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post #11 of 19 Old 01-17-2016
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Re: Is This A Problem?

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Originally Posted by travellerw View Post
You guys are making me feel better. I was worried the seals on my boat were 10 years old. I haven't seen the dreaded milky oil, but I was expecting it soon..



Since my boat is out of the water, I'm gonna do both seals to make myself feel better.

I think their is some confusion around seals. The seal the OP is talking about is the big rubber membrane that keeps the ocean out of the boat. That is clamped to the drive leg and drive bed.

The seals that keep the ocean out of the saildrive oil are small lip seals like used in raw water pumps. They are installed in the prop shaft housing.

Changing the former is a bit of a project, while changing the latter is very quick and easy.

Our main boot seal is 18yrs old and looks new. I have extensively searched for examples of this seal failure and have found none that did not include it as incidental to some other catastrophic event (running up on a reef, etc). However, I just bought replacements and will change them next haul out. While they were expensive, I think they were less than $300 each, and not as much as Bob's cost.

Mark

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post #12 of 19 Old 01-17-2016
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Re: Is This A Problem?

Mark you are correct.. I was confused as to what seal they were talking about...
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post #13 of 19 Old 01-17-2016
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Re: Is This A Problem?

I also have a Volvo sail drive. While I was a bit apprehensive about buying a boat with one, my concerns have proved to be unfounded. The seal is a tremendously strong part and I can't imagine what it would take to damage it while sailing. I purposefully tried to drive a knife through a 14 year old seal which proved to be really difficult. When I finally managed to poke a hole in it, the hole closed up as soon as the knife was removed. The seal is attached to the engine mounting bed about 6 inches higher than the bottom of the hull. Even if the boat experienced a catastrophic grounding, it is highly unlikely that water would enter the boat from the seal. The hull would have to be extremely damaged before the seal would become exposed and vulnerable. The damaged hull would most likely cause water to enter anyway. I've owned both types of drive systems and by far I prefer the sail drive because it is quieter and has less vibration than a typical strut/shaft arrangement. I would have to say that anyone considering purchasing a boat with a sail drive should not be concerned about the integrity of design and the quality of the parts.
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post #14 of 19 Old 01-17-2016
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Re: Is This A Problem?

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Originally Posted by bobperry View Post
Sail drives are far more efficient than a shaft and a P bracket. Less drag, better prop angle. Better in reverse. Bone dry bilge. Less noise and vibration. My sail drive required only minimal annual spring maintainence. Nothing could have been easier.
With all due respect Bob (and others): while I agree with you about better prop angle, less drag? It seems to my (simple) mind that there would be more wetted surface area, therefore more drag with a sail drive.

Better in reverse, is subjective. I know and anticipate prop walk. And, bone dry is only as long as the membrane seal is intact. Otherwise...

My motor mounts are relatively new, so noise and vibration are not an issue...

Maintenance on my PSS Shaft Seal is: every 6-8 years I must:
  • unbolt the coupling
  • back the set screws out of the coupling
  • remove the coupling from the shaft
  • remove the clamp collar from the shaft
  • remove the set screws from the stainless steel seal
  • slide the propeller shaft aft
  • remove the stainless steel seal
  • remove the two stainless steel hose clamps from the PSS "bellows"
  • remove and replace the "bellows"
  • re-assemble with NEW SET SCREWS

I don't have to touch the engine mounts (don't need a block & tackle), as I believe is the case with the Sail Drive.

I readily admit that this is far MORE complex than simply repacking a traditional stuffing box, but the stuffing box is designed to leak a few drops into the bilge while in operation. I also believe that noise and vibration are slightly more of an issue with the traditional stuffing box...

Not looking to start a "mine is better than yours" thread, but I would like to learn your opinion.


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post #15 of 19 Old 01-17-2016
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Re: Is This A Problem?

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Originally Posted by BarryL View Post
Visited my boat last week and this is what I saw.

Is that hole going to be a problem?


Barry
Nah, the surface pressure of the water will keep it from coming in. You can use it to fish, or explore like a glass bottom boat.



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post #16 of 19 Old 01-18-2016
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Re: Is This A Problem?

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Originally Posted by eherlihy View Post
With all due respect Bob (and others): while I agree with you about better prop angle, less drag? It seems to my (simple) mind that there would be more wetted surface area, therefore more drag with a sail drive.

Drag is going to depend on the specific boat. If you have a prop shaft that exits the boat only a few inches, then your drag is less. Anything more, particularly if it is at a large angle, and the drag is substantial.

Hull types where a sail drive is a viable option are usually of the latter, and contain a strut for support.

The sail drive leg is a foil shape, which also helps reduce drag along with its orientation.

The discussion around changing the main boot seal is in regards to something that only needs to be done every 10-20 years - it isn't a regular maintenance thing. The only regular maintenance is changing the oil every 250 hrs. Some change the lip seals every few years for good measure.

Mark
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post #17 of 19 Old 01-18-2016
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Re: Is This A Problem?

eherlihy, agreeded that this is not a "mine is better than yours" topic. There are some misconceptions that saildrives don't stack up to their traditional counterparts of shaft and strut designs. Many people who take a superficial look at a boat with a saildrive don't realize that what they see on the outside of the hull is NOT the seal keeping water out of the boat. It is strickly a rubber fairing membrane to reduce water turbulence around the protruding saildrive leg. The actual seal is located about 6 inches above that and is protected by the hull proper. On my C&C 110, the engine has to be slid forward about 2 inches in order to remove the saildrive. No block and tackle was required and it was accomplished by one person.

The PSS dripless shaft seal is a great product and I had one on my previous boat. It also has some periodic required maintenance which is less expensive than replacing a saildrive seal. But on some boats, the rudder has to be removed in order to install or replace the bellows of the PSS dripless shaft seal which can be difficult and expensive too. Even conventional stuffing boxes can have issues. The rubber hose clamped to the shaft log can detriorate over time or clamps can break. I have seen struts break causing lots of hull damage, ruined cutless bearings and bent shafts too. I think that most of us will agree that there is no perfect solution when it comes to dealing with holes in the bottom of a boats.
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post #18 of 19 Old 01-18-2016
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Re: Is This A Problem?

eherlihy:
Nope, sorry but you are wrong. There is less drag with a sail drive than you would have with an exposed shaft and strut.

How can I be so confident about this?
I have been at this game professionally a long time. In my days designing IOR boats there was an allowance , EPF "engine propeller factor" for the different styles of installation. This was a very important factor as it was a direct multiplier of "L" Without dragging out my IOR book I'll say there were drag factors for each kind of installation that were used in determining EPF. This also included engine weight, engine location and propeller depth and size. The drag factors for the different installations were determined through tank tests at the Delft tank in Holland.

In short, the foil shaped alu strut of the sail drive with the prop tucked neatly behind the strut has less drag than an exposed length of round shaft ( round is always high drag) and a strut.
At Carter's office before saildrives were common place we used hydraulic drives buried quite low in the keel with the prop tucked up as close to the trailing edge as we could get it t get the max EPF of .965. We did anything we could to avoid an exposed shaft. Colemj refers to this type of installation.
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Last edited by bobperry; 01-18-2016 at 01:40 PM.
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post #19 of 19 Old 01-19-2016
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Re: Is This A Problem?

Thanx!

Bob, that is particularly helpful!

When discussing prop walk, prop wash, and keel shapes, I would have the class join me for a walk around the marina. There was one older boat with no exposed shaft, and the prop tucked right against the keel. I wondered how the drive line was configured, and guessed that there was a jackshaft arrangement. Now I know (better) that it is hydraulic.


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