Comparing RIBs to HP air floors

[willk]

The other thing I should have mentioned is that shorter hulls can need more power to get on the plane - I never really had much success planing mine "2 up" with the 9.8 - although I could get 18kts solo!

[Chuck Hawley]

Originally Posted by fxykty

So why does my Tohatsu 9.8B 2-stroke plane with one but not two with our 9’ 6” aluminium RHIB? I’ve read all these posts about people ‘easily’ planing with two people and 6 and 8 hp engines, and same for others with our engine. So what’s wrong with our setup?

Longer boats with more hull surface in the water will plane more easily, up to a point. Less bow rise, less mushing along. Small boats dig a hole and can't get out of it.

I just sold a Novurania 360 with a 40HP Honda. While I used it in the Sierra, where there is about a 18-20% power loss, it would barely plane with three adults. Once up on a plane, it wanted to be moving along pretty quick or it would transition into semi-displacement mode.

I don't know for sure, but I bet your engine would be able to plane two of you easily with a lightweight 11' inflatable (either aluminum hull or air floor.)

Chuck

[Bean Counter]

MAy have been mentioned already but a pair of hydra fins attached to the cavitation plate make a big difference in keeping nose down for quick planing.

[MLOI]

Originally Posted by fxykty

So why does my Tohatsu 9.8B 2-stroke plane with one but not two with our 9’ 6” aluminium RHIB? I’ve read all these posts about people ‘easily’ planing with two people and 6 and 8 hp engines, and same for others with our engine. So what’s wrong with our setup?

Weight too far back in the boat so you are digging a hole?

My 3m Achillies HP floor with the same motor planes easier with my 45 kilo son in the bow (plus 10 litres of fuel and an anchor and 5m of chain than it does with just me. When I'm alone I struggle to get my weight far enough forward to keep the nose down. Gas, back off, then roll on power as the nose comes down from backing off.

Perhaps play with tilting the outboard forward a stop? - it's easier to get on the plane fully loaded when I do this, but we do get more cavitation.

We never have issues planing with me and kids and gear - perhaps 200 kgs payload all up. Likewise with 2 adults and gear.

Mike

[fxykty]

Lots of suggestions, thanks.

The previous owner single-handed and put hydra fins onto the outboard and we’ve left them on.

I will try trimming it in one hole to see if that helps getting onto the plane.

I don’t think the weight distribution is the problem as we have tried all combinations. Typically my partner is on the bow seat, along with small anchor and 5m of chain in there and the 12l fuel tank sits right up against the bow locker under the seat. I sit on one of the tubes and have tried sitting further forward as well as further back.

Most of the time it feels like we’re plowing along in a level attitude, definitely not bow high.

Regarding weight, the boat is 43kg and engine 26kg, say another 20kg for fuel tank and anchor and chain, so this isn’t a heavy boat. We’re 150kg between the two of us. Still not that heavy.

Oh well, will try some options this weekend.

[Jim Cate]

One other comment about air floor dinks, garnered from our one experience owning one/ This was a ~12 foot Zodiac Futura air floor which we bought second hand when our RIB was pinched. For me, it seemed that the thick air floor raised the sole to the point where there was significantly less internal volume than in conventional boats of the same size.

The kinda odd Futura design may well have also been a contributing factor. In any case, when the air floor became herniated we donated the whole thing to a club in Jervis Bay that catered to disadvantaged kids, and they made a plywood replacement floor which seemed to work much better (they didn't need to store deflated). Had more room for stuff, planed better and was more directionally stable (they said).

For the OP... with a 25 foot boat, the advantages of some sort of rollup dinghy outweigh any performance benefits of any other type IMO. Deciding between a slat floor and an air floor may come down to availability and price!

Jim