Ship Simulator

English forum => Small talk => The Chat Lounge => Topic started by: MokMok on October 12, 2014, 12:16:45

Title: Older ferries have a striking bent below the bow area.
Post by: MokMok on October 12, 2014, 12:16:45

I see that many older ferries (built in the 60s, 70s and early 80s) which have a bow visor door, have a striking edge just below the bow area at the prow above the waterline. The Papenburg Sisters and the former Olau Hollandia (1981) and the former Olau Britannia (1982) are examples of ferries which have this striking edge. When the clam door type bowdoor became common, this feature disappeared. Why do have these ferries this striking edge along the underside of the bulbous bow area and has it to do with the water resistance and the seakeeping qualities?

The former Olau Hollandia (1981), notice the striking bent just below the bulbouws bow:
(http://upload.wikimedia.org/wikipedia/commons/3/34/Nordlandia_180507.jpg)

A Papenburg Sister:
(http://upload.wikimedia.org/wikipedia/commons/1/18/Faehre_Alandia.jpg)

Title: Re: Older ferries have a striking bent below the bow area.
Post by: Mr Robville on October 13, 2014, 07:59:57

To my knowledge, the crease can be compared to a spray rail on smaller boats. The crease will direct the "rising" water outward instead of flowing it further upward making the bow jump back up again. If the bow goes deeper, it creates a sudden increase of bouyancy.
This may have something to do to protect the bow door or to prevent water from overtaking the bow as much as possible. Or just to increase speed in rough weather.

Title: Re: Older ferries have a striking bent below the bow area.
Post by: clanky on October 13, 2014, 09:28:22

I think the idea is to keep the underwater hull more like a traditional hull (thin at the front and gradually widening to the centre while allowing maximum vehicle deck space.  This is due to the belief that this hull form offered the least hydrodynamic resistance.

Modern ship designers have realised that, while a more traditional hull offers less resistance, it is also less stable and have gone for more box like underwater shapes so the modern ferries are not as thin underwater as the older types, the increase in breadth still happens, but it is already underwater.

Hope this helps.

Title: Re: Older ferries have a striking bent below the bow area.
Post by: Captain Cadet on October 13, 2014, 17:29:03

I know the stena Europe comes out of the water at its stern end. Is it for the same Idea?