DP-G outdrive cooling...homegrown

[mr. sandman]

VP outdrives IMO suffer from overheating when running for any lenght of time and is a contributing reason on their short life expectancy. In reality, it would be great if the transmission was properly cooled. All transmissions need to be cooled. Since there is no way to easily cool the fluid with traditional heat exchangers, some have resorted to "drive showers" esp in the high performance world. Measurements have shown a 50 deg drop in fluid temps on some of these high performance rigs. The VP duoprop set up is not really a super high performance rig but if you run it at cruise for several hours the transmission is completely out of the water and dry. Yes the lower unit is submerged but the real business end of the drive is hot as hell.
Instead of a drive shower I am considering drilling a few holes in the lower part of the upper gear housing COVER. This cover does little and creates a cavity around the back side of the upper gear housing. This will drain dry if running. My idea was to drill a couple holes at the top and a couple smaller holes near the bottom. The bottom holes would be plumbed to a simple ram style pick-up on the cavitation plate. Thus when running you flood the cavity and water which would exit the top of the cover spilling over the front and sides of the upper gear housing nearly surrounding the gearbox with cool seawater. I think this will keep the trans temps a lot lower and is nearly foolproof. The cavity will drain at zero speed.

What do you think?

 

[GLENN M]

Re: DP-G outdrive cooling...homegrown

not being an engineer or any modification expireance on that setup i cant give you anything to go on but i will say,and probly shouldnt that it sounds pretty good idea.myself i would hang back and wait for the R&D to take place,but it sounds feasable to me.goodluck keep us posted.

 

[sqbtr]

Re: DP-G outdrive cooling...homegrown

I would worry about pressurizing that area. The shift cam seal is back there.

 

[Don S]

Re: DP-G outdrive cooling...homegrown

I would worry about pressurizing that area. The shift cam seal is back there.

I agree 100% Those seals tend to leak water into the drives even without pressure.
When I was in Alaska, we had one charter boat that had a big block and a DP-S drive that daily went 50 miles one way to fish, and it was done at WOT. The drive oil was burned bad when changing at 100 hours. We built a drive shower out of hose and made a pickup that attached to the transom. The water only hit the drive on the front of the top cap, but after 100 hours, the oil was not burned and looked normal.

 

[wire knot]

Re: DP-G outdrive cooling...homegrown

Interesting thread/thought.
I've seen showers for the merc stuff, are there no showers available for VP?
Got me wondering, will my NEW sx get hot?

There are plans for two hr runs in my future.
Not WOT, but sustained 3/4 trottle.
Did he say short life ?
Is this hyjacking? sorry if so

Wire Knot

 

[Don S]

Re: DP-G outdrive cooling...homegrown

Yes, it's hijacking. To answer your question, I seriously doubt if a single run of 2 hours one way and back will cause a problem. The constant everyday of 4-5 hours of hard running is the problem. If you have further questions, I'd suggest starting a new thread.

 

[mr. sandman]

Re: DP-G outdrive cooling...homegrown

I agree 100% Those seals tend to leak water into the drives even without pressure.
When I was in Alaska, we had one charter boat that had a big block and a DP-S drive that daily went 50 miles one way to fish, and it was done at WOT. The drive oil was burned bad when changing at 100 hours. We built a drive shower out of hose and made a pickup that attached to the transom. The water only hit the drive on the front of the top cap, but after 100 hours, the oil was not burned and looked normal.

Thanks for everyone's thoughts. I am an engineer and was going to (over) size the top holes so that the pressure in would be low (a couple inches of water). I was (am) concerned about the shifting seal as well but I thought it could withstand some water on the outside of of it. If you have seen leakage into the unit thru this seal I may re-think this. I really like the idea of surrounding the transmission with seawater while running. I may see if I can come up with a some kind of a cap to install over the shifting seal to keep the water off that region.

The primary problem I have seen with these drives are from guys that run offshore (say 3-5 hours, fish for a day and then run home) the long sustained runs with a transmission in air overheats and burns the oil and dramatically shortens the lifespan of the unit, which is pretty costly. In my unit they use a 75-145 viscosity gear oil which I am sure is used in an attempt to deal with the temp. range of the unit. IMO the right solution is proper cooling not exotic lubricants. You are not solving the problem with oil viscosity.

Not to de-rail this thread but really like the new ZF pod drive with has the transmission inboard and is cooled in a traditional manner.