Same stability for deep and shallow draft???

[GTom]

Originally Posted by ardbeg

My 2 cents worth. Do not know about the formulas however I will tell you I had a 2006 Hunter 33 with a shallow winged keel. I found the boat very tippy and the wind pushed it off course. ( Made it slide).

I now have a 2011 Catalina 375 with deep keel ( 7 foot draft when tanks full). This boat points better to the wind and digs in to the water. No slip what so ever. I regularly sail back and forth across Lake Ontario. I will never go back to a winged keel on a production boat. I think the winged keels on racing boats were deep whereas the winged keels on production boats are shallow.

Thank you for the observation! I am leaning towards deeper keels too, even if I have to skip a few places.

[robert sailor]

Originally Posted by hamburking

Hunter used to make deep draft and shoal draft versions of the same boats (in the late 80s?). I read that they conducted a series of match races, with identical deep draft and shallow draft boats competing against each other. They also swapped crews and skippers to eliminate that from the equation.

What they found was that the shallow draft versions, with their winged bulb keels, performed either the same or better than the deep keel versions. So the winged keel became standard equipment.

FWIW, the winged keel gained notoriety at the 1983 America's Cup, and was attributed for the win. So winged keel production boats were quick to follow.

The water is thin and the bottom mostly rock here in the 1000 islands region, which is my home cruising area, so I appreciate shallow draft AND good sailing performance. However, the first time I put my winged keel Hunter (1994 Legend) into a mud/clay bottom, I came to appreciate how much that keel also resembles a bruce anchor.

Wings on shallow draft keels were by and large an out crop from the America Cups drama. Keep in mind that the winged keel was a rule beater on boats designed to a specific rule. Wing keels on cruising boats is nothing more than good marketing, I'm not sure any builder uses them anymore. I'm a skeptic on Hunters results because everything else equal the deeper draft will always go upwind better than any shoal draft keel.On other points of sail there would be very little difference if any between a shallow draft and deep draft keels so it's only the windward leg where the difference would be that noticeable. I sail a boat with a Scheel keel and while it's one of the more efficient designs I give up pretty close to 4 or 5 degrees to windward over a deep draft sister ship and that's probably normal.

[barnakiel]

OK.

Looking at STIX formula inputs (as seen in the xls) I can see draft will not affect the formula's result.

Draft is not directly present in inputs, only indirectly (via CLR).

b.

[barnakiel]

Originally Posted by GTom

Knowing the formulae wont do much good for us if we don't know all parameters required

By looking at full formula and the inputs you can see if draft is an input and whether is is offset by anything.

It is not, in STIX. It is only indirectly present in the CLR component and can be offset there by underwater area shape distribution (e.g. a different ballast or stub shape).

Thus the data in OP's request may be 100% correct.

Cheers,
b.

[barnakiel]

Originally Posted by barnakiel

By looking at full formula and the inputs you can see if draft is an input and whether is is offset by anything.

It is not, in STIX. It is only indirectly present in the CLR component and can be offset there by underwater area shape distribution (e.g. a different ballast or stub shape).

Thus the data in OP's request may be 100% correct.

Cheers,
b.

Correction:

The input: 'GZ at 90%' will be affected by moving the ballast higher up. All other things equal, this alone would affect the STIX figure.

So I must take back my earlier post and conclude that to offset the ballast higher up, something else would have to be modified in the design to stay at the same STIX number. Since the hull remains the same, buoyancy distro is the same, so the only thing to change is to chop the stick off or give her a lighter rig.

b.

[IslandHopper]

Originally Posted by hamburking

Hunter used to make deep draft and shoal draft versions of the same boats (in the late 80s?). I read that they conducted a series of match races, with identical deep draft and shallow draft boats competing against each other. They also swapped crews and skippers to eliminate that from the equation.

What they found was that the shallow draft versions, with their winged bulb keels, performed either the same or better than the deep keel versions. So the winged keel became standard equipment.

FWIW, the winged keel gained fame at the 1983 America's Cup, and was attributed for the win. So winged keel production boats were quick to follow.

The water is thin and the bottom mostly rock here in the 1000 islands region, which is my home cruising area, so I appreciate shallow draft AND good sailing performance. However, the first time I put my winged keel Hunter (1994 Legend) into a mud/clay bottom, I came to appreciate how much that keel also resembles a bruce anchor.

Fixed that for ya

[Cadence]

I wouldn't appreciate any underwater appendage capable of snagging something.JMO

[hamburking]

Originally Posted by robert sailor

Wings on shallow draft keels were by and large an out crop from the America Cups drama. Keep in mind that the winged keel was a rule beater on boats designed to a specific rule. Wing keels on cruising boats is nothing more than good marketing, I'm not sure any builder uses them anymore. I'm a skeptic on Hunters results because everything else equal the deeper draft will always go upwind better than any shoal draft keel.On other points of sail there would be very little difference if any between a shallow draft and deep draft keels so it's only the windward leg where the difference would be that noticeable. I sail a boat with a Scheel keel and while it's one of the more efficient designs I give up pretty close to 4 or 5 degrees to windward over a deep draft sister ship and that's probably normal.

