Hello Matt: > Picking the kayak up and balancing it determines the position of the centre > of mass of the kayak along its length. Then plonk the boat in the water, and > the centre of buoyancy is at that point. Tell me if I'm wrong.<< > You're wrong. I don't think so. And certainly not by the example you give which follows:- > Put a huge amount of weight in the bow > (only) and find the kayaks center of mass by lifting it at different places > until it balances. Put the kayak in the water and now sit on that balance > point (for the sack of example, say the bow hatch). ... In order to > keep the kayak LEVEL the paddlers weight would have to be further back (far > enough back so that the CofB and the CofM lined up when the kayak is LEVEL). In this example you agree with my proposition above. Rather than continue to talk at odds, and pick up every wrong point, let me state this suggested method for trimming a sea kayak, without dividing your gear into two piles one twice as heavy as the other. We want to determine a convenient method of deciding if a kayak will float at trim, with its paddler and load on board. We pick up the unloaded boat, and find the balance point, which will be somewhere along the cockpit. We note that point. We locate the seat such that the paddler's CofM will be at the balance point just found. We load the boat with gear. We again pick up the boat at the previously found point, then adjust the gear until the boat again balances fore and aft. We put the boat on the water and get in. The boat then floats trim and level. You may care to disagree with this, or introduce other considerations, but it works. >...talking about an empty kayak and how its mass is distributed. On > its own (no paddler in it) it [swede form kayak] would likely sit in the water with a bow down > trim. In order to get a LEVEL trim the paddler will have to sit a little > further back in it than in a fish form kayak. and >You seem to be assuming that when the centers > line up the kayak will be LEVEL. OF COURSE I have been assuming that an unladen kayak floated on the water will be trim and level. It seems to be the case with all sea kayaks with which I am familiar. No kayak manufacturer paints a plimsoll line along the boat like a freighter. Do you know of any kayaks which are not level when they are on the water unladen? Is this anything more than a theoretical point? Can you name a kayak which requires the paddler to place his or her CofM at a point other than at the CofM of the unladen kayak to make it trim? In particular, can you name a swede form kayak that requires this? If you can, the distance will be so small that it will not have any practical effect on the trim method I have described above. > You are correct that a kayak balanced when moving forward will blow at some > angle downwind (where the forces balance) if it is not moving forward. First > you are not talking of a huge difference due to different wind speeds (or > over normal paddling speed ranges) and secondly you have things backwards at > higher speeds. "Wind puts more pressure on the end of a long symmetrical object angled into the wind than one angled away." Hmmm. Think of this: Place a brick at 45 degrees in a wind tunnel, with the long side of the brick across the windstream. Mark one end of the brick "A", and the other "B". Look across the brick from end "A", and then again from end "B". Did the wind pressure on the brick change when you changed your viewpoint? And, we are taking a beam wind as the example here, which I think of as being the maximum weathercocking situation, and not having the kayak angled into the wind or away from it. "Strong winds ... tend to reduce both weather helm and lee helm." Interesting. The worst weather helm experienced is on flat water, such as when wind blows offshore, with very short fetch over low land. Weather helm appears to me to worsen as the wind increases in these situations. In other higher wind situations, when the water is rough, the weather helm effect is hard to distinguish from the push and shove of waves, and wind on the bow at the crest, etc. Although all the forces on the boat are greater in higher winds, you would expect, from say a vector diagram analysis of the weather helm effect, that the weather helm effect rises too. Isn't it just that it is masked by other greater forces relatively? Cheers, PT *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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