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Old 09-10-2010, 14:58   #1
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Boat Hunting

I'm looking for a boat for world cruising, but haven't sailed modern beamy cruisers much. I chartered one in Tahiti for a week and found the rudder to cavitate easily. Is this a common problem? Any modifications help?

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Old 09-10-2010, 19:13   #2
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Hi Kealani and welcome aboard. We have a few members in Hawaii. Beautiful place. I lived in Oahu for a couple of years. Sure miss the place.

Why do you think the rudder was cavitating? Was that during tacks or did you have to hold helm to hold a course?

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Old 09-10-2010, 22:04   #3
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rudder cavitation

We were sailing on a close reach, I was impressed by the boats initial stability, the wind in the high teens. The helm had some weather presure but not much, in the lee of Bora Bora, when she suddenly rounded up. We slacked the sheets and bore off only for a repeat. While it was close to reefing time, I've never had a boat lose it like that. We reefed and rolled only to make 4 kts in ideal conditions
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Old 09-10-2010, 22:29   #4
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Welcome to the forum Kealani.
I have no first hand experience with these modern designs, but am interested to see what the other members think.
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Old 10-10-2010, 00:14   #5
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What make and model of boat were you on?
Was there much weather helm before you rounded up?
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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Old 10-10-2010, 13:11   #6
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She was an 05 Jeanneau 46. The helm had a little weather pressure, the seas were flat in the lee of Bora Bora. After the round up we slacked the sheets, fell off to a reach and trimmed the sails carefully as we sailed back to a close reach. Within 5 minutes she rounded up again, forcing us to reef the main and slog along at 4 kts.
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Old 10-10-2010, 14:10   #7
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As a former delivery skipper, I think rudder cavitation is a very common problem with modern designs. Modern designers have incredible pressure to produce boats with huge butts (to accomodate that spacious aft cabin queen bed and extra head) and limited wetted surface (shallow keels and tiny rudders) and flat bottoms. These boats motor nicely and fast and provide big accomodations spaces and are fast enough downwind to make up for their compromised windward sailing performance. Unfortunately, sailing characteristics seem to be far down the line of priorities when designing something to sell the missus. But don't blame the designers or manufacturers, they sell what people buy. Most folks buy boats for charter, the dock, and the missus--if you get to sail, well, that's nice. There are new boats out there that do everything well (Hallberg Rassey is an example) and a number of older boats at various price points that are treasures that have excellent sailing characteristics (almost anything by S&S will get my vote) but they are not the vast majority.
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Old 10-10-2010, 14:43   #8
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most rudders will cavitate when they come out of the water.

by the same token, most modern, fin-keel boats in the 46"+ category will generate significant apparent wind when going to weather. my boat falls into this group, and I can easily hit eight knots going to weather in 15 knots true wind, which means my apparent wind will be close to 23 knots. if the wind is at all puffy at that point it becomes important to depower the main, if not by reefing than at the very least by flattening it and easing the traveler a bit.

if the only way you could control the boat was to reef so deeply that you could only close-reach at 4 knots, then in my opinion this is a sail-trim problem, not a rudder problem. I realize it's a lot easier to blame the boat, or even to blame all modern production boats with fin keels, high SA/D ratios and significant beam carried aft, but the point remains that you don't sail these boats the same way you'd sail a narrow, full-keeled boat with a low SA/D ratio.

ask yourself, honestly, what the chances are of a rudder suddenly cavitating for no reason whatsoever and causing a round-up. pretty slim. chances are better that you got caught trying to sail a modern boat the way you'd sail an old-fashioned boat, and got spanked in the process. if this is the case, the main lesson to learn is: don't blame the boat.
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Old 10-10-2010, 17:44   #9
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G'Day all,

Interesting situation, this!

My first thought is that this isn't cavitation at all, but either ventillation (air being sucked down the rudder when it's upper surface is too near or even penetrating the surface of the water) or stalling, with the latter being most likely. As I understand it, as steering loads increase (weather helm)one increases the side force generated by the rudder to compensate. One does this by increasing the angle of incidence of the rudder (turning the wheel/tiller). All goes well with this up to a point when the flow across the rudder stops being laminar and becomes turbulent. This will eventually happen with all rudder designs, and when it does there is a sudden loss of steering force, and you round up out of control... just as described.

I'm not at all familiar with this boat design, but if the rudder is on the small size as suggested above, greater angles of incidence will be required than with a larger rudder, and stalling is a likely result.

I also suspect that with the beam being carried so far aft there is a tendency for the top of the rudder to be exposed at big heel angles, with ventilation and loss of steering force a very possible result, again leading to sudden loss of control.

Finally, I too suspect that boats designed for the charter trade may well trade off sailing qualities for accommodation size. From conversations with many charterers here in Oz, they often select the boats to charter by number of berths rather than sailing ability, and this trend is reflected in what the charter companies buy, and that surely influences the designs offered by the big manufacturers. I'm not trying to start up the anti Benevarihuntalina wars here, but I do think that these factors should be considered by potential buyers.


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Jim and Ann s/v Insatiable II , lying Pittwater, NSW fora while.
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Old 10-10-2010, 20:59   #10
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Thanks for the replies and I tend to agree with most opinions. My last boat, a gulfstar 50 would tell me to reef by angle of heel, weather helm, or comfort. Not once in 20000 miles did she ever cavitate, ventilate, or round up. This boat had a taller rig , theoretically should be reefed earlier but never heeled beyond 15' or so, so I was enjoying the boats ability to stand up to so much canvas. The helm didn't feel heavy and I don't remember too many details about the mains trim other than it happened again after carefully trimming as we headed up. I agree with the theory that the rudder is very close to the surface when heeled over and may break the surface, ventilating instantly. Ray, during deliveries, are you reefing early to prevent this? Is this simply a big butt problem? Does anyone have any retrofit ideas like different rudder, fences, twin rudders?
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Old 11-10-2010, 11:30   #11
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Aloha Kealani,
It is definitely the design problem of the newer boats. Some are more pronounced than others. Just look for older boat designs and you'll find some of the old tried and true around.
Although condition is a key I like the Allied Princess 36 on craigslist at Keehi.
kind regards,

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