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Old 06-24-2014, 05:58 AM   #21
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Bay Pelican has a 3.2 meter AB RIB with a 9.9 hp two stroke. The 9.9 hp two stroke is a compromise. We can plane with two people on board (the usual) but not with three. The two stroke uses more gasoline (4 US gallons per week usually) but requires less pull to start so that my wife can start it. It also weights significantly less than a four stroke so lifting the dinghy and motor to the upper deck is reasonable.

If I change the carburetor it would be a 15 hp. Even though we frequently travel a couple of miles to a dinghy dock I have not felt the need for additional speed (except when it is raining of course).

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Old 06-24-2014, 06:33 AM   #22
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I've powered my 10ft Avon RIB with a Merc 3.5 2 cycle and a Johnson 8 hp 2 cycle. With the Merc it will not plane. IMHO the small 2 cycle 3.5 and under are not reliable enough to carry on a cruising boat. My 8 hp will plane with me and the dog and is at the max weight for me to carry. I've installed a Weiver leaver system so I don't have to carry it often.
Ideally I would like a 15 hp Yamaha 2 cycle, but it is at the max weight limit for the Weaver leaver.

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Old 06-24-2014, 06:37 AM   #23
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Roll up 10' WM inflatable with a 2hp Honda suits our needs fine.

Maybe because rotomolded kayaks or Minto dinghy with oars is first choice for shore excursions.
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Old 06-24-2014, 06:41 AM   #24
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We have a 10-4 Achilles RIB powered by a 15 HP 2 cycle Yamaha. It's quiet at idle speeds, and will easily get the boat on plane with 4 adults. At top speed its fast (26 mph) and very stable.
What I can't believe is how little fuel it uses esp when cruising at low speed. And how easy it starts.
By far the best dinghy we have had.
I have a 2.2 Merc 2 cycle as a backup engine.
I also have a Humminbird portable fish finder for exploring, works great.
Jay Leonard
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Old 06-24-2014, 07:32 AM   #25
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OK I'll play.

10' RIB(hyperlon) with 15 hp Yamaha/ 2 stroke, great combination lives on the davit off the back of the boat.It planes with 4 up, can tow the kids behind at a fair clip, and goes likes the proverbial clappers with one or two up.

The two stroke Yamaha's seem indestructible.
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Old 06-24-2014, 07:32 AM   #26
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HopCar, I think it's pretty easy to just start with the dinghy manufacturer's min and max recommendations, and then work from there. Discussion follows.

We started with a West Marine RU-285 inflatable; roll-up "teak and holly" floor with an air keel underneath. Minimum recommended HP was 5, max was 8. We used a 5-hp Johnson 2-stroke (built by Suzuki) which weighs 46-lbs... partly because I could also use the same motor on our square-stern canoe (max: 5-hp), and partly because we carried the dinghy deflated, installed the motor on the spot, brought it all home is separate pieces for winter storage, etc. Maybe the 5-hp would plane that boat, with only me on board, if I sat in the right place, held my tongue just right, and flogged the snot out of the motor. Otherwise, it made a very reliable putt-putt to take the various First Mutts to shore and back.

Added a davit mount to the big boat's swim platform (not pictured in the avatar), leaving dinghy inflated with motor mounted for the season. Still needed to mount/remove the motor in spring and fall, but otherwise, much easier to handle.

Changed to a Walker Bay Genesis 310 RIB, using the same motor. Min recommended is 10-hp, max is 15-hp. It planed once -- and only once -- in the 5-hp configuration. And that was a bit of a fluke. I was flogging the outboard, 90-lb First Mutt was in hood-ornament position up forward, and an overtaking boat's wake lifted us up on plane. What a surprise! But mostly, it made a good putt-putt for taking... etc.

In the meantime, we acquired a trailer; no further need to lift the outboard as a separate unit. Yay!

Have since changed to a Suzuki 15-hp fuel injected motor. (Still in the break-in period, actually.) Big difference. Planes in a heartbeat, runs like a scalded cat. Weighs 106-lbs (electric start version) but I don't really care, since that's well within the limits of our davit system, and we still have that nifty trailer.

It happens Suzuki's 9.9-hp EFI version is built on the same platform as the 15s and 20s... sort of a departure from previous outboard practices. In that case, I found no benefit to using Walker Bay's minimum HP recommendation. Other 9.9s are lighter, although the gap is closing; still other brands may offer a weight advantage to some.

