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jraymer 12-14-2013 06:14 PM

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.

CalebD 12-14-2013 06:29 PM

Re: direct drive
 
Quote:

Originally Posted by jraymer (Post 1219306)
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.

jrd22 12-14-2013 10:12 PM

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.

capttb 12-14-2013 10:26 PM

Direct drive is sometimes used to denote a conventional drive as opposed to saildrive.

boatpoker 12-15-2013 12:27 AM

Re: direct drive
 
Quote:

Originally Posted by jrd22 (Post 1219938)
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.

Geoff54 12-15-2013 01:48 AM

Re: direct drive
 
Quote:

Originally Posted by boatpoker (Post 1220274)
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....

http://i1277.photobucket.com/albums/...ps19bf1298.jpg

http://i1277.photobucket.com/albums/...ps17e9ef8f.jpg

boatpoker 12-15-2013 06:24 AM

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

jraymer 12-15-2013 12:47 PM

Re: direct drive
 
Quote:

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

mitiempo 12-15-2013 01:54 PM

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.

Faster 12-15-2013 02:05 PM

Re: direct drive
 
Here's a V drive transmission:

http://i213.photobucket.com/albums/c...psfab0f075.jpghttp://i213.photobucket.com/albums/c...psf06a166a.jpg

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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