Shaft brake

[Notorius]

My boat have twin CAT 3208 435 Hp DITA. I use it as a trawler for a good 60% of my cruises. 1000RPM , 8,5 Knots. These engines are nor designed to run at 1000 RPM for many hours, so I would like to install shaft breaks to use only one engine at 1400-1500 RPM. At this rev the turbo is working perfectly , no issue with deposits etc.

Without shaft break I may damage the transmissions on the mid-long term.

Any of this forum have it on the boat? Any advice about the kind of shaft brake to install?

 

[O C Diver]

What size propellers do you have? Locking the shaft means you will be dragging the propeller through the water. A significant amount of the fuel savings will evaporate dragging that fix propeller. In addition, you will further limit the fuel reduction by keeping the rudder turned to compensate for the drag on the other propeller.

The fuel savings will be the reduction of turning the engine at 1,400 RPM out of gear, less the drag factor or the locked propeller and the constantly turned rudder. Then there's the question of how much increased load will be on the running engine, with the locked propeller.

I can't see you saving 1 GPH as opposed to running both engines at 1,400 RPM. The other issue is how long it takes to unlock that engine if the first quits.

I understand you didn't solicit this comment, but most people who consider locking a shaft, don't consider the downsides.

Ted

 

[Notorius]

Thank you for your opinion. Actualy I am not so enthusiast to spend 3-5K $ to install the shaft brakes. The reason to go with a single engine is not fuel saving, but running the 3208 at a REV that don't cause problems or damages, which is 1400 RPM or more.

I need to do some test with both engines at 1400 RPM and see what happens .

 

[rslifkin]

Based on the shaft brake concern, I'm assuming your transmissions have a warning against letting them freewheel for too long?

As far as running too slowly, do your engines come up to normal operating temperature when running at 1000 RPM? And do they have the updated warmer thermostats I've seen mentioned for 3208s? If they do, I wouldn't be too concerned about running them slowly as long as you throttle up for a few minutes every few hours to get things hot and burn the exhausts and turbos clean.

 

[MV Moira]

Thank you for your opinion. Actualy I am not so enthusiast to spend 3-5K $ to install the shaft brakes. The reason to go with a single engine is not fuel saving, but running the 3208 at a REV that don't cause problems or damages, which is 1400 RPM or more.

I need to do some test with both engines at 1400 RPM and see what happens .

OK, I'll reveal my ignorance here: instead of a shaft brake, how about leaving one engine off but in gear?

 

[rslifkin]

OK, I'll reveal my ignorance here: instead of a shaft brake, how about leaving one engine off but in gear?

Assuming the transmissions in question are hydraulically shifted like most larger transmissions that won't work. As soon as the engine stops, the trans pump stops, so there's no more hydraulic pressure to hold the clutch packs together. At that point it's in neutral regardless of where the shifter is placed.

 

[MV Moira]

Knew it was too simple...

 

[Notorius]

Based on the shaft brake concern, I'm assuming your transmissions have a warning against letting them freewheel for too long?

As far as running too slowly, do your engines come up to normal operating temperature when running at 1000 RPM? And do they have the updated warmer thermostats I've seen mentioned for 3208s? If they do, I wouldn't be too concerned about running them slowly as long as you throttle up for a few minutes every few hours to get things hot and burn the exhausts and turbos clean.

The idarulic transmission warms up because the oil pump stops when the engine is off.
What I am doing now , every 1-2 hours, running 10 minutes at 2400 RPM

 

[rslifkin]

The idarulic transmission need twarms uo because the ol pump stops when the engine is off.
What I am doing now , every 1-2 hours, running 10 minutes at 2400 RPM

Out of curiosity, what model transmissions are they? Some hydraulic transmissions allow freewheeling, some don't.

When you run the engines up to 2400 after a period of running slowly, are they excessively smoky at first? And are they sooting up the transom when running slow?

 

[Notorius]

Out of curiosity, what model transmissions are they? Some hydraulic transmissions allow freewheeling, some don't.

When you run the engines up to 2400 after a period of running slowly, are they excessively smoky at first? And are they sooting up the transom when running slow?

Yes, first a big cloud of smoke for 20-30 seconds . When I run slow the smoks comes back to the transom, it makes it dirty, and we can smell it from the fly bridge too. It desen't happen when we go fatser.

