We have been rethinking the ultimate dinghy concept and are looking at a big custom designed RIB for our new FPB 78. Not having experience with properly designed deep V RIBS, we have a few questions and are hopeful the SetSail community can provide real world answers.
This is a very rough concept sketch: to check weight, basic dimensions, and how this design might fit on the aft deck of the FPB 78. We are at 4.85m x 1.95 meters overall or 15.8′ x 6.35’. The hull is a constant 24 degree deadrise V-shape.
This dink has three jobs: a shore boat where there are docks at which to disembark, for exploration far from the mother ship, and as a primary escape vehicle instead of a life raft. As such we are interested in comfort, which means ride and dryness, and seakeeping in sub-optimal sea states. The ability to maintain good turn of speed in chop also has value.
We are looking at a displacement of around 800/900 pounds (360/410 kgs) rigged, but not including passengers.
Now some questions:
- How does a RIB like this compare in terms of seakeeping to a more traditional flatter bottom dinghy?
- Is it drier or wetter in chop?
- What about beam to length proportions? We are 2.5/1. Narrow by dinghy standards, but a little chubby by the criteria of big rescue RIBs.
- Any projections on performance and fuel burn with a pair of 20/30 HP two stroke outboards?
- We have assumed 4mm/3/16” bottom plate, 1/8”/3mm deck, same for frames at 12”/300mm on center, with 6mm1/4” transom + local stiffeners in our weight budget. We want to be fault tolerant. How do these scantlings sound?
- Suggestions for tube construction details, materials, what to look for and what to avoid, and vendors are solicited.
- Tube diameter? We are showing here 450mm/18”. Sufficient or should it be larger?
- Tube clearance from waterline at rest, with two crew aboard, and when heavy?
- Deadrise angles forward and aft?
- Other details on rigging, store, etc are always welcome.