Same questions different forum location....I was recently out on my friends boat, Oday 23 with a swing keel and we were hit with a gust that put the leeward deck rail in the water. So I was wondering how resistant to knockdowns are these swing keel boats compared to lead keel boats? Are the swing keel boats also heavily weight at the bottom? Would the boat go over easy if the keel was retracted? Thanks,Ray
- Status
- Not open for further replies.
R
Ron
knockdowns
The O'Days have a pivoting centerboard, not a swing keel. The centerboard slides up into a trunk in the keel, it's function is to reduce leeway, not to keep the boat upright. Resistance to heeling is accomplished by the hull form (bigger beam means less heeling) and by the weight of the keel. To a lesser extent, the lift produced by the centerboard moving throgh the water will also contribute to resistance to heeling, but only while moving, and only slightly. The centerboard is made of fiberglass; sometimes there's plywood encased in the fiberglass, and sometimes there's a small amount of lead. My O26's centerboard weighs only about 40lbs or so, and appears to be solid fiberglass. Sailboats with keels can be knocked down quite far by wind, but at some point, the angle of the sail begins to spill wind. Combined with the form stability and the keel weight, this will keep the boat from heeling further. The boat will still heel dramatically, especially in gusts, but it won't be pushed all the way over by the wind. It takes breaking waves to heel a boat beyond the horizontal.
The O'Days have a pivoting centerboard, not a swing keel. The centerboard slides up into a trunk in the keel, it's function is to reduce leeway, not to keep the boat upright. Resistance to heeling is accomplished by the hull form (bigger beam means less heeling) and by the weight of the keel. To a lesser extent, the lift produced by the centerboard moving throgh the water will also contribute to resistance to heeling, but only while moving, and only slightly. The centerboard is made of fiberglass; sometimes there's plywood encased in the fiberglass, and sometimes there's a small amount of lead. My O26's centerboard weighs only about 40lbs or so, and appears to be solid fiberglass. Sailboats with keels can be knocked down quite far by wind, but at some point, the angle of the sail begins to spill wind. Combined with the form stability and the keel weight, this will keep the boat from heeling further. The boat will still heel dramatically, especially in gusts, but it won't be pushed all the way over by the wind. It takes breaking waves to heel a boat beyond the horizontal.
J
justin - o'day owners' web
Adendum
Ron puts it well but I would point out that the size of the wave needed to knock you down is not as large as you might want. The rule I've been told repeatedly is ~ 805 of the max beem. So - a decent chop combined with a puff could do it. The answer is to sail with the boat shut up if the conditions are iffy. Getting knocked flat isn't fun but your boat will recover just fine as long as it doesn't flood. If your hatches are closed and your hatchboard are in place, the boat will leak but not flood and you'll be ok. The most important rule, however, is to shorten sail and avoid the whole issue. Justin - O'day Owners' Web
Ron puts it well but I would point out that the size of the wave needed to knock you down is not as large as you might want. The rule I've been told repeatedly is ~ 805 of the max beem. So - a decent chop combined with a puff could do it. The answer is to sail with the boat shut up if the conditions are iffy. Getting knocked flat isn't fun but your boat will recover just fine as long as it doesn't flood. If your hatches are closed and your hatchboard are in place, the boat will leak but not flood and you'll be ok. The most important rule, however, is to shorten sail and avoid the whole issue. Justin - O'day Owners' Web
B
Brian
Re: Adendum
I agree with Justin. Gust in my neck of the woods occur without much warning, usually when you have every piece of sail up begging for some wind. Good rule of thumb: If the sails are up, the hatches are closed. P.S. IMO the 23's sail best when heeling over just a bit.
I agree with Justin. Gust in my neck of the woods occur without much warning, usually when you have every piece of sail up begging for some wind. Good rule of thumb: If the sails are up, the hatches are closed. P.S. IMO the 23's sail best when heeling over just a bit.
L
Larry Baygents
knockdowns
I agree with everything Ron said. However, when a boat can change its center of gravity that can be another issue. Practical sailor did a study on righting moments and was concerned about some boats. Their design was marginal. Especially boats with swing keels. The righting moment can be altered with the keel. I specifically know of a Catalina 22 that went over permanently in 10-15 knots. The water was shallow and the skipper raised the keel, changed the center of gravity and was knocked down never to return. Often these captains think swing keel means shallow water. Not true. The keel is for placing the boat on a trailer. Period. I have been on several swing keel boats that have hit stuff with the keel and the resulting damage is serious. I would also be concerned about water ballast boats without the water in the tanks. Odays are well balanced. The centerboard is so light it does not affect the righting moment. Therefore no concerns. Tell your wife the boat cannot go over no matter how much water is coming over the rail. The Oday 25 likes to sail not too healed over to go faster. We do the rail thing to entertain kids.
I agree with everything Ron said. However, when a boat can change its center of gravity that can be another issue. Practical sailor did a study on righting moments and was concerned about some boats. Their design was marginal. Especially boats with swing keels. The righting moment can be altered with the keel. I specifically know of a Catalina 22 that went over permanently in 10-15 knots. The water was shallow and the skipper raised the keel, changed the center of gravity and was knocked down never to return. Often these captains think swing keel means shallow water. Not true. The keel is for placing the boat on a trailer. Period. I have been on several swing keel boats that have hit stuff with the keel and the resulting damage is serious. I would also be concerned about water ballast boats without the water in the tanks. Odays are well balanced. The centerboard is so light it does not affect the righting moment. Therefore no concerns. Tell your wife the boat cannot go over no matter how much water is coming over the rail. The Oday 25 likes to sail not too healed over to go faster. We do the rail thing to entertain kids.
R
Ray
So? (from the author)
Is the primary purpose of the retractable center board for point of sail and less to do with balast or righting moment? And wouldn't the centerboard offer some resistance to heeling and or knockdowns? Thx for the responses so far,Ray.
Is the primary purpose of the retractable center board for point of sail and less to do with balast or righting moment? And wouldn't the centerboard offer some resistance to heeling and or knockdowns? Thx for the responses so far,Ray.
M
Mike
more centerboard stuff
for the Oday 23 and other keel/centerboard boats, I think the main purpose of the design was to facilitate trailering. For those of us who don't trailer, the main benefit is the reduced draft. Because the centerboard is so light (relatively), it does not provide much in the way of additional stability or righting movement. It does make it much easier to sail to weather.
for the Oday 23 and other keel/centerboard boats, I think the main purpose of the design was to facilitate trailering. For those of us who don't trailer, the main benefit is the reduced draft. Because the centerboard is so light (relatively), it does not provide much in the way of additional stability or righting movement. It does make it much easier to sail to weather.
- Status
- Not open for further replies.