Disadvantages of RIB's?

I know the obvious advantages of RIB's, but what are the disadvantages of them compared to a typical monohull? Talking about a length of about 12 metres/40 feet.

 

Are we talking real RIB or what passes as a "RIB" such as a SAFE Boat? Home https://safeboats.com/

 

I would say, less interior space, probably no enclosed cabin, more prone to damage from sharp objects, and more drag/less speed.

 

More the safeboats style, potentially with hull and tubes all made from aluminium.

 

This will hopefully be a 12 metre/40 footer with a small enclosed cabin at the bow, and hopefully be all-aluminium construction.

 

In addition to gonzo's comments:
More expensive
Heavier - depends on what is the same between the boats being compared (overall beam or usable space, etc.)

 

Here in Egypt the main construction material for dive boats is still wood - low initial cost but typically the external timbers have to be replaced every two years which means a lot of maintenance expense and time that the boat is out of the water. Boats manufactured outside of Egypt attract a lot of import duty which prices them out of the market in most cases, so we accept that any boat we build will be fairly expensive initially but will have less ongoing maintenance costs.

What do they handle like?

 

Disadvantage
Inflatable round tube style ribs
1) Inside space, as mentioned before. With round tubes you need an extremely wide boat as using say a 24 inch tube takes 4 feet off the usable cockpit/floor space
2) longevity of material, certainly the new fabrics have pretty good UV resistance, but generally, the fabrics will last only so long. As compared to fibreglass or almuminum
3) low freeboard- dependent on the shape of the rigid hull, and the diameter of the tubes,
4) prone to puncture, Gonzo covered this

Safeboat style, rigid pontoons
Technically then not a RIB anymore
1) with a "D" shape tube cross section you gain two important advantages- 1) more inside cockpit space 2) for the same displacement of water, you then end up with a higher gunwale
2) with a rigid tube, the the puncture resistance increases dramatically
3) with a fibreglass or aluminum tube, the life of the hull increases
4) A downside is weight- I believe ABYC , the US safety standard, requires that there is level floatation if even one or ( perhaps) two of the largest enclosed floatation volumes are punctured. And I think that
there is also a maximum volume that a chamber can be. If you are interested PM me back and I try to find the precise wording

An issue with Ribs or regular inflatable tenders with round tubes is that due to the tube diameter, the amount of water that the tubes displace is much more than needed to satisfy level floatation, required in North America.
(And probably the rest of the world that requires safety minimums. )
Over the past several years, there have been aluminum boats built as a monohull with polyurethane D-shaped collared tubes. Puncture proof and designed to float the boat so to speak. I have not heard how long the poly foam tubes/bumpers
last but the tubes provide floatation. One link is Lifeproofboats. The two smaller pictures

The top picture is of an aluminum chambered boat, actually ACB by name I think which has a cabin

 

I was expecting as much as a inflatable RIB 12m/40ft has significant weight and structural issues.
Gonzo, DCockey, and Barry have summed up most things but here are a two I think were not mentioned.

For similar sized V hulls, RIB's ride hard and wet. This is because of the original premise of a RIB (which was ease/safety of personnel/casualties over the side) led to soft, rounded, low freeboard tubes which slam harder.

The reason for the proliferation of foam tube "RIB"s in the SAR/military roles is the resistance to sinking. Notice I did not say damage. Even with many small (or even large) punctures/tears, it is almost impossible to actually sink one. This is important in the "get everyone home" business.

 

Fellow a few stalls down had a 26 foot acb, it was ugly as sin but did real well in rolling Swell at lower planing speeds. We pulled a lof subsistence pots with it a few years ago, it was good and stable.

Caught a hard westerly that stacked up a 4 foot vertical chop right off the beach. It pounded like I'd never seen a clean mono hull do, every odd angled surface caught or aspirated spray. It was a pilot house boat with open back wall, the water going over the roof required coming of plane to let the scuppers catch up.

Outside that narrow range it seems like a decent boat. He likes it, despite the nearly constant harassment of its aesthetic short comings.

 

I hate these websites that want to tell you everything except the most basic facts like what are their boats. I'm GUESSING its a mostly stiff foam collar that is covered by some fabric, but I'm guessing.
Anyways, what I'd like to see is hard boats but with baked in mounting points to add inflated tubes of various diameters and lengths.

 

ABYC is a voluntary standard, not a regulatory standard in the US. US regulatory standards for level flotation and similar only apply to recreational boats 20 feet and shorter. There are no US regulatory level floatation standards for recreational boats longer than 20 feet.

 

The reason your wood boats fail so soon is due to the employed construction practices. Not only do the builders use the cheapest wood available, but they also nail it with electroplated nails.
Your best bet from a price/longevity point of view is fiberglass, even with cheap chinese resins the boats will last a long time. More importantly, any needed repairs are easy and there is no need for specialized equipment and workforce. Aluminium boats while in theory better, need special precautions in use regarding galvanic corrosion (right down to the antifouling you can use), and repairs need a trained workforce with the right tools.

The foam is usually closed cell polyethylene like you find in life jackets, sleeping pads and insulation. It is covered with an acrylic fabric for UV protection.

 

You are correct. I did forget the length parameter

 

Lots of good points there - much appreciated.

Definitely the "D" shape tube seems the way to go - or something like those ACB boats.

From what I have seen here there would not be any local standards regarding level flotation etc. - the local wooden boats have cavernous engine rooms etc. and no flotation chambers - if the local boats hit a reef etc. then they usually sink

Many thanks for that photo of the ACB boat - have not seen them before, they might be a better option than a RIB with D shaped tubes