OK......
Boarding units can be D4 or D6 or D8 (reflecting troop quality/improved tech).
To-hit is 1/2 the die type. IE 2, 3 or 4 plus the following modifiers:
Combined momentum of attacking and targeted vessel (Per Dan):
up to 2 combined momentum = +0
up to 3 combined momentum = +1
up to 4 combined momentum = +2
up to 5 combined momentum = +3
up to 6 combined momentum = +4
This means the involved vessels could have a combined SPEED that turn as high as 12". Ideally, you shouldn't be trying unless the combined speed total was 4". And to be moving the max combined SPEED will make an attempt impossible by all but the best units.
The other mod, I still think, should be the number of LGs or machine guns equipped on the tageted ship. Heavy weapon crews may not be necessary, because TMW is introducing machine guns, which are mean to serve as a kind of point defense.
So, for every N number of LGs or machine guns that can fire out the targeted arc, +1 to the roll. I still like the idea of defensive fire.
I don't think range should be a mod, on second thought. Just set a concrete distance, as the tethers connecting these guys to their parent vessel can only be so long, and their unit integrity remain over a certain distance. So say 3", max. Besides, you don't want too many mods.
Finally, the natural 1 would be a fumble and see the boarders tumble off into space, lost forever.
Damage could be purchased just as it is with any other weapon, simulating the size of the boarding party. Which means bigger ships will have more room to pack a greater number of hard hitting units. Damage is applied as crew casualties.
But the actual attack would be conducted during the End Phase, because since Light Guns need to be neutralized, the attacker would wait til the last moment to release its marines.
Example: A Southam class cruiser has taken some Thrust hits, dropping its top Engine Performance to 2. Its Momentum entering the Current Turn was 3, and it floors it as best its able. Its speed reaches 5, and its momentum at the end of its Movement Phase will be 2.5, rounded up to 3.
An Italian battlecruiser is able to close within 3", and its momentum is 3. So the combined momentum is 6, or a +4 modifier. This would make an attack possible only by a D8 unit, and even then, not if the defending ship still had enough LGs to interfere with the boarders' attempt.
The attempt is made AFTER the combat phases, in the hopes that Light Guns will have been attrited.
The Italian ship's boarding stats might be D8(X2), meaning a succesful hit will see two crew casualties marked off. Again, during the End Phase.
This makes for a potentially damaging, but very limited weapon.
How does it sound?
Matt