Sail Drives VS direct drives

[belizesailor]

Originally Posted by roland stockham

You missed what is for me the clincher. With a sail drive the integrity of the hull relies on a large rubber seal around the leg. to make it worse it is a long leg. Even a small impact at the prop risks breaking that seal and no pump system will stand a chance if it fails. On a mono where it is behind the keel it has some protection but on a cat there is probably nothing.

Many cats are built with a water tight bulkhead separating the engine compartment. So, flooding due to bellows failure is typically limited to just the engine compartment. On some older FPs I user to run, a bellows failure leak would not even get the engine electronics wet.

[belizesailor]

Originally Posted by PhiSig1071

While I abhor feeding the trolls, I do have an honest question:


Is it true that the Volvo's have a rubber gasket and the Yanmars don't? What about Beta's?

No, Volvos have a single rubber belows and Yanmar's is double. Dont know what Beta uses.

[rabbi]

Originally Posted by belizesailor

A number of Lagoon models do. The biggest pain is when backing a lot...the friction wheel locks they use are not strong enough to hold the wheel against the prop wash...esp on bigger Lagoons like the 50...PITA to keep fighting the wheel and working throttles while backing...usually in tight quarters of course. Ive assigned a crew member just to hold the wheel before, but dont always have one available.

Also eliminates the possibility of directing forward thrust prop wash with the rudders, but thats not something you do often on a cat anyway.

But OTOH gives you the possiblity of using reverse prop wash.

Seriously: backing can be an issue but I quickly developed the habbit of just fixing the wheel with the knee. I don't even think about this anymore, happens automatically. May not work on big boats, don't know.

[belizesailor]

Originally Posted by rabbi

But OTOH gives you the possiblity of using reverse prop wash.

Seriously: backing can be an issue but I quickly developed the habbit of just fixing the wheel with the knee. I don't even think about this anymore, happens automatically. May not work on big boats, don't know.

Ha, yeah, good luck with that (reverse wash)! [emoji6]

I also stick my knee in the wheel or jam my hip against it, but on bigger Lagoons its still hard to hold the wheel in place.

[rabbi]

Originally Posted by belizesailor

Ha, yeah, good luck with that (reverse wash)! [emoji6]

reverse wash does work! But somehow its mind blowing complex to think this through, at least for me. which way to turn the wheel and which engine to engage fwd and reverse...

But you have to admit its a unique selling point! Theoretically a least

[SVNeko]

Originally Posted by smj

Priming and bottom painting when hauled.
Changing the oil every 100-250 hours.
Changing the seals every 5 years.
Changing zincs before they disappear.
Changing shaft seals when needed.
Most of these items require a haul out.

Oil can be changed from boat and is dead simple.
Nobody changes their seals every 5 years. Ours is 13 years old and fine.
Shafts have zincs also. Change them in the water.
Shaft seals are changed when bottom painted.

Really, not a big deal and no saildrive-special haulout is ever needed.

[belizesailor]

Originally Posted by SVNeko

Oil can be changed from boat and is dead simple.
Nobody changes their seals every 5 years. Ours is 13 years old and fine.
Shafts have zincs also. Change them in the water.
Shaft seals are changed when bottom painted.

Really, not a big deal and no saildrive-special haulout is ever needed.

Agree, not a lot of additional maintenance hassle for an SD, but sometimes there are SD specific haul outs needed. Like when the shaft seals start to leak.

Slickest option I've seen for this was large lift bags at a charter base in Martinique. Just attach under aft bridge deck to lift stern for SD access.

[Palarran]

Originally Posted by rabbi

Lagoon and Fontaine Pajot are built differently, at least the ones i owned.
FP has watertight bulkheads with no penetrations below bridge deck level.
Lagoon has penetrations even in the deepest bilge area for houses, wires and fuel lines, somewhat sealed using PU spray foam.

IMO, it is critical to seal the engine compartment penetrations completely on any catamaran and failure to do so is inexcusable. One feature I really like on Palarran is the number of separate bulkheads and bilge pumps. I have the standard forward crash bulkhead, main hull with two large capacity bilge pumps in each one, engine compartment, and stern compartment - both with bilge pumps. So a total of 4 bulkheads and 4 bilge pumps per hull. Flooding a hull is a concern for me, but catastrophic flooding, not so much.

One thing I have noticed with sail drives vs shaft is they do seem to turn tighter when docking or med mooring. They are also quieter.

[moseriw]

Originally Posted by roverhi

A cat sank in Thailand when a line got caught in the sail drive prop and torqued the drive enough to break the seal. A shaft drive can have a catastrophic failure like complete loss of the shaft but you can still plug the puka. Not the case with a sail drive seal failure.

AND YOU CAN STUFF UP THE BOX UNITL IT IS TIGHT IN ANY CASE.

[SVNeko]

Originally Posted by belizesailor

Agree, not a lot of additional maintenance hassle for an SD, but sometimes there are SD specific haul outs needed. Like when the shaft seals start to leak.

Slickest option I've seen for this was large lift bags at a charter base in Martinique. Just attach under aft bridge deck to lift stern for SD access.

Or connect a header tank above the waterline to keep a positive pressure in the gearbox.

[beiland]

This is what I would want, a silent-chain drive leg like the one that PYI built at one time.

And I would mount mine in a Tennant style CS hull

Tennant Hull V ChainDrive

[beiland]

...another discussion of these drive legs. regrettable one of the forum discussions with lots of photos got deleted somehow.
Belt Drive - Page 3 - Boat Design Forums

Originally Posted by brian eiland

At one time I was doing quite a bit of study of this subject in anticipation of producing some units...maybe over in Asia. But the boat market is less than well at the moment, so I'm not persuing that subject at the moment.

I started out favoring the idea of toothed belts over chain. But over a period of time I came to the realization that the silent chain approach made much more sense, and would be easier to impliment. This is particularly true when you start talking of HP greater than 20-30.

If you start looking thru the tables of pulley diameters (minimum dia) recommended by the belt manufacturers for specified powers transmitted you will find the diameters of the pulleys getting quite big which might require thicker struts, and all of this interferring with the prop...etc...etc

[Sos]

If there was an inherent safety problem with sail drives you
can be sure your insurance premiums would reflect it

Mine don't !

[belizesailor]

Originally Posted by SVNeko

Or connect a header tank above the waterline to keep a positive pressure in the gearbox.

Works if the boat is already equipped with that...and you always run the same boat.

[admiralslater]

Originally Posted by belizesailor

Agree, not a lot of additional maintenance hassle for an SD, but sometimes there are SD specific haul outs needed. Like when the shaft seals start to leak.

Slickest option I've seen for this was large lift bags at a charter base in Martinique. Just attach under aft bridge deck to lift stern for SD access.

+1