Sail Drives VS direct drives

[beiland]

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

I missed that quote. That is a slick idea.

[admiralslater]

I wish that I had taken a photo of the sterns of an Outremer 55 3 feet out of the water with both outdrives removed and in the next slip an other large cat lifted the same way for rudder repairs. All they use to lift is a shopvac.

[beiland]

Originally Posted by beiland

...another discussion of these drive legs.
Belt Drive - Page 3 - Boat Design Forums

Just found this posting I had made on another forum....

Originally Posted by brian eiland

Some chain drive technology I'm familiar with, referred to as 'silent chains'.

Fundamentals
Ramsey Products | Silent Chain Fundamentals

Advantages
Ramsey Products | Advantages of Ramsey Silent Chain


....some chain efficiency discussions
Transmission, Driveline, Hybrid Drive engineering - roller chain efficiency

...more discussions here:

Diesel Electric Propulsion | Page 9 - Technical Discussion | YachtForums: We Know Big Boats!

[beiland]

After my recent sailing trip aboard the 75' Ppalu catamaran I am reconsidering some thoughts of mine on 'propulsion'. Ppalu has a single 150hp outboard mounted on a skid under the bridgedeck. It is far enough forward of the aft beam that it does not 'jump' out of the water surface that often, even in the good size swells we were in. If I were redesigning or modifying the arrangement, I would provide for a slightly more 'protective' skid, and I would definitely have the outboard motor steerable in unison with the helm/rudders when it was being utilized. Other than that a good old outboard motor was a relatively cheap and useful aux for this vessel.

To take it a step further I would 'divide' the outboard engine up into its powerhead,... and its drive leg portions. The powerhead portion would be my aux engine in its own very accessible 'box' up on the bridgedeck, and the drive-leg would be a fabricated silent-chain drive unit. That chain drive leg might be a retractable unit like the case of the outboard engine, OR it might be a fixed structure with a folding prop on the shaft. In either case it would be a pretty simple chain driven leg that could be steered with the rudders.

The aux powerhead engine portion might be a lightweight Steyr hybrid engine with its own 'generator' incorporated into the bellhousing.


If I were looking at a twin engine installation for a more often utilized motorsailing application, then I would still be considering a chain driven prop arrangement something like this:
Tennant Hull V ChainDrive

[belizesailor]

Originally Posted by beiland

I missed that quote. That is a slick idea.

Yes it is. Saves a lot of time and money for charter ops. Also have a friend with a Shuttleworth 65'. Haulouts are expensive. So he had lift bags custom built...not cheap, but will pay for themselves over time.

[clockwork orange]

Great idea those lift bags but no need for them to be expensive, you can easily make your own out of the 18 oz vinyl truck tarp material and glue the seams with the HH66 contact adhesive that is made for this. My son and I have made airbags presses for pressing snowboards this way and they ran about 100 psi in them, I would expect lift bags to only run maybe 2 - 3 psi so should be easy and you would only need to use halkey Roberts valves like in your inflatable dinghy for that pressure.

Steve.

[DotDun]

Originally Posted by clockwork orange

Great idea those lift bags but no need for them to be expensive, you can easily make your own out of the 18 oz vinyl truck tarp material and glue the seams with the HH66 contact adhesive that is made for this. My son and I have made airbags presses for pressing snowboards this way and they ran about 100 psi in them, I would expect lift bags to only run maybe 2 - 3 psi so should be easy and you would only need to use halkey Roberts valves like in your inflatable dinghy for that pressure.

Steve.

Hmm, how would 2-3psi lift a 30,000 pound boat ???

[Sailmonkey]

Originally Posted by DotDun

Hmm, how would 2-3psi lift a 30,000 pound boat ???

by displacing a volume of water and floating (3 psi over a large enough surface area can do miracles).

[Training Wheels]

At 3 psi you'd need 10,000 square inches to lift 30,000 pounds. About 70 square feet, so an area of about 7' X10'. If my math is correct......,

[Sailmonkey]

Originally Posted by Training Wheels

At 3 psi you'd need 10,000 square inches to lift 30,000 pounds. About 70 square feet, so an area of about 7' X10'. If my math is correct......,

Now, keep in mind you only need to lift the stern........Not such an insurmountable task.

[admiralslater]

Originally Posted by Training Wheels

At 3 psi you'd need 10,000 square inches to lift 30,000 pounds. About 70 square feet, so an area of about 7' X10'. If my math is correct......,

They are large but they are still just using shopvacs . I am happy to be corrected but is it not all about the ability to displace water, so not a per square inch but a cubic inch issue.
Archimedes might have an opinion

[Training Wheels]

True. A cubic foot of water is about 64 pounds, so you'd have to displace about 470 cubic feet, about 7' X 10' X 7'.

[Training Wheels]

Speaking of displacing water, I found it curious that on my documentation, my 10,000 pound boat has a gross tonnage of 68 tons!

[StuM]

Originally Posted by Training Wheels

Speaking of displacing water, I found it curious that on my documentation, my 10,000 pound boat has a gross tonnage of 68 tons!

Gross tonnage has little to do with the weight of a vessel, it is based on usable "cargo volume" of the the hull and superstructure (the original spelling was "tunnage", referring to the number of tuns, or large barrels that a ship could carry) generally one "tonne" is 100 cubic feet.

[StuM]

Originally Posted by Sailmonkey

Now, keep in mind you only need to lift the stern........Not such an insurmountable task.

And as you lift the stern, the bow will submerge more, giving greater overall bouyancy, so your 30,000lbs boat may only require lifting 10,000lbs or so to get the stern clear. Which means you would only need to displace 156 cubic feet of water - which is a ball about 7 ft in diameter.