Rigid Buoyancy Boats?

[RThompson]

Hi there,
I'm looking for information on RBB's (Rigid Buoyancy Boats).
I'v turned up several manufacturers through the web, but no information or discussion on design theories of RBB's or RIB's.
Why are they so, ie whats the underlying principle? How does that impact the hull/pontoon shape (and other relevant considerations) as compared to a "normal" small (moderate V) planing boat?

Any comments, websites, or even threads on this forum I haven't found?

Rob

[hilux38]

Hi,

I'm in the process of getting a RBB built 7.9m hull, 9.55m LOA, external beam 3.3m. A centre console version, constructed totally out of aluminium. The boat builder is Alucraft, but if you're looking for the story behind the RBB and why they are referred to as the "4wd of the Sea" go to the link www.dinkiedi.com/rbb_story.htm hope this helps!

Paul

[RThompson]

Thanks Paul, excellent link,
That is the closest description yet of RBB’s.

Basically it appears that RBB's bottom shape would be the same as a "normal" hard chine deep V planning monohull boat designed for given conditions. (generally for rough water)
Suggesting to me that there are two chine flats one being the bottom of the sponsons, the other being the "chine real"
So at low speed the effective chine flat is increased for higher lift, then as the boat lifts onto the plane the sponson chine flat (and its associated drag) is lifted clear of the water

The joy of an RBB seems to be:
Great stability at rest (countering the deep V)
Ultimate buoyancy
Harder wearing (as compared to an RIB)

However,
From pictures it seems that the chine runs low a long way forward so that would suggest a blunt entry, and/or narrow chine beam. Narrow chine beam is possible because the sponsons provide stabilty at rest -but narrow chine beam means a narrow/small lifting surfaces for planing.?
The engine power is about the same, (maybe slightly lower, I think because the boats are lighter.)

There is an enormous amount of buoyancy directly above the chine.
So, assuming below the chine was the same as a "normal" boat:
When you are getting along at planing speed and you run into a wave there is no "gentle" increase in bouyancy as the bow submerges into the wave. Most reserve buoyancy is presented almost immediately the chine is submerged. That should provide a particularly exciting ride. (read: violent)
There is also a large increase in drag (the sponsons) every time the chine is submerged.

A lot of the larger boats (6m +) seem to put the outboards on a pod aft of the transom. Is that significant?

The sponsons obviously have entrapped air, do the sponsons tend to provide all the flotation, or is there a significant reliance on “underfloor” flotation (between the cockpit sole and the hull)?

So I’m still not out of the wood’s yet…
I guess my question is: What is the chine beam, and how does it relate to overall beam? – how much of the sponson volume is inboard of the chine? Or, better put: Does anyone have some cross sections of an RBB they might share?

Thanks for your time,

Rob

Also take a look at All rounder boats based at Tweed Heads for a GRP Version.

www.allrounder.com.au

[hilux38]

We use the rbb "mussel boat" featured on the Alucraft website on the mussel farm, but now has a 230hp deisel instead of the 250hp outboard. This is how I know how safe they really are. We load it up with 2-3 tonnes of mussels everyday and drive it through ANY weather, virtually unsinkable.

The features of the RBB we use are ultimate stability, low planing speed and high load carrying ability.

You stated that when at planing speed and you run into a wave there is no gentle increase in bouyancy, therefore ride could become violent. All I can say is that if we are in sea conditions where we (being in a 8 metre vessel) run into a wave we would be going fairly slow. In the past we have run into waves and where a vessel without the flotation sponson would bury the bow or go through the wave the RBB bow will create lift.

The opposite if in a following sea if going down a large wave the sponson collar will prevent the bow from burying in the following wave therefor reducing broaching effect.

With the rbb I use the sponsons are barely touching the water at the stern at rest, therefor the vessel isn't relying on the sponsons for floatation or stability. Only when the vessel is loaded do the sponsons come into play.

Hope this helps, if you would like some pics of the Alucraft vessel just let me know your email.

cheers
Paul

The lighter and stubby the boat, the more stabile in almost any NON WINDY condition. Wind and or boat speed are the only real dangers, other than a reckless driver. Rich.

[tom kane]

HI RICH,your local library coud have some good books,such as Rigid Inflatable Boats by Colin Jones,for a starter.When some one takes the time and effort and research to write a book,the info is usually reliable,if you read a lot of books on the same subject and the writers all agree on certain topics that info should be good.Have a look at www.sealegs.com

Thanks, Tom. Rich.

[hilux38]

Originally Posted by Richard Petersen

The lighter and stubby the boat, the more stabile in almost any NON WINDY condition. Wind and or boat speed are the only real dangers, other than a reckless driver. Rich.

so rich does this mean that the heavier and less stubby a boat is the more stable in WINDY condition?

Yes.Ever hear of the following blowing over? Nuclear sub- super oil tanker-Queen Mary - USS ENTERPRISE- any really big ship? USA lost a lot of small ships, destroyers and smaller sized, to typhoons in WW II Pacific storms. I remember one north atlantic NATO cruise in a storm when all 100 ships were told. "Break formation and save yourself if possible, good luck, that is all." Rich.

[hilux38]

so does this mean you're talking about the "size" of the vessel rather than the shape, which was earlier discussed? (sub-marines????)

So, keeping all other variables the same...........

does this mean that the heavier and less stubby a boat is the more stable in WINDY condition?

in other words, you are saying a heavy, skinny vessel is more stable in a windy condition?

I do agree that a significantly larger vessel ie super tanker, queen mary would be more stable than your average 30 footer.

USN now uses both rigid and inflatable craft to put special forces ashore. Why? They carry the most weight- shallowest draft loaded- takes hundreds of holes and still functions- repair holes instantly with a roll of duct tape- moves very fast when empty due to very high HP TO WEIGHT RATIO -take rough water best- USCG swears by them in ROUGH but not high wind seas, they risk their lives every day like the Special Forces do also. We haven't come up with a better shallow water design yet. Shallow water always come down to -pounds per square foot, and or, pounds per cubic foot. I don't think I can say this any clearer. Rich Oh, I forgot the most important reason! Cheap, Cheap, Cheap. Rich.