The trip curve determines how quickly an MCB will trip in response to overcurrent. A curve is the most sensitive, too much so for a boat. B curve Trips at 3-5 times the rated current and is the most common in domestic installations. C curve Trips at 5-10 times the rated current.
I think your head is in domestic wiring mode Alex
Lighting on boats are usually DC 
Depends wether or not you want a mains light or notI think your head is in domestic wiring mode Alex
If there are only sockets i'd just fit a 16A RCBO, I like SP&N RCBOs for boats as they are single module, so less space,
https://www.screwfix.com/p/british-general-fortress-16a-30ma-type-a-sp-n-b-curve-compact-rcbo/969vf
B curve rather than C ?
Otherwise agree. also with B curve.
Depends wether or not you want a mains light or not
Just to further clarify when talking MCB's and RCD's (RCBO's) it can be absolutely confusing in relation to type and curve. The manufacturers and retailers don't help with their descriptions.
Curve A,B,C or D as you have pointed out is the tripping time curve for the Circuit breaker. Type AC, A, B. etc is the type designation for the Residual current device. AC will trip with standard ac current but can be come saturated with a DC component and fail to operate. Type A, B etc will trip with different levels and forms of ac and DC current present. That is a very simple explanation. The modern thinking is to fit Type A in most domestic type installations, where DC components from inverters and other electronic devices such as phone chargers etc can be present. I believe that in Germany for example Type AC is now banned.
AC are banned in the UK now for new installations.Further to my last. RCD(RCBO) Types. N.B. The type fitted by the OP (F&S) is type AC
View attachment 203947
Good
Yes, that's correct.
Looks like 2.5mm cable so OK for sockets.
Look like they are more expensive than in the UK. How about : RCBO 16AMP 6KA B CURVE 30MA CLASS A 2 POLE 2 MODROI.
Okay,I gotcha on that.
I'm after reliability and durability. Cheap is not the goal
They're not especially expensive items anyway.
Maybe 6 ampGood
Yes, that's correct.
This one takes up the same space as one of the old MCBs in your consumer unit https://www.screwfix.com/p/british-general-fortress-16a-30ma-type-a-sp-n-b-curve-compact-rcbo/969vf
Only use it for the 4 sockets you have described. If you have anything else fit them with their own RCBO. If you fit a mains charger, for instance, fit it with its own, correctly rated RCBO.
You can use Wago connectors, in the Wago box, suitable fixed/supported to join the cables.
He could use the spare one from the old mains lighting circuitMaybe 6 amp
That looks better as it is a 2 pole RCBO. Most of the narrow ones are only single pole so if you are in a marina with reversed live and neutral you will not be protected.
Yep, almost everything is more expensive here.
Does the SP not stand for Single Pole?
