excessive rounding up from rudder ventilation?

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Sep 13, 2009
Hunter h33 Sydney
My hunter 33 (1977) sails wonderfully under most conditions, but i experience a sudden loss of rudder control at high wind velocity and large heel angles. In particular, at larger heel angles, it rounds up uncontrollably, even with maximum trimming to move CE forward. I've been told that this was because these boats were built with an undersized rudder, and hadn't questioned that explanation until late this season, when i noted that every time a the boat hit the point where rudder control was lost, a heavy trail of bubbles could be seem in the wake in line with the rudder. So i'm now fairly convinced that rudder ventilation is the culprit(not an undersized rudder or stalling of the rudder) . I'm also thinking that i'd enjoy my heavy weather sailing better if i managed to fix this. (There is a little bit about the ventilation issue in "Yacht Design Explained: ...", by Steve Killing, Douglas Hunter, pg 117)

So i'm thinking of doing some rudder mods as a winter project, in particular adding one or more anti-ventilation plate(s).

But now that the boat is out of the water for the season, i'm regretting that i never managed to actually watch the root of the rudder under round-up conditions. So i'm left wondering how far down the rudder the plate should be installed. (yeah, that means that i'm missing direct observation of the ventilation effect, so i'm left to infer it from the 100% correlation with round up and bubble trails)

I'd appreciate any comments on the subject, or answers to these questions:
Has anyone else experienced excessive loss of rudder control and round up on these boats? Anyone observed the bubble trails i'm seeing? Anyone have a sense of how much the top of the rudder comes out of the water at larger heel angles on an h33 1977?
Dec 2, 2003
Hunter 376 Warsash, England --
When this occurs a quarter or up to one third of your rudder might not actually be in the water.
Are you playing the traveller to keep her 'on her feet'. i.e. 22° - 25° max heel? If not then try it.
Surprisingly she'll go faster and point higher too.
One presumes you don't have excessive mast rake. About 6" (or less) is believed to be about the max measured with normal crew weight in the cockpit.
Sep 13, 2009
Hunter h33 Sydney
Thanks for the comments, 1/3 is a lot of dry rudder, that would certainly contribute to setting up ventilation.

I don't have an inclinometer so can't say for certain what heel angle i'm on when i lose control, but the rail wouldn't be in the water when it happens. I know that I can minimize the effect if i really reduce sail, but at the expense of slowing down more than i like. i also know that i can't affect it much through fore aft sail trim (surprisingly similar from jib only to mainsail only). So when i think about it, maybe it is a hull shape issue. The maximum beam point is well aft, so i wonder if that contributes to stern-up trim when heeled?

btw, I have zero rake in the mast with just me on board tuning the rig, not sure what this translates to under crew-in-cockpit trim.

Ed A

Sep 27, 2008
Hunter 37c Tampa
healing over is not as fast as sailing the boat on its lines. then you loose it to a round up the boat is trying to save you! You are actually going a lot slower. think about the rudder, when the boat is healing over the rudder is dragging you down because you have to turn it to hold course. NO GOOD. let the boat stand up as sail about 17 to 20 degrees heal and look at your gps. youll be going faster than when you heal more.

Lots of boats round up when over powered, thats a good thing! Try sailing it with just a little helm pressure.
Dec 2, 1999
Hunter Vision-36 Rio Vista, CA.

I think you will find if you have old baggy sails this problem is more pronounced.

Try reefing when the winds are approaching 13-15 kts (and building). If you are just getting gusts this should not be much of a problem. If you are sailing in sustained winds over 15 kts with a full main/jib it is not going to be comfortable or fast.

These boats get more power out of their jibs than the later boats with a fraction rig do. You may also want to check out your rig tuning to be sure that it is adjusted properly. Weather helm can be a good safety factor but you want to be sure that you are sailing in bounds for the boats sail plan and characteristics.
Jun 21, 2007
Hunter Cherubini 36_80-82 Sausalito / San Francisco Bay
Yep, a lot of sailboats do as you describe. Not only your boat. I remember a couple of years ago watching from the vantage point of the shoreline cruising keel boats of various sizes trying to beat out under the Golden Gate bridge against a very strong wind blowing in from the ocean. Probably a half hour earlier most of these boats were sailing in much calmer conditions. So they had full sail flying -- not reefed. In the strong wind conditions, most all the boats I observed looked like they were fighting weather helm. Some would even round up uncontrollably into the wind as the gusts over-powered the sail plan and caused extreme heal.

