Both the shape of the hull f the Potter 19 contribute to the stability of the boat.
The shape of the hull provides most of the the initial stability. As the sails develop power and the boat heels, the hard chines are forced down. As the chines dig deeper into the water, they displace more and more water. This creates an upward "bouyancy force" from water pushing up against the side of the hull. In other words, the heeling force is balanced by a bouyancy force, and the boat stiffens up.
The hard chined form of the Potter 19 hull quickly produces a lot of "righting moment" at very low angles of heel to keep the boat very level. This makes the boat very "stiff" initially. This is called "initial stability". On the Potter 19, most of the initial stability is produced by the hull form.
Past a certain degree of keeling, the shape of the hull can't produce any addition righting force. That's when the ballast in the Potter 19's keel becomes important.
If the boat is knocked down sidways by a mighty gust when you have too much sail area flying, it's the weight of the keel being lifted sideways that brings the boat back upright. In the event the boat is knocked down past horizontal, you don't want the keel to slide out of the trunk -- that might precipitate a full 180 degree capsize. The weighted iron keel in the Potter 19 is the boat's ballast and stick out as far as possible from the hull to do its job of righting the boat.
When the keel is lowered and locked down at its full depth of 4 feet, it provides even more and more "righting moment" as the boat heel more and more. This is called "reserve stability". On the Potter 19, most of the reserve stability is produced by the ballasted keel.
Don't ever raise the sails without putting down the keel first -- the boat will heel very quickly past the limits of the initial stability provided by the hull form. Without the reserve stability from the ballasted keel in its locked down position, the sails will push the boat over sideways until it capsizes with the mast in the water. Without the keel locked down (and all hatches closed), the boat won't come back upright.
(There are some situations in which you can safely raise the keel the with sails up if you need to, but beginners should avoid it. If you must raise the keel to clear the keel of seaweed or get off a grounding, be sure the jibsheets and mainsheet are free first. Experienced skippers may choose to raise the keel as much as 12 inches when sailing dead down wind in calm seas, or in shallow water. Some skippers have drilled holes thru the keel to support the weight when raised. My 1985 has two holes drilled thru it to support it on top of the trunk at about a 12" lift)
In rough water, locking the keel down prevents water from squirting up the keel trunk and into the cabin. The keel has some room to move inside the trunk, and when you heel or change tacks, this pressurized the water on one side of the trunk. Most of the pressurized water will go out the bottom opening of the keel trunk, but some of it may find its way out the top between the keel cap and the trunk. In really rough chop, a loosely locked keel can "pump" a couple of gallons a day into the cabin if the gasket material is deteriorated and if the keel is bouncing around.
To keep your cabin dry, replace the gasket material when it starts to wear, and keep your keel locked firmly. If you don't have any gasket around the keel, get some closed cell weather stripping from the hardware store and stick it onto the bottom mating surface of the keelcap, without any gaps.
If the weather gets really rough, and you're planning on spending a few days on the boat, try a wrap or two of duct tape around the keel cap. Before I changed the keel locking system, we used to use duct tape when we spent weekends on the boat in deep swells. Not a drop of water got in.
The type of keel used in the Potter 19 is called a lifting keel. Though it's a very old design, it's used to this day in high-tech racing boats that are trailered to races. It's a great way to get a lot of ballast down low where it can do its job most efficienctly and without adding excess weight to the boat. (Take a look at some ultra-performace racing sailboats like the Antrim 27. It has a lifting keel and a keel trunk with a very similar shape)
Over the years, there have been three basic designs for locking down the keel on the Potter 19's.
The first design is found in the HMS-18's which were built when Herb Stewart owned the company in the 1970's. It's found on hulls #1-78. It's a line and cleat. It works well for holding the keel trunk down in the event of a knockdown. It prevents water from splashing up from the trunk while sailing in rough water. It doesn't cause additional damage to the keel trunk in the event of a grounding, as far as we know in the Potter Folklore.
The second design if found in the Potter 19's built when Joe Edwards owned the company, from about 1978 through the early 1990's. It consists of a horizontal bolt passing sideways thru a hole drilled in the keel and the trunk. It can potentially damage the keel trunk during hard grounding. There are several historical examples of damage from grounding with this system.
The third design is found in the Potter 19's built after Joe Edwards sold the company. It si the design used from the mid-1990's to this time (2002). It consists of two vertical bolts on each side of the trunk that slide into forks on the keel cap. It works well for holding the keel trunk down in the event of a knockdown. It prevents water from splashing up from the trunk while sailing in rough water. In the event of a hard grounding, the bolts will bend and/or pull out of the side of the keel trunk They are easily replaced at a cost of about $10 each and an hour's work
Herb Stewart's original HMS-18 design - an elegantly simple and effective system.
