Report on Cynthia Woods

[Peter Ross]

IMO wing keels are hard to do well. Very small changes to the geometry can make huge differences in performance. Not all keel shops can get work in tolerances of < 1 degree. But a 1 degree difference in the wing angle at the keel or the twist of the wing can make the whole system very significantly worse. And cruising boats generally sail slower beat less than racing boats and wing keels make up time at speed uphill and lose time off the wind... My general take on it is that a bulb with a low Cd is a better bet for most cruisers.

Just to add some pictures I did a quicky run in XFLR5 of a simple deep keel (1.8 meters) the same keel with winglets and wings and then a shallow longer cord version (1.4 meters) with wings.
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If you look at the streamlines you can see that the wing has to interact with the tip vortex of the keel in very complicated way and the ideal angle of attack of the winglet changes along it's length for any given speed and angle of attack of the keel... The leeward winglet is pretty much just baggage but you need symmetry so you've got to optimize the winglets with that in mind, too... And the flow is way to complicated to make the computer models believable and robust so you have to go to the tank with all of its problems and .... Well, bottom line, they're hard to design right and hard to make right... But there's probably no real harm in them for cruising -- the losses, if any, will probably be below the threshold of noticability for most -- but I wouldn't pay extra for one either...

I like Ericsons. The one I saw had some issues but I wouldn't want anyone to draw conclusions from a sample of one.

That sounds right. In the case I saw they wanted to add a bilge pump and re-plum the existing pump (which used the head's sink drain). So they had to run pluming from the bilge to the transom and to do that they had to dissemble the port side of the boat from midships aft... Bummer. Also I noted a lot of solid PVC pluming glued to hoses and some of those connections were not readily inspectable and were marginal too. I'm not sure if that was as built or something that happened later -- but it was done with the furniture out...

--Tom.

You're good Tom, very good.
I see you're from Honolulu, have you ever been to Navatek? They have quite an amazing yard and tons of lift body stuff. I flew there a few years ago to set modify a high speed rib for the Navy. I was amazed at some of their winged bodies, which reduced displacement without lifting the boats out of the water. I couldn't help think they would work on a sailboat.



I agree, some irregular glass issues should not steer someone away from those boats.

I did see one of the PS built boats and it was a very nicely done boat. No complaints or remarks, just clean and crisp.

I would like to add that a wagging keel is not so unusual and can be easily fixed with additional floors. Early J24's are a perfect example of wagging sumps, very easily repaired.

I guess in retrospect, removing the finger pointing, it is safe to say the days of bump and run are over. You hit bottom, you better haul out and get a good survey. Kind of like bumping a new SUV at 3mph, will result in thousands of dollars to repair.

 

[tsmwebb]

...
I see you're from Honolulu, have you ever been to Navatek? They have quite an amazing yard and tons of lift body stuff. I flew there a few years ago to set modify a high speed rib for the Navy. I was amazed at some of their winged bodies, which reduced displacement without lifting the boats out of the water. I couldn't help think they would work on a sailboat.

Peter,

I'm marooned in the Mexican desert as I type this. I surely do miss Honolulu. I haven't been to the Navatek yard. I have seen some of their work and have ridden-on their SWATH tour boat, the Navatek II. That's a very, very interesting ship. I don't know if it has any lifting foils per se -- it does have a very fancy ballast system -- as I haven't seen it out of the water and wasn't able to charm my way onto the bridge (sadly I'm not very charming). But I have seen another more conventional tourist cat that I think they did that has a interesting foil system that lifts but doesn't fly the boat. In older literature that I have read about hydrofoils it is taken as axiomatic that partially lifting is worse than planing or flying... But now I'm sure that was an oversimplification. I gather that the new foiling moths are actually a little bit faster than the non-foiling versions in near flying conditions. They, like the cats, have very narrow displacement hulls and I think that is probably the significant difference from the old analysis of foilers with planing hulls. Big racing tri's have been fitted with "C" (Bruce) foils that partially support them for some years now and both potential AC contestants will be fitted with lifting foils. But flying isn't always fast. I gather the the foiling "C" class cat that was developed for the last Little America's Cup was significantly slower than the non-foiling version they won with. I did a little project to see if I could make my dingy foil with two people and a 5 hp motor. Technically it worked -- though I had some control problems -- and it was a fun ride but top speed was barely and better than the boat run clean... Anyway, it's wonderful to see some of this moving into the sailing world and it is so early in the curve that I think we can hope for big advances -- if I win the lottery my next toy will be an RS600FF.

I agree, some irregular glass issues should not steer someone away from those boats.

I did see one of the PS built boats and it was a very nicely done boat. No complaints or remarks, just clean and crisp.

I would like to add that a wagging keel is not so unusual and can be easily fixed with additional floors. Early J24's are a perfect example of wagging sumps, very easily repaired.

I guess in retrospect, removing the finger pointing, it is safe to say the days of bump and run are over. You hit bottom, you better haul out and get a good survey. Kind of like bumping a new SUV at 3mph, will result in thousands of dollars to repair.

Amen to all of that.

--Tom.