zhiffir (portal-carrying) is traveling from a nearby star system to Ulubis to reconnect the system with the wider portal network. There's no mention of the specific tech used to hump a portal around, but it would seem that it's possible for a non-emplaced wormhole-end to be within a gravity field without exploding. It's only once it's emplaced that it needs to be in zero-g.

The Engineership Est-taun Zhiffir, portal-carrying, set out from Zenerre for Ulubis less than a year after the disaster, with a travel time initially given as 307 years, later reduced by increments to level out at 269 as the Eship upped its velocity even closer to light speed, the Engineers aboard fine-tuning the systems which insulated the hauled portal from the effects of its own and the ship's relativistic mass. - _{^{The Algebraist}}

Since we know that...

• The dwellers are perfectly capable of non-FTL travel
• Non-emplaced portals can be moved around, even within gravity fields.

...that would strongly suggest that the Dwellers moved their portals in precisely the same way, by leaving them closed until they need to.

Speaking of plotholes, it might interest you to notice that based on the fact that the Eship can be communicated with at distance, a portal can apparently be opened (presumably wide enough to pass a radio signal) without going all explodey, even if it's within a gravity field.

It's not a plothole. One of the key plot points of the book is that the Engineership Est-taun Zhiffir (portal-carrying) is traveling from a nearby star system to Ulubis to reconnect the system with the wider portal network. There's no mention of the specific tech used to hump a portal around, but it would seem that it's possible for a non-emplaced wormhole-end to be within a gravity field without exploding. It's only once it's emplaced that it needs to be in zero-g.

The Engineership Est-taun Zhiffir, portal-carrying, set out from Zenerre for Ulubis less than a year after the disaster, with a travel time initially given as 307 years, later reduced by increments to level out at 269 as the Eship upped its velocity even closer to light speed, the Engineers aboard fine-tuning the systems which insulated the hauled portal from the effects of its own and the ship's relativistic mass. - _{^{The Algebraist}}

Since we know that...

• The dwellers are perfectly capable of non-FTL travel
• Non-emplaced portals can be moved around, even within gravity fields.

...that would strongly suggest that they moved their portals in precisely the same way, by leaving them closed until they need to.

It might interest you (speaking of plotholes) that based on the fact that the Eship can be communicated with at distance, even within a gravity field, a portal can apparently be opened a little bit (presumably enough to pass a radio signal) without going all explodey.

It's not a plothole. One of the key plot points of the book is that the Engineership Est-taun Zhiffir (portal-carrying) is traveling from a nearby star system to Ulubis to reconnect the system with the wider portal network. There's no mention of the specific tech used to hump a portal around, but it would seem that it's possible for a non-emplaced wormhole-end to be within a gravity field without exploding. It's only once it's emplaced that it needs to be in zero-g.

The Engineership Est-taun Zhiffir, portal-carrying, set out from Zenerre for Ulubis less than a year after the disaster, with a travel time initially given as 307 years, later reduced by increments to level out at 269 as the Eship upped its velocity even closer to light speed, the Engineers aboard fine-tuning the systems which insulated the hauled portal from the effects of its own and the ship's relativistic mass. - _{^{The Algebraist}}

Since we know that...

• The dwellers are perfectly capable of non-FTL travel
• Non-emplaced portals can be moved around, even within gravity fields.

...that would strongly suggest that they moved their portals in precisely the same way, by leaving them closed until they need to.

Speaking of plotholes, it might interest you to notice that based on the fact that the Eship can be communicated with at distance, a portal can apparently be opened (presumably wide enough to pass a radio signal) without going all explodey, even if it's within a gravity field.