Reply to the OP.
I get this from two Marines, a US Marine in the Fleet Marine Force and a Royal Marine Commando who both did hostile boardings in the Persian Gulf.
My personal experience is US Army, and I'm deferring to their experiences on this one.
Ive also trained for Boarding Ops and totally concur, the new Boarding Rules in the Mercenary Specialist Forces certainly favour Free Boarding by individuals rather than docking with any other craft.
Defending ships if still maneuvering can tumble and with a successful check prevent docking altogether. Also unless you have a Breaching Tube to make your own Breach trying to enter through a defended airlock is tantamount to suicide if the defenders are well armed.
The Boarding rules in MSF could have been written clearer and edited better though some of the DMs are wrong giving - instead of + etc.
Hope its ok to post this here?
Basically if a ship fears being Boarded it can: (this my summary from the descriptive text.)
To Enter an Effective Tumble to try to prevent Boarding attempts requires D3 Rounds, during which the Pilot may not maneuver in any other way, and a Routine Pilot Check 6+. (During these rounds no DM is mentioned for Docking Attempts) Can Maneuver as normal afterwards.
Check Failed. Ship in Inconvenient Rotation. DM-1 to all Docking and Free Boarding Attempts.
Check Passed. Ship is in Effective Tumble. DOCKING is NOT possible, Free Boarding only. See Pg 114 for DMs.
Does not say the defending Pilot can not try again.
So any ship that fears being Boarded would try to enter a Tumble as a matter of course.
To effect a hostile Boarding and remain attached: (Again my summary)
Attacking Pilot Check 8+ (CRB says Routine 6+ with a Bane) Id apply the Bane in any case.
If Defending Ship Uncooperative: DM-3 per point of Thrust defending ship is using.
DM+1per point of Thrust attacking ship is using.
If attacking ship is using Forced Linkage also apply the Pilot Check DM for the FL (High Guard, Pg 43))
Success means docked obviously with a Breaching Tube anywhere if no BT then at the defenders airlock which is still and must be forced/cut open.
If the Either ship then tries to break docking or uses Thrust at all that is not matched by the other ship: Average Initiating Pilot Difficulty Check 8+
Dm+1 for each Thrust point in use, DM-6 if Forced Linkage in use,
Reacting Pilot may make an Average 8+ Pilot check to counter the break away with the effect of their check used as a DM to the break away attempt.
If the ship breaks away each vessel takes D3 damage for each point of negative skill effect of Reacting Pilots failed counter check and any engaged Airlocks outer doors are damaged and open to Vacuum.
So any Boarding vessel really requires Forced Linkage and a Breaching Tube. So Docking with a ship that doesnt want the connection, remaining attached with out Forced Linkage is very difficult.
The epdf High Guard Deployment Shuttle is 50tons and designed for Boarding Ops but even that describes tactics of multiple "attempted" feint Breaches with the Breaching Tubes and Individual Marines making other breaches through the Hull. Adding a FL to this Shuttle would be advantageous. But in the pdf the BT is used more as a distraction to confuse the defenders rather than as a means of Boarding.
Thats why ships are usually only Boarded when they realise resistance is futile because they are outgunned or their drives are shot out. And the Boarding Forces have a ton of Fire Support. Most Pirates Board with the victim ship being cooperative because of threat.
So basically Hostile Boarding Actions are High Risk/Dangerous Operations in which you want to stack all the cards in your favours. Docking with a still manoeuvring ship would be a last resort op, only attempted if the ship couldn't be fired on for example Hostage Rescue. Still then if the defending ship had weapons its going to be extremely difficult and you would need multiple coordinating Boarding Teams.
(I as a GM would not allow Jumpbreaker Missiles to be detonated on the nose of a craft I know RAW says they do no damage but thats shipscale damage. See The Companion for gravity effects on crews in combat aboard ships. If such an action was attempted I would probably draw up some fluctuating Gravity effect chart to see what happens to the crew using the Companion Gravity rules as a guide.)