I encountered this yesterday. Overall, the winds in the central San Francisco Bay were near the max (for me anyway) for flying my full main sail and the 100% jib. The choice of sail plan was good except when close-reaching back to my marina when some stronger wind surges cascaded down from Hurricane Gulch above Sausalito. A couple of times, my boat heeled almost to the rail and strongly rounded up into the wind. Full opposite rudder couldn't compensate for the tendency. Being short duration gusts, I eased out the main sheet to spill air which is also quicker for me do than easing the traveler.

As Steve Dion cited, reefing is the key. For example, my boat performs fine in 25-30 knot sustained range with a second reef on the main; and then I will play with how much head sail to let out from the furler. I might keep some turns on it for close reaching. Or let it all out for beam reaching or running. As Ed A commented, when the wind gets fresh, I also find that keeping the boat from heeling too much actually yields better speed in strong wind conditions. And the ride is a lot more comfortable and controlled.
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Jan 22, 2008
Hunter 37-cutter Bradenton
All sailboats should round up when overpowered. Boats with lee helm are dangerous because they fall off instead of round up. Loss of controll when falling off results in accidental jibes can rip rigs out of boats or even kill people. Generally speaking, the more you heel, the worse you point. You will also go faster, flatter. As far as your rudder is concerned, Hunter had a tendency to put the same rudder on both the deep and shoal draft models. On the 37cutter this was plenty of rudder for the boat but it drew the same as the shoal keels and was often bent. On the 30 it was not enough rudder and the boat was harder to controll. I have helped two friends with thirty's modify their rudders to balanced spades and increased the draft 8 inches. Losing the skeg and changing the rudder completely changed the boat. It now sails just like my 37c. I can't speak to your 33, but I would assume it is similar. By the way, the first 33 was built just as a race boat with a double spreader rig and a bubble deck.
Nov 8, 2007
Hunter 27_75-84 Sandusky Harbor Marina, Ohio

Reef the main and genny until the boat is on it's feet (15 degree heel) in the steady state winds. That yields the best speed, and gives some reserve to maintain control with the help of the traveler and a flattened main in the gusts. How big is your genny? A big foresail can easily generate weather helm and heel on it's own.

Another reason that the rudder stalls in a round-up is that in an excessive heel, more and more of the rudder's force is directed down versus to the left or right. Then more rudder is needed for the same turning force, at the same time, more turning force is needed to counter the weather helm. And a stall and round up is the result.


Jan 26, 2006
Schock Wavelength 24 Lake Murray, SC
First I have to agree with Steve Dion's comments on baggy sails. When I replaced 10 year old sails last Summer my weather helm problem was greatly diminished.

Second, here's a technique I use when my mainsail is overpowered and I don't want to take the time to reef it, like during a race. I am assuming that your main sheet passes through multiple pulleys (blocks) to gain a mechanical advantage.

1. Cleat the controlling end of the main sheet with the boom about two feet further out than the correct position when the wind is steady. In other words cleat the main where you need it to be when a gust hits.

2. Have your crewman grab one line of the main sheet between the blocks and pull it to windward to bring the boom into the position needed when the wind is steady, i.e. closer to the boat's centerline. If he selects the line nearest to the controlling end he will still have a lot of mechanical advantage.

3. Now your crewman can quickly release the boom a little for a little too much heeling or a lot for a lot of heeling. I tell my crewman "When you see heel increasing past about 15º let the boom out. When the boat gets less than about 10º pull the boom in. " With a little practice he can play the line to precisely control heeling.
Sep 13, 2009
Hunter h33 Sydney
The comments on reefing, trimming and avoiding baggy sails are all great, but i was really hoping for a little discussion about what i think is a weakness of this (otherwise wonderful) boat.

Compared to my other sailing experience, i think my 1977 hunter 33 has a significant weakness in heavy weather, in terms of excessive loss of control as described in the initial post. I feel that my hunter does great up to 20 knots, and it really does appreciate a reef at 15+. But over 20, i find that however i trim, it rounds up with total loss of control. This includes sailing under storm jib only, which, as Paul correctly points out, should create lee helm.

I base my comparisons on my previous boat, a herreshoff Islander 22, a wonderful classic design with full keel and attached rudder, and various c&C's. The herreshoff's rudder configuration is hydrodynamically inferior (less moment and rudder in disturbed flow), but i always had plenty of steering, and the boat responded to sail trimming as expected (ex. lee helm under jib only). Likewise, none of the c&c's that i spent time on have had the stern kick out like my hunter.

