Association Forum - Seaworthy - Originally Posted by gerardolau

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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

Seaworthy - Originally Posted by gerardolau

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Initially Posted - 08/24/2014 : 04:56:38

What is better for the sea.. Wing keel or swing keel water ballast? I assume swing keel could be a bit fragile due that its a completely separate part of the boat... Opposite the wing keel..

Thanks
Gerardo
1995 C250 SK/WB

Note: Originally posted as a reply to another post but should have been posted as a new subject. - Paul - Admin

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bear
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Response Posted - 08/24/2014 : 05:10:01

Gerado, That's a centerboard not a swing keel and I wouldn't take my C250 out to sea, not a good match.

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Arlyn Stewart
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Response Posted - 08/24/2014 : 08:41:43

If by sea... you mean which can handle a seaway better, I think the answer is the water ballast. A full keel compared to a center keel has long been established to be the more comfortable boat in a seaway and the water ballast reacts more like a full keel than center keel.

The reasoning is fairly simply. In a seaway, the center keeled boat reacts to the swell in a pitching motion, pivoting on the heavy keel, whereas a full keel boat with the weight distributed fore and aft, resist pitching.

I've a fair amount of sailing experience on the Great Lakes with most of it on a C250 water ballast but some on a C30 center keel. The C-250 hobby horsed considerably less than the C-30.

Several times when coming into a harbor at the end of a passage, remarks were made by those that had stayed in harbor because of the conditions and it struck me that on the C-250 the conditions were of little concern or discomfort.

I've read the same words from San Francisco Bay sailors, who found that the C-250 water ballast was more comfortable on the normally choppy bay than was other center keeled boats they had sailed.

Edited by - on

TakeFive
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Response Posted - 08/24/2014 : 09:35:54

IMO the issue of hobby-horsing is entirely about fore-aft moment of inertia, which resists the pitching motion. So having the water ballast spread over the length of the boat can reduce this more than an unmodified wing keel C250.

Like many with the C250 wing keel, I had some difficulty early on with the boat resting bow-high. This led to several issues, including leakage through the front hatch (which is designed to have water in the gutter draining forward into the anchor locker) and greater than optimum weather helm.

I added about 300 lb of pebble and sand ballast to the bow to get the boat resting on her lines and eliminate the leakage through the front hatch. This also reduced weather helm to an acceptable level. An unexpected benefit which also resulted was significantly reduced hobby horsing in chop.

It would be very interesting to see calculations of the moment of fore-aft inertia for water ballast vs. added mineral ballast. The water ballast is spread over the fore-aft length of the boat, but I believe that the bulk of it is amidships where the boat is widest. Rocks and sand which I used are higher density than water, and also concentrated at the bow instead of spread over the whole boat. That ballast is offset by the weight of the motor, gas tank, and batteries at the transom. It is possible that having the mineral ballast right at the bow leads to a higher moment of inertia than the water ballast spread over the length of the boat. It would be interesting to see some numbers on this.

Edited by - TakeFive on 08/24/2014 09:36:40

Arlyn Stewart
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Response Posted - 08/24/2014 : 18:45:21

Hi Rick.... I'm sure in agreement that balancing the boat was important for the several reason you noted.

An interesting aside to this may be of value in pointing out as some may be new to this dynamic and some explanation may be in order.

Generally weather helm increases as the bow is trimmed down on sailboats but that is not true on the C-250. Years ago, I found myself in an argument over this on the Trailer Sailor Forum with a couple of guys who were convinced that they knew it couldn't be true, even though they didn't own C-250s and couldn't determine the issue from personal experience.

I'll try to explain why. First, let me say that if in fact trimming the bow down on the C-250 reduces weather helm, it must be because there is more than one dynamic at play and reduction is because one of the dynamics has a net greater effect than the other. There is no doubt that normal theory is at play and that trimming the bow down reduces whetted surface aft. which normally increases weather helm.

Ok... so what is the other force that is at play that provides a net reduction in weather helm? I personally believe it is the asymmetrical hull shape when heeling. It is my theory that it has a lift quotient.

To understand this, take a look at the Hobie 16 catamaran. It had no dagger boards but was wicked going to weather and climbed to windward very well. The reason was simple, it used amas (cat hulls) that were asymmetrical. The shape lifted toward the center of the boat. When heeling going to weather, the leeward ama was immersed far more than the wx ama so the net gain was to weather. Of course, off wind the design was a bit slower than symmetrical amas using dagger boards because the lift forces of the hulls produce some extra drag. I think there were other beaching cats that used the same dynamic of asymmetrical hulls.

Back to the 250. When heeled, the whetted hull form is asymmetrical and thus will have lift. That lift will manifest effort either to weather or leeward and unless the center of that lift corresponds with the center of lateral resistance or lateral boat balance point, it will produce a yaw force. My theory is that the asymmetrical heeled hull form lift force center is aft and that when trimming the bow down, it shifts the center of that lift forward closer to the boat CLR and thus reduces the yaw force causing the weather helm.

BTW... trimming the bow down usually increases speed off wind as a sailboat that drags her stern is usually slower off wind. It is very common to see a race crew moving forward off wind. Part of that is to raise the rudder and reduce its drag. On a cat, a racing skipper will almost always raise one of the rudders off wind but he also rarely takes a cat directly down wind, so he will raise the leeward rudder as the shallower windward rudder usually provides adequate steerage.

