Fiberglass Hulls v Multiple Floats

Hello, I'm doing initial planning on a large boat, most believe a fiberglass hull design will be the best option (this is a 65-70ft x 30-40ft catamaran design) for this vessel, but one person really really wants to put this on those big HDP floats strung together as pontoons (example being the Nautilus SuperPontoon). I'm looking for some 3rd party, not attached in any way thus unbias, thoughts and opinions on why this would either work or not work.

For a bit more context, this vessel would be aimed at hosting several dozen people at any given time, travel range would be minimal, most time in calm bays, but ability to travel in open water is desired where routine waves are 1 to 1.5m at 5-7sec periods.

I appreciate all feedback to share with my group. Keep a Good Thought,

 

Welcome to the forums.
Since you state that you are posting from Roatan Island in Honduras; and with the given size and type of vessel you are considering; I immediately jump to the idea of a dive or party vessel. In this case it would be prudent to consult your state requirements before getting too far along. A permanently moored floating bar is, regulatority, a far different situation that an active vessel. Honduras is a signatory to the International Convention for the Safety of Life at Sea (SOLAS). It is party to the 1974 version of the convention.

 

The orignal design was a "permanent barge style" where the floats would've been perfect; but they won't license that anymore so we are going mobile and changing up materials as such...one hold out wants to make a "mobile barge" but yeah...no. Thank you for pointing out this information, very helpful!

 

Not sure the sor is defined well enough; for starters.

For example, you don’t even describe power wishes, or who would captain, or where it would stay, mooring or slip, etc.

 

Why won't 'they' (the Honduras Licensing Authority?) license a 'permanent barge style' with floats?
Do they not like the Nautilus Super Pontoons, or do they say that a vessel has to have adequate propulsion, or is there a problem with crew certification, or......?

Here is a link to the Nautilus website -
Pontoons – Nautilus https://nautilusfloats.com/pontoons/
Have you got a quote from them for the various pontoons required to build a 65' catamaran?

As Fallguy notes above, your Statement of Requirements (SOR) is very vague - you need to have this as detailed as possible.
List everything that you want this barge to do, and everything that you want to have on board - like number of passengers and crew, quantity of supplies (food and drink) to carry for each trip, water and fuel tank capacities required, all of the outfit items (bars, bathrooms, seating, safety equipment including lifejackets, anchors and cables, a liferaft or two if required under the Rules...... everything that you can think of.
Then do some rough initial weight estimates for everything and everybody that will be on board - be realistic about this. And you will be surprised to see that weight adds up very quickly!
A weight estimate is very important, especially on a catamaran with relatively narrow hulls, as you need to provide the required amount of buoyancy in the hulls to support all this weight.

The average barge built with simple pontoons like those Nautilus floats and with a low bridgedeck clearance will not be very happy at all if it has to undertake passages in open water with wave heights of 3' - 5'.
I think that for conditions like this you would be better off with proper hulls (fibreglass, or aluminium, or even steel, if you have the labour and the skills available locally to build in these materials), while ensuring that you have a high enough bridgedeck connecting the hulls so that it does not 'slam' while underway.

Re how the travel range will be 'minimal', does this mean that the vessel will simply be moved occasionally to different locations with no passengers on board, or will it actually be undertaking proper cruises with passengers?
If it will always be anchored when you have pax on board, then the slamming issue would not be so important, and you could even just tow it to different locations as required, rather than having a dedicated propulsion system on board.

 

Thank you -

It isn't allowed to sit in one place, the Environmental Authority won't allow that, so it has be to move regularly (daily nearly) and as such needs to be a "boat" not a "barge" - with different license regulations here - meaning independent propulsion, etc.

I have weight estimates, I have engineers, I have an operating plan, etc...I'm really just looking for "ammo" to convince one of the investors that we can't drive the original "barge design" in ocean waves. And thus we're changing to fiberglass hulls. So your last two statments are quite helpful - thank you.

The operation would ideally move with pax on board - so slamming would very much be an issue. And the fiberglass allows us to be higher easier - with a built up hull to support estimated weight with pax, where as the floats just don't - you'd have to build a sub structure on floats then the deck on top of that...too many connection points for ocean waves to wreck havok on, I think .

 

Thanks for the update above, that helps to clarify things.

I am sure that others on here would agree with me when I offer an opinion that it would not be very sensible to try to build a passenger vessel with Nautilus floats that can operate underway in the open ocean in 3' - 5' waves with passengers on board.
You do need properly designed hulls that allow for reasonable bridgedeck clearance to avoid slamming while underway in the anticipated sea states mentioned.

 

A barge with a tug to move it would probably meet regulations. What is the minimum distance and how often does in need to move.

 

I must echo Gonzo. A barge and a tow can operate in 3-5’ seas.

But it lacks all curb appeal.

Develop the complete sor.

 

The objector is an investor, so the best argument is financial. The pontoons aren't cheap, the Nautilus super goes for ~900$/unit, you need 14 units per hull. To this you add: shipping and handling, import taxes if applicable, stainless steel connecting structure plus raisers, specialist HDPE welder (you need to weld the units to each other), and the need for a customized propulsion housing solution.

The fiberglass hulls need some cheap local wood, chicken wire and PE sheets for the mold, polyester resin, fiberglass matt and rowing, consumables and cheap local labor.
I can't imagine the pontoon solution beeing cheaper overall. If it even starts getting close you get the engineering department to work some magic with wooden stringers to lower the amount of fiberglass and resin to a tolerable level.

 

What is the budget?
From the description I would just get a barge. And some kind of boat to push it. Make an ATB.

 

Articulated Tug and Barge Systems - Robert Allan Ltd. https://ral.ca/articulated-tug-and-barge-systems/