Sail boat for the 21rst century?

[cruisingram]

I read a sci-fi book a long time ago, when I first started sailing as a teenager. I got out of sailing in my early 20s, and never progressed much past my little 16' sloop and daydreams. I had a friend with a 20m Yawl, and I worked with him a few times, as it was a charter-pleasure craft out of Australia- and state of the art for the 80s. We had some B.S sessions, some based on this description of a boat in this sci-fi mag. There were a couple of things that intrigued us about this fantasy design-

1) It too was a yawl rigged boat, with a center flybridge and huge aft cabin
2) Also 20 meters

It was hypothetically turbine powered- too expensive for our tastes! But in today reality- a bio-diesel would be the thing to have these days

But another interesting part was the idea of an impeller type prop, and when it was under full sail, the impeller would turn, and turn a generator, giving another method to re-charge the batteries.

The bio-diesel is no problem for me- but is the impeller that is built into the line of the keel practical as a design?

I will try to draw and scan it some time, as I don't have auto-cad on my computer LOL

[Minnewaska]

My entire day can be made or ruined by 1/10th of a knot. Drag is your enemy. I wish I could relax.

[sailingdog]

Why would you want a flybridge on a sailboat? A ducted impeller also doesn't make much sense on a sailboat. If it did, someone would have done it by now. Building it into the keel weakens the keel and adds a lot of complexity that really isn't necessary.

[dacap06]

SD is right about the flybridge. It increases the hull sail area - generally a bad thing since you can't control it to help move you. However, he's both right and wrong about ducted propellers.

The kind ducted propeller known as a Kort nozzle is a good way to improve thrust and efficiency by eliminating tip turbulence and increasing differential pressure. There are a number of marine applications where these nozzles have been applied successfully. I've seen some tugs fitted with them, for instance.

At first blush, Kort nozzles sound good for a sailboat -- an application involving high efficiency and slow speed using heavily loaded (by design) props coupled to diesel engines that generate high torque at low speed. But as soon as you begin to investigate details you see they only make sense for boats that are on the move a lot of the time (read commercial). As soon as you ruin the Kort's airfoil shape with marine build-up from barnacles or algae, they become more of a hindrance than a help because the increased drag outstrips the added thrust. Recreational sailboats sit still a lot of the time, which encourages buildup. Additionally, Kort nozzles make backing down worse, which is already a problem on many sailboats. Further, they have tight tolerances and can be a maintenance nightmare because of it. If you hit something in the water and ding the Kort, it often requires a trip to the yard (without using the propeller) to straighten it out again because the prop will no longer turn without hitting the nozzle.

I looked around on the net to see if there is a simple, short article on Kort nozzles and found one. If you are interested in learning a little more about ducted propellers, take a look at this article in Wikipedia.

[flyingwelshman]

[QUOTE=sailingdog;661210]Why would you want a flybridge on a sailboat?QUOTE]: he didn't say he wanted one, he said there was one on the boat in the science fiction book he read.

[QUOTE=sailingdog;661210]A ducted impeller also doesn't make much sense on a sailboat. If it did, someone would have done it by now.QUOTE]:
"A medicine that destroys bacteria does'nt make much sense. If it did, someone would have done it by now."

"A vehicle that can travel faster than a horse, and doesn't need a horse to pull it doesn't make much sense. If it did, someone would have done it by now."

"powered flight doesn't make much sense. If it did, someone would have done it by now."

With the better understanding of stress dynamics, and the development of new materials, a lot of what previously made no sense might now become a reality.

[sailingdog]

Dacap—

He's looking to build the ducted impeller into the keel... that would require a tunnel running through the entire keel, greatly weakening the structure.

Originally Posted by dacap06

SD is right about the flybridge. It increases the hull sail area - generally a bad thing since you can't control it to help move you. However, he's both right and wrong about ducted propellers.

The kind ducted propeller known as a Kort nozzle is a good way to improve thrust and efficiency by eliminating tip turbulence and increasing differential pressure. There are a number of marine applications where these nozzles have been applied successfully. I've seen some tugs fitted with them, for instance.

