Ride quality

[tonyjh63]

I've been curious about something. Given the same basic hull design (best if it's the same model, like Glastron does with their runabouts), would the ride in an OB boat be worse than with an IB/OB, seeing as how it would weigh quite a bit less? I just instinctively think that a lighter boat would have a harsher ride than a heavier one.
Has anyone driven the same model boat with the two different configurations?

 

[Bondo]

Ayuh,.... Ride quality is about the boat's bottom, not how it's powered,....

A 10*bottom boat will beat ya to death,.....
A 24* bottom boat will ride like a dream in heavy seas,....

 

[roffey]

kind of true in life as well, its all about the bottom...

 

[ahicks]

Well, I've been in outboard and IO powered 18-20' Starcraft boats, though it's been quite a while. Memory has it the IO is smoother for sure, but I don't know if I would go any faster with with one than I would the other in an 18" chop for instance.

 

[dingbat]

The weight of the propulsion has an effect on overall ride quality, but its effect on how a boat behaves under certain condition is much more pronounced.

For rough water performance, it's either a displacement hull with a inboard (low center of gravity) or outboards for the geometry (weight parallel to the transom, not cantilevered off the back) and weight to HP ratio.

My hull performs much differently (better) with outboards than an I/O. To the point that the OEM stopped offering my boat in an I/O powered version long, long ago. Far too much weight in the stern for a boat designed to run with the front 1/2 of the boat out of the water when on plane.

 

[briangcc]

You got me thinking....


150HP 4 Stroke Merc tips the scales at 455lbs

https://www.mercurymarine.com/en/us/engines/outboard/fourstroke/75-150hp/



4.5L v6 sterndrive (which is pretty common these days) tips the scales at 761lbs

https://www.mercurymarine.com/en/us/engines/inboard-and-sterndrive/mercruiser/45l/#specifications


Difference is roughly 200lbs heavier for the sterndrive. That ain't that big of a deal, roughly 1 more person on board for a stern drive boat vs. outboard.

**Sure...I didn't consider the outdrive on the sterndrive but we're not talking about a ton of weight difference.


So all things being equal, I would expect equal ride performance between same sized boats with the varying drives.

 

[QBhoy]

I think just about any glastron will have a pretty poor ride in anything more than a flat calm. They in particular are well known for being pretty poor. They are what they are though.
Most North American boats are the same really. If we are considering the usually budget brands. The budget bit...almost makes up for it though.

 

[JimS123]

While I never personally compared the 2 in EXACTLY the same hull, I have read many, many articles over the years on that subject. Trailer Boats magazine often did "shootouts" comparing different powerplants on equal boats provided by the manufacturers..

That said, my gut feeling is that if the hull were truly the same, any difference would be because of a weight difference....with the heavier boat riding better. However, as just pointed out if you added one more fat person on the OB version, the 2 would then be the same weight. Regardless, I doubt that 300# more or less would be significant.

The 150 OB vs. 4.5 I/O weight comparison above was interesting. Our most recent boat purchase came with either of those 2 powerplants. In the case of SeaRay, the dry weight of the OB version was actually 75# HEAVIER than the I/O. The hulls that are in the water are the same. I would guess that since the OB is cantilevered out to the end of the swim platform, the added stringers more than make up for the lighter weight engine.

 

[dingbat]

You got me thinking....


150HP 4 Stroke Merc tips the scales at 455lbs

4.5L v6 sterndrive (which is pretty common these days) tips the scales at 761lbs


Difference is roughly 200lbs heavier for the sterndrive. That ain't that big of a deal, roughly 1 more person on board for a stern drive boat vs. outboard.

**Sure...I didn't consider the outdrive on the sterndrive but we're not talking about a ton of weight difference.

. Ugh, that's engine weight only. The Alpha drive weighs another #80 making a total "static" weight of #841.

The #80 outdrive cantilevered 3 ft. off the transom in effective becomes #240 hanging off the back of the boat. Looking at an effective/ dynamic weigh of almost a #1,000

To put it in perspective, the Yamaha F350 (V8) weighs #763. The F250 (V6) weighs #551. Either engine would run circles around a 250HP stern drive

 

[JimS123]

. Ugh, that's engine weight only. The Alpha drive weighs another #80 making a total "static" weight of #841.

