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Old 23-11-2016, 11:57   #1
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Outboard Size For Dingy

I am looking to upgrade my tender (I currently have a 2.4 meter slatted bottom inflatable and 2.3 HP outboard). Seems to me their is a huge jump in price, size and weight when you go from a 6 HP outboard to an 8 HP model for a small power gain. So what I want to know is if 6 HP is enough to get a 2.7 meter rib/airdeck dingy (ie walker bay genesis etc) to plane?

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Old 23-11-2016, 12:04   #2
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Re: Outboard Size For Dingy

Depends, the RIB will plane with one person, maybe two.....

The air deck however is a different beast, and may plane, or may just suck down on the water. Depends on how the inflatable keel (if there is one) shapes the bottom.
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Old 23-11-2016, 17:07   #3
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Re: Outboard Size For Dingy

How much weight do you have in the boat? We have a 6hp that gets our 10ft RIB on plane with 340lb of people, but if we have an extra person or lots of heavy things it won't get up. We chose the 6hp for its lighter weight since we don't have dinghy davits and have to manually put it on the stern mount when not in use.
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Old 23-11-2016, 17:26   #4
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Re: Outboard Size For Dingy

If you ultimately decide on the 8hp, consider going up to 10-15hp. Most 8hp outboards are just "detuned" 10-15's (ergo the jump in weight) so you might as well add a few more HP for when you need it without much weight or cost penalty.
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Old 23-11-2016, 17:27   #5
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Re: Outboard Size For Dingy

My Walker Bay 310 airfloor will plane with a Yamaha f6 and 390 lbs. of load.

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Old 24-11-2016, 11:33   #6
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Re: Outboard Size For Dingy

It depends a lot on the dinghy, and the weight of engine and load. We had a 6-horse four-stroke on a inflatable floor 2.7 m dinghy. It would plane (just) with one person and no cargo. Anything more, no hope. And it was not directionally stable when on a plane.

We now have a 10.5 ft AB aluminum floor RIB (which we love). We bought an 8hp Yamaha enduro 2-stroke. This was not much cheaper than the 9.8hp model, but it weighs about 30 lbs less, and that makes it much more manageable. It planes easily with one person, can get up to a plane with 2 people in flat water or downwind.

We have found that in the Caribbean, small 4-strokes don't survive very long. The market share for Yamaha approaches 100% on some islands. Rare to see a local fisherman with anything else.
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Old 24-11-2016, 12:49   #7
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Re: Outboard Size For Dingy

Quote:
Originally Posted by Suijin View Post
If you ultimately decide on the 8hp, consider going up to 10-15hp. Most 8hp outboards are just "detuned" 10-15's (ergo the jump in weight) so you might as well add a few more HP for when you need it without much weight or cost penalty.

This, determine how much weight you can tolerate, then find the highest HP motor at or just under that weight.
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Old 24-11-2016, 14:50   #8
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Re: Outboard Size For Dingy

Quote:
Originally Posted by Suijin View Post
If you ultimately decide on the 8hp, consider going up to 10-15hp. Most 8hp outboards are just "detuned" 10-15's (ergo the jump in weight) so you might as well add a few more HP for when you need it without much weight or cost penalty.
I think you shall find that that the 9.9hp range are detuned 15hp's. Check the engine weight and CC rating for confirmation. In my opinion the 8hp is a good sized engine for two people on s smallish dinghy - manageable weight but enough to plane.
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Old 24-11-2016, 15:31   #9
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Re: Outboard Size For Dingy

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I think you shall find that that the 9.9hp range are detuned 15hp's. Check the engine weight and CC rating for confirmation. In my opinion the 8hp is a good sized engine for two people on s smallish dinghy - manageable weight but enough to plane.
Talking two stroke....most 6's, 8's, 9.8's are 167/ 169 c.c.
When you go 9.9 (same motor as a 15 usually) and above you can expect to have to lift another 10 kg minimum out of the water.
My Zodiac 2.7 rib has a very deep "V" hull but will plane with the 5hp Merc 2 stroke. With two adults it will not plane with the 8hp Merc. Hull "V" is too great and waterline too short.
Bieng such a short foot print, the WB rib will be almost dangerously twitchy when on the plane at full speed with an 8 or above. There is MUCH more water line BEAM than waterline LENGTH, so directional ability suffers. Not so bad in a ten footer Because beam of a ten footer usuall same as the 2.7.
If I recall correctly, only Honda 8 is a detuned 15. May be wrong.
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Old 24-11-2016, 19:44   #10
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Re: Outboard Size For Dingy

