Offshore passenger cat hull design

So for about 2 years now I've been bouncing back and forth on a medium size passenger boat 65'x24' approx. the question is planing z bow cat or displacement style hulls?

The intended service would be a mainly be offshore fishing and some whale watching in New England. 40 passenger average load, 149 passenger max with twin props and a targeted cruise of around 22+ kts. Trying to weight out stability at drift, sea keeping and efficiently. Also a factor is deck height, the vessel will need to maintain a flat main deck for passengers. Any thoughts?


Here's some examples:

Nice day too:
I like the hull design just not the superstructure.
http://www.geoshipyard.com/nice-day-too.html

Nethanial bowditch:
85' Incat design z bows shes great sea boat
http://www.flickr.com/photos/11368020@N03/5778475847

 

149 pax on an inspected vessel 65' long sounds like too many, may not even be possible with stability rules, and when you jump beyond 49 pax the vessel rules change and become slightly more difficult (Read: increased cost) to comply with. Larger vessels also need more pax average per trip to be profitable, so where you decide to operate and how much potential market you have should dictate if you choose to cross the 49 pax threshold.

Nice Day Too, by Malcolm Tennant, who is highly regarded, looks like a better vessel for fishing / whale watching, all around single deck height, especially with covering deck aft of the deckhouse, and looks a lot less expensive to buy and operate than

the Salem Ferry, which looks like a, well ferry. Not looking up her specs she looks faster, bigger and with the two decks a lot more expensive.

Ferry's need speed to make the commercially viable, fishing / whale watching vessels need to be more efficient to operate profitability.

To answer your question: IMHO the displacement hulls will be more efficient for the intended use, unless speed is more important than operating cost, as in with a faster boat you can get in an extra trip a day, or if having a faster boat is a real advantage over competition.

 

50 to 149 passengers is a big step. Google abletasmanseashuttles go to fleet, their largest is 24metres, is licenced for 150 to my knowledge 100 on top deck Their diesels can change their ratings to whatever load they are carrying for fuel efficiency

 

This is a purpose-built whale watch cat, 24m for 245 passengers supposedly, powered by twin Yanmars around 900 hp from memory.

http://www.compositesworld.com/news/composites-selected-for-australian-ferry

 

Ok well a little history on me I guess I currently work for one of the largest ferry/whale watch companies in the east coast, limited to 1-2 days a week now because I own a Marine fabrication shop, Before the welding shop i was part of a famly buisness and we had 3 passenger boats and 2 crew boats, now were just looking to get back into the game.

I've gone back and forth with Noah who designed that particular boat in harvey bay a few times. It just dosent quite fit our service and also it's a composit hull. 149 pax is cake on a 65-70' cat I have run a 200 passenger 65'er designed by morrelli& Melvin and the 90' incat I'm currently on is created for 240. Cg regs and stability isn't is not a problem at all were just stuck on a hull form. I have quite a few hours on the incats just very limited exposure to displacement cats. I've done quite a bit of reading and they seem to be superior sea boat in theory I just haven't had any real world experience with them.

 

The Hervey Bay boat is not operating on the open sea in it's whale-watch tours, more a large open bay rarely subject to oceanic swell in the season. But if the GPS screen visible on board tells no lies, it easily cruises at 20 knots.

 

24m Spirit of Hervey Bay

The last I heard, the vessel with 245 PAX was at 22 knots cruise speed, drinking 90L per side. Top speed was 26, but I don't know if that was lightship or not.

 

Little wonder that cats are the preferred vessel type for whale-watch tourism, a whale surfaces on one side of the boat, and everyone rushes across to that side to view it, a more tender type of boat would heel over alarmingly.

 

PAX crowding

A whale watcher is completely different to a ferry where everyone is seated for stability calcs. Try 245 PAX @ 75kg =18375 kg of free moving weight from one side to the other when a whale breaches. In todays real world the average passenger / tourist has to be around 85-100kg... You need good hulls for a starter.

 

Stability calculations for passenger vessel take this into account. Thus whether looking at whales or not, the vessel must pass this criterion within a max allowable list angle in both intact and damage stability.

 

When I went out it was about half-loaded and dashing around from place to place at between 20-22 knots. The bows seem very full, was that necessary to accomodate bow thrusters ?

 

Very true. Some whale watching vessels are designed to allow access around the vessel where a ferry may not have the same access designed for passengers crowding.

 

No, it was to accommodate the weight of the passengers on the front grandstand area, and also to do with the size of the lower hull rooms with viewing windows as per the clients request. Also during the build some weight was moved aft, and this may have had something to do with it riding a bit higher in the bows.

 

I think you're missing the point.

Public access for passengers, no matter whether sat in seats or roaming around is "Public Access". What ever the function of that public access, watching whales, looking at plants/birds or simply in transit makes no difference, statutory passenger crowding must be taken into account in all publically accessible places. The function of the public access is immaterial.

 

Ad Hoc, you are right.