All this has led me to believe the dinghy manufacturer's probably have a bit of a clue, and their min and max recommendations for a given boat are useful as a starting point. If motor weight is an issue, go lower (and maybe go 2-stroke), and expect to go slower with the reduced HP. If weight is only partially an issue, the min recommended HP will likely plane the boat under some circumstances, but not necessarily all the time. If weight is not much of an issue, the max recommended HP is likely to work 80-90% of the time... and when it doesn't, other contributing factors (overloading, unfortunate load distribution, etc.) might be the cause.

But I think you knew all that

South River, Chesapeake Bay
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Old 06-24-2014, 07:49 AM   #27
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We carry 2. An 11.2 ab roll up with a 2 cycle Yamaha 15. Planes with two and four aluminum 80's. Rated for 20hp. The other is a nautica 12.5 wide body with a 4 stroke Yamaha 40, which is rated up to a 60hp. Fast enough and better range than running a 60.

Via iPhone.
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Old 06-24-2014, 07:57 AM   #28
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As much as we use dinghies, we do understand boats limited to smaller sizes and less motor, but the concept of having to pull it up and remove the motor is one that would greatly lessen our use. Most boats will accommodate a davit of some sort and we'd certainly go that route with capacity for boat and motor. I say this only because that plays a role in motor selection and removing the requirement to be able to life the motor off and on is a big step.
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Old 06-24-2014, 08:36 AM   #29
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First, I say the main factor is where you use your boat and dink. If you only use it in a protected bay you have many options and can go as big or small as you wish.

Here in the Pacific if you go cruising you will encounter anchorages where going ashore means crossing the surf line and pulling your dinghy up on the beach away from the rising tide. Also towing isn't a guaranteed option when crossing the channel to our islands you can encounter high winds and seas.

This meant for me, an 11' Avon RIB light with a 2 stroke 8 HP Johnson. I can take that engine on and off and pull the dink up on the swim step. I don't want davits because I have a fishing cockpit and love to kill bait.

I don't know what the rated HP of the RIB is but my guess would be 15. We can plane it with the both of us but it isn't easy to do.
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Old 06-24-2014, 08:43 AM   #30
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Just a little 2.5 Tohatsu on a small inflatable. Gets me around as fast as I want to go, sips gas as daintily as a hummingbird, and is light enough to handle easily.
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Old 06-24-2014, 10:04 AM   #31
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Depending on the capabilities of your boat....
Crane or davit.. as big or heavy with as much HP as the crane/davit will take..

No davit/crane?.. as big or heavy with as much HP as you will be able to lift..

There is no substitute for Hp or length to make a dinghy more useful and stable. We take two dinghy's along a lot of the time.. one for kids.. one for the skipper. The kids used to have a 3hp tohatsu, now replaced with a 15hp yamaha. The yamaha uses more gas but is way quieter. Ran the small motor for years so they could run it all day and not use much fuel, start it themselves, and couldn't go too far and get into too much trouble. The 15hp is now on a 11' high pressure floor Zodiac and its rated for 10hp.

On my Avon 3.45 sportboat I run either a 40hp Johnson or a 25hp Mariner.. the 25hp is ok and will plane 4 adults.. the 40hp is dangerous and makes the skipper smile!.. and uses a significantly larger amount of fuel.

Attached pics in different configurations.

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Old 06-24-2014, 10:09 AM   #32
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This is good info!

It seems that if you don't have a way to mechanically hoist the motor / boat, you shouldn't plan on planeing.

You're not going to be happy with the minimum recommended HP. This often seems to be about 60% of max hp.

A lot of manufacturers don't set a minimum recommended hp.

You're not going to be unhappy with the maximum recommended hp.

I'm getting more comfortable telling people that if they expect to plane the boat, they should install an engine of at least 70% of the max rated hp. More is better.

Has anybody put a 5 hp. on a 12 or 14 foot aluminum boat? While a 5 won't plane a large inflatable (10 feet +) will it plane a hard boat?
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Old 06-24-2014, 10:15 AM   #33
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"The 15hp is now on a 11' high pressure floor Zodiac and its rated for 10hp."
Hollywood, you're a naughty boy!

