Wouldn't the pump be pulling water from both the thru hull and the shaft log? That would bring cool water in through the shaft log, past the seal and then into the engine.
Dripless Shaft Seal Cooling water
- Thread starter Blitz
- Start date
What is the force which drives the water from the head intake to the seal. Is
the seal at a significantly lower elevation ?
And yet here the fitting act as a vent and not a supply of water. I dunno. Does the SureSeal require a source of slightly pressurized water. The one thing I do know is that a negative pressure supply is not what you want connected to the seal.
Why not? The vendor themself seems to say it’s ok, and as Dave pointed out either negative or positive pressure will pull water through the seal, just in opposite directions.
These are obviously the instructions for a power boat :
I'd really feel more comfortable if their general instructions had additionally included alternate instructions for a sailboat. It's the fact that these seals are so unforgiving when something fails that keeps me o edge.
Way too many questions for this chicken. I'd stick with the Volva Penta. Looks simpler than the SureSeal and less to go wrong.
I'd really feel more comfortable if their general instructions had additionally included alternate instructions for a sailboat. It's the fact that these seals are so unforgiving when something fails that keeps me o edge.
How do you get flow through the seal when under sail ? If the injection point is connected to a water supply, it can't act as a vent as does a line which only extends above the water line and vents to air.
Way too many questions for this chicken. I'd stick with the Volva Penta. Looks simpler than the SureSeal and less to go wrong.
The vendor doesn't really know squat about the products he's selling. He's just there to get you to buy something, anything. It's the manufacturer you want to talk to for the technical requirements. Ask them, as a sailboater, do they want you to install their seal so that it has :
1. A supply of slightly pressurized water for flushing their seal.
OR
2. A vent to eliminate air from their seal.
You can't have both. And powerboaters don't have sails. They shut down the engine(s) and the prop stops.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,746
I cannot imagine that the physics is uniquely different between the various seals used and the various engines on a sailing boat.
While sailing there is little or no activity in the shaft log. You are not spinning the shaft fast enough to cause cavitation. If the hose is open to the air the water level in the hose may move some down as the fluid seeks a level status with the water outside the boat. But then as the boat settles any bubbles escape and there is again equilibrium with the water in the hose equal to the water level out side the hull. That is why the hose needs to be vertical and the end at least 12” above to water level outside the hull, open to the air.
When installed (tapped to say the HE) the engine off sailing, the fluid is in a trapped closed state. No fluid moving. The prop shaft spins slowly again no cavitation. Perhaps if in a storm high seas condition you go over a wave top and the stern goes into the air for some seconds and the water-in the shaft log drains, as soon as you start the engine the water in the shaft log is pressurized out of the HE clearing all bubbles from the shaft seal.
Your worst condition will be with the engine in reverse trying to get off a sand bar. Then you will be stirring the sea bed and the rotation of the prop/shaft could suck up gritty water into the shaft log.Then the positive pressure water injection into an around the shaft seal will be helpful.
While sailing there is little or no activity in the shaft log. You are not spinning the shaft fast enough to cause cavitation. If the hose is open to the air the water level in the hose may move some down as the fluid seeks a level status with the water outside the boat. But then as the boat settles any bubbles escape and there is again equilibrium with the water in the hose equal to the water level out side the hull. That is why the hose needs to be vertical and the end at least 12” above to water level outside the hull, open to the air.
When installed (tapped to say the HE) the engine off sailing, the fluid is in a trapped closed state. No fluid moving. The prop shaft spins slowly again no cavitation. Perhaps if in a storm high seas condition you go over a wave top and the stern goes into the air for some seconds and the water-in the shaft log drains, as soon as you start the engine the water in the shaft log is pressurized out of the HE clearing all bubbles from the shaft seal.
Your worst condition will be with the engine in reverse trying to get off a sand bar. Then you will be stirring the sea bed and the rotation of the prop/shaft could suck up gritty water into the shaft log.Then the positive pressure water injection into an around the shaft seal will be helpful.
that is exactly why I burp mine each time to go out and come back…hard reverse could blow some air back into the shaft log, or large seas could (maybe) let air into the log (but I don’t know how big of a wave that would be
).On my boat, my engine intake water thru-hull is in the engine bilge, and since I always close the thru-hull when not on the boat, it is really quick and easy to give the VP seal a little squeeze when I am opening or closing the thru-hull. I will say I never get much air out, so I think the seal has plenty of water. I also have checked the temperature of the seal and shaft when motoring, and very cool.
In the end, to each his own. Some boats may not have an accessible shaft log, and in that case, I may want something with an air vent of some kind. Water injection seems totally unnecessary on most boats with an open shaft log.
Time to go sailing!
Greg
That's a good point. In my case (and that of many Beneteau's that use the Volvo seal) the log is a skeg that's enclosed all the way to the back of the cutless bearing. So Beneteau's use of water injection in those cases might be as much about lubricating the cutless as the seal.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,746
I suspect that is true. Not that there should be much of an issue. On my boat the cutlass bearing is at the end of the shaft log. There was a nipple in the shaft log that was connected to the HE. I plugged that nipple and attached the HE source to the nipple on my PSS shaft seal. Easy connection. With the volume of water through the raw water pump the small amount to the shaft seal is no issue.
I will caution that inspection of the shaft seal nipple occasionally is warranted. When I got my boat I found that the previous owner had ignored this maintenance issue. The nipple was plugged with salt crystals. A pipe cleaner broke up the plug and as water entered I put on a new hose.
Here's the installation instruction on my LasDrop Gen II
Why can't Sureseal have instructions like your LasDrop Gen ll ? Another negative point against Sureseal. If I was choosing a shaft seal, they would be off the list. I don't think the advertising clowns had a clue as to what the designers had in mind for this product.
I agree, Tides Marine Technical support advice given via the phone conflicts their online instructions, and their online instructions are not specific to sailboats. I get it that their are lots a variations in boats and they want to cover their assets but if I didn't call I would have never known their recommendation not to use one of their shaft seal kits. The tech actually told me they had a training event specifically on small auxiliary powered sailboat engines (3 cylinder) that experience more movement than larger engines and guided me on a larger Housing and their hose which steps down from the larger 2" housing to the 1-3/4" shaft log. I guess the moral of the story is you have to call. (I haven't ordered mine yet since some things are still pending with the Boat Yard)