We've noticed that the bow on our CP19 seems to plough into the waves in a choppy sea and 15 kn winds rather than riding high as she does in lighter air. Does this have anything to do with the rake of the mast? Or does anyone have an answer to why this happens?
I find this plowing into the waves very interesting.
Usually happens 'at speed' vs slowly advancing.
In my racing days on Star boats, Rhodes 19 [keel], Lightings, Penguins I alway tried to 1~Lighten the boat as much as possible. 2~Put as much weight up front a possible.
I highly doubt that the rake of the mast [which ought to be straight up and down] has anything to do with 'plowing' I rather think that this simply is caused by 'speed' and wave action [wave height], shape of the hull, and how much of the boat [hull] is tilted over, [C-P 19's sail best when straight up and down hull wise], as this changes the hull's shape while cutting through the water. My only advice is get that mast where it should be, and don't make those standing rigging too tight. One can site right up the mast and look for kinks and check straightness from the open hatch while laying on the V-birth, at least on my boat, hull #588. On some the hatch open in the opposite direction as on my friends C-P 19, Wind Rover.
If I ride in a car and stick my hand out of the window and make my hand act like a wing...genteel inputs result in gentle lift. However much steeper angles of attack jerk my hand around...I think something like this is happening to the hull as she travel through the waves...but what do I know.
NASA designed the weted surface of the CP-19 and who am I to argue? I figure it is correct and the nature of this boat. skip.
With all due respect to skip, whom I'm sure could sail circles around me, I think the mast rake may be the culprit here!
In reading my books on sailing (typical engineer, doesn't even have his boat home yet and has 6 books on the subject, haha), I read there is a relationship between the center of effort (CE) and the center of lateral resistance (CLR) that the boat designer must engineer into the boat to make it perform satisfactorily.
The CE is the center of force on the sails, the CLR is the resistance to that force by the keel, center board, hull shape etc. The desired tuning is to place the CE just behind the CLR so that in a moderate wind the vessel will have a slight weather helm (3 or 4 degrees). If the CE is too far aft, you will have excessive weather helm, making the boat hard to handle. A forward CE produces a lee helm with the boat constantly wanting to bear away.
All of these centers of force change as the boat heels and/or weight is varied due to cargo and crew. Your goal is to adjust the rig and boat to give the right amount of weather helm so the boat heads up in a gust, falls off in a lull, comes into the wind on if left on its own and imparts a gentle pressure on the tiller to feel alive in your hands.
I suspect perhaps the weight is too great in the front of the boat, or the rake of the mast is too far to the aft. We could expect that too little jib would contribute to the CE being far aft also.
You say this happens more prevalently at 'speed' or when the force on the sails is greater. Of course the greater the wind, the greater the effort on the sails and the more noticeable the CE would be if it is too far aft.
If I am wrong please disregard all comments above! It makes sense to me though.
I've found on my 19 that when I'm sailing close hauled and getting a pretty good heel on the bow wants to dive down.
Thusly causing the so called plowing action. On a slower and flatter sail the bow rides higher allowing it to ride over.
At least that is my observation and I have no explanation for why it does it. ;)
-Kevin
HI Kevin,
My experience with this is mostly from RC sailboats, but they can provide a wealth of tuning practice because they are so easily adjusted. It sounds like you may have too much forward rake.
Imagine if you will, the boat is "pivoting" at the point where the mast meets the deck... now think in very exaggerated terms...
If the mast is raked waaay back, the force would be mostly on the rear of the pivot point and pushing up on the front. Inversely, if the mast is raked too far forward, it would be pushing down on the front of the pivot point.
I was going to suggest too much weight up front, but your description makes me think you might want to experiment with the rake. I would adust it for the most common conditions you sail in (balanced for light or heavy air).
Best of Luck to you. By the way... are you still thinking of a 23? I'm still very happy with my 16.
Dale
I don't think it is caused by mast rake which, once set, you wouldn't normally adjust. Rake is always aft, and perhaps 2" to 4" between masthead and deck. Mast bend is a different thing, but unless you have a backstay adjuster is pretty much fixed anyway.
