Sheer and Shelf Clamp

The chine log is the major structural stringer on the lower part of the frames, and the sheer and shelf clamp are the major structural stringers on the higher part of the frames. These three stringers tie all the frames together and spread the loads around, evenly distributing the forces on the hull throughout the other members.  

The sheer is the top strake that runs on the outside of the frames. The shelf clamp is the strake that runs on the inside of the frames. These two stringers tie the tops of the frames together into a very rigid and strong unit where forces are distributed throughout the members of the hull.

The sheer and shelf clamp also go by many different names which do serve to denote their position, but are not the most correct of terms for these pieces of wood on a boat. 

The sheer is also called the gunwale or outwale. The shelf clamp is often called the inwale. The terms inwale and outwale are rather informative, identifying the strakes that run on the inside and outside of the top of the hull. Gunwale came to be because guns sit over the top of this strake as they aim out towards other vessels. While these names are commonly used, it is still preferred to call them by their correct names: Sheer and Shelf Clamp. 

The sheer is considerably thicker than other topside planks and is ideally made out of a single continuous piece of lumber. If the span is too long to make it out of a continuous piece, scarfing is acceptable and preferred over butting.  

The shelf clamp is crucial as it ties the sheer to the top of the frame and attaches the deck above it. The sheer and shelf clamp are through fastened, tying the top of the frame to the rest of the members with considerable pressure, negating the posibility for any movement to develop and loosen this junction. The deck then attaches to the top of the shelf clamp, forming a very strong component that ties the whole boat together in unison. 

With these two stringers connected, the frames will become incredibly resistant to forces placed upon them as the boat is being tied together. 

Fastening the Chine Logs

The chine logs run through the frame notches at the turn of the bilge and terminate at the back of the stem and front of the transom. The transom has yet to be built and the stem has yet to be attached to the keel, so for now the chine logs simply extend further than they are needed. Once the stem is attached, the chine logs will be cut flush with the back of the stem and set in place permanently. 

The hull turns towards the bow to meet at a central point while the aft section is relatively flat. The hull is composed of five frames, and only the last two are set relatively flat. This means that the front three frames are pretty much in line with each other until the hull curves towards the transom. 

To make installation and fastening easier, I began at the first station and worked my way aft. The chine log was held in place by hand and a pilot hole was drilled through the chine log and into the bottom futtock.  

With the first three stations screwed into place, the chine logs were bent back into place and aligned with the chine notches of the last two stations. As they were held in place, the pilot holes were made and the bronze fasteners were screwed into place, securing the chines and tying the whole hull together. 

Titebond III was also liberally applied to the faying surfaces between the chine log and frame notch, further reinforcing the bond between these structural members.  With the chines in place, the frames already feel much more secure and stable!

Notching the Frames

The chine log needs to be set into the frames at the turn of the bilge. This means that the corner needs to have a section cut out of it which will hold the chine log. If you a building a large craft where proper lofting was carried out, the chine log notch would have been cut when the futtocks were being cut out and assembled.  

Since we are building a small dinghy, we do not have a full set of plans and proper lofting was not carried out. The futtocks were cut out and shaped with no regards for bevels or future stringers, and simple assembled onto the keel where they await further fabrication. 

They say the beauty of building a dinghy is you can make up your mind about the finished product as you go! This statement could not be more true. You start off with a set plan in mind and then modify this plan based on materials you have access to and ease of building. 

The depth of the chine log was cut into the corner using a handsaw. Once the cuts were made, the retained wood was chiseled out in small quantities. The end result was a rather well fitting notch that will retain the chine log and tie the frames together, offering loads of rigidity to the hull of our dinghy. 

Once all the frames were notched, the chines could be test fitted to ensure that they will lay fair and flush with the curves of the hull. 

One important point that does require some forethought is the fasteners that connect the futtocks need to be set in a way that they won't interfere with the chine log. I set the lower screw more inboard and the upper screw outboard. The upper screw and lower screw were set outside the imaginary area that would become the chine notch. This allowed me to simply cut out the notch without needed to relocate any fasteners. 

When Do You Have to Shut Down the Reverse Cycle

As the temperature drops well below freezing, your reverse cycle heater will be forced to work even harder. This will keep you very comfortable while inside your yacht, but can you keep this up all winter long?

