I'm thinking about some specific enchantments Janus can do. Now, we're not doing a magical ship but rather a very good but still mundane ship which is improved by enchantments. So all devices need to be at least R:Touch...well one could make a magical sail...But this way the devices can be dismantled and moved to another ship if the first one is destroyed or we build another type of ship, or a larger one. Granted a larger ship may wreck havock with some enchantments' Size, so not likely then.
The hull of the ship:
I was thinking of something to make the hull durable, but a constant effect Warps the ship, so rather an effect to repair stress and damage like Ranulf from MoH's talisman staff, an effect like Shadow of spring times departed Cr(Mu)He Base 3. This effect - when actively turned on - repairs damage, bringing the piece of wood back to its original state, but not growing naturally with leaves, roots etc.
Ranulf's effect has D:Sun (for +2 mags) so each sunrise/-set ther eis still damage seen the effect is activated again. This device notes that grave damage can take months to repair.
As for Target Janus could go for T:Ind but how many size magnitudes to add for a ship? The PeHe spell Curse of the Rotten Wood is T:Group and has +1 Size and can affect a house or a small inn, but it this spell unoptimized (inoptimized?) or can the wooden components here not be viewed as an Individual? So can a ship? IMHO an object or structure made of several components of the same material can be an Individual if they are clearly put together and now form a distinct object. So a pile of wooden beams, no. But the same beams crafted into a bridge, yes.
A base Individual for Herbam is " a plant roughly one place in each direction" which makes sense for living plants. Ir represents smaller branches and leaves etc. and not just a tree trunk. A very generous interpretation of this for for wood usable for buildings things would be 1 cubic pace, but for purposes of balance probably significantly less. Is 0,5 cubic pace a realistic number?
Instead of affecting the entire ship, how about getting fresh and designing the device with T:Part and then +1 Size? So it can affect a damaged area of wood (on the hull, masts, superstructure or whatever) up to a volume of 5 cubic paces. Going metric here and assuming 1 pace= 1 meter (and rounding oft to simplify) then a wooden beam 30 cm (1 foot) in diameter and 70 m long is the upper limit for the object to be affected - if I get my math correct.
So now I have Base 3, +1 Touch, +2 Sun, +1 Part, +1 Size = 20. Penetration is not important, but uses per day needs to be improved. +5 levels give 25 uses per day and that should be enough. Final effect Cr(Mu)He 25
As for physcial object I haven't been through the entire S&M catalogue but something wooden has a nice bonus to 'affect dead wood' and perhaps some sort of woodworking tool?
Janus' lab total including Familiar excluding S&M and with no apprentices is 56. Theoretical maximum S&M is equal to his effective Magic Theory of 12, but likely much less is used. His Herbam is only 8 so he might hit the books a bit before embarking on the ship project especially if he is going to build more than one Herbam device.
Seeing as he should easily reach a Lab Total of 60 he might as well enhance Duration from Sun to Moon to make it a round level 30, it won't cost any more vis and the crew does not need to active the device twice daily on each piece of damaged wood.