Avon 280 RIB w/ 15HP Outboard

[janders]

Hey all, we're in the process of upgrading the dink's outboard. We targeted a 9.9hp 2-stroke but I've found a couple 15hp 2-strokes that look pretty attractive.

My dilema: the dinghy is an Avon 280 fiberglass RIB and rated at 10hp. What's the perils of putting a 15hp on this dinghy? I'm open to strengthening the transom with a bit of extra glass if need be.

That 15hp is looking pretty sexy.

Jason

[Dockhead]

I wouldn't do it if I were you. The boat is rated for 10hp for a reason -- weight of the motor, stability under power. I've found that the maximum rated hp for ribs is really very much the most power you can use.

We had a 15hp two stroke on a rib that size on the old boat. We figured that since it was a two stroke, and the rib was rated for a 10 hp four stroke, it could handle the weight. Well, it couldn't, and couldn't use the power, either. We sold the 15hp at a loss, changed to a 5hp, and were very happy.

On the new boat we have an Avon 340 rib with its maximum rated hp -- a 25 horsepower two-stroke. It's just the right amount of power -- you just about need full throttle to get it on a plane with the maximum rated load on board.

If I were you, I would stick to the rating.

[capngeo]

I'm one of those guys who ALWAYS overpower my dinks. A lot of times (especially with the 2 strokes) the next size HP rating was exactly the same weight and dimension, as the HP increase was carbs, intakes etc.

The naysayers will point out the dangers of overpowering, which if it were going to be used by a 15 year old, I'd agree. As adults we can hopefully restrain ourselves from unnecessary WOT. Having the extra HP for emergencies or extra heavy loads is damned handy. Not saying drop a 50 on the back of your dink BUT a 15 if comparable in weight, shouldn't be a huge problem.

Throw the above out the window on roll-up boats BTW... RIBs are much stronger!

[janders]

Based on the engine weight alone, I think a 15hp two stroke would be fine. From what I can tell, the 15hp two stroke weighs in at around 80lbs. Whereas a 9.9hp four stroke weighs in at over 110lbs.

[edited to add:] A Mercury 9.9hp seems to be the same engine as a 15hp plus some sort of fuel governing. It weighs the same as the 15hp.

I guess the concern then would be how much thrust the engine is putting out and whether the transom is strong enough to handle it. I don't have a sense of whether or not that extra 5hp is a problem on a fiberglass RIB that's in good shape. I wouldn't consider this with a roll-up or inflatable floor.

[Vasco]

Go for it. One trip to the Bahamas will open your eyes as far as hp and size of small boats. The Bahamians love to get their boats completely out of the water, just skimming along on the ob skeg.

[Laidback]

Originally Posted by Vasco

Go for it. One trip to the Bahamas will open your eyes as far as hp and size of small boats. The Bahamians love to get their boats completely out of the water, just skimming along on the ob skeg.

The USCG may say that AVON only rate the 280 for max HP of 10.

Length Beam Weight Capacity Max Engine Max
Overall Overall Boat Persons Payload Remote Tiller Performance
ft/in m ft/in m lbs kg lbs kg hp kW hp kW mph kph
R 280 Rib 9’2” 2.80 5’3” 1.60 135 61 3
+ child 1014 460 10 7.5 10 7.5 19 30

[shamrock]

I have a Honda 9.9. It is the same motor as the 15 horse except it comes with a screw preventing the throttle from opening up. if you take the screw out, it gets you to about 13.5 HP, there is a slight difference in the carburetor jets which will give you the extra 1.5

Have it on a 290 RIB rated for a 10 and it is a lot of power, but With the boat loaded, it does not hurt.

The reason they manufacture 9.9s is because there are certain lakes that limit HP to under 10. maybe put the screw back in when your kids use it!

anyway, have you guys found any good mounting solutions? The out of the box stern rail mounts are all limited to 100 lbs. My Honda Is 108 without fluids. Also, any boat I've seen that mounts outboards on the stern rail gets a ton of stress cracks on the deck under the stanchions.

Has anyone had success storing a 110lb+ outboard?

Thanks!

[MarcHall]

Originally Posted by janders

Hey all, we're in the process of upgrading the dink's outboard. We targeted a 9.9hp 2-stroke but I've found a couple 15hp 2-strokes that look pretty attractive.

My dilema: the dinghy is an Avon 280 fiberglass RIB and rated at 10hp. What's the perils of putting a 15hp on this dinghy? I'm open to strengthening the transom with a bit of extra glass if need be.

That 15hp is looking pretty sexy.

Jason

A few years back I had the AVON 280 RIB with a Mercury 15 HP. The motor replaced a dead 9.9 HP. I went with the 15 HP as I was trying to get the boat
up on plane with 2 divers and gear. No luck. Needed a longer boat with weight the extra HP alone would not do it. Eventually went with a roll-up Avon 3.40 with the same motor and was able to easily get it up on plane with 2 divers.

Without substantial weight in the boat you need to careful about how quickly you throttle up as it can get a bit squirly.

Marc Hall
"Crazy Fish" , Crealock 37 based in San Diego

[Bash]

Originally Posted by janders

That 15hp is looking pretty sexy.

Sexy?

I once saw a guy flip an overpowered dink where the bow went aft and the stern went forward.

It was ugly.