May be if we go faster we solve a lot of problems!

 

[cafesport]

My boat have twin CAT 3208 435 Hp DITA. I use it as a trawler for a good 60% of my cruises. 1000RPM , 8,5 Knots. These engines are nor designed to run at 1000 RPM for many hours, so I would like to install shaft breaks to use only one engine at 1400-1500 RPM. At this rev the turbo is working perfectly , no issue with deposits etc.

Without shaft break I may damage the transmissions on the mid-long term.

Any of this forum have it on the boat? Any advice about the kind of shaft brake to install?

I made a set for our 29” inch props. Shaft diameter is 2” and the brake bore is 4”. It uses a 3” by 3/4” 2.5t wll hitch pin to stop the rotation.


We have 4 blade props and lock the blades vertically behind our skegs deadwood. Rudders are toed in so there is no helm adjustment needed to hold course.

My boat have twin CAT 3208 435 Hp DITA. I use it as a trawler for a good 60% of my cruises. 1000RPM , 8,5 Knots. These engines are nor designed to run at 1000 RPM for many hours, so I would like to install shaft breaks to use only one engine at 1400-1500 RPM. At this rev the turbo is working perfectly , no issue with deposits etc.

Without shaft break I may damage the transmissions on the mid-long term.

Any of this forum have it on the boat? Any advice about the kind of shaft brake to install?

 

[Comodave]

I would check with the transmission manufacturer and see if the transmission is rated to freewheel. There may be a time limit. But this is the easiest way to get where you want to go.

 

[Mac2]

I have twin Cat 3208N with twin disc transmissions. I looked into the same thing awhile ago and there is a thread here talking about it. My transmissions can freewheel without issues. You also have to have the crossover for the shaftseals. I’ve heard both versions of the drag concerns of a locked shaft (more drag, less drag when locked). The below shaft lock is the best I found (excellent customer service/information as well). The shaft Lok disengages automatically when put in gear.

 

[cafesport]

If you have cross connected drip less shaft seal don’t shut down an engine unless you have a way to isolate the water flow from the shutdown engines exhaust elbow. I know of a few sister ships to ours that hydro locked their engines doing this. It’s one of the reasons to reconsider conventional shaft seals on twins.

 

[SteveK]

cross connected dripless shaft seals? what would be a reason to even consider this?

 

[sealandsky]

Just stick a pipe wrench on the shaft.

 

[Mac2]

If you have cross connected drip less shaft seal don’t shut down an engine unless you have a way to isolate the water flow from the shutdown engines exhaust elbow. I know of a few sister ships to ours that hydro locked their engines doing this. It’s one of the reasons to reconsider conventional shaft seals on twins.

How is that possible? The crossover goes from one dripless to the other. The engine is isolated from the crossover. There is a ball valve in the crossover if you need the shaft seals isolated.

 

[Mac2]

cross connected dripless shaft seals? what would be a reason to even consider this?

In case an engine breaks down or you shut it down.

 

[SIBERNUT]

Have props re+pitched

 

[MV Moira]

The relevant line from the PSS installation instructions seems to be:

Note: Twin engine boats that can exceed 12 knots on a single engine must run a crossover line between seals to ensure both seals maintain water flow while running on only one engine. (emphasis added)

That leaves me out, so no need for me to worry about the crossover line nor attendant danger of hydrolock mentioned earlier.

 

[petehdgs]

I might be late to this thread, but depending on the marine gear used you may be able to run an external lubrication pump to feed the gear with lubrication oil pressure while the shaft freewheels. If this can be done it is not as expensive as a shaft brake and shouldn't cause as much drag as a stopped prop, and prevents damage to the gear when the engine is not running. The gear manufacturer may actually have this available as an option.

 

[Flatswing]

The relevant line from the PSS installation instructions seems to be:

Note: Twin engine boats that can exceed 12 knots on a single engine must run a crossover line between seals to ensure both seals maintain water flow while running on only one engine. (emphasis added)

That leaves me out, so no need for me to worry about the crossover line nor attendant danger of hydrolock mentioned earlier.

