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Old 18-08-2015, 05:50   #1
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what size outboard for dinghy?

We just got a used 10' Avon RIB that came with an anemic 6 hp outboard. I need to know what size outboard will make that RIB plane with up to 4 people in it. I expect we'll be doing some longish side trips on our next cruise and would like to be able to cover a lot of ground quickly.
Thanks
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Old 18-08-2015, 05:53   #2
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what size outboard for dinghy?

Prob 15 hp min. Have fun wrestling the beast.


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Old 18-08-2015, 05:58   #3
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Re: what size outboard for dinghy?

15hp. Is perfect
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Old 18-08-2015, 06:16   #4
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Re: what size outboard for dinghy?

15hp will be good, but if going for a new 4-stroke, the 20hp versions are the same size/weight as the 15hp and only sell for a bit more money. I would go 20hp.

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Old 18-08-2015, 06:24   #5
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Re: what size outboard for dinghy?

The Avon Rover Compact 310 (16" dia tubes) is only rated to 10 HP; whereas the Rover Rib 315 (17" dia tubes) is rated to 15 HP.
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Old 18-08-2015, 07:15   #6
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Re: what size outboard for dinghy?

For reference, I have the Avon 310 Lite RIB (which sounds like the Compact that GordMay referenced). This model has the fold-down transom, to fit in a bag. We have an 8 hp Yamaha, 2-stroke. With two 200-lb men, it will plane. On takeoff, you need to lean forward (bow) to get the stern up. Just a short distance. At WOT, will go 23 mph.

With my wife, daughter and myself, that is about 450 lbs total. It will still get up on plane, but just takes a bit more running room to do so. It helps some that weight can be distributed a bit more with three than two.

With four adults, we just count on not getting on plane. However, I was trying to keep the weight down on the solar arch panel (dinghy is hoisted from the water using that structure), wanted load light enough where I didn't have to remove the motor, and the combo works well for the two of us - which is situation 90% of the time.
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Old 18-08-2015, 07:27   #7
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Re: what size outboard for dinghy?

How you prop an outboard makes an enormous difference on being able to climb onto plane too. Of course once on plane, you may have to use some common sense with the throttle to keep from over revving the engine.
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Old 18-08-2015, 08:42   #8
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Re: what size outboard for dinghy?

All good information. I don't think my stern rail would hold a 20 hp outboard, however.
Our Avon is oldish and a hard V bottom. Don't know if that makes a difference with getting on a plane.
Any thoughts on the viability of sailing with the outboard still mounted on the dinghy? Do I need to stick it on the rail every time I haul it up? Does that happen before or after I haul it up or is this like everything else sailboat and it varies from boat to boat?
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Old 18-08-2015, 08:58   #9
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Re: what size outboard for dinghy?

Quote:
Originally Posted by Rick Williams View Post
We just got a used 10' Avon RIB that came with an anemic 6 hp outboard. I need to know what size outboard will make that RIB plane with up to 4 people in it. I expect we'll be doing some longish side trips on our next cruise and would like to be able to cover a lot of ground quickly.
Thanks
I would not go on the sea in a moderate windy day without a 15 HP
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Old 18-08-2015, 09:03   #10
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Re: what size outboard for dinghy?

Quote:
Originally Posted by Rick Williams View Post
All good information. I don't think my stern rail would hold a 20 hp outboard, however.
Our Avon is oldish and a hard V bottom. Don't know if that makes a difference with getting on a plane.
Any thoughts on the viability of sailing with the outboard still mounted on the dinghy? Do I need to stick it on the rail every time I haul it up? Does that happen before or after I haul it up or is this like everything else sailboat and it varies from boat to boat?
The 20hp 4-strokes are the exact engine as the 15hp ones, only with some tuning tweaks for the extra 5hp. If your rail can handle the 15, it won't know you have a 20.

If you intend to lift the engine off the dinghy regularly, I would not go above 6-8hp. You move into an entirely different weight category above that, where lifting just isn't really practical on a regular basis unless you have a lift or similar.

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Old 18-08-2015, 09:05   #11
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Re: what size outboard for dinghy?

I would say get two outboards: a 3.5HP and a 15HP. The 3.5 at 22lb you will love when you only need to go ashore or to a neighboring boat. No wrestling the heavy tank and motor, it's installed in one minute. But if you need to go a mile or will be staying put for awhile then the 15 will be a blessing.
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Old 18-08-2015, 09:09   #12
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Re: what size outboard for dinghy?

You dont say what country you live in nor where you intend to cruise

So I guess you are American and u will cruise Chesepeake Bay and will not offer advice re type of ob.

I have an 18hp and that does 4 adults no problem and would handle a few extras too.

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Old 18-08-2015, 09:11   #13
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Re: what size outboard for dinghy?

What horsepower engine is your RIB rated for?...you can't safely exceed that amount obviously.

For Yamaha outboards at least, the 20 Hp and the 15 Hp both weigh 132 pounds. The next size down, a 9.9 Hp weighs 93 pounds.

The 9.9 will not get the boat and that many people on a plane. Given the 20 and the 15 weigh the same, I think that the 20 would be your best choice, provided your davit is rated for the weight of the boat, engine and equipment.

These engines have speed governors so that over revving them is not possible....6000 RPM max.

Reference: Motor Specs, Portable Engine | Yamaha Outboards
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Old 18-08-2015, 09:12   #14
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Re: what size outboard for dinghy?

Depends on how much these people weigh.

You are limited in engine choice (as well as in payload) by what the transom plate says.

I am riding a 40hp rib now and then and I can guarantee 40hp is enough.

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Old 18-08-2015, 09:22   #15
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Re: what size outboard for dinghy?

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You are limited in engine choice (as well as in payload) by what the transom plate says.
Why is that? The dinghy is not in warranty. Those HP ratings have more to do with controlling engine weight than HP. Since the 15 and 20 weigh the same, no reason not to go with a 20, even if the plate says 15 - one needn't use the entire throttle range if things get squirrely...

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