Rigid Inflatable Boat Proposal
...a cover ltr I sent to a few persons several yearrs ago....thought there might be some interest
Over the past few years I have been conceptionalizing a small RIB (Rigid Inflatable Boat) tender for the use on cruising sail and power vessels, and sportfishing vessels in particular. It would put emphasis on a number of enhanced features that I do not believe are adequately addressed in the current market. I had written briefly on two previous occasions:
1) I was searching for a short, wide, open-transom tender/dive/sport craft that could be carried on the front deck of a gamefishing catamaran of my design (preferable two such tenders). I was seeking a relatively small craft that comfortable could carry 4/5 persons with some dive and/or dive/fishing gear. Too many of the existing RIBs are too confining in their interior space, particularly with their big round tubes. I wanted two persons to be able to sit on the tubes directly across from one another, and yet still have the leg-room and passage room to clear a central straddle-seat that might house a jet-ski type power plant. That would necessitate a fairly wide craft with a central hull that could house the water-jet drive unit. A wide craft needing a central hull rules out the cat configuration. I could have a transom for its structural contribution, but it needs to be ‘open’ to allow for immediate evacuation of any water that might swamp it as a result of a large wave washing over the bow stowage area of the mothership. With width I could accommodate the people without excessive length, and thus keep the boat size small and light-weight for the continuous hoisting service it will experience.
2) To another party I had written, “you chose to build your own tender. I have one in mind myself. It would be a RIB, possible with a foam collar rather than inflatable tubes. It would be virtually transom-less, or at least maybe just a rigid frame at the transom. The purpose being it would totally self-bail in an instant when subject to a big wave, and particularly when stored on the bow as with many sportfish vessels. It would be ‘extra wide’ for its length for increased capacity and ‘across the aisle seating’. It would have a modified ‘tri-hull’ bottom akin to XXXXX for superior performance in a chop as opposed to shallow deadrise of a very wide deep-vee. It would have a central saddle seat that would cover an optional inboard jet-ski style engine in lieu of a traditional thief-prone outboard….also safer no-prop diving usage. Ultra light model in carbon fiber, traditional model in stamped ABS.”
I made a trip to the Miami boat show this Feb 06, and I was disappointed again. As I look thru the market I’m not finding a RIB tender/sportboat that could be carried on deck, or in davits, that is really ‘self draining’. They all appear as a captive ‘tub’, that if flooded by a random wave would become a very heavy ‘big bucket’ of heavy water hanging from the davits or sitting on the foredeck. So I am seeking a virtually ‘transom-less design’, or at minimum a ‘framed-transom’ that would allow for very quick water egress.
I also find most of the smaller RIBs to be very confining and tight on the interior space as a result of the full diameter tubes utilized in their design. The actual width of the boats between the innermost tube sides is very confining with respect to allowing for two full size adults to sit across from one another, let alone a steering console, cooler etc. Then if you add in all of the ‘stylized’ seats for passengers, center console for driver, engine mountings and drains, etc,etc, you end up with very little interior volume to carry people, dive equip, etc, and all of those other items (food, supplies, bikes, etc) being transported to and from the shore. Remember, in the islands your tender becomes your car!!
One solution to increasing the onboard space of any RIB is to make use of only ‘half-round’ or ‘D-shaped’ buoyancy tubes at the beam extremities of the craft. This idea is at the core of the ‘SAFE’ system (I’ve attached a reference drawing). These ‘tubes’ might be constructed of either an inflatable material as normal for the current industry, or simply be a foam collar that might be glued on, or a combination of both.
Another solution to increasing the onboard space of the smaller RIBs is to make them wider…exaggerated wide. One manufacturer currently refers to this as his “wide body” models. The problem here is the deadrise angles at the bottom surface of the hulls become pretty small, or as it might be termed more ‘flat-bottomed’ rather than V’d. This results in a vessel that slaps or pounds more on the water surface, particularly a choppy one. And this flat bottom loses it directional preferences (control).
My design reconfigures the bottom of the RIB into a sort of tri-hull arrangement. This totally changes the shallow deadrise equation of the main hull, and provides two ‘channels’ that allow for a sort of air suspension within them. The outer rib keels, or what might be termed sponsons of the tri-hull configuration, act to contain the channels themselves, provide additional buoyancy at the extreme beams of the vessel, and provide a turning edge much like the tunnel sides of the older tunnel-hulled craft. These outer sponsons do not extend forward to the bow area of the craft, which might be confused with being similar to the old ‘cathedral hull’ that was so poor about pounding in choppy waters. It’s totally different. It’s referred to as a stabilized monohull, a slender monohull shape stabilized by two outer sponsons. The more ‘convoluted bottom shape’ of the design will lend ‘form strength’ to the bottom surface, as well as longitudinal rigidity to the whole vessel, allowing for a lighter fiberglass lay-up to achieve proper strength than is the case with the large flat-panel areas of the traditional V-bottomed hull.