At first blush, Kort nozzles sound good for a sailboat -- an application involving high efficiency and slow speed using heavily loaded (by design) props coupled to diesel engines that generate high torque at low speed. But as soon as you begin to investigate details you see they only make sense for boats that are on the move a lot of the time (read commercial). As soon as you ruin the Kort's airfoil shape with marine build-up from barnacles or algae, they become more of a hindrance than a help because the increased drag outstrips the added thrust. Recreational sailboats sit still a lot of the time, which encourages buildup. Additionally, Kort nozzles make backing down worse, which is already a problem on many sailboats. Further, they have tight tolerances and can be a maintenance nightmare because of it. If you hit something in the water and ding the Kort, it often requires a trip to the yard (without using the propeller) to straighten it out again because the prop will no longer turn without hitting the nozzle.

I looked around on the net to see if there is a simple, short article on Kort nozzles and found one. If you are interested in learning a little more about ducted propellers, take a look at this article in Wikipedia.

[dacap06]

Originally Posted by sailingdog

Dacap—
He's looking to build the ducted impeller into the keel... that would require a tunnel running through the entire keel, greatly weakening the structure.

SD,

I agree with you that a tunnel through the keel is not practical. When I read what he wrote, I interpreted it differently than you did. He asked whether an impeller that is built into the line of the keel [is] practical as a design? To me, that question did not imply the impeller was in the keel or that it used a tunnel running its length. I took his note to mean a tunnel in line with but separate from the keel. Is that what the OP meant? Who knows? Only he can say. All I can tell you is that is what I heard.

Kort nozzles use a very short tunnel, much shorter than the propeller diameter, and would not need to be built into the keel. What I had in mind is similar to the one shown in this picture. Where that picture departs from my idea is that it shows some sort of motor built into the trailing edge of the keel. I had in mind a more traditional setup where a shaft protrudes from the hull just after the keel and runs to a Kort nozzle.

BTW, another reason not to do the Kort routine is that it requires a better class of cutlass bearing, or at least replacing the current type more often. When the cutlass bearing becomes worn and sloppy, the propeller will scrape the nozzle.

[cruisingram]

Wow- great answers- I was not sure if I was asking a stupid question, and my questions regarding the flying bridge are because of the use of the boat- inter-Island travel, and the boat would be hauled out regularly at a boat launch not far from my house- you would not BELIEVE how cheap sail boats are to buy on Oahu, if I sail it over here to the big Island, I won't have to pay a slip fee, the reason that folks are wanting to unload thier boats for butt-cheap prices. A seriously 50k boat is going for 2500 bucks- no joke! Between the economy failing, and the high costs of property on Oahu, along with the monster slip fees, folks just want to get out from underneath the payments. So this is a unique opportunity for me, since I have easy access to dry dock, a free place to store a boat, I can capitalize on all this now- for the first time in years!

My family and I, uncles, dad, cousins, brothers, all want to build a boat though, so we are starting to look into it, and, instead of both re-inventing the wheel OR sticking with designs from the 19th century, we want to look for some innovation, but not for world cup racing either LOL

I hope that clears things up- the longest voyage we ever contemplate is possibly to LA, otherwise, pretty much inter-Island cruising via the trades

Here is just one example:

22 foot sailboat

[sailingdog]

Going to LA (Los Angeles) is a pretty big deal from Hawaii. You need a pretty solid boat to do it. If you're seriously interested in building your own boat, it is going to be pretty expensive to do, since almost all the materials will have to be shipped to Hawaii. IMHO, you're much better off buying a decent boat from the ones there.

I'd highly recommend you read the Boat Inspection Trip Tips thread I started that is a sticky in the boat buying forum as a good place to start. It will let you get a baseline on whether any boat you look at is worth going any further with.

[cruisingram]

Originally Posted by sailingdog

Going to LA (Los Angeles) is a pretty big deal from Hawaii. You need a pretty solid boat to do it. If you're seriously interested in building your own boat, it is going to be pretty expensive to do, since almost all the materials will have to be shipped to Hawaii. IMHO, you're much better off buying a decent boat from the ones there.

I'd highly recommend you read the Boat Inspection Trip Tips thread I started that is a sticky in the boat buying forum as a good place to start. It will let you get a baseline on whether any boat you look at is worth going any further with.

I threw the LA thing out there as the most ambitious thing I would even contemplate- doubt I will ever do it- most likely just inter-Island, Hell, I am already in Hawaii- why leave!

I have been going over both the boat inspection threads and the books threads- great advice- thanks!