Inboards vs. standard outdrives for wake shaping

[c9403]

So, I have been around boats most of my life, but I am no scientist. I sold my deckboat after realizing that all my friends had inboards (Centurion's and Supras) and that the wake was better.

While at the Kansas City Boat show this weekend, my small group of inboard / wakeboarding crew was discussing the fact that all the I/O boat manufacturers are putting towers on their boats now. The question that came up centered around why does it have to be an inboard to make a better wake? Or in other words, since all the boat builders tout hull design for wake shape and wake height, why does the inboard make such a difference.

My basic thought was that since the inboard keeps the prop in front of the trailing edge of the boat, the last thing to "touch" the wake or the water column is the well designed hull, rather than the spinning prop of a traditional outdrive an an I/O. With a traditional inboard (non-V drive) you have more weight in the center of the boat. But, with a v-drive, the weight is still in the rear and when you add ballast, the first place you add is in the rear.

So, what scientific point am I missing about why the inboard thing makes a difference? I love my inboard, but I do miss going backwards in a straight line! LOL

Chris

[chrisk]

Chris, I'm also Chris, and I'm also in Missouri!

You're right when you mentioned the prop spin thing, the wake coming off the back of an inboard will be much smoother and well-shaped than that of a stern drive that is getting blasted backwards behind it. Additionally, inboards give a more stable base to work from for wake shaping when you start adding weight.

Also, possibly the most important factor is the safety concern. It's downright hard to come in contact with the prop of an inboard when getting in and out of the boat as much as a crew does when wakeboarding for a day - it's relatively easy to kick the prop or jump on it when using a stern drive.

[sybrmike]

It's also about the handling - originally through the slalom course. Tournament inboards originally all had turning skegs as a pivot point for the rudder to act against - much easier to hold a straight line than the vectored thrust of a stern drive simply pushing against a bare hull.

[KG's Supra24]

Also water displacement due to weight and hull shape. Inboards typically have deeper v's in the front and deeper draft in the rear, especially when weighted.

I'm not certain, but I bet a cobalt has a better wake than a Tahoe our crownline, attributed to weight and deep v.

Sent from my DROID RAZR using Tapatalk

[csuggs]

It's also about the handling - originally through the slalom course. Tournament inboards originally all had turning skegs as a pivot point for the rudder to act against - much easier to hold a straight line than the vectored thrust of a stern drive simply pushing against a bare hull.

Exactly! Also, keep in mind that when inboards became popular for skiing, they were categorized as a utility boat instead of a pleasure boat. That meant that it was designed with a single purpose in mind - that of running through the slalom course at 36mph with almost no wake. Even though the use has changed where most of us run at around 20-22mph, we need the hp and torque to maintain those speeds at relatively low rpm all while pulling a load that is inconsistent. So I think torque plays a major role in the performance and with a direct drive setup you don't lose as much through the transfer of power to the prop. I'm not actually an engineer, I just have an opinion!

[jet]

Also runabout hulls are made to skip across the water not manage the water like a wakeboard boat does. Also the biggest negative about them is the nose-up for the 1st 100 yrds. There nice but NOT what your looking for. Dont do it man..just walk away. Jet

[cadunkle]

Good point KG about hull shape. A lot has to do with hull shape. I've been behind I/Os with deeper V that just make really washy wakes, particularly on one side. My last I/O had a shallowed V, less deadrise. It has a small wake, but nicely shaped and fairly clean. A deep V I/O will make a bigger wake, but depending on the shape it may be very washy. As Chris mentioned this has a lot to do with the outdrive and prop having more influence on the wake as it's the last thing to touch the water as the boat passes. There is no hull after it to smooth out prop wash.

Of course other factors are greater acceleration and less bowrise. Sure you can have an I/O that accelerates as well as an inboard but you're making up for it with more power/bigger engine and lower gearing in the drive/prop... Then you still may have a washy wake, you'll still have more sensitivity to ballast adversely affecting acceleration, bowrise, and dialing it in. They're just different boats each suited best to different things.