Planing Dinghy: Hp vs Dinghy type vs #Passengers

[Adelie]

I'm compiling info about how much horse power it takes to get a dinghy on a plane. The length and type of dinghy and the number of passengers aboard makes a difference. If you have personal knowledge whether from your own dinghy or being on somebody else's I would appreciate the info. If the knowledge is 2nd hand, what somebody told you their dinghy would do please indicate that. I'm not tracking whether the motor is 2- or 4-stroke currently but if you know include the info.
For passengers indicate the number of adults. If the boat would plane with 2 adults & some gear or 2 adults and a kid but would not plane with 3 adults then indicate 2+. If it would only plane with 2 adults but no gear then indicate 2.
I am differentiating between RIBs & other inflatable.

The briefest post with usable info would indicate:
Inflatable, 8.5', 9.9hp, 2+ adults.
If you want to include dinghy weight or make & model 2-or4-stroke that would be great. If you have info for more than one dinghy awesome, just make sure each dinghy gets it's own line of info so everything is clear.

If you want to provide more info and detail, great.

The following graphic includes data I gleaned from going thru 30-40pages of this site.

EDIT: Link to Oct-8 Update. https://www.cruisersforum.com/forums...ml#post3498738

[tkeithlu]

General comments:

Two vs. four stroke will make no difference in theory, and the weight of modern four stroke engines is not far different from their two stroke analogues, so I doubt that you will be able to separate the two in your data - there are too many other variables you can't control.

Dinghies with inflatable bottoms may plane in theory, but it's a near thing. Just a little softness and drag takes over. If you want a planing hull, go with a true RIB. Actually, unless you have to pack it away in a suitcase, go with a true RIB. If your situation is marginal for space, consider a folding transom RIB, stored upside down on deck.

[cr180]

AB 10 RIB, Yamaha 4 stroke 20hp, 4 adults, boat planes

[desodave]

Zodiac 300 (10ft), 105 lbs, Yamaha 6hp 4 stroke, eventually planes with me (225 lbs) and prawn traps in it. It's a single skin RIB. Never with another person. New boat had a smaller Highfield and 9.9 Merc with it - I kept the Zodiac because it was bigger and sold the Highfield with my old boat. The Zodiac with the 9.9 gets on a plane immediately with me in it - haven't tried it yet with another person in it but I suspect that it will plane even then given the immediacy with only one in it.

[chris mac]

We had a highfield rib 2.9m with a 15 hp Yamaha 2 stroke. With 1 person it jumped up and planed almost instantly. 2 people took a while and we had to shift forward to get on plane. 3 people, no chance of plane.
We just bought an achilles rib 3.1m. Same outboard. With 1 person it catwalks and takes a few seconds to get the nose down and planing. With 2 people it gets on plane almost instantly. We have yet to try with more people or extra weight.
The weights are almost identical, The achilles is the ul version. so the extra length has made a significant difference.

[Nicholson58]

Caribe 9.5 ft RIB,:15 HP 2-st. Scary fast with one. Planes with two or three. 2 with groceries. Must have ethanol free for the HP boost. This is easy in the Caribbean.

Friends have 10 foot OC tender. Will plane easily with 10 HP and four people.

[wingssail]

Inflatable (High pressure air floor) 11.8', 15hp, 2+

So many variables! Length makes planing easier. Can you move the passengers forward to get on plane? weight of dingy itself. with High Pressure Floor can you get it to 11lbs/sq inch? (needed for planing). is there a full length keel? Do you plan on having a planing enhancing plate on the motor? How heavy is the motor? Do the dingy tubes extend aft of the transom? Where is the fuel tank located? How big is the fuel tank?

With our 11.8' High Pressure Air floor Zodiac, and the 15hp merc, we can plane 2 people and one week's worth of supplies and 6 gallons of gasoline at 4000rpm going 11kts, which is the minimum we can go before the boat begins to come off a plane. That is not full throttle. I don't have numbers for full throttle. At the power setting I mentioned it uses less than 3 gallons per hour, (as best I can tell)

We have planed three people but it takes full throttle to do so.

A RIB is more efficient and a better handling boat I think due to better hull shape. However it is heavier. We chose High Pressure Air Floor to be able to completely deflate the dingy and stow it below decks, no davits, nothing on the bow. (the motor goes below also). This ability comes at the cost of a less efficient boat and much more work to inflate it every time we wish to use it.

[Mike OReilly]

Looks like you already have my data point on the graph:

3.5hp 4-stroke, 10' Portabote. Planes easily with one (fat) person in it, even with gear. Will plane with two adults, but only in flat calm.

[JPA Cate]

1) flat bottom, wood panel floor Zodiac, hypalon inflatable; 13 ft.; 15 hp Johnson 2stroke; planed with four adults, one large (#300)

2) DSB hypalon inflatable, V floor, ~12 ft., 15 hp 2 stroke; planed with same 4 adults

3) Rib, Gemini, hypalon; 11.3 ft.; 15 hp 2-strokes; same four adults; has been re-tubed twice,

[wingssail]

Originally Posted by JPA Cate

1) flat bottom, wood panel floor Zodiac, hypalon inflatable; 13 ft.; 15 hp Johnson 2stroke; planed with four adults, ...

I had one of these, Zodiac MarkII, with Merc 25. Outrageous boat, planed six! but I could not assemble it on the deck of my boat. And then the seams all let go anyhow.

[chrisr]

3.2m aluminium / hypalon RIB by Gemini. 8hp 2-stroke mariner

will plane with 2 onboard if water is reasonably flat. easily with 1 even in rough water

cheers,

[Chotu]

You definitely need to define an “adult.” How much does one weigh?

Is it me (145-150lbs) and my girlfriend (95lbs)? Or is each one 200lbs? Maybe a few are 250lbs?

[Dallasron]

OK,,,I just bought the largest dinghy that fit my boat 38' with a 350. it will take a 25hp but i got a 20. Same weight as a 9.9. Get as much as you can and you will be glad. Buy the davits and maybe a hoist. I dont use all the horsepower or space in my pickup but when i need it -- its there

[marty9876]

High field 310 with Mercury 5 hp 4 stroke - don’t plane at all. Almost if a fat man wiggles his way low, in the middle and forward but just not quite

[Adelie]

Originally Posted by Dallasron

OK,,,I just bought the largest dinghy that fit my boat 38' with a 350. it will take a 25hp but i got a 20. Same weight as a 9.9. Get as much as you can and you will be glad. Buy the davits and maybe a hoist. I dont use all the horsepower or space in my pickup but when i need it -- its there

Is the dinghy a RIB?
How many adults can you put on it before it doesn't want to plane?