Lower HP for outboard vs inboard.

[agallant80]

What gives with HP ratings on inboard and outboard boats? I am seeing that some boat makers are offering the same boat with an inboard or outboard option but the HP difference is huge. You can get a 330HP I/O but only a 250HP Outboard. Are outboards more effecent?

 

[QC]

Re: Lower HP for outboard vs inboard.

Are outboards more effecent?

No. They are lighter by 500 lbs in the example you gave +OB

Also, the I/O bolts to the Stringers, and the outdrive to the transom. In the case of the OB, all of the power is bolted to the transom +I/O

OB get's more trim leverage as it is further aft, so trim "leverage" is increased allowing for higher trim angles and less boat in the wawa +OB

Edit: Define "efficient". If the definition is lbs of fuel per hp hour, which is the standard definition of an engine's efficiency, then OBs lag a little as they give up some features by being crammed into a tiny place. If "efficient" means how fast an engine can push a given load, the weight savings gives the OB an advantage as some of the "load" is reduced. So this means that the application of the OB can indeed be more efficient. In practical use, modern OBs and I/Os are about a push in the same application i.e. 2 - 22 footers that haul people around to play.

Edit 2: There are exceptions to pretty much all I posted. This can be an engine discussion, a hull discussion, a trim discussion, etc. etc. etc. Even though it is touching on an engine discussion I think this is more of a general boat application discussion and belongs in this section. We'll see where it goes....

 

[blackhawk180]

Re: Lower HP for outboard vs inboard.

op2:

 

[agallant80]

Re: Lower HP for outboard vs inboard.

Just wondering guys. For example the smallest motor you can get in the boat for I/O is 260HP but the smallest ourboard you can get for the same boat is 200. Is it just plain old under powered with the 200HP OB or is the way the OB delivers power better.

 

[QC]

Re: Lower HP for outboard vs inboard.

Just wondering guys. For example the smallest motor you can get in the boat for I/O is 260HP but the smallest ourboard you can get for the same boat is 200. Is it just plain old under powered with the 200HP OB or is the way the OB delivers power better.

No, it's the weight. Put two extra 250 pound guys in your boat and you will understand what I am talking about

 

[nickcunn]

Re: Lower HP for outboard vs inboard.

 

[H20Rat]

Re: Lower HP for outboard vs inboard.

Edit: Define "efficient". If the definition is lbs of fuel per hp hour, which is the standard definition of an engine's efficiency, then OBs lag a little as they give up some features by being crammed into a tiny place.

I'd say that has actually flipped around now. I/O's need every component to be marine rated. You can't just safely stuff a chevy 350 in the engine compartment and hope it works. Hence, fuel injection only took off when the EPA forced it, and there is no direct injection marine I/O on the market that I know of. Fuel injection has been out for a long time on outboards, and DI has existed for quite a while also. DI 2 stroke outboards can be more efficient and pollute less than a 4 stroke.

 

[QC]

Re: Lower HP for outboard vs inboard.

I would argue that space limitations still requires higher RPM which does cost fuel. I do understand your point though. If you were completely accurate, all OB applications would be better on fuel, and they just aren't.

EPA didn't force EFI on anybody. Technology limitations did, and there have been EFI systems on I/Os since early 90s, so not sure that point is fair. With that said, I was kinda thinking of DI two strokes. They still suffer some on fuel compared to I/O and 4 stroke EFI, but they make it up with weight savings. That's fairly well understood I think.

 

[wrench 3]

Re: Lower HP for outboard vs inboard.

Back to horse power ratings. I'm inclined to think that the output ratings are accurate for both types of engine configurations. But that the different weight distribution allows the boat to safely handle the higher horse power.

 

[QC]

Re: Lower HP for outboard vs inboard.

The ratings are the same. NMMA guidelines, and at the propshaft.

 

[pckeen]

Re: Lower HP for outboard vs inboard.

I think I'll just sit back and enjoy this one.

:fencing:

 

[Watermann]

Re: Lower HP for outboard vs inboard.

To compare say a 200 HP 4 stroke OB and a 220 HP Mercruiser IO (4.3L). I was wondering the some of the same things and have looked around checking the weights. The weight difference isn't 500 Lbs, the average 200HP 4 stroke OB is around 600 Lbs and the 220 HP IO Merc is 850 Lbs with outdrive assembly. I don't really know exactly why the OB if offered in a lower HP over the same boat with an IO other than lower weight and it's distribution. As you go up in HP to V8's both the motors start getting weightier as do the craft they're offered in.

 

[thumpar]

Re: Lower HP for outboard vs inboard.

Most of the pros/cons have been stated. One for me on the I/O is the work on them. I grew up on cars and trucks and know how to work on them. Other than a few things to remember it crosses over. You can't beat the sound of a nice V8 either.

 

[agallant80]

Re: Lower HP for outboard vs inboard.

Im not looking for pros vs cons of the I/O vs outboard debate. I was just wondering why the same boat offered with your choice of I/O or outboard seams to come with lower HP outboards. The question is, in this situation would the lower HP outboard yeald the same performance (water sports, top end, etc) as a higher HP I/O.

I guess we will never know the answer to this question.....

 

[QC]

Re: Lower HP for outboard vs inboard.

I have answered it multiple times. 500 lbs! Go to Boat test dot com and compare similar boats with I/O and OB and you will have your answer. It is the weight savings, the weight balance and trim leverage that makes those two examples you gave perform similarly.

Although horsepower is EVERYTHING despite what many claim, it is horsepower against weight, hull design and wetted surface that results in speed. The OB reduces weight and wetted surface so it takes less horsepower to go the same speed if all else is equal.

 

[Watermann]

Re: Lower HP for outboard vs inboard.

I guess we will never know the answer to this question.....

Yes!

 

[chambers1517]

Re: Lower HP for outboard vs inboard.

Actually it is torque then Horsepower. A 200 hp outboard powered boat will smoke a 220 hp powered i/0, until you add 8 people then the I/0 pulls ahead. The I/0 has more torque. Race a Ferrari against a diesel truck, no contest then strap 20000lbs behind both and see what happens.

 

[QC]

Re: Lower HP for outboard vs inboard.

You can't separate torque and horsepower in the way you have. It is simply math, math that matters a lot, but you can't do much of anything with just torque, you must have RPM. When you add RPM, you have horsepower. Semantics stuff, but still valid.

 

[bruceb58]

Re: Lower HP for outboard vs inboard.

What gives with HP ratings on inboard and outboard boats? I am seeing that some boat makers are offering the same boat with an inboard or outboard option but the HP difference is huge. You can get a 330HP I/O but only a 250HP Outboard. Are outboards more effecent?

Now that you are switching trucks again, does that mean you are switching boats now too?

 

[chambers1517]

Re: Lower HP for outboard vs inboard.

While this is true both engines have similar HP but the IO is more powerful because of mor torque. Th OB has a weight advantage but strap both boats together and the IO will pull the OB all over the place. Less torque equals less twist to spin the engine to create HP.