Planing Dinghy: Hp vs Dinghy type vs #Passengers

[Adelie]

Originally Posted by 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?

An adult is at least 15, 16, 18 or 21 years depending on whether you are talking about age of consent, age to get married, age to enlist/vote or age to purchase alcohol.

I chose not to define it specifically because I expect that people vary a lot, I don't want to ask that kind of a personal question and I am hoping to get enough data that median would be obvious. I would rather get a lot of OK data than a small amount of very good data.

Honestly I would guess that most couples cruising together probably weigh between 275 & 350lb.
]

[Jammer]

Interesting thread, thanks.



My dinghy is a 14' aluminum boat made in the early 1960s by Crestliner. It weighs 215 pounds empty without motor. I have a 9.9hp electric start Yamaha on it, 4 stroke, that weighs about 100 pounds.


With this hull there isn't a clear transition from planing to not planing.


With just me (250lb) it goes 14 kts. The prop is chosen so that the engine reaches target RPMs in this configuration.



With me and a young person (150lb) it goes 11 kts.


With me and another adult (250lb) it goes 10 kts.


With me and another adult and a young person (250+250+150=650lb) it goes 8 kts. At this point the engine is somewhat below the target rpm range and would benefit from a different prop.


I have not had a heavier load in it.

[rslifkin]

I'm definitely interested in this. Our dinghy is an aluminum 12 footer (semi v hull, not a RIB), 150 lbs empty. So far it's oar powered, but we'll probably put an outboard on it at some point. It's rated for a 15hp, but that's more weight than I want and likely to be faster than I ever care to go. It'll be interesting to hear what kind of power a few of the other hard dinghy users have and what speed it gets them.

[LeaseOnLife]

AquaPro 290, 9.5ft alu rib (pre Highfield, same hull), 9.8HP 2 stroke, 2+ adult in any sea state, 3- in flat water after a while

[Panope]

10' High pressure floor inflatable (70lbs ). 6 horsepower engine (60lbs.) Will plane 2+ (400 lbs ) and remain on plane at (a bit) less than full throttle.

Steve

[Bruce K]

3.5m Al V nose punt. 15hp 4stroke Suzi. 28kt 1 up. Planes with 4 adults and 1 dog, plus some gear.

[Adelie]

Like Oliver said, "Please sir, I want some more."
Keep posting info and I will update every page or so.
Here is the table updated to Panope.

[Bellinghamster]

10ft inflatable with plywood floor and 9.9 (95lb) 2 stroke planed well with 3 adults (~140lbs averate).

12ft inflatable with plywood floor and 8hp (57lb) 2 stroke planes well with 2 adults, reasonably with 3 and *almost* but not quite with 4 (again, average ~140lbs).

I just bought a 10'2" HP inflatable-floor dinghy and a 9.8hp (57lb) 2 stroke but haven't had a chance to try it yet. New dinghy is about 50lbs lighter than the 12ft. I'm hoping lighter boat and 2 more hp will make it plane with the 4 of us, but worried the inflatable floor will counter the other gains... even if it doesn't plane it's still a LOT easier to assemble/disassemble on the foredeck and carry up the beach.

[Paul Howard]

Avon RIB 3.1, 6hp Johnson 2stroke, planes with one (me, 220lbs) but not with two.
With 9.9 Johnson 2stroke, planes with three.

[Gerry Connolly]

AB 9.5' Aluminum haul rib and a Mercury 8 hp 2 stroke. Easily planes with 2 180 lb adults in any and all conditions. Same boat and a 2.3 hp honda won't plane period.

[Dallasron]

Adelie - Yes it's a RIB WM350 (11.5') Planes with 4 and beer (sit somebody up front for the first few moments) Havent had more than 4 so not sure what the max would be. You also have to figure your prop. if its just you and you want to go faster add some pitch. Do a power prop if you want to carry weight and plane quick.

[j.g.evans]

I had a 10', 100 lb, AL, Force 4, RIB with a 75 lb, 15 HP, Mercury 2 S. I often had 3 adults planing. I did 26 knots alone. It had a V bottom and had good control. Planing is the only way to stay dry. A lot of fun.
I now have a 10', AL, Zodiac and was able to plane, me alone, with a 5 HP, 2 S, Mercury. I wish I still had the 15 HP.
I think the 2 stroke engines are about 25 lbs lighter than a 4 stroke. I uses a crane to lift the 15 HP 2 S onto the stern rail.
I recommend carrying a small, light, motor too. 95% of the time I would go short distances and use the small engine. I had a 2 HP which I could lift with 1 hand and later a 3.3 HP which required 2 hands.

[Jenta]

3DTender ULTRALIGHT RIB Aluminium 310
- 3.1 Meters / 10.2 Feet long
- 1.54 Meters / 5 Feet wide
- 34 Kg / 75 lbs

Suzuki 15hp 4 Stroke, 15" shaft
- Stock prop, no planing fin added
- 59 Kg / 130 lbs

Planes easily with 350 pound payload. Easily 20-25 knots of speed.
With 350 - 450 it gets iffy and will require the "everything to the front" to get on plane and must maintain speed or risk dropping back to the snowplow position.
Anything over that and you're not getting anywhere in in style.

We just purchased a 25hp Yamaha that is 126lbs (4 pounds lighter) but won't be using it until next April. Should be overkill, but I'd rather throttle back then run out of throttle.

[MicHughV]

I've had a variety...

9' Fiberglass dink with 2 hp Suzuki 2 stroke. limited to 2 people and 4 mph....slow, but good on gas, getting in and out from the water only for the young and fit. Engine can be picked up with one hand.

11' inflatable with plywood floors and 15 hp Suzuki 2 stroke.....too much power for such a dink, floors want to fold. Engine too heavy, can zip along at prodigious speed, but very squirrelly. Excessive gas consumption.

11' RIB with 15 hp Yamaha 4 stroke. As above, plenty of zip and power, maybe too much. Engine is heavy and difficult to attach or remove from dink in water. Also a gas hog.

11' RIB with 9.9 hp Yamaha 4 stroke...basically the same engine as the 15, but with slightly slower speed. Slightly better gas consumption, but only slightly.

11' RIB with 8 hp 2 stroke Yamaha. By far and away my favorite combo. Enuff power to get 2 people up on plane....with groceries, a bit of a struggle, but can do it. Engine can be lifted with one hand. Good gas consumption. It's not made anymore, but my fav.

Like most, I favor more power, but it comes at a cost in weight and fuel consumption.

the 15 hp plus is great for getting out to the reefs for some diving, but in an anchorage, I find the 8 hp more suitable.

[Redline452]

Zodiac YL310 (10') inflatable (wood floor, inflatable keel under) 2 adults 1 child would plane with 8 HP.

Replaced with YL310R RIB version, no longer planed with 8HP, does plane with 15HP with 3 adults (aforementioned child is now 14).