I do think the effect is caused by sail trim. These boats have limited headsail adjustment, mine only has one sheet lead (I'll be adding jib sheet track and cars in due course), so that as the wind strengthens you can't flatten the sail which would depower it, reducing the tendency for the boat to nose dive. Typically you would move your jib sheet leads aft as the wind got up, flattening the jib. You can achieve some depowering by deliberately over sheeting the jib, hauling it in tight, tending to kill the drive. Or you can switch to a smaller jib.
As you depower the jib the effective centre of effort will move aft tending to induce weather helm, the tendency for the boat to head up into the wind, so you need to flatten the main also to keep things in balance. A slight amount of weather helm is good, lee helm is never good.
I'd try playing with sail trim to find the right set up for going to weather comfortably in a chop.
Hope this helps; fair winds.
If my mast is raked one way or the other it is very minor, I can't really tell looking at it, it seems plumb but I'm sure it favors one or the other. As far as sail trim, still working on perfecting that skill if ever.
Hey Dale,
I was out on Bob23's 23 the other day and yes it is much larger but it seemed to sail the same. I've had my eyes on several different boats of varying makers and lengths of which Bob can attest too since I work with him and he has to listen to my every whim. ;)
-Kevin
I think mast rake can tend to slowly change as rigging is adjusted, stretched, replaced etc.
The forward drive of the sail vs the resistance of the water on the hull. In effect, the sail, and rigging is dragging the hull forward with great resistance from the water. The resistance of the water and the faster forward moving sail causes the bow to dip.
Similar to the action of a boat oar. The top of the oar handle passes very easily through the air, but there is a great resistance on the oar where it meets the water.
Area of sail..... Hight and location of mast vs the resistance of water on moving hull. I am no expert, but that makes sense to me
Regards and good sailing
Terry
Hi Kevin... I dream of a 23 sometimes... untill I think about setting it up or waxing the hull...
I must disagree with Jon S here... I spent quite some time tuning the rake of my 16 and now it's balanced enough to steer with the sails alone or even by shifting my weight around on the boat. Rake to stern = weather helm... rake forward too much = lee helm... heading down or "ploughing". His idea of reducing the power of the jib is correct though even if he has the method backwards... To flatten the jib you move the sheeting point FORWARD. This pulls DOWN on the LEACH thus reducing the "twist". You can flatten the "belly" of the jib by sheeting it tight front to back. The same thing is done by the boom vang ... it pulls DOWN on the LEACH to flatten the main in heavy weather.
There is a pretty good article on shaping sails at the North Carolina Sailboat site. (they have some sweet Com Pac refurbs also)
Here is an excerpt and the link (click on "sailing tips").
Have FUN!
http://www.ipass.net/sailboat/
Genoa Track Adjustment?
Adjust the Genoa luff with the jib halyard for the appropriate wind strength. Adjust the Genoa track to make all of the windward telltales move as one. When we point up, the windward telltales go up and when we fall off, they come back down. When the windward telltales move from a vertical position to a horizontal position, we have changed our heading by 3 degrees. When the windward telltales point up, we are at the luff point for the headsail and it should be shaking or losing power and when the windward telltales drop or point down, lower than horizontal, we are stalled. Going from luff to stall is 3 degrees of heading or less. If we have a very flat sail, it could be less than 3 degrees. Makes for very difficult steering.
With this boat we are going to try and keep the windward telltales at a 45 degree angle. Our boat is sailing on flat water in about 10 knots of wind. We know it's 10 knots because we see a white cap now and then. White caps everywhere would be 12 knots of wind. Our headsail twist is correct because we have all of our windward telltales at the same angle. We are doing a great job and the boat is in the grove. We test the telltales now and then by pointing up just a little bit to see the telltales move higher and then fall off just a little to regain the 45 degree position. Most sailors test the luff now and then to make sure they are not stalling the headsail. A stalled headsail looks good, but makes the boat heel more and produces less power.