Anyway, when i put my experience, bubble trail observations, and Donalex's observations together, i'm thinking this is an inherent part of the hull design (long entry, heel with forward force pushes the boat onto front side, excessively pushing rudder out of the water?).
Dec 2, 2003
Hunter 376 Warsash, England --
The Designer's Dilemma

When heeled the centre of effort of the sailplan is way out to the side of the hull.
Thus the driving force exerts a couple which turns the hull to windward.
Different hulls of differing shapes, beam and underbody configurations may, or may not, resist this force to a greater or lesser extent.
The designer is faced with a compromise based on initial stiffness, sail area, mast location, keel/rudder size and position.
Reducing sail area plus increasing keel and rudder areas plus increasing ballast all help.
They also help to make the boat only sail nicely in conditions when most folk would rather be at home.
He cannot win on all counts!

The owner can help also by not trying to sail the boat on its ear.
Jan 2, 2008
Hunter 33 (Cherubini design Forked River, Barnegat Bay, NJ
The major piece of information you have left out is whether your 33 is the deep draft or shoal draft. It sounds like shoal draft just like mine. Mine exhibits the same characteristics.

I have always felt the rudder had too little surface area. At one point several years ago I slapped a pair of thin plastic plates on the sides of the rudder toextend it aft and while it seemed promising they fell off before I could decide if they made any real difference.
Idid however add about an inch and a quarter to the aft edge of the rudder and about 1 quarter inch to the forward edge to maintain balance. While not a major increase in area id does seem to help a bit. I have been planning to add more area and being as the boat is currently in my side yard it will probably happen this spring. I'll probably add about three inches to the aft edge. Can't add any more ththe forward edge because it is already very close to the 3 bladed prop.

Just to add to the equation, one thing I did which helped was to move the tack point of the head stay forward 18 incheson a bow sprit/anchor platform I had made up a few years before. That modification taught the boat some manners. I can now hold sail in slightly higher wind and can actualy get the rail wet without quite as much helm. (Not that that is all that desirable.) It allows me to be a bit lazier about reefing. One thing about Barnegat Bay is that there is almost always lots of wind, and often more than enough. While I have reefing Genoa and have set up the main for one minute reefing on the first and second reefs, sometimes (actually most of the time) I just get lazy and hold out, thinking the gusts will go away.

I think a lot of what you are seeing in the water flow behind the rudder is more disturbance rather than cavitation. The princess fairing that forms down from the hull just above the russer supposedly is there to maintain the water flow withoul admitting air. I haven't been able to get my head out far enough to see for myself so I can't confirm it. At those heel angles it takes more rudder angle than on most other boats to maintain course. Based on GPS speed readings it seems to me I get best speeds at heel angles of 20 to 25 degrees in higher winds, but it is right on the edge. As far as sail trim in higher winds I keep the main halyard, outhaul and main sheet tight and drop the traveler way down. It helps a lot.

Quantum 2+2 main and 130/135 genoa still in like new shape. If you want, after the weekend I can post pictures of the modifications.
Sep 13, 2009
Hunter h33 Sydney
SamLust - sounds like you appreciate the issue that i'm talking about - these boats are a little light on rudder power in heavy weather relative to other boats, even assuming we're competent at sail trim and don't sail like yahoos :) We get loads of wind here in Cape Breton, especially in the fall, and I love sailing in that weather. But i really don't like the degree of roundup i experience, relative to my previous boat as well as other boats that i sail on from time to time.

My boat is deep draft, so we're talking about different boats. I'm not sure if the rudders are different - on the deep draft is a foot or so shorter than the keel (picture attached), does the shoal draft have the same rudder or did they shorten it as well?

Your forestay mod sounds really interesting, any chance you could post some pics? Also, I'd be grateful if you'd share any info on your rudder area mod should you go ahead with it.

Although i started with the assumption of 'too little rudder area', i changed to believe that we were really seeing 'too little rudder force' but was unsure of the cause which was likely either too little rudder area, rudder stall, or rudder ventilation. [I'm using 'ventilation' (drawing of surface air down the low pressure side of rudder) vs 'cavitation' (production of water vapour by extreme low pressure).] I want to make sure i don't do too much work for nothing, so i want to ask the right questions first , thus the post. (But then again its not really work when you're having fun, is it? :)

When i took those pics yesterday, i thought maybe i could test the rudder area theory by measuring my rudder area and comparing it to some similar boats in the boat yard, including a c&c 35 that i know is much better behaved under similar conditions and trim. I'll do that this week and let you know if i see any patterns.

I doubt there is a major issue with rudder stall relative to other boats, as the rudder looks to be a proper airfoil shape and its aspect ratio looks fine (ie. subjectively, it looks like a good rudder design). But if the top of the rudder is coming out of the water as Donalex says, beyond the fairing, then there is a loss of rudder area to begin with, and ventilation may be involved.

