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post #1 of 21 Old 12-14-2013 Thread Starter
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direct drive

Hi everybody;

I'm boat shopping and was looking at a 2001 jeanneau so 37 that said the shaft is direct drive.
I'm wondering if there are transmissions or drives that I should be careful with?
Does direct drive mean the prop turns at the same speed as the engine?
Thanks for any info.

Jim.
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post #2 of 21 Old 12-14-2013
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Re: direct drive

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Originally Posted by jraymer View Post
Does direct drive mean the prop turns at the same speed as the engine?
Yes. 1:1.

On larger, heavier boats it is more common to find a reduction gear of, say 2.x:1. With the reduction gear a larger prop can be spun giving more thrust.

That said, there is nothing wrong with direct drive transmissions if the prop can be sized to efficiently move the boat with some power left over for when needed. You would need to do a sea trial under power to asses how the drive train performs.

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post #3 of 21 Old 12-14-2013
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Re: direct drive

I'd be surprised on that new of a boat that it is truly a direct drive (on older boats direct drive meant no transmission at all, you shut the engine down, pulled a lever that moved the camshaft and then started the engine again, rotating the opposite direction). I would guess they are just meaning there is no V-drive, but you never know.
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post #4 of 21 Old 12-14-2013
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Direct drive is sometimes used to denote a conventional drive as opposed to saildrive.

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post #5 of 21 Old 12-14-2013
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Re: direct drive

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Originally Posted by jrd22 View Post
I'd be surprised on that new of a boat that it is truly a direct drive (on older boats direct drive meant no transmission at all, you shut the engine down, pulled a lever that moved the camshaft and then started the engine again, rotating the opposite direction). I would guess they are just meaning there is no V-drive, but you never know.
jrd22 has it right and that model does not have a direct drive. You can't always trust that the broker who wrote the ad' actually knows what he is talking about.

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post #6 of 21 Old 12-15-2013
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Re: direct drive

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jrd22 has it right and that model does not have a direct drive. You can't always trust that the broker who wrote the ad' actually knows what he is talking about.
Sorry to disagree with you ( again ) but in this case I think the broker who wrote the ad' actually does know what he is talking about.

I was pretty sure but I checked, just in case....




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post #7 of 21 Old 12-15-2013
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Re: direct drive

[quote=Geoff54;1220378]Sorry to disagree with you ( again ) but in this case I think the broker who wrote the ad' actually does know what he is talking about.

Sorry, I don't understand what you mean. Your diagram clearly shows a gear reduction unit and all your photo shows is a shaft drive which does not mean it is a direct drive.

"direct drive" is a very specific type of drive without a gear reduction unit. No production pleasure craft is built that way. For more information on what is is, try here Tugboat Society of America

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Last edited by boatpoker; 12-15-2013 at 05:49 AM.
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post #8 of 21 Old 12-15-2013 Thread Starter
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Re: direct drive

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Sorry, I don't understand what you mean. Your diagram clearly shows a gear reduction unit and all your photo shows is a shaft drive which does not mean it is a direct drive.
Thanks all, I think I get it. So how about more info on saildrives and v-drives.

Jim

Last edited by Faster; 12-15-2013 at 12:59 PM. Reason: fixed quote
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post #9 of 21 Old 12-15-2013
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Re: direct drive

V-Drives often make it hard to service the engine as the service points - waterpump, alternator, etc - are hard to reach/

Saildrives are basically like the lower drive unit of an outboard coupled to an engine mounted inside the boat. Lots of aluminum in the water and if strict maintenance is not adhered to there can be serious corrosion problems. Easy for the builder though.

Conventional shaft drive like the diagram above is the simplest most reliable system.
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post #10 of 21 Old 12-15-2013
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Re: direct drive

Here's a V drive transmission:



Ignore the arrow in the right hand image, intended for another discussion.

The engine sits 'backwards' in the boat, the gearbox at the forward end, and the shaft exits the V drive under the engine.. Many such installs put the stuffing box and its gland/seal directly under the oil pan in an almost impossible-to-access place. A most compelling reason to install a dripless seal, as a spraying leaky gland can do nothing good for the pan.
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