It depends on the water temperature where you are moored. The reverse cycle heater works by extracting heat from the water you are floating in, and by default, cooling the water that is pumped out the side of your boat. As the water temperature gets colder, the unit will have to work even harder to cool the water and extract all the heat available.

If the water is too cold, the unit can cause the water to freeze while inside the tubing. When the water freezes, a few things happen: The water stops flowing through the tubing; and the water in the tubing will expand.

When the water stops flowing, there is no more new water flushing through the unit and it will not be able to continue to produce heat. You will notice this when cooler air starts to flow out of the air ducts and the boat will begin to cool down.

When the water freezes, it expands. The problem is most reverse cycle units have metal tubing that does not take kindly to any expansion. Freezing water will usually crack the tubing and wreck the entire unit!

As you can see, running your reverse cycle into the winter months may sound like a good plan for heating your yacht until you factor in the limitations of the reverse cycle unit. 

A good friend of mine who installs and services marine refrigeration and air conditioners gave me some insight on the matter. He recommends shutting them down when the water temperature drops below 40F to play it safe, and an absolute minimum operating water temperature of 38F.

Excellent, now you know that when the water temperature gets below 40F, it's time to shut it down, and if you feel lucky, you can wait until the water temperature gets down to 38F before shutting it down. But how can you tell how cold the water is?

The simplest method is to pull up a bucket of water and stick a thermometer in it. This will tell you what the water temperature is right by your yacht without much involved. If you do not want to play around with buckets of water on frigid days, the other method is to look up the buoy data in your area. 

If you are in the Baltimore, MD area this winter, you can find the water temperature by clicking on the link below

All other buoys operated by NOAA can be found here, and you can search the list to find the weather station nearest your yacht. 

Keeping an eye on the water temperatures can give you plenty of warning when "shut down time" comes. The good thing about water temperatures is they don't change too quickly. If the temperature was acceptable this morning, it will be about the same this afternoon. Things that can make the water temperature fluctuate quickly are rain and snow. If you have a rain or snow storm, the water temperature where you float will change as the new water and its temperature flush out the old standing water where you are.

Shutting down your reverse cycle heater at the appropriate time this winter will keep you warm and the machinery in your boat operational for as long as possible.

Chines

Boats come in a variety of different shapes and styles, but one very simple distinction is denoted in the way the hull connects to the topsides. This area is called the "Turn of the Bilge" and can either be a soft turn or a hard corner. Soft turns are called soft chines while hard corners are called hard chines. Each has its own tendencies and characteristics.

Soft chines are easier to tip and roll around. Sailboats tend to have soft chines since they are designed to heel over and sail on one side of their hull.

Hard chines are considered more stable and are less easy to tip and roll. Powerboats tend to have hard chines as they offer more stability in a boat that is designed to stay upright all the time.

From a construction standpoint, chines offer another advantage: they offer a lot of strength and rigidity to the hull.

The chine itself is called a "chine log" and is one of the structural stringers that run the length of a craft. This stringer is the turn of the bilge and is set into the frames so that the planks can lay flush against it.

This stringer really stiffens up the frames of a wooden boat and transmits considerable amounts of load amongst the frames in the area on that side of the hull. Since the frames work more in unison, the frames can actually be spaced further apart and be made considerably smaller than if the hull had soft chines.

Less weight in frames translates into less weight overall. This is yet another reason hard chines are favored on powerboats where speed is the priority and keeping weight down is imperative.

Hard chines also make initial construction and later repairs much simpler. On a hard chine vessel, there are very few curves and the curves that are present tend to be very subtle. This means that the planks follow relatively straight paths and require very little twisting or bending to get into place. Not having to custom contour each plank means that fabrication can proceed much quicker. If you have to replace a rotten strake, fitting the new plank will also be a much easier endeavor, as it will pretty much be a straight strake that runs its length in a flat manner.

The simplicity in construction is all thanks to the chine. The topsides run down straight and meet the chine log where they end. The bottom planks run from the garboard up to the chine where they also end. There is no rounded section that needs to be fitted with scrubbed planks and corners to fair off as you try to blend a curvature into the turn of the bilge. The planks run along until they get to the corner where they simply stop and start again in a new direction without any effort on the part of the builder.

Ease of construction, ease of repair, and greater stability all make hard chine boats desirable powerboats and dinghies for your sailboats.