The Genoa track is correctly adjusted to produce the telltale action above. We need to mark this position as our upwind or pointing position for our Genoa track. Now that we have everything the way they should be, we are going to change our heading to a beam reach. The wind will be off our beam. We need to readjust our headsail trim for this heading. The leading edge or luff of the headsail should be pointing into the wind. To do this we must let the jib sheet out to a point that the headsail almost luffs. We are back to the 3 degrees again. Let it out to much and the sail luffs. Pull it back in to much and the sail is stalled. Remember the story about the 3 bears and the 3 bowls of porridge. There is only one position that's just right. That position in sailing is "almost luffing".
When we change course to a beam reach, the twist in the headsail increases at the top of the sail to a point that a large portion of the headsail at the head is luffing. What can we do to improve this situation? We can move the Genoa track as far forward as it will go. When the Genoa track goes forward, the pull on the Genoa leach will increase and the foot will decrease and more of the headsail will be in trim from top to bottom. That means we have two adjustment points for the Genoa track, the upwind position and the beam reach position. In reality, we have more than two positions, but we will save the other adjustments for the next installment of Genoa Track Adjustment.
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Mainsail Twist?
As a sailboat moves through the water, air at the head of the sail is moving faster than air at the foot of the sail. This is caused by drag induced by the water's surface. Air close to the water moves slower than air 10 feet above the water and air 10 feet above the water moves slower than air 30 feet above the water and so on. As we pass through the air, the trim angle of the upper mainsail is pointing at it's trim point and the mainsail bottom is pointing at it's trim point. If the sail maker did a good job, the rest of the sail in-between is also in trim.
A good sail is designed to handle this difference in wind direction from top to bottom with twist. It's cut to provide the necessary twist and with tell tales on the batten pockets, we can verify that twist is correct. The hard part is trying to maintain twist in light air with the weight of the boom pulling the sail down and removing the twist. Holding it up a little by hand normally works OK.
Our job as sailors is to maintain twist. If we pull the main sheet tight so we can point higher, we remove the twist and stall the upper part of the mainsail. A stalled upper mainsail will provide very little lift and a lot of heel. If we have a force trying to turn us over and that force is pushing at the top of the mast, it has a big advantage because of it's location at the top of the mast.
The tools of the trade for maintaining twist is the mainsheet and traveler. The mainsheet sets the twist and the traveler adjusts the angle of attack or trim angle. If you do not have a traveler, you can use a vang to prevent the boom's upward movement and then use the mainsheet for angle of attack adjustments
Quote from: lblindsley on July 05, 2007, 02:39:18 PM
We've noticed that the bow on our CP19 seems to plough into the waves in a choppy sea and 15 kn winds rather than riding high as she does in lighter air. Does this have anything to do with the rake of the mast? Or does anyone have an answer to why this happens?
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A lot of discussion on this bow ploughing thing. I do not think the original poster was asking about lee/weather helm, instead simply how CP19 tends to bury the bow into choppy sea. I have sailed CP16, 19, and 23 and yes, the CP19 does "pound" into chops as oppose to CP16/23 "roll" with the chops. This is due to CP19 has flatter bottom profile that offered a stiff and roomy boat, but not as gentle ride when sailing into chops.
Yes can depower the sail to slow down the boat a bit to get gentler ride, or falls off to take the waves on the quarter. Experiment with both to see what works for the crew.
Well after completing the ASA Basic Keel Boat course this weekend I can say that I've had a lot of bad sail trim on my boat. Learned "When in doubt, let it out!" I have always tending toward keeping things way too tight. Went out today and tried a few things and have found much improvement. :)
-Kevin
Sailing courses are great things!! ;)
It is so easy to trim in too much. Everyone knows when a sail is luffing. But, it's more difficult to tell when a sail is stalled. Finding that balanced happy medium is all part of the fun for us.
