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Why no trim on inboards?


Jimmypooh

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I was reading the high speed topic for the new engine and got to thinking...Why don't any inboard manufacturers create a trim system for an inboard boat? As I see it, that would add a new dimension to these boats that some people might find appealing. I understand that this adds a level of difficulty to the engineering (universal, drive dog, hydrolic trim, and beefy strut support) , but my question is: Is it possible? And would the trim increase speed and/or hours per gallon ratio? I would think you would gain some promosing characteristics of an I/O drive with the ability to change the thrust angle parallel or better. Likely this would be used when not doing sports behind the boat since it would produce a propwash for the skiier, but that would be up to the driver. Has anyone ever heard of a mod like this being done. This is purely accademic, but interesting all the same.

Similar to this but mounted under the boat instead of behind the boat

Strudder%201.gif

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Trim definitely adds a level of complexity to the system. I'd settle for trim tabs. Any monkey could pull that off. And why Tige was ever allowed to patent it is beyond me.

I know a number of guys who added Bennets to old MC v-drives when they had the porpoising issues. Problem solved.... for like $300.

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The old Supra Comps had an adjustable Cavitation Plate. They had a nice slalom wake. The old American Skiers had a non-adjustable Cavitation Plate. New Nautiques have the Hydrogate.

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Trim definitely adds a level of complexity to the system. I'd settle for trim tabs. Any monkey could pull that off. And why Tige was ever allowed to patent it is beyond me.

I know a number of guys who added Bennets to old MC v-drives when they had the porpoising issues. Problem solved.... for like $300.

Trim tabs wouldn't help get the nose out of the water for increased speed and efficiency woudl it?

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Trim tabs wouldn't help get the nose out of the water for increased speed and efficiency woudl it?

Not as well as adjustable trim does. But it's simple & does force the bow down.

Yea, I knew that Supra had a fixed tab of some kind. Haven't played with it much myself.

Hydrogate is similar, bit it seems even less efficient than a tab. It's a totally vertical plate that bascially increases drag rather than pushing down on the wake table.

Polished%20Hydrogate400%20.JPG

Edited by Bill_AirJunky
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I've thought about this too quite a bit. Also thought, what if you would just ditch the shaft and rudder setup altogether and go to more of an azipod type setup. You could mount the engine lower in the hull, adjust trim, and have 360 degree control of the thing.

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I've thought about this too quite a bit. Also thought, what if you would just ditch the shaft and rudder setup altogether and go to more of an azipod type setup. You could mount the engine lower in the hull, adjust trim, and have 360 degree control of the thing.

That could be possible but seems like a whole other type of a beast.

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I've thought about this too quite a bit. Also thought, what if you would just ditch the shaft and rudder setup altogether and go to more of an azipod type setup. You could mount the engine lower in the hull, adjust trim, and have 360 degree control of the thing.

Yes, but docking the boat wouldn't be so exciting!

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martinarcher

One thing I like to live by when designing things is you can't make anything more reliable by adding parts. Any additional part adds a new failure point.

Imagine the hull damage if that U-joint separated in the top pic. That thing would do some damage in a hurry. At the very least it could rip the shaft support right off the bottom of the boat.

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Yes, but docking the boat wouldn't be so exciting!

Reversing to the right would be gone :(... but watching the ballet and near divorces at the boat launch would be some much less fun

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Martin,

That diagram is of a arneson type drive and in the go-fast world they are the strongest drive system.

I know adding parts adds potential but I honestly wouldn't be worried about it if the guys running 1k+ hp trust them.

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The problem in my mind is cost. The cost required to make something like this beneficial and relatively worry free would be prohibitive. Particularly on boats that start at $50k.

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I've wondered about trim tab's on the back that not only move up and down, but seperately, tied to the steering. Like a planes elevators on the tail.

Add to that, canards on the front, tied to the steering. You could even put a yoke at the steering wheel. Pull up and the nose comes up, push down, nose goes down, etc.

Steve B.

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i've often wondered what the result would be if you could change the angle of attack on the wedge.

i'm wondering if slalom wakes would improve if you could lift the stern.

I think thats one of the ideas pitched when you see/read about Centaurian's Switchblade.

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Trim tabs and adjustable trim on the prop would do the opposite things wouldn't they? Having trim tabs would lift the back of the boat up and force the bow down, whilst trimming up the prop would push the stern down and lift up the bow.

Ive always thought it would be cool to have a cutout in the hull above the prop and a system that could raise the prop up so it is almost tucked up inside the boat so you could manoeuvre slowly through shallow water and pull it up on the beach easier.... you would probably have to have retractable fins and rudder too.

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Trim tabs and adjustable trim on the prop would do the opposite things wouldn't they?

Only if you don't know how to use them.

Having trim tabs would lift the back of the boat up and force the bow down,

True

whilst trimming up the prop would push the stern down and lift up the bow.

Maybe if you just rolled off the trailer & forgot to adjust the trim. Adjustable trim is the ultimate in adjusting the attitude of the boat. You can make the bow rise or go down.

Edited by Bill_AirJunky
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One way that inboards have won people over is the added safety of the prop being underneath instead of hanging off the rear. That and then the added cost which is a big hurdle over less expensive i/o's and I think potentially you could end up w/ less sales.... Interesting concept though.

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One way that inboards have won people over is the added safety of the prop being underneath instead of hanging off the rear. That and then the added cost which is a big hurdle over less expensive i/o's and I think potentially you could end up w/ less sales.... Interesting concept though.

I was thinking the prop would still be under the boat. It might move back a little because you wouldn't need a rudder, but still not as far back as an I/O.

Anyone know the effeciency of an I/O vs a VD vs a DD?

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Sounds like a business oppotunity. Who's got an extra 10Mil to start up a company selling this drive system?

Sounds like a business joke I heard.

How do you make a small fortune? Start with a large fortune and buy a sports team.

If it's going to be under the boat, smart money (and lots of it) would be on azimuth pods. Boat prices would certainly jump substantially.

Trimable prop under a boat will not be as efficient as one behind the boat in changing the attitude of the hull. The back of the hull at the transom will still be behind the prop creating drag and working against the change in trim.

Now....where's that pic of the Enzo that someone rough fiberglassed a stern drive on.............. :whistle:

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as a prior I/O owner I think the main advantage to the ability trim the prop is that you can essentially lift the boat out of the water at high speed by changing the attack angle of the hull. However, you loose maneuverability in the process, less of the hull strakes are actually contacting the water. And a rudder system is actually more efficient for steering.

I prefer my inboard. I lost top end - and high speed cruising is far less efficient, but the ride is better, the maneuverability is incredible and I still draw less water in every possible condition. Plus not having an expensive to maintain outdrive is nice as well.

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  • 2 years later...

Now....where's that pic of the Enzo that someone rough fiberglassed a stern drive on.............. :whistle:

OH WOW WOW WOW!!! I hope this is a joke! If not, I need to see this train wreck...

Edited by formulaben
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I've wondered about trim tab's on the back that not only move up and down, but seperately, tied to the steering. Like a planes elevators on the tail.

Add to that, canards on the front, tied to the steering. You could even put a yoke at the steering wheel. Pull up and the nose comes up, push down, nose goes down, etc.

Steve B.

I hope you mean this as a JOKE, as how scary would it be to have YOKE action when going over waves and holding onto your steering wheel and bouncing up and down and pulling it in and out and making things worse!

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