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Talking two stroke....most 6's, 8's, 9.8's are 167/ 169 c.c.
When you go 9.9 (same motor as a 15 usually) and above you can expect to have to lift another 10 kg minimum out of the water.
My Zodiac 2.7 rib has a very deep "V" hull but will plane with the 5hp Merc 2 stroke. With two adults it will not plane with the 8hp Merc. Hull "V" is too great and waterline too short.
Bieng such a short foot print, the WB rib will be almost dangerously twitchy when on the plane at full speed with an 8 or above. There is MUCH more water line BEAM than waterline LENGTH, so directional ability suffers. Not so bad in a ten footer Because beam of a ten footer usuall same as the 2.7.
If I recall correctly, only Honda 8 is a detuned 15. May be wrong.


Agree Brian. I personaly would not go with less than 10ft/8hp if that were my only dinghy and I were going cruising. Smaller is adequate for marina only use. My kids dinghy is only 2.6m but is rated for a max of 30hp and we have tried the 25hp Yam 2-stroke on it and she is rock solid in all types of sea's. Much is dependent upom the manufacturer.
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Old 24-11-2016, 20:55   #11
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Re: Outboard Size For Dingy

I think much boils down to davits. If you have to dismount the motor, tiny is better. It also depends on the area. Where I cruise, I very seldom run the throttle above ~ 1 hp. Faster would feel rude.
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Old 25-11-2016, 08:57   #12
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Re: Outboard Size For Dingy

I do not understand the desire to get on plane. Unless you plan to anchor in areas of very fast currents a small (2-5 hp) outboard will get a 10' RIB where you need to go. It might take an extra 10 minutes but the easier lifting of the motor to the rail more than compensates.
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Old 25-11-2016, 10:53   #13
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Re: Outboard Size For Dingy

Dave, there are numerous reasons to get on the plane. Much shall depend upon your cruising area. For long term cruising we have big outboards as well as pottering engines.
The planing engines are used for distance travelling which can be necessary for recreation/fishing/shopping/ etc or just visiting. It is generally also more economical. I can travel 10 miles across an open sea way using the same amount of fuel with my 25hp, keeping the dinghy just on the plane as I would plodding along with our 3.5hp flat out - but taking hours to do the same trip.
We also can use our dinghy as a tug, tow or drag other boats and in a big sea its vastly safer as we dont get pushed around by waves, we can deploy a second anchor if required as we have the power to drag the chain.
Even with a dinghy loaded to the gunnels (around 12 adults) we can still power our way across a mooring.
We also have the speed to react to emergencies and to go fishing/scuba diving/exploring etc.
As we dont carry a seperate life raft our philosphy is to take to our dinghy if possible and use the 25hp engine as appropriate. A 5hp would not cut the mustard for us.
All four outboards are Yamaha 2-strokes, a Malta 3.5hp, 5hp and two Enduro's, a 15hp and a 25hp. The baby engines get used the most but the bigger engines are invaluable.
I might agree to a smaller engine if just in protected waters or in a marina. If I just had one engine it would have to be my Yamaha 25HP Enduro, its big and heavy but is such a great motor.






Quote:
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I do not understand the desire to get on plane. Unless you plan to anchor in areas of very fast currents a small (2-5 hp) outboard will get a 10' RIB where you need to go. It might take an extra 10 minutes but the easier lifting of the motor to the rail more than compensates.
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Old 25-11-2016, 12:52   #14
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Re: Outboard Size For Dingy

Go to Key West and try to get under that bridge from the mooring field to the town when the tide is running, and you will understand the need for speed

We often go on dinghy rides for miles, just to look around, would be less likely to do that in a displacement dinghy.
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Old 25-11-2016, 13:10   #15
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Re: Outboard Size For Dingy

A 6hp will usually plane a non rib with 2 people.... barely, but easily if an air floor dingy.
A 9ft RIB you will want 10 hp. 8 may get you there on a light one.
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