More than asked... but some sailors find theory interesting... especially racers who want to know every go fast trick in the book.

Edited by - Arlyn Stewart on 08/24/2014 18:52:06

gerardolau
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Response Posted - 08/24/2014 : 18:54:39

Hello, by sea I didnt mean open sea.. sorry I did t make myself clear., by sea I meant sailing on the beaches here in Mexico like Vallarta, Acapulco, Los Cabos, etc.. Not crossing the pacific ocean sorry..

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TakeFive
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Response Posted - 08/24/2014 : 18:55:00

FWIW, another effect of trimming the bow down is to reduce the effective mast rake, which I believed reduced weather helm for me.

I had had difficulty getting mast rake down to 4" because I had cranked the forestay turnbuckle as far as it could go without interfering with the furler drum. Trimming the bow down got the rake the rest of the way down to the specified value. I had attributed the reduced weather helm to the change in rake, but you are right that wetted hull area also has an effect.

Edited by - TakeFive on 08/24/2014 18:55:57

Arlyn Stewart
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Response Posted - 08/24/2014 : 21:55:25

Rick... when starting my battle with the helm, I raked my mast as far forward as I could get it and even countersunk the furler drum an additional amount and it seemed to make little difference. This would have been perhaps the summer of '96. Another owner took a more drastic step and had his forestay shortened (I can no longer remember the amount) and reported no noticeable help.

I concluded from the two examples that raking the mast forward was not going to help an appreciable amount. The C250 had monster weather helm and mast rake wasn't going to fix it.

It should be remembered that the C250 hull was designed for water ballast. It has what the industry designers call hard chines, where a rather beamy hull has side sections that come down more perpendicular to the water line and then turn more sharply to a flatter bottom. The purpose is/was to add righting arm to assist the water ballast.

Consequently, when it heels the whetted hull shape becomes more asymmetrical than a traditional sailboat design. The C250 suffers pretty bad leeway when heeling excessively likely because of the increased leeward lift of the hull compared to other sailboat designs.

Modern racing designs for International One Meter RC competition, actually have hull shapes that lift to weather when they heel. Instead of a flatter bottom and hard chines, they have what is called increased rocker (a rounder bottom area)and a narrower beam with soft chines and a very deep high aspect ratio deep bulb keel to compensate for the loss of righting lever arm of the hull. They are extremely wicked to weather because of the lift to weather rather than leeward lift.

It of course is necessary to balance the forces of that hull lift or it will produce unwanted helm forces.

I've believed for a long time that ideally the C250 might be fitted with dual asymmetrical skegs. They would counter the yaw force and relieve the requirement of an oversize rudder. When heeled, only the leeward skeg would remain immersed and if they were set at around 15° camt, would then be fairly vertical where the lift force would do the job that is now done by the oversize rudder. Keep in mind, that the rudder has to be sized to compensate for depth loss during heeling. Remember, Catalina was caught with their pants around their ankles regarding the rudder on the 250, having grossly missed what would be required to hold control.... but so was MacGregor and Schock with their water ballast designs. They all needed to be retro fitted with larger rudders.

The rudder that Catalina ended up offering for the water ballast model is/was inadequate for aggressive venues. If my 2nd generation beaching should crater forcing me to use the 3rd blade, I will add the skeggs that I envision.

An interesting aside to this is the wing keel. It of course rescued the 250 design when water ballast initially suffered such a bad rap as not being an effective ballast method. The hull shape stayed the same and Catalina then thought, hey with a heavy deep keel and the extra righting arm of the hull... produce the wing in a tall rig and it will be a bomb. It bombed all right but not the way Catalina intended. Just as with the water ballast, when it heeled, it suffered monster weather helm due to the same hull form.

The wing keel with standard rig turned out to be the best model, though it would not have been a boat that served my needs of hauling from Texas to the Great Lakes yearly as was done for a great many years.

While I agree with you that getting the wing keel on its lines likely helped reduce the hobby horsing, the concentration of center mass still remains something that the boat pitches around. Slightly more pitching of a wing keel is certainly a great trade for its virtues. More headroom, no center board issues, and no water ballast tank issues. A better boat for a slip or mooring.

Edited by - on

ruachwrights
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Response Posted - 10/29/2014 : 10:10:32

Gerado,
Granted, I have never sailed in a water ballasted boat, but as a C250 sea sailor, I would argue for a wing keel without added bow ballast for those who own a C250 on the ocean. I think it is common knowledge that having more weight lower makes a boat much more storm and sail worthy. With due respect to Alyrn's experience on the great lakes on a water ballasted c250, whether or not the boat "hobbie horses" should not be as important of a consideration as whether or not the boat will capsize or be knocked down in a gale. At sea you are also more likely to spend days and weeks on the 250 and that added bit of headroom is a good thing. Also, if you are near the ocean your are less likely to be needing to trailer your boat around, which in my mind is the one benefit of the water ballast.

As far as adding bow ballast, in my experience of sailing with ballast and without, the boat sails much better on ocean waves with a lighter bow than a heavier one; it springs from one wave to the next with a lightness and agility that you need. It may be true that some of you experience better performance in flat lake conditions with bow ballast, but the ocean is not flat. Also, though I'm no naval architect, just by looking at the hull shape of the C250 WK, the more rounded stern shape, as opposed to the more abrupt lines from the bow to the mid-line of the craft communicates to me that the boat is designed to be more aft heavy when at heel than bow heavy.

Vern Wright
"Hajime"

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