As I said previously, on my last overnight trip in October, i carefully watched our wake as we attempted to sail the last 10 nautical miles into the harbour on a reach in relatively flat water, as the wind blew up to 25 knots plus. Even under a small jib only, we struggled with uncontrollable roundup on the top of every gust. I noted that the trail of disturbed water changed to a bubble trail during the roundups. I wanted to watch the rudder to see if the top was out of the water and if air was being sucked down the low pressure side. But i was a little too lazy at that point in the trip to climb onto the swim ladder, although I now wish i had. so i'm left without any

A possible fix for ventilation is to apply some horizontal strips along the rudder to break the downward flow of air. I think that will be pretty easy to do, unlikely to cause harm, and easy to undo should it fail. If i do so i might also think about something to address tip stall at the same time.

The downside (other than failing to improve situation) is that i might create a more effective lobster buoy rope catcher (that would suck where i sail), and i'll have the funniest looking rudder in the boatyard :)


Feb 14, 2010
Hunter H33C Quincy, MA
Sam, I also have a shoal draft 33 (1981); I'm curious about your rudder mods. You mentioned that you added to the front and rear edges, what about the height? I seem to recall reading here about taking ~ 7" off the bottom - due to the rudder being lower than the shoal draft keel. . . (I experienced my inaugural kissing of the bottom in my new boat)
As far as sailing goes, I've had her out in 20 - 25 knot breeze and she just about sailed herself. . . I've also been out in 25 knots where I also had the same problem as the original poster - uncontrollable rounding up. . . the latter situation I had too much sail up, got lazy about reefing. . .
Dec 2, 2003
Hunter 376 Warsash, England --
Thanks for posting the pics. Now we see the rudder is below that sizeable skeg and, as the hull is of the older narrow sterned type, it would not expose nearly as much rudder when heeled as later wide sterned hulls. Also she is not one with a tubby waterplane area like today's boats so should not be hell bent on rounding up. Again ventilation ought not occur until a serious heel angle like 35° to 45°.
If the fore and aft C of E of the sailplan is okay then your guess of insufficient rudder area is likely to be right.
Do you know a yacht designer to ask for an opinion as there certainly looks to be plenty of scope to provide more area lower down by making the leading edge rake much more vertical - again like today's designs. This will also ease the rudder balance problem as the pivot point looks to be very close to the leading edge and this is then immediately cut away - but don't goo too far.
Any chance of having an all new rudder built or would the expense break the bank?
Jan 2, 2008
Hunter 33 (Cherubini design Forked River, Barnegat Bay, NJ
I have always felt the rudder on my 33 was less responsive than I would like under almost all conditions and less effective than it should be as things go extreme. Downwind control is rough and on the few occasions when we were out on the ocean in fairly big stuff, (we saw them as six footers) the boat was mostly out of control with little effect from the rudder. I have attributed to the rudder being undersized. Just in looking around at different boats in the yards during the winter it seems to me most have relatively larger rudders. (Would a psychologist call this rudder envy?) The inch or so I added aft and the balancing quarter inch forward seemed to increase responsiveness a touch. i currently do not have a rudder balance problem at all. The wheel takes only fingertip pressure in most conditions. Of course I have all sheave angles and play set optimally so there is no induced drag. The main reason I have hesitated increasing the size aft is I don't want to loose the balance. There was a member here who cut off a bunch off the bottom of his rudder. He may also have added more aft. My recollection was that he was very happy with it.

I thought the shoal draft 33 was more prone to severe round- so I'm surprised to hear your standard draft boat does it. In my observation of other 33 rudders I have only seen rudders that appear to be the same size as mine. Even the earlier boats seem the same. The picture showing my keel and rudder illustrates the depth of the rudder. The bottom edge of the rudder is almost as deep as the keel where you say your rudder is about a foot higher than your keel. This indicates that they are the same rudder. My picture actually depicts the technique I used to straighten the rudder shaft after a "bump and run" with six guys inn the cockpit. After that the rudder was hitting the princess fairing. That one was on the last day of the season so it wasn't devestating. The second was earlier and rather than haul out I just backed the boat up against a steep sand bank (the local mayor's private beach actually)
and fixed it right up.

