Joost Bulter commanded a brand new ship at the Battle of the Gabbard. This was a ship that had been recently built for the Admiralty of Friesland, perhaps as part of the new building program. That might mean that we would know the ship's approximate dimensions: about 130ft x 32ft x 12ft. Perhaps the new Zevenwolden was of a similar size.
I realized that Dr. Ballhausen had a reference about Joost Bulter's ship from The Life of Richard Deane, one of the more obscure books that I own. On page 649 of that biography, it says that Joost Bulter's sunken ship carried 42 guns. The ship is not mentioned by name.
On page 94 of Dr. Elias's book, Schetsen uit de Geschiedenis van ons Zeewezen, Vol.V, Joost Bulter's ship is named Kameel.
Vol.V of The First Dutch War, on page 22, has C. T. Atkinson's translation of Tromp's account of the Battle of the Gabbard from Aitzema, Vol.III, page 821. I happen to own Aitzema (Saken van Staet en Oorlogh), and the statement is actually "capiteyn Joost Bulter van Stadt en Lande". C. T. Atkinson had translated this as "Captain Joost Bulter of the Town and Country", as if the name of his ship was named Stad en Lande, a very plausible Friesland ship name. Stad en Lande is much more plausible than Kameel, to my mind. The whole passage translated by Atkinson is: "There was also lost in the heat of the struggle Captain Joost Bulter of the Town and Country which went down with about thirty men, the rest being saved by Captain Willem van der Zaan, who was next to the sinking ship, and that evening the enemy's fleet was reinforced by six or seven ships, some say more." My reading would be that Joost Bulter was from the "Stad en Lande" (Groningen).
In Oud Holland 17 (1899), my translation of the passage from the article about Willem van de Velde de Oude says:
"While De Ruijter thus won the wind from Lawson, Tromp's squadron lay between those of Lawson and Monk, and the first of these was caught between two fires. This masterly tactic achieved only partial success, because Monk and Lawson quickly could recover, and because Tromp's guns were not strong enough to sufficiently damage even a weaker enemy in a short time, and to put them out of the battle. 1) The struggle was now a general melee, where by the English broke through Dutch fleet to win the windward side. In this furious battle, we look for Lawson to cut off the captains Willem van der Zaan and Joost Bulter. The ship of the last, the Kameel, sank; Van der Zaan rescued himself. One hour after sunset, the ship of Cornelis van Velsen blew up, due to gunpowder in the air. The night brought an end to the struggle. Both fleets drifted, due to wind and tide, towards the Flemish coast, not far from Nieuport."
The Oud Holland article, therefore, also calls Joost Bulter's ship the Kameel.