As others have said: check with your transmission manufacturer, some like my ZF220’s were ok to run for several hours freewheeling, with much less drag.
I can also vouch from experience-checking the PSS seals regularly with an accurate temp gun, that the freewheeling shaft seal temp never rose above sea ambient (mine had no crossover lines) at trawler speed.
Many past posts on this subject have verified that, since the same amount of HP is required for a given speed whether on 1 or 2 engines, you probably burn more fuel with 1 shaft locked than using 2, and the only saving, running on 1 is overall engine hours.
I had other issues to consider such as Naiads were driven by PT engine and the big alternator was driven by the STBD. Once I had the engine hours equal, just easier and safer to run slow on 2 and open them up for a few minutes each day where safe navigation permitted.

 

[WallyM]

My boat have twin CAT 3208 435 Hp DITA. I use it as a trawler for a good 60% of my cruises. 1000RPM , 8,5 Knots. These engines are nor designed to run at 1000 RPM for many hours, so I would like to install shaft breaks to use only one engine at 1400-1500 RPM. At this rev the turbo is working perfectly , no issue with deposits etc.

Without shaft break I may damage the transmissions on the mid-long term.

Any of this forum have it on the boat? Any advice about the kind of shaft brake to install?

Ahoy Notorius;

I just bought an Albin 37 with twin Cummins turbocharged diesels and have the same problem as you. My boat will do about 5 knots at dead idle (950 RPM) in still water. I end up cruising for hours at idle speed on Canadian inland waters (Trent-Severn) where there are lots of speed-limited and no wake zones. My engines are loading up with carbon and there is fuel sheen water coming out of my exhausts until I get on open water and run the engines hard for at least 10-20 minutes.

I do not believe that my boat with twin diesels and a semi-displacement hull was designed to operate for hours of low speed cruising.

I have two sets of propellers for the boat and have engaged a propeller specialist company that is going to re-pitch and cup one set. He believes he can achieve a 300-400 RPM change in engine/propeller performance to get the engines running at 1200-1400 RPM in order to achieve 5 knots. Unfortunately winter is closing in on us here in Canada so I will have to wait until next June to learn the results.

I would appreciate learning about anyone else's experience in resolving this problem.

Wally - MV Belisama

 

[petehdgs]

Ahoy Notorius;

I just bought an Albin 37 with twin Cummins turbocharged diesels and have the same problem as you. My boat will do about 5 knots at dead idle (950 RPM) in still water. I end up cruising for hours at idle speed on Canadian inland waters (Trent-Severn) where there are lots of speed-limited and no wake zones. My engines are loading up with carbon and there is fuel sheen water coming out of my exhausts until I get on open water and run the engines hard for at least 10-20 minutes.

I do not believe that my boat with twin diesels and a semi-displacement hull was designed to operate for hours of low speed cruising.

I have two sets of propellers for the boat and have engaged a propeller specialist company that is going to re-pitch and cup one set. He believes he can achieve a 300-400 RPM change in engine/propeller performance to get the engines running at 1200-1400 RPM in order to achieve 5 knots. Unfortunately winter is closing in on us here in Canada so I will have to wait until next June to learn the results.

I would appreciate learning about anyone else's experience in resolving this problem.

Wally - MV Belisama

Just be aware that increasing the RPM at the same speed will not change how much power the hull will use at 5 knots, and therefore will not increase engine load. You'll just be running at a higher RPM. The boat will likely accelerate faster because the engine will have more leverage against the water but at the same time the top speed will drop, because the governor will limit the RPM before using all the power the engine is capable of. That means for the new wheels the engine will be overpowered for the hull. These changes may or may not give you the improvements you are looking for. Just be careful before spending your hard earned money.

 

[WallyM]

Thank you for those thoughts. This is an entirely new problem for me and I have no experience with high horsepower twins.

Prior to the Albin I had a 34' Marine Trader with a single 120 hp Lehman. That boat was perfect for the low speed cruising on inland waters that my wife and I like to do. I never should have never sold that boat - but that's another story.... .

I'm beginning to think that I have bought the "wrong" boat for what we want to do and am struggling to come up with a (reasonable cost) way to make it better-suited to slow speed cruising. If we were spending a lot more time on open water (Great Lakes & Georgian Bay) I would not change a thing because the boat performs well in those situations.

Any suggestions that forum members can offer based on knowledge and/or personal direct experience would be greatly appreciated.