Each boat model is different. IMHO Hunter made some of their best boats in the 90's, then went on to make some really bad boats, the Vision series in particular. They raised the cockpit to make bigger aft cabins and the boats gained too much windage. Nice at the dock, not great sailors. Some good innovations like stern rail seats and single line reefing, but some bad ideas too, like below deck furling drum and the B&R rig. Most manufacturers have their duds...the C&C Mega for instance...we just have to avoid them.

I agree, if you have the water depth, go deep. But around here that limits you to the "main channel" which is hardly any fun at all. Every boat is a compromise.

[Stumble]

Originally Posted by barnakiel

Correction:

The input: 'GZ at 90%' will be affected by moving the ballast higher up. All other things equal, this alone would affect the STIX figure.

So I must take back my earlier post and conclude that to offset the ballast higher up, something else would have to be modified in the design to stay at the same STIX number. Since the hull remains the same, buoyancy distro is the same, so the only thing to change is to chop the stick off or give her a lighter rig.

b.

Not necessarily, each STIX subcataory has min/max values, and shifting the ballast up by a bit while adding mass will have a pretty minimal effect on GZ. The bigger hit may be how the additional mass of the ballast effects lightship weight, but the change is probably a rounding error on the final calculations.

You could run the numbers, but lightship weight differences between a 6' and 5' keel are probably on the order of 300lbs for a 40' monohull.


In other words, I don't think abs or stix is a granular enough measuring stick to tell the difference. Extend it out to four decimal places and it may show up. Or i think you are trying to measure a grain of rice with a cars odometer.

[barnakiel]

Yep. This may be the case too. However looking at values change in that xls sheet I would guess the tool is sensitive well enough to moving so much of the total mass by so much.

With the xls in hand, one can be tempted to input actual Bene values there and see what happens. Except that the GZ of the boat must be known (both ballast up and down). II know publishing STIX is obligatory, but what about GZ values?

Mailing Bene and asking the question outright could explain things too.

b.

[Stumble]

Originally Posted by barnakiel

Yep. This may be the case too. However looking at values change in that xls sheet I would guess the tool is sensitive well enough to moving so much of the total mass by so much.

With the xls in hand, one can be tempted to input actual Bene values there and see what happens. Except that the GZ of the boat must be known (both ballast up and down). II know publishing STIX is obligatory, but what about GZ values?

Mailing Bene and asking the question outright could explain things too.

b.

This is probably a question that should go to boatdesign.net to get a NA's take, but the more I think about it the less I think it matters.

1) increasing lightship weight by shortening the keel and adding mass to keep the RM the same is going to have a deminimus effect on B (center of boyancy) due to bringing B deeper in the water. But on a 40' boat we are talking in the tenths of an inch range. The extra mass is likely a couple of hundred pounds, on a boat with 1,000ppi it just isn't significant.

2) this decreased GZ again is going to be close to zero. Not quite zero, but a tad. So the boat I sail a little less stable, but again we are talking about very tiny differences over a big boat.

3) RM is actually going to increase just a touch as a result of more mass. Again, a very very tiny increase, but not nothing.

So the net effect is probably somewhere approaching zero. Not quite zero but close.


How big of an effect are we talking here? Well assuming a 40' boat I am betting to works out to about the same stability difference as placing a gallon jug of water next to the mast. Possibly less.

Note that I think is only true for the special case where the shoal keel is designed to maintain the same RM (though almost all shoal keels are designed this way). If the new keel has a different RM then the entire thing has to be calculated from scratch.

[deluxe68]

We used to own a Beneteau 36.7 and I did a ton of research before I bought the boat. Every single Beneteau I looked at had different ballast weights for deep and shoal drafts. It's as simple as that.

[GTom]

Thanks! Just figured the same for Jeanneau-s. What is the advantage of the deep draft then/why are people reporting deep-versions to be more reliable?

[deluxe68]

Originally Posted by GTom

Thanks! Just figured the same for Jeanneau-s. What is the advantage of the deep draft then/why are people reporting deep-versions to be more reliable?

The deep draft is usually better at sailing upwind, it can point a little higher.

[s/v Jedi]

Just to toss in another variable: I know boats that have a deep draft version that have a concrete ballast, while their shallow draft version has a lead ballast, resulting in the shallow draft version outperforming the deep draft version.

Of-course, a deeper keel reduces leeway... but only at equal heel angles. Reducing heel angle is the best way to reduce leeway