The #80 outdrive cantilevered 3 ft. off the transom in effective becomes #240 hanging off the back of the boat. Looking at an effective/ dynamic weigh of almost a #1,000

To put it in perspective, the Yamaha F350 (V8) weighs #763. The F250 (V6) weighs #551. Either engine would run circles around a 250HP stern drive

The I/O is not "cantilevered", it's mounted directly on the transom. Sure, any OB of equal HP would blow the doors off of an I/O, but that's not the issue. The OP wants to compare ride quality.

 

[mr 88]

If the outdrive weighing 80 lbs is " cantilevered " 3 feet off the transom and with your multiplication factor of X3 = 240 lbs ... Then the outboard , @ 455 lbs , which also " hangs " off the transom would be = to 1365 lbs of static weight , Clearly out weighing the I/O setup in dynamic weight by 355 lbs.. At least that's what I come up with and not being a marine engineer to verify anything one way or another being posted.

 

[JimS123]

Boy the math is too difficult to figure out. I went to engineer School almost 50 years ago and I forgot everything I ever knew......LOL.

All moot points. The question is re. "ride'. If you put 2 fat ladies on the swim platform and have them cantilever, does the ride change? Is the extra weight "significant"? Would you buy one or the other powerplants because of it?

I dunno. Als I know it that after switching from having an I/O for 35 years, to a new OB I'll never go back.

 

[mr 88]

Boy the math is too difficult to figure out. I went to engineer School almost 50 years ago and I forgot everything I ever knew......LOL.

All moot points. The question is re. "ride'. If you put 2 fat ladies on the swim platform and have them cantilever, does the ride change? Is the extra weight "significant"? Would you buy one or the other powerplants because of it?

I dunno. Als I know it that after switching from having an I/O for 35 years, to a new OB I'll never go back.

You can have the " two fat ladies " , I will go with 4 hot chicks in appropriate swim wear for said experiment ! hehehe

 

[cptbill]

Really it's all about how the weight is distributed, IO is farther forward, an IO boat(or at least most) of the same kind will sit in the water differently for example at the local marina there is a wellcraft 270 coastal with an IO and I have docked next to them with my 270 coastal with twin Yamaha 250s, the 2 boats sit very differently in the water

 

[roffey]

You can have the " two fat ladies " , I will go with 4 hot chicks in appropriate swim wear for said experiment ! hehehe

i'm repeating my self here but ... its all about the bottom...

 

[froggy1150]

Yup.... all four!

 

[dingbat]

The I/O is not "cantilevered", it's mounted directly on the transom.

Cantilever....a long projecting beam or girder fixed at only one end.

Sure looks like it fits the definition to me

 

[JimS123]

Cantilever....a long projecting beam or girder fixed at only one end.

Sure looks like it fits the definition to me

I guess we just like to argue, even when we aren't answering the OP's question.

Yes, a cantilever is a bean or girder (or "structure") fixed at one end. When I originally used the term I was trying to explain that my OB is not mounted on the transom, but is mounted on a "structure" that extends beyond the transom. The reason for my comment was to explain why the OB version was heavier than its I/O counterpart, because all that extra structure and the needed stringers to support it more than offset the weight of the I/O block and outdrive.

If you follow the logic of some of the previous posts, then you could say ANY outboard is cantilevered as well, so what's the difference?

(Boy, the outdrive in that last pic looks like its seen better days. Surely needs a new prop and maybe some zincs as well.)

 

[Texasmark]

I think just about any glastron will have a pretty poor ride in anything more than a flat calm. They in particular are well known for being pretty poor. They are what they are though.
Most North American boats are the same really. If we are considering the usually budget brands. The budget bit...almost makes up for it though.

"Most North American boats are the same really." Have you had too much of the juice......again?

What's your experience with Glastron? Apparently not much!

 

[Texasmark]

Having had both, I vote for the OB for several reasons and salt water (especially) corrosion and accessibility are a couple. Safety another with gasoline engines. As far as weight distribution and effect on the ride, PTT pretty much mitigates most of that and if not enough trim tabs could seal the deal.

Something else that may be different in your same boat different powering types is the stern seats that usually accompany I/O's. Put a couple of fat bottoms in those and compare that to an OB and the (lack of usually) availability of those seats and location and surely the OB wins that one too.

Last I/O I had the engine, making up the majority of the weight, was mounted to the hull stringers, not hanging off he back of the transom.