RIB - Dive Boat - First Boat Build - Help Please!

Under 2.5, but over 2, most likely. (Sharkcat 560)

 

Yeah, that'd be more than I'd be willing to tow 600km for a week or 2 of diving. I know I can't build the impossible though.

I'd be happy to sacrifice diver capacity and comfort to reduce weight and tow costs, it's just about finding that balance for me.

 

You should get under two tonnes with a six metre mono, I really would not go much shorter in boat length, both for internal space, and seakindliness.

 

I am thinking a slightly stripped down version of this, could be the go for me (ignore the show).

 

Where do you get the foam collar, assuming you are not using air tubes ?

 

I'd look into forming it then carving into shape, just depends what shape the material comes in (or if it is 2 part expanding). You can also get many foam suppliers to supply various shapes.

 

You would need something pretty resilient, a rigid foam would not do it, unless very high density, and that would be too heavy, and too expensive. You might get Kapten Boat Collars to fabricate something, in flexible polyethylene, but it is expensive.

 

Seems like this sort of thing could fit the bill - Ethafoam 220 Closed Cell Foam | Ideal Packaging Foam https://metrofoam.com.au/ethafoam-220.html

 

" It is used as the core material in surf boards, boogie boards and lifesaving equipment."

 

If you are simply looking for reserve buoyancy, boxes on the sides of an aluminum hull will do the trick without complication. Otherwise, what is the reason for the collar?

 

Presumably as a buffer for divers coming back to the boat.

 

Divers normally come up a ladder at the stern.

 

Or at the side. I've made a few dozens of pivoting side ladders for small pangas, one diver getting out at the side is not a stability problem. The stern of small boats has a lot of things like outboards with propellers, gas tanks, aggressive and/or delicate hardware like hydraulic items and so on. Not a lot of place for a ladder plus divers.
RIBs are fragile when diving as the diving material is able to pierce and destroy the hypalon of the chambers. Worst hypalon is cooked by the sun in tropical climates, and it's short lived. Rigid foam is at the same time heavy and fragile, so it's not interesting. Just a complication.
On small diving boats, it's simpler to have a wide comfortable top on the hull, so divers can sit on.
If you want a kind of "dynamic insubmersibility", on small boats it's simpler to have a floor with closed chambers that you can inspect. The floor must be a few centimeters above the waterline, and it's advisable to have rather large openings at the stern so the intruding water does not stay in the boat. As soon in, as soon out. The boat must empty in seconds. Sometimes beefy bilge electric pumps are needed.
That works flawlessly as I've seen myself in choppy seas and acrobatic beach arrivals with waves. The lone precaution is to put a fishnet at the openings so the sun glasses, diving masks, PADI member cards, shoes and other things do not end in the sea.
You can put rubber flaps so the water does not enter by the openings in following seas.
I almost forgot. You have to see the Australian or your country rules. I have a doubt that small light boats are authorized to go 20 NM into sea.

 

Not as commercial operations plying for hire, but there is no limitation on what private citizens can do.