Moving the forestay forward has helped a bit also. I think i"m off on my own on this one but I have always felt that Cherubini intended the boat to be a cutter and placed the mast further aft on the boat than he would have otherwise. The earliest boats I have seen had a Schaefer mast (maybe double spreader, but I'm probably wrong about that) with a baby stay forward to the deck, possibly attaching on deck a couple of feet behind the aft edge of the anchor well. It seems to me Don Bodeman's early 33 was like thatand if he's lurking around he mighrt confirm it or tell you I'm crazy. For some time I have wanted to put a "solent stay" in. It would mount about 2 feet down from the top of the mast so running back stays would not be neededand attach on deck at the aft edge of the anchor well. I don't know if it would help with rounding but it would be really cool.

As Donalex says all of the choices a designer makes are compromises. I have felt that Hunter asked Cherubini for a boat that performed better in light air rather than heavy. My boat goes better than just about anything out there when the wind is next to nothing. there have been times in the fall when the water is like glass and I have literaly sailed circles around other boats. But thatdoesn't help when we're out of control in a blow.

In answer to Paul Rusyniak, Many of these boats which have high aspect mains and large head sails exhibit these symptoms. The main on my boat does not really do much at all, but the genoa seems to provide about 95c percent of the go. Even on genoa alone it will round up. I have seen the same on a number of similar boats. I have never had anything even approaching lee helm on my 33. I did have it on my 260 untill I added more rake to the mast. For the record my 33 mast is close to vertical. any more rake and the rounding seems worse. Also, again, my sails are very good. My Quantum salesman, being from Barnegat himself, knew the conditions and had them built heavy. I think their shape is great.

If I get to the rudder project I will try to take pictures and post them.


Sep 13, 2009
Hunter h33 Sydney
I finally got out to look into the 'not enough rudder' theory by measuring some other boats in the boat yard. We've been having torrential rains and flooding here in Cape Breton, 140mm rain in a day last week, and similar this week, along with 100km/hrs winds. When i went to check the boats last week my boat was in a large puddle of water. I went back a couple of days ago to find that the puddle had disappeared, but the ground had softened, and one of the legs on my middle jackstand had sunk several inches into the ground, and the pad on top of the jack slid about 2 ft. Fortunately, the front and rear stands were holding the boat up just fine. I'm thinking i might end up buying a couple more stands for redundancy.

Sam, i'm totally with you on your statement of the trade off issue. The boat just has less control than I'd like to have.

Anyway here's the results on rudder area:

My Hunter 33 - 5 sq.ft
Modern Beneteau 325 with high aspect rudder: just under 6 sq.ft
C&C 35 mkII - 5.5 sq.ft

So the beneteau has a little more area. The c&c has 10% more, but the boat is 2 ft longer. I know that c&c sails well, with plenty more control in high wind than i have, although the rudder is unbalanced and therefore the wheel can be heavy. I'm prone to conclude that this is not an area issue. (that doesn't say more area wouldnt help).

Donalex, in response to your question, i might well build another rudder. I'm lucky enough to have access to 3d CAD, laser cutting, and engineering, and can build any shape i want. But i want to have a reasonable shot at improving things before i go with anything. Thus i'm thinking i may wait until next year which would allow me to directly observe the rudder during loss of control to see if ventilation is involved.

Finally, here's one more thought. We are experiencing round up under jib only. Given the position of mast and keel on these boats, there is really no way that the rounding up is a result conventional 'weather helm' under simple sailing mechanics, that is, yawing caused by center of effort of sail being behind the center of lift of the keel. In fact, with jib only, one should experience lee helm. Thus the apparent weather helm must be a result of the asymmetry of the heeled hull. Any comments on that reasoning?
Dec 2, 2003
Hunter 376 Warsash, England --
And the fact that the C of E is waaay out to one side off the centre line when heeled - as viewed from above - so it hardly matters where the fore and aft C of E is.

BTW for English viewers C of E means Center of Effort not Church of England which is on 95% of all servicemen's records!
Jan 1, 2006
Slickcraft 26 Greenport, NY
I'm nowhere near savy about design but I enjoy discussion of same. So ... that rudder seems pretty small to me. And I'm not sure that skeg helps. I'm thinking of a surfboard carving a turn when you're heeled very much over.
If you are going to alter the rudder I would lengthen it rather than make it wider. Refer to Dave Gerr's article in a recent Sail Mag about aspect ratio in foils. His point is that there is probable only attached flow on the leading surfaces with increasing turbulence and drag as the flow of water approaches the trailing surfaces. So widening the blade would increase drag and turbulence. Lengthening it would increase lift and add less drag. Of course you don't want it longer than your keel.
The much easier solution to the problem is to reef. There aren't any boats I've sailed on that don't sail better upwind with a reef (Or other means of depowering the main)after 15 to 18 knots of true wind. If a boat can go at all in light air, its going to need less sail in a blow.
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