What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

[Garrett Lipus]

I have an inflatable that is 10'6" and it's labeled that it's rated to support up to a 15hp outboard. I have a 20hp Honda 4 stroke that only weights about 110 lbs. Is that a bad idea to try this out on my boat? Does anyone use a motor that is over the rating on their inflatable? How did it work out?

The obvious answer is no, but does anyone have any success or fail stories from using a larger motor than recommended by the manufacturer?

I called the manufacturer, Newport Vessels and they said that basically I shouldn't use anything larger than what the boats is rated for, but based on their tone, it sounded like they had to say no, because of liability, not because the boat actually couldn't handle it. I'm interested to hear from people.

 

[Trotter]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

I can't imagine you'd be able to open full throttle being over the rating. On my 10'8" inflatable rated for 15hp I do have 15hp. Once I have it open all the way I can get to about 35-38mph, but the nose starts to fish tail a little forcing me to slow it down.

 

[Sea Rider]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

You'll need to have that sib properly inflated to 3.5 psi when on water, balance/distribute sib weight correctly towards front, check tech specs if transom can hold the weight of that heavier 4 strokes engine, you could limit the throttle acelleration as not to go into full throtthle (wot range) check internal adjusting screw if available. You can always place a sumo fighter as bow mask to eliminate bow rise . If you have legal issues in your area for using larger engines, that's another story.

Impossible to achieve 35-38 MPH with a 15 HP, probably max 20 MPH.

Happy Boating

 

[Badburn]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

I have a 20 hp merc on my 10'6 zodiac. Its a hardbottom (fiberglass bottom), and it works great. Plenty of power, and real fast if you're brave enouth to hold it wide open. I run mine pretty hard, usually 3-7 people plus gear on board, even towed broken down boats with it. Just use your head when operating. I have sat on top of the outboard while idling (don't try this at home kids) when the boat was packed with ice chests and gear, so I dont think a little extra weight on the transom is an issue. (I'm 210 lbs)

 

[Sea Rider]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

I have a 20 hp merc on my 10'6 zodiac. Its a hardbottom (fiberglass bottom), and it works great. Plenty of power, and real fast if you're brave enouth to hold it wide open.

A rib performs much better than a sib with a bigger engine, are two completely different beasts behaviours.

Happy Boating

 

[Howard Sterndrive]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

I run a 25HP on an 11'2" sib.
my motor only weighs 77 lbs.though. Not sure I'd want another 30 lbs. back there. The transom gets some pretty crazy gyrations going over a chop at full speed.

 

[ill13]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

I have an older Achilles spd-4ad [10'4"], I run a 1977 Evinrude 18hp and a 1954 Johnson 10hp. It's entirely too much fun with one person and the 18hp. I have to sit low in the bow with a tiller extender if i want to run WOT to keep the bow down. I've been tossed once -and I was very glad to have retrofitted/installed a kill switch and lanyard [on both engines]. With just me+18hp, I'd say I get just under 30mph, I can say that the 18hp is scary fast, even with 2 people

The 10hp will get me around with 2 people on a plane, not exciting, but it gets around. I'd say around 15-18mph at WOT with a maybe 10-11 mile range

The 18hp, I'd guesstimate I get about 1-1.5 hours out of the 3 gallon tank, maybe about 7-9 mile range

There are some issues with the 18 that need to be rectified, for one, it seems to vibrate the drain screw out of the float bowl. This spring I have some medium maintenance to do...

 

[TOHATSU GURU]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

It's not unusual to see 25's all the way up to 50's on some. There may be race class up to 90 hp by now. Crazy, yes. But, the South Africans and the Austrailians have more guts than the rest of us...Or maybe they are just nuts

 

[Sea Rider]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

Have seen 320/330 inflatables with 25 HP engines just for cruising around at slow speed, if you are not experienced or a heavy weight user definitely will be out of this world to go into full throttle with engines that exceed max HP rated at transom, do sane, not insane boating. Those Australians and South African nuts use catamarans hull type boats, not plain standard sibs..

Happy Boating

 

[jurassiccoast]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

Hi
The Honda 20 is one of the heaviest in its class, but its the same weight as the Honda 15, so weight shouldn't be the issue. If you don't use full throttle, it would be okay, but the transom is only rated to handle the torque of a 15hp motor, and therefore is only warranted for a 15hp motor.
The maximum design speed of a SIB can also influence motor choice: Some SIB's have a higher drag factor so top end for the 15hp and 20hp might be the same anyway.
Jurassiccoast.

 

[Sea Rider]

Re: What's the Biggest Outboard Anyone's put on a 10ft Inflatable?

Drag should not be an issue if standard sib has tubes and keel well inflated to their recommended factory working pressure, therefor, 5 Hp difference is noticeable when testing both engines at full throttle.

Happy Boating