Hello All!
Sorry I have been off the air for a while. Time is a problem when you have more to do than running a Blog. But I am writing some interesting articles to post in the next week or so so stay tuned. Comments are welcome. If you have any questions pertaining to small craft design or marine electrical/electronic systems please send them along.
If you have ever installed or replaced a commercial circuit breaker or fuse panel then you need to ask yourself… Have I ever heard of the”Total Cumulative Current” specification? Most people probably haven’t and this will include people who do this type of work. The more familiar specifications such as number of positions or fuse/breaker positions, the current ratings of the individual breakers/fuses, the size description are pretty much self explanatory. But a more obscure specification is the “Total Cumulative Current” specification sometimes called ” total current draw” or “max amperage” on the product data sheet. This specification tells you how much current you can draw from ALL of the circuit positions at one time. If you exceed this spec you may be on your way to a panel failure or worse a fire. Here is an example, If you have an 8 position panel with eight 15 amp circuit breakers or fuses installed, you might think that you can draw about 15 amps from each circuit simultaneously. This means drawing 120 amps total out of your panel. But wait, the total cumulative current rating of this panel might be 100 amps. This means you would be drawing 20 amps more than the panel is rated for. This will overheat the main panel feed wire and could potentially cause a fire. You must keep the total current under 100 amps.
Most installations probably will not exceed the total cumulative rating. However if you are installing a panel and are trying to keep costs down you may want to get the most out of a smaller panel by heavily loading each breaker/fuse position. In this case you may find you are overloading your panel. To avoid this, plan your installation carefully and do not try to shortchange yourself on breaker positions. If you have a lot of electrical equipment and need many breaker positions, you may need to divide them up around multiple panels. You may come away from this with the idea that designing your system will be harder but keep in mind that how much power you need is somewhat dependent on how big your boat is. A larger boat could potentially hold a lot of equipment and probably require a couple of panels minimum to do the job, but a small boat may easily get along with a single 8 position panel. The number of panels needed and the total current draw from the panel(s) may simply work itself out based on boat size and complexity but check it anyway! Also, the number of panel breaker/fuse positions do not determine the “Cumulative current” specification. In other words a 16 position panel may not have a larger cumulative current draw than an 8 position panel. So always CHECK THE DATA SHEET! Panels from different manufacturers do not have the same specifications just because they have the same number of breaker/fuse positions.
With this new knowledge take a look at your existing panel(s) or your new installation and figure out your total current draw to see if you are exceeding your panels limit. You will need the panel’s data sheet to figure this out. When you are doing this calculation, carefully assess whether or not all of your equipment would ever realistically be “on” simultaneously in normal or abnormal operating conditions. Under these conditions everything may be okay BUT if there is a chance that every load on your boat can be turned on simultaneously (such as kids playing) and that in turn could exceed your panels cumulative rating, then either change your system design or make sure someone is ALWAYS monitoring what is going on on your boat. You are the captain and ultimately responsible for everything that goes on on your boat.
The Calculations:
Calculation 1
Calculate the total current draw from each breaker/fuse position on your panel and add these current values together. This normally will not be the actual breaker/fuse rating installed.This total quantity must be less than the panels cumulative rating. You need to know the current draw of all of your equipment to do this calculation.
Calculation 2
Sometimes you can multiply the total number of positions by the breaker/fuse value (if the values of fuses/breakers are all of the same) and if that value