There is a line anchored to any eyestrap on the top of the keel trunk. The line is cleated to a jamming horn cleat when the keel is lowered.
Stewart designed the keel trunk so that the opening is longer at the bottom than at the top of the keel trunk. The trunk slopes aft as it goes from top to where it joins the hull. There is about 2 inches of extra space at the aft bottom where it joins the hull. That extra 2 inches allows the keel to shift aft upon impact without punching a hole in the boat below the water line. In the overwhelming majority of Potter 19 groundings, there is no damage to the integrity of the trunk.
With over 1300 Potter 19s produced since the early 1970's and still being sailed, there are only a handful of stories of grounding that caused any damage at all to the trunk. There are no reports of boats taking on water through the keel trunk from grounding.
There are several advantages to Stewarts's original lockdown design. First of all, it's quick and easy to use -- it only takes a second to cleat or uncleat the keel. Secondly,when you're sailing in shallow waters, you can leave a few inches of slack in the link, in case you run aground. With a little slack in the line, the keel can lift up a few inches as it rotates, preventing damage to the keel cap and keel cap bolts.
The close-up pictures above are modification I did to my 1985 Potter 19, hull #266, "Redwing". I copied Herb Stewarts original design for my 1985 Potter 19.
This system permits me to raise the keel up 12", insert two thru bolts thru the keel that rest on top of the keel and then tighten the line to hold the keel in place in case of a knockdown. At least that's the theory... I've never been knocked down while the keel is rasised 12" -- I don't sail with the keel raised, even though my boat theoretically can do it.
|Above: Note that most of the boats built while Joe Edwards owned HMS Marine had no floor as part of the cabin liner.|
In 1978, Joe Edwards bought HMS Marine from Herb Steward. He changed the name of the HMS-18 to the Potter-19, but kept the company name. My boat, Redwing, hull #266 was built in 1985. Her registration and title say she is an HMS-19, but the decal on the side of her says West Wight Potter 19.
When Joe Edwards resumed building the big Potter, he started with hull #200. He made may changes in the boats. Among the many changes was the keel lockdown system.
The system installed on Redwing and the 1980 through early 1990's boat is a through bolt passing thru sideways through the trunk and keel. You can damage the keel trunk if your boat has this system and you hit something that's very hard, immovable, and you're moving at several knots of speed.
I modified the lockdown system on Redwing after a really hard grounding on a submerged boulder caused some damage. (Please note that the damage did not in any way compromise the safety of the crew or vessel)
The through-bolt acted like an axle, and the keel rotated around on the bolt. The front/top of the keel took a 1" chunk out of the top/front of the keel trunk. The front bolt holding the keelcap to the keel was sheared and the keel cap was cracked. Fortunately, the bottom part of the trunk was undamaged. We never took on a drop of water, and at no time were we in danger of sinking, The damage wasn't structural, so I sailed the boat until the end of the season, after replacing the busted keelcap bolt. I repaired the keel trunk after the end of the season.
The third design is found in the Potter 19's built after Joe Edwards sold the company. The company was sold to Larry Hart in the early 1990's. He changed the name of the company to International Marine. He began implementing the first of many evolutionary n the boats. One of the early changes was the keel lock down sytem. In 2001, the company was purchased by Dave Dressler, who has continued to use the same system through the present time (2002)
The present design consists of two vertical bolts on each side of the trunk that slide into forks on the keel cap. It works well for holding the keel trunk down in the event of a knockdown. It prevents water from splashing up from the trunk while sailing in rough water. In the event of a hard grounding, the bolts will bend and/or pull out of the side of the keel trunk They are easily replaced at a cost of about $10 each and an hour's work
There are many boats on the market which have a lifting keel design. For example, the superb racer, the Antrim 27, and (I think) some of the Ultimates, all of which are trailerable, have lifting keels inside vertical trunks. The keels are very deep and provide lots of righting moment so those boats can carry lots of sailpower.
Suggestion 1) These boats have a piece of high density rubber or shock-absorbing plastic at the bottom and aft part of the keel trunk to act as a shock absorber. I'd recommend shapeing a piece of rubber and attaching somehow into the 2" of extra space at the bottom-aft of the keel trunk.
Suggestion 2) Maybe IM could design a new keel by cutting away an inch or so away the top front edge, where it contacts the upper front of the keel trunk, like the lifting keels designed by Jim Antrim.
That would make the keel design on the Potter 19 truly (almost) bomb-proof. It would keep all the maintenance and performancce benefits of a lifting keel system over a swing keel system. (no pivot bolt to maintain, bearings to wear, no potential bending of pivot in a grounding; simple lifting mechanism with no cable or inaccesible parts below the waterline; lots of ballast leverage from having a very deep keel; great performance upwind)
Last updated 12/05/2002