RE: the plowing bow. How much plowing is too much. 15 knts with a long fetch could create waves sufficient for any boat to tend to plow. Plow vs. banging: Tsaiapex makes a good point about the nature of the hull of the 19 vs the 16 or 23. It's flatter and tends to slap/bang the trough of waves. lblindley doesn't mention sail trim. But, assuming all is trimmed appropriately, maybe she just has a bone in her teeth. ;)
$0.02: Just keep experimenting with trim and adjustments. There are some good articles out there on sail trim. Then you can base the boat's behavior on your experience and then know what to expect in such conditions.
Hi Multimedia-smith,
'To flatten the jib you move the sheeting point FORWARD.'
To use a good old English expression: Bollocks! Moving the lead forward reduces twist by tightening the leech because the sheet pulls down rather than aft; however, the sail becomes fuller. To flatten the sail in heavy air move the car aft so that the sheet pulls aft rather than down, flattening the sail and opening the leech.
This is a fairly basic fundamental of sail trim and I'm surprised you haven't grasped it before now. A good rule for heavier weather trim is "the harder she blows, the tighter she goes". This comes from Steve Falk, winning racer and author on sailing.
Your comments about the boomvang are also bollocks - on the wind the mainsheet provides so much downward effort that the vang does virtually nothing - off the wind the mainsheet cannot provide the downward pressure to stop the boom lifting and opening the sail so you use the vang. But I digress. The original poster asked if mast rake was causing his CP19 to plough in heavy weather when it didn't in light airs. If he has his forestay too short and has forward rake this may contribute to the problem but I'm inclined to think, and said so, that rake had little to do with the problem, it was more likely to be just a matter of trimming differently for heavier air. I'm still of that opinion.
Hi John S,
I don't want to belabor the point, but the comments on the vang were pasted directly from the North Carolina sailing tips site. Plus personal experience... While you're correct that the main sheet does pull downward when the boom is centered (which is likely to stall), the vang is required to provide that force when on any other point of sail when the boom is extended beyond the centerline. The downward force keeps the "twist" from grabbing too much air and forcing the rail into the water. Likewise, the jib needs downward force to reduce the "twist"... from that same forward sheeting point there is still ample leverage to pull sternward to either create more or less air foil shape in the foot of the sail. These examples are for control under heavy winds... and your quote is correct... stronger winds, sheet it in... hard. What we're talking about is sail shape... flatter.
Generally for average conditions, I sheet the 155 at the very rear of the track when beating and move the sheeting position forward for a reach. This is consistent with both the attached text and my personal experience.
We're leaving for vacation tomorrow, so I won't be able to pick up the discussion for a month. Hopefully we will be on to other more productive topics.
I have heard that the flatter hull on the 19 does "pound" more going to weather in lumpy conditions... but I was under the impression that the characteristic described was caused by too much power forward...
Happy sailing to all
Dale
M-S,
Enjoy your vacation.
The finer points of sail trim are endlessly debated wherever sailors get together. If you were less dismissive of the points of view of others and a little more informed in your own views you would be less likely to be accused of 'talking bollocks", and a more pleasant atmosphere would prevail.
I agree about when in doubt let it out. I always sail my boat loose. Out till it luffs. In till the luff goes away and tell tails sails aft. skip. Let the sail take a shape. Don't make it flat.
Well, This has certainly been one lively discussion and continues to be so. Lest we forget, the reason we sail is for fun...always remember that word. Although I've learned alot from reading the above posts about sail trim, mast rake, and bollocks, the one thing that can't be taught is to know how to enjoy the magic of sailing.
This is why I don't race. I don't want to reduce the magic to minutes and seconds. I want to continue to be captivated by the ship, wind and the movement of both.
As an aside, the other evening, I had a wonderful sail, sort of. Went out for a sunset sail, there was no wind, so I motored out in the bay, drifted and enjoyed a great sunset! Never raised any cloth but had a wonderful time. Of course, I'd rather sail than motor but the point is, great times are a-waiting but are sometimes disguised. I don't want to get to technically oriented that I forget the fun!
Ok, now what were you guys saying about bow plow? I've never sailed a 19, but hope to soon. As far as my 23 is concerned, we get along just fine. She forgives my shortcomings as a skipper, and I try to treat her well and keep her looking sweet.