What is the Avon rated for?
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Old 06-24-2014, 10:17 AM   #34
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We have a Zodiac RIB with center console 11 feet. The model is YL340

It has a 30 hp honda on it and gets moving pretty good even when loaded down.

We store the skiff on the boat deck, and use the Bayliner factory stock crane to deploy it. The total process takes less than 5 minutes for one person.
Kevin Sanders
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Seward, Alaska
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Old 06-24-2014, 10:39 AM   #35
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10.5 Avon air deck with 8hp 2 stroke, planes nice with two persons and the dog, but over that it struggles onto plane.

Having witnessed a number of setups, one thing I've noticed the longer the raft like in the 10' catagory the better at planing they are, the short rafts really need a lot of power to get on top, which I'm guess is the limited lift area.

75% of our time is displacement speed, but it sure opens up a lot of options if you can get on plane.
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Old 06-24-2014, 11:09 AM   #36
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Originally Posted by High Wire View Post
I have an 8'6" AB Inflatables RIB and a 6 hp Tohatsu 4S. It will not plane with 2 adults at WOT. A 3.5 hp 2S would do the same job with a lot less weight. Fortunately I have a davit system so I do not have to mount and dismount the engine each use.
I have the same size, different brand, RIB with the same engine. I am very disappointed in the 4s Tohatsu. It is even difficult to get on plane with one person. Only has about 5 hours on it but I am trying to sell it and will pick up a two stroke. I also have a davit system and stayed small to keep the weight down.
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Allan & Ann
If your floatin' your boatin'!!!
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Old 06-24-2014, 11:14 AM   #37
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Minimum useful size

For years I got along with a 10 Zodiac rib on weaver snap davits. Powered it first with the 25hp Mercury which was fun but dangerously fast. That's when I sold that 25 and bought the 15hp mercury which was much lighter and planed the rib nicely to 28knts. I also used a 3.5 hp Mercury as a go to shore easy easy to take on and off. The rib was rated for 15hp and was very light. My kids could water ski and knee board behind the little rib. I had a engine mount in the cockpit for the 15 and with the stability of the snap davits it was possible to hang the 15 on the back of the rib off the swim platform. The dingy was usually carried on the snap davits on the platform even though I had a davit to put it on the salon roof. This little rib rowed very well and this is how it was often used. It took nano seconds to launch with the davits and was very easy to drag up above the tide line. this was an extremely useful boat. At the same time I had a 10', Avon sport boat with a 25hp Yamaha, center council with power trim, running lights, power antenna and aluminum fuel tank. This was a totally useless boat for me. It came with the boat and after a couple of years I traded it in for a open 12' Achilles rib with wide beam and large tanks. This boat is the boat with a 20 hp Yamaha which is the max rated hp. This is now the work horse as the 10' Zodiac was given away because the fabric was wearing out. This boat rows well but because of it's greater weight it is seldom rowed. It's launched with deck crane from the salon roof. I will mount snap davits to the swim platform as a way to stabilize the dingy for loading and unloading but not as a way to carry and launch.
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Old 06-24-2014, 11:30 AM   #38
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Originally Posted by caltexflanc View Post
Get the highest HP it is rated for if you want to make some time. Anything else and you are not getting the most from the craft.

+1 to that.

You can always throttle back a higher hp motor and cruise slower. And with the higher hp motor you can throttle up and go faster or move a heavier load if need be.
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Old 06-24-2014, 12:37 PM   #39
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Algae is 7' fiberglass dinghy circa 1972. She's got a 30 pound thrust trolling motor (fresh water variety) that has seen some tough times. But she still works. And when this motor goes belly up I'll drop another $100 bill in the Amazon coffers and buy another 30 pound Minn-Kota trolling motor for fresh water.

For slipping along little creeks and bayous, Algae is so quiet Skipper and I can glide by birds and get up close and personal with the wild life. I think we see more too at a slower pace.

The thing I like best about the trolling motor is I simply flick a switch and she goes. I do not have the upper body strength to start a regular outboard.

For the most part though, I'd rather go faster.
Janice aboard Seaweed, living the good life afloat...
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Old 06-24-2014, 01:30 PM   #40
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Go fast or go home.

Ours is a Caribe DL-12 Rated at 40HP with a 40HP E-Tec. I can get it to do 33-35kts trimmed right.Click image for larger version

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Thanks, Oliver
M/V Oliver
Nordhavn 47 Hull #12
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