Basic Concepts and Techniques

Moderator: GreenLake

How to careen your boat

Postby GreenLake » Mon Feb 22, 2021 5:46 pm

Sometimes you need to access the underside of your boat. Perhaps to free a stuck centerboard, or to remove one for repairs. Or to inspect for and fix some damage.

There are many techniques for how to achieve that, but let's focus on careening your boat, as this is the one technique that you'll need if you find yourself in an emergency situation.

This works in shallow water or if the boat is beached. With the boat afloat at a dock you can use the same technique if you need to get at something higher up on the mast. You can also do it in your yard, by launching the boat from the trailer onto the lawn or a bit of old carpet (to prevent scratches).

Careening.GIF
How to careen your boat
Careening.GIF (9.78 KiB) Viewed 4592 times


The mast needs to be up and the rig tensioned, but if you aren't sailing, you wouldn't rig the boom. If you are out on the water, you'd secure the boom with topping lift and mainsheet.

When you have the boat beached or on the ground, you take the jib halyard or spinnaker halyard and pull sideways. If in shallow water or at the dock, you may need a helper to hold the boat so it doesn't just follow your pull. Once you get the hull to rotate, it will get progressively easier to counteract the righting moment. With the boat horizontal, you can tie the sheet off to a concrete brick or a bucket filled with sand and it will hold the mast down.

Note that the diagram shows the jib halyard and not the main halyard. The reason is that the main halyard exits at the top of the mast, which is unsupported. This is of particular concern when you have removed or no longer have the jumper stays. (They aren't needed otherwise, so it's fine to remove them, just be aware that you then can't use the tip of the mast to careen your boat).

The jib and spinnaker halyard sheaves are near the point where the shrouds meet to stabilize the mast. If you pull at that point, the loads get taken up by the shroud and you don't end up bending or breaking your mast. That's the reason you want to make sure your mast is properly supported and the rig tensioned before you careen your boat.

The whole process takes only a few minutes and is great for freeing a stuck centerboard or to make a quick repair to a broken uphaul or downhaul. With the boat on its side, you have convenient access to both the opening of the centerboard trunk, as well as the centerboard controls on the inside.

At the dockside, you should be able to get the boat to float on its side in order to reach a wind indicator or fix something that has gone wrong with a halyard. You probably need to empty the boat and later bail it, while freeing a CB for a beached boat can be done even with a boat that's loaded. (You may need a helper as it will initially quite strongly resist tipping).
~ green ~ lake ~ ~
GreenLake
 
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Displacement Mode

Postby GreenLake » Thu Jun 16, 2022 12:48 am

As the name says, this is the mode where the hull displaces water, in other words, it pushes it aside. That creates a bow wave, which will take some energy, causing drag. At low speeds, other forms of drag, for example drag from the water flowing over the hull, so called skin friction, may be the more significant component. Therefore, light wind sailing techniques involve methods to reduce the wetted surface, or how much the hull is immersed. That was the reason for the advice covered in “Light Wind Sailing” to heel the boat to leeward.

Displacement-mode.GIF
Displacement mode at slow speeds
Displacement-mode.GIF (46.47 KiB) Viewed 1752 times


The bow wave that the boat produces has the speed of the boat. That first wave crest, after all, travels with the bow. Now, one interesting feature of surface waves on water is that longer waves go faster (and shorter ones go slower). That relation holds even if you create a wave of a given speed: the faster the bow wave, the longer the distance between crests, or its wavelength.

On a day with variable low winds you should be able to observe that the tiny ripples that your boat makes when it barely moves are much closer together than the bow wave once you get going.

Also, as you speed up, more and more energy is needed to create these faster waves. At some point, skin friction becomes less important than wave drag and your sailing technique adapts: it’s faster to sail the boat flat.
~ green ~ lake ~ ~
GreenLake
 
Posts: 6800
Joined: Mon Jun 18, 2007 3:54 am

Hull Speed

Postby GreenLake » Thu Jun 16, 2022 12:58 am

If you end up going so fast that the length of the bow waves becomes twice the boat’s length, your stern is in the trough and the bow rides up on the crest. You literally sail uphill. As you approach that speed your wave drag goes up very rapidly to the point that you stop going faster from just a little bit more wind. This limit to your speed is the hull speed. Because it depends on the wave length, which is related to the speed by basic physics of water waves, your hull speed depends on the length of your waterline (or rather, its square root).

Hull-speed.GIF
Hull Speed Limit
Hull-speed.GIF (47.79 KiB) Viewed 1752 times


The formula is Hull speed (in knots) = 1.34 * Waterline (in feet). For the DS that works out to about 5.4 knots. This is an idealized value. Hull shape has some effect and you’ll find that you can push your DS to a bit over 6 knots while still basically in displacement mode. Some people call this extra range the “forced mode”. (The exact figures depend a bit on the hull shape's "prismatic coefficient".)

As you approach hull speed, you’ll notice that there is also a pronounced stern wave and that the wake you are leaving behind will begin to look a bit like that of a powerboat. These drawings are too schematic to capture those details, go out on the water and observe. Try to accurately guess your speed through water based on the wave system.
~ green ~ lake ~ ~
GreenLake
 
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Joined: Mon Jun 18, 2007 3:54 am

Planing

Postby GreenLake » Thu Jun 16, 2022 1:05 am

Under the right conditions, a relative light boat that is flat at the stern like the DS can climb on top of the bow wave and start planing. Planing speeds can be much faster than displacement or forced mode, and the boat will go over the water in ways that are similar to a power boat. At that point, the boat will level out again and you’ll want to adjust your seating position and sit further aft.

Planing.GIF
Planing
Planing.GIF (47.37 KiB) Viewed 1752 times


Unlike some other boats, the DS does not plane upwind, and it requires a bit more wind to get going on a plane. If you have following wind waves, surfing down on their fronts may be one way to give you that bit of extra push to get over climbing uphill on your bow wave and getting up on a plane.

Some people report that in heavier winds and waves their DS gets to be more controllable when on a plane.

There’s some more to all of that, but techniques for getting on a plane and sailing while on a plane are perhaps a bit beyond the basics and not everyone has the right wind conditions for it.
~ green ~ lake ~ ~
GreenLake
 
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Joined: Mon Jun 18, 2007 3:54 am

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