Blue water dripless shaft seals no longer dripless..

If your turning rpm with a clean bottom with average loads, I would not mess with the props.
Dirty bottom is killing more than RPM, MPG takes a big dive quickly and extended wear on the equipment.

Get a diver to keep things clean monthly.

If both seals are the same age, I suggest replacing them. Can you install spare seals on the shafts?

+1

You should expect about four years of service from your dripless shaft seals. You may be able to just change seals or you may find the shafts need to be serviced too. Yes you should do both at the same time.

Are the props original specs? With added weight and a few thousand engine hours those Cats can get a little smokey. Are you getting black smoke from load on the motors? I've had success getting rid of smoke on older Cabos by removing an inch of pitch, sometimes two inches from original specs. But again it depends on what you have now.

I'd do both shaft seals if it's not too much trouble. If it's easy to haul your boat (near a yard) and you're not doing long distance travelling to off the beaten path places I'd be inclined to maybe do one. If the RPM's you're turning is with full fuel, I wouldn't touch the props.

I would replace both sides. Do you have the newer system that allows a seal change without separating the shaft? Check to be sure all your water lines are delivering the required volumes. Check the shaft at the spot the seal will seat to be sure you have a nice mirror. Also inspect the old seal for the reason for its failure.

If black smoke clears and you make max loaded RPM no need to mess with the props.

[QUOTE="Jrms80, post: 224975, .... Any guesses on what to expect on costs to do the seals? Hauling the boat is not difficult I'm in San Diego so I could do one now and do the other when I haul to redue the bottom paint in a few more years.[/QUOTE]

Do you have extra seals in a keeper attached to the dripless on an older model, or do you have the newer model that allows you to add new seals without disconnecting the shafts? If you have one of these situations, it is only a few hours work. However if you have one of the older models and no spare seal already on the shaft. you will have to separate the shaft, tranny and couplers to get the replacement on the shaft and that could be considerably more hours.

Also, go to the Tidewater site they have an nice installation video.

If you are JUST barely making 2800 rpm at WOT, full fuel/full water/ no waste /clean bottom and all gear aboard, you do have an option to take a 1/2" of pitch out to ease the load on the engines and get some extended life. This is done on commercial boats all the time, prop it a bit light to extend the engine life.

Say if your max cruise is 2600 out of 2800, and now it is 2600 out of 2875, she is breathing a little easier, working not as hard. You may drop off of speed a little bit, not more than a knot, and you can always grab that knot by bumping the throttles to 2675, but if your concern is to extend the engine life, then you have that option. The end result is you have now increased the working power band for your vessel, which comes in handy, especially when the weather kicks up or you are all loaded down with all that fish and ice.

For reference, 2800 rpm is the MIN WOT throttle you target, while 2875 would be the MAX WOT target. It also makes a difference if you are doing this work in August vs. January, as the Air/Water temps make a difference on the engine performance as well.

I wouldn't touch the props, there is no need.

Fresh fuel filters, clean bottom, don't mess with the wheels.
New shaft seals, spares on shaft.
Resupply of rum and bait.
Get in- get out- don't ,,, stay in the yard,, go fishing...

If CAT says they need to see 2800, then 2800 is fine. Ganing 50 rpms over by cutting the props isn't going to really extend the life of the engines very much if you're making WOT. You're not running a heavy boat that takes 2+ minutes to get on plane and hammers the engines everytime you do.

Yes, you have to drop the shafts down to change the dripless seals. You shouldn't have to align the engines as they don't move from their mounts and neither do the struts to change dripless seals.....however if you see one side of the seals heavily worn than something has been out of alignment.

Jrms80, you post a great question that all boat owners face as their boats age. You can breakdown the propeller /rpm matching question like this:
2800rpm is the minimum wot that CAT requires you to keep all warranties intact. After the warranty period expires, you can do whatever you want. Prop them to 2700rpm or whatever. Since you have 1800 hours and are concerned about your Time Between Overhauls (TBO) you have the option of setting your own propeller match point.

You can break it down to increments - 2800 / 2825 / 2850 / 2875. Note that a boat that just turns 2800 rpm, say 2805, is just 10 rpm away from being considered overloaded. By unloading the prop a bit (decreasing pitch) you can achieve 2875 rpm. Now, if you operate your vessel the same, and cruise at the same rpm, you have decreased the engine load at that point and therefore you will extend your engine life and TBO. That is a fact of mechanical diesel principals and physics, which some posters choose to ignore, but that is there prerogative. You may drop a knot or so on cruise, but you can always push the throttle to get that speed back if that is what you want. You may also burn less fuel and save money.

At the very least, while you are hauling the boat out, you may want to send your prop out to be re-conditioned to ISO Class 'S' tolerances, you will enjoy the feel of a smoother more balanced wheel with or without touching pitch, if that is your decision.

[QUOTE="
Yes, you have to drop the shafts down to change the dripless seals. You shouldn't have to align the engines as they don't move from their mounts and neither do the struts to change dripless seals.....however if you see one side of the seals heavily worn than something has been out of alignment.[/QUOTE]


If you don't have a spare on the shafts you will have to separate things. Before reassembly be certain you know the cause of the present seal failure so that you can correct it if necessary while things are apart. May be just simple wear.

My Driplesses were installed in 1998 and only failed last year

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A couple of comments from the least mechanical person in this thread.

First, when you haul the boat then look at everything before deciding what to do. Do the props look like new or could they use a little work? What caused the seal issue? Is it alignment or just a failed seal? How does the other one look?

The failed seal is a sign. A sign to haul it and look at things and do what is necessary. Perhaps a sign of age that also says while at it do both sides. I certainly would have both done. And if there is a way to add spare seals and simplify next time then I would. If there's any alignment issue address it now. And then to the props. What I'd do largely is dependent on their condition. If showing wear I'd send them to a prop shop. It's a convenient time.

I look at a haul out as always a good opportunity to take a very close look, even closer than you're getting if diving and checking. If a seal has failed, understand why before just replacing it. This is all part of your propulsion system and very minor deviations or mis-alignments are troublesome.

Now, as to the props. If they're turning the specified rpm under your normal conditions then they're the right props. Unless you have some issue beyond what you've told us, I see no reason to change the size and pitch. If you were telling us it wouldn't plane properly or were telling us it wasn't turning 2800.

As to 2850 or 2900 being better for engine life, a lot depends on where you're running it. I'm assuming you're not always running it WOT so if you're running at say 80% load then 80% is 80%. If you're trying to hit a certain speed when cruising then a prop change the decreases the load at that speed might help engine life. I wouldn't be surprised to see you gain through reconditioning if it hasn't been done in years. I've never been one to change props to increase the rpm above spec, but if my rpm was not maxing, was not reaching specs then I'd always change as I've always considered overloading to be more of a potential issue.

Just don't shortcut what needs to be done this time. I see people all the time complaining about constant maintenance and it's because they do half jobs each time and leave something they shouldn't have.

My shaft seals started leaking earlier this year so decided to change from Bluewater to Tidewater so they could put a spare on each shaft.
Its not uncommon for those elbow fitting on the hose to clog from trash/zincs, etc and once the shaft is not getting water it will heat up and start leaking. About once a year I pull off the hose to check and make sure water is flowing to seal.
Also had yard put a crossover line between the two shafts seals in case we lose an engine we don't have to worry about tying the other shaft up to prevent the seal from overheating.