Source: Tides and the Catalan Atlas [1375] Vicenç M. Rosselló i Verger* Universitat de València

What is displayed here is a diagram for the tides in a circle with 14 circumferences divided itself in 16 sectors.
One sector is 1 hour and a half based on the posiiton of the moon, port and wind.
The letters P and B. meaning  P=high tide and B=low tide. 
Outside are the wind directions' first letters:  G(reco), Scilocho, Labetzo, Ponente, Magistro
On the top is the northern star.

Text in the circle = text on the cart = reflects real (current) name:

sayn = sein = Enez Sun = Ile de Sun
sanmae = s mae = Pointe de Saint Mathieu
forndartus = forno = Le Four (canal on the Iles Molene)
insula de bas = base = Enez Vaz (Ile de Batz)
setrilles = Ar Jentilez (les Sept Iles)
granexo = Guernsey (Guernesey)
ras branzard (Cap de La Hague)
porlam = cauo de Porlan = Portland
uhic = huic = Wight
beocef = beacep = Beachy Head
gillsalexeo = guinsalexeo = Winchelsea
romaneo = Romney
sanux = samux = Sandwhich Bay
sayna = sayno = ? mistakingly seine river ?