Sorry I've strayed a bit off subject here...hope it's been informative!
Jon S,
Your reply to me states: "If you were less dismissive of the points of view of others and a little more informed in your own views you would be less likely to be accused of 'talking bollocks", and a more pleasant atmosphere would prevail"
Sorry to take so long in my response, but we only recently returned from our "month of coolness" to the stifling heat that is New Orlean's Summer...
I have to admit I was put off by your reply (quoted above)... I don't think that I've ever been "accused of talking bollocks" or for that matter I can't remember myself or fellow members breaking the code of cordiality to each other in this forum... so much for creating "a more pleasant atmosphere"!
As for being "a little more informed".... I do try to offer informed points of view... (apart from my own empirical observations) I recently came across a link that I had saved that reiterates exactly what I was trying to convey about sail shape. As they say, there is no perfect sail shape as conditions are always changing. Our previous discussion centered on how to de-power sails in really strong winds. Everyone knows we want full twist and deep camber in light air, but in heavy air, flatter is better. To achieve flatter, downward force is needed on the leech... the vang controls that on the main and sheeting position does it for the jib.
Here is a link to my source for the info:
http://www.wb-sails.fi/news/98_11_PerfectShape/Main.htm#
to quote the article:
While the heeling force grows in a quadratic manner with wind speed, the heeling is best controlled by feathering the sails (twisting the head off) and flattening them especially in the upper part. This lowers the aerodynamic center of effort, making it possible to keep the boat upright.
The article is long and has a wealth of information as does the NC sailing site... It's fun to study and then to put into practice to see what works.
Let's keep it positive and stop talkin that trash!
Dale
Just an FYI.
Any time I hit the link in the above message, my security software goes ballistic. States it's a dangerous website. I don't know much about these things, but I can assure you it's consistent. My software has not given false positives in the past. Has anyone else received such warnings?
Too bad, really. It looked like it would be very informative. Maybe it has to do with it being Finnish, who knows.
After the warning, I did read the article you linked us to, Dale. I found a few points contrary to what I learned over the years. That's OK. I'm open-minded about such things. But, I can't help but wonder if things might be lost in translation (Finnish and what not). I'm not trying to make any weird claims here, but I do keep a skeptical eye out.
Yea, I know, my mind is open, but my eyes are skeptical. Paradoxes abound. ;D
Regarding the sail trim issues, it sounds to me that John, Dale, and the quote from "The Sailboat Company" are all talking about the same animal, but different parameters, making this discussion somewhat dead-ended.
I love the simplicities and complexities of sailing. I know, another paradox. But, that's part of what makes sailing so wonderful. There are a number of books and online articles regarding sail trim. Just remember to keep the principles in context of the given sailing environment. (And, in English, to boot!) ;D
Well, this is a lively thread!
I have sailed both the 16 and 19 a lot. Both boats bow down in a gust and the 16 does tend to weather helm with more force than the 19.
The 16's bow is shaped like a football. No matter how you heel it it keeps its shape.
The 19's bow is like a dinner plate the whole way back to the keel. There's almost no shape. In a chop and going to windward it slaps every wave. If the waves are about 8 feet apart the bow will ride down the wave and plow in.
I have never seen either boat ride bow down for more than a moment and its always when hit by a cold spring or autumn gust. Might sound silly but I swear its partly due to the jib getting hit first by that gust.
I wouldn't adjust the rake.
Also, I experienced some very bad performance from my old original sails. The people at North sails showed me the difference between old and new. My old sails weren't pulling the boat forward. The shape was gone and I was getting excessive heeling force. New sails made for a new high performance old girl!
Finally, I think the 19 is designed really well for what it was intended to do. The compromise is the slapping sometimes from that flatter bow. I accept that over the 16's tendency to heel so much and roundup so quick. The 16 scared the crap out of a lot of passengers in heavy weather, whereas the 19 can be very sedate and yet sail faster and point better.