Strange malfunction on my 3208s

[Pietro]

So, last week-end was the first to the islands. Some 40 miles off-shore. The boat, though shiny as new, did not go well… the engines seemed to have lost 40% of their power!

Engines accelerated up to 2300 RPM, then portboard was not able to go past that figure, and starboard only reached 2500. So I set the rpm to 2300, 22kts and an unbelievable 17 gph per engine!!! This is what they normally burn @ 2500 rpm.

I thought there was something in the port engine as it was not able to exceed 2300 rpm. Or was it fuel?
Hull and props perfectly clean, no smoke from the exhausts, new Racors…strange...

This morning I tested the boat on a perfectly flat blue sea with my Caterpillar mechanic. Pressure gauges connected to the turbos.

After warming the engines up, I pegged the throttles and… starboard clutch slipped!!! The engine revved up as the boat was turning to starboard as the only engine engaged to its prop was the starboard one…

After some adjustments, the gear started working again and afterwards my 390 run like crazy. 2900 rpm, 29.5 kts with ¾ fuel and water and 4 big guys aboard. No vibration from the props! Stunning!

Later today the mechanic will check oil pressure in my Twin Disc transmissions and I will install oil pressure gauges.

I’ve learned another lesson… :smt001

 

[Boatingnut]

Curious, what was the "adjustment" that was made? What model gears do you have? Was it just low on fluid/oil?

 

[Pietro]

Curious, what was the "adjustment" that was made? What model gears do you have? Was it just low on fluid/oil?

I have Twin Disc MG-705

Adjustment was made on the cable in order to make the lever on the box work correctly.
Possibly the lever was not fully opening the oil valve. The valve activates the clutch and if there’s not enough pressure it will slip.

Oil is new and level ok. Oil pressure in the transmission could be low and that’s why he will check this also. If so I need a new oil pump...

 

[BLmicro]

Well that tells me that the female guest(s) you were hauling off to islands 40 miles offshore weighed more than 4 big guys + 3/4 fuel and water :smt043




(just kidding Pietro! Nothing like humor intended insults from the states heh? :grin So what would your female guests say to me in Italian? (I'll run it through the online translator :smt001)

-BL

 

[Pietro]

Well that tells me that the female guest(s) you were hauling off to islands 40 miles offshore weighed more than 4 big guys + 3/4 fuel and water :smt043




(just kidding Pietro! Nothing like humor intended insults from the states heh? :grin So what would your female guests say to me in Italian? (I'll run it through the online translator :smt001)

-BL

Yes, they were a dozen....so definitely heavier!!! But, believe me, you are overestimating me!!!

I believe the typical Italian female aboard my SR would say exactly what I'd like to hear :grin: :grin: :grin:

 

[Boatingnut]

Always nice when the fix is easy. Rule number one about tracking problems: Start with the easy and obvious. Glad is was something small. Thanks for the response!

I have Twin Disc MG-705

Adjustment was made on the cable in order to make the lever on the box work correctly.
Possibly the lever was not fully opening the oil valve. The valve activates the clutch and if there’s not enough pressure it will slip.

Oil is new and level ok. Oil pressure in the transmission could be low and that’s why he will check this also. If so I need a new oil pump...

 

[Gofirstclass]

Yes, they were a dozen....so definitely heavier!!! But, believe me, you are overestimating me!!!

I believe the typical Italian female aboard my SR would say exactly what I'd like to hear

Pietro, do you make them line up and take a number? :grin:

 

[Pyrojodge]

Sounds like she finally moving through the water. Hope you have a great Season Pietro. Glad you like the prop scans. I'm going to eventually go from 3 blade to 4 so well see how that works with my gasses... Happy Boating my friend.

 

[ssousa]

Pietro,

what size props do you have on your boat. I bought a 1986 390 this year that was converted to 3208's. I am only getting 21 kts at full throttle.

 

[Pietro]

Pietro,

what size props do you have on your boat. I bought a 1986 390 this year that was converted to 3208's. I am only getting 21 kts at full throttle.

At 21 kts there must be something wrong.

Sea Ray states 28-32 kts @ 2900 RPM with 20”x25” props. This is a little optimistic to me, but could be achieved with an unloaded boat.

From Sea Ray:



I have now 21”x23” four blades props that I sent to Prop Scan. They run like silk, no vibrations and they push the boat out of the hole really vigorously!

Shaft should be replaced as the original 1.5” one is too weak (I broke one after fitting the new props!), so I went to 45mm (1.77”).

It’s quite a modification, but I would suggest it should you decide to keep your 390 for a long time :wink:

 

[ssousa]

Thanks for the info Pietro!
I finally got an answer from the local Cat dealer and it seems the cats in my boat are 300HP 3208's. The props are 21x22 but I'm sure have not been touched by a prop shop for many years. While I'm sure to not get the same performance as you with 150 less HP, I still think the 21kts at WOT is 5 or 6 kts low. I am not all that into speed and run with sail boaters most of the time, but I still want it to run like it should.
Thanks for all the info you provide on here, I have a trip I am taking in a couple weeks, but when I get back I will pull the props off and take them in, I will let you know what happens.

Cheers.