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Old 20-04-2016, 21:25   #1
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What Actually Happens If You Oversize The Dinghy Outboard?

...may be a stupid question, but bear with me.

I'm thinking about a Walker Bay 8' rigid dinghy. It calls for a 2HP. I'd prefer a 4HP, because that could double nicely as an auxiliary engine for the mothership, to get in and out of tight harbors. The weight difference between the two is negligible (some of the 4HP are actually lighter than some of the 2HP). So that can't be the problem. What happens if the dinghy is overpowered? Do I just waste gas (no biggee), or something more serious?

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Old 20-04-2016, 21:40   #2
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

The walkerbay wont go any faster just bog down in the back more. It won't plane.

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Old 20-04-2016, 21:55   #3
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

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The walkerbay wont go any faster just bog down in the back more. It won't plane.

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It won't plane regardless, AFAIK, which is fine.

What do you mean by "bog down" exactly?

Speed is not important, just don't want to be taking on water, capsizing, etc.

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Old 20-04-2016, 21:57   #4
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

The back will just sink further into the water from the extra torque of the engine with no extra speed.

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Old 20-04-2016, 22:05   #5
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

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The back will just sink further into the water from the extra torque of the engine with no extra speed.

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Alright, well that might be a problem...

But if you keep the throttle down, that would prevent this from happening?
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Old 20-04-2016, 22:15   #6
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

This seems to work for some folk. Might want slightly larger fenders mounted aft for additional buoyancy.
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Old 20-04-2016, 22:35   #7
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

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This seems to work for some folk. Might want slightly larger fenders mounted aft for additional buoyancy.


Good idea, thanks.
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Old 20-04-2016, 22:44   #8
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

Probably not an issue with just 4HP, but the transom is engineered for the rated HP. So, too much over rated HP and you can damage the transom.
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Old 20-04-2016, 22:55   #9
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

In the U.S. Coasties, Park Rangers and others can give you a ticket for exceeding the capacity plate.

From:
Boat Weight Regulations - BoatUS Magazine

Federal requirements mandate that outboard-powered boats 20 feet and under must be built with enough flotation to keep the passenger-carrying area at or just below the water's surface, in the event of swamping or capsizing.
~~
If an overloaded boat swamps or capsizes, its built-in flotation may not be sufficient to keep the hull from sinking.

Horsepower capacity deals with two concerns that must be addressed when attempting to match an outboard engine to a boat: horsepower and weight. Too much power can make a boat difficult to control and too much weight, whether "live load" or gear, can lead to stability problems.
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Old 20-04-2016, 23:08   #10
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

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Originally Posted by belizesailor View Post
Probably not an issue with just 4HP, but the transom is engineered for the rated HP. So, too much over rated HP and you can damage the transom.
Ahhh...I hadn't thought of that.

It's a solid plastic dink, so I might be able to rig up some kind of support plate to spread the load. But as you say, maybe it doesn't matter for just a 2HP difference.

Quote:
Originally Posted by cal40john View Post
In the U.S. Coasties, Park Rangers and others can give you a ticket for exceeding the capacity plate.

From:
Boat Weight Regulations - BoatUS Magazine

Federal requirements mandate that outboard-powered boats 20 feet and under must be built with enough flotation to keep the passenger-carrying area at or just below the water's surface, in the event of swamping or capsizing.
~~
If an overloaded boat swamps or capsizes, its built-in flotation may not be sufficient to keep the hull from sinking.

Horsepower capacity deals with two concerns that must be addressed when attempting to match an outboard engine to a boat: horsepower and weight. Too much power can make a boat difficult to control and too much weight, whether "live load" or gear, can lead to stability problems.
Weight won't be an issue.

Control, maybe, I have no idea.

Has anyone actually done this?

...only way to know for sure, I suppose.

As for the USCG regs, I should be well out of their jurisdiction.

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Old 20-04-2016, 23:25   #11
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

It is pretty simple: if full throttle gives you issues of control or flex in the transom (which I really doubt), back off on the throttle. Ain't no rule sayin' you must run full throttle ever.

I would not worry about the 4 hp at all; YMMV

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Old 20-04-2016, 23:39   #12
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

Quote:
Originally Posted by KISS View Post
Ahhh...I hadn't thought of that.

It's a solid plastic dink, so I might be able to rig up some kind of support plate to spread the load. But as you say, maybe it doesn't matter for just a 2HP difference.



Weight won't be an issue.

Control, maybe, I have no idea.

Has anyone actually done this?

...only way to know for sure, I suppose.

As for the USCG regs, I should be well out of their jurisdiction.

Just 2 more HP shouldn't create any of these issues.

Ive run significantly over HP'ed dinks and the handling issues can be rather disconcerting.
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Old 20-04-2016, 23:45   #13
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

There won't be any practical problems, but if you get involved in any kind of incident there could be legal or insurance problems.
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Old 20-04-2016, 23:48   #14
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

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There won't be any practical problems, but if you get involved in any kind of incident there could be legal or insurance problems.
Well, could just design a quick release to drop the outboard into the ocean.

"Sir, you were motoring overpowered."

"What motor?"

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Old 21-04-2016, 00:29   #15
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Re: What Actually Happens If You Oversize The Dinghy Outboard?

Quote:
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Well, could just design a quick release to drop the outboard into the ocean.

"Sir, you were motoring overpowered."

"What motor?"

And go to jail for littering and pollution!



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