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Strange idea.

Old 01-30-2005, 10:56 AM
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stevblutu15
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Default Strange idea.

A company by the name of Volvo Penta makes gas and deisel engines for real boats. They recently came out with a design that instead of a pusher outdrive, it pulls the boat through the water. They say that it increases acceleration, speed, economy, and produces a smoother ride. Here's what i was thinking. Take a boat hull, and mount the engine as far back as possible, with the output end facing foward. Then have a strut coming out from though the hull, and get a prop that will pull the boat through the water. On a perfectly calm day, with the prop in the right position, it would act like a pulling surface drive, possibly creating signifigant speeds. Add a large pair of trim tabs on the back to get the bow down, with all the weight from the engine, and it could possibly be a good design. Im sure there are many things that wouldnt work, but has anyone ever thought of this or tried it. Im thinking of trying it, but would like you to try and talk me outta it if it is indeed a bad design. What do you think?


Here's a pic of the drive
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Old 01-30-2005, 01:54 PM
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Ron Olson
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Default RE: Strange idea.

Weird! One obvious downside as a former full-sized boat owner. The fin on the boat serves a dual purpose, one is for steering, the other helps to keep high Dollar props from damage. This design puts the props in harms way for debris and and the bottom of a lake that comes up on you too quickly.
In R/C form, it could be worth a shot. I wouldn't talk anyone out of thinking outside of the box although I don't see any advantage here.
Old 01-30-2005, 03:10 PM
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stevblutu15
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Default RE: Strange idea.

It actually replaces regualr old shafts in real boats instead of outdrives sry. However Volvo claims, a 35% fuel economy gain, 20% top speed gain, less vibrations, so idk. It def looks cool ill tell you that.
Old 01-31-2005, 09:55 AM
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Default RE: Strange idea.

I'd like to see it mounted into a boat. I'm assuming that it goes through the bottom and not out the transom like stern drives. The boat would need trailers specially made to haul this. they would have to be built higher than normal for clearance. If there is any power tilt you can't raise the drive up high enough in shallow water.
As for an R/C version things could be done differently and some of the problems with their design could be changed. I wouldn't do the counter-rotating props, that has been tried once for R/C and there was a big problem with breakage.
Old 01-31-2005, 12:02 PM
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Default RE: Strange idea.

There were actually outboard motors like this back in the 1930s and 1040s. This type of drive is called a "tractor" drive because of the way it pulls instead of pushes. They were discontinued for safety not performance. Prop damage would be another serious consideration.
Old 01-31-2005, 04:43 PM
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Default RE: Strange idea.

but in rc boats. who's worried about prop damage that much? also in a real boat with shafts, unless you have tunnel drives you dont have much protection eiter, except the strut.
Old 01-31-2005, 11:53 PM
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Default RE: Strange idea.

After my last posting, I had to go into the Volvo-Penta website to see more about it. I didn't see a lot of spec's on it.
For R/C use, try it and let us know what happens. How to do it, I don't have a clue. Maybe start with a K&B OB lower unit and modify that from there.
Old 02-01-2005, 03:26 PM
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Default RE: Strange idea.

im thinkin a standard inboard, with a forawrd facing stuffing tube, like take everything in the baot and turn it around.
Old 02-01-2005, 03:42 PM
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Default RE: Strange idea.

two more quetions, where can i find a cheap small .15-.30 inboard marine engine, and does any body know of sites that sell abc hobby parts. They have a drive i think will work, from the old nitro Freedom RZ. Ive checked Horizon Hobby, and Ehobbies.

anyone have a K&B outboard or OS.21 outboard, theyre willing to sell cheap for the cause?
Old 02-01-2005, 11:34 PM
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Default RE: Strange idea.

iIve been using .12 car and truck motors in my little boats with no trouble. The mid-priced ones do a good job. From the spec's that I've seen, the OS .18 has a lot going for it in that range.
As far as the ABC Hobbies outboard has a lot of wasted usage of power using 2 belts and a jackshaft setup. The lower belt has to make a lot of turbulence ahead of the prop. I was thinking of a modified K&B lower unit rebuilt to simulate the Volvo Penta drive.
Old 02-02-2005, 10:01 AM
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Default RE: Strange idea.

i was thinking, take a K&B drive, and make custom mounts, and just turn it around, or mont it right through the bottom of the boat, with a water proof seal, and use a rudder.
Old 02-02-2005, 10:02 AM
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Default RE: Strange idea.

i was thinking, take a K&B drive, and make custom mounts, and just turn it around, or mont it right through the bottom of the boat, with a water proof seal, and use a rudder.
Old 02-02-2005, 04:24 PM
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Default RE: Strange idea.

i have a .25 HPi Nitro Star engine outta my monster truck, i guess i can use that. How big would a hull be do you think?
Old 02-02-2005, 11:40 PM
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Default RE: Strange idea.

My guessimate would be at around 36 inches or more to do it like close to how Volvo Penta set theirs up.
Old 02-08-2005, 02:25 AM
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Default RE: Strange idea.

Back in the day, I had a gill net boat that had the outboard engine mounted right up in the bow of the boat.

Imagine this:
A boat with a box coming up through the middle bow. Outboard engine mounted in there.

Unlike most outboards on the back, where you turn the steering left, it goes right. With this, due to the engine being in the front & no pendelum effect, you turn the engine left, it goes left. LOL.

I'll have to dig up some old pics & scan them.

Not the same as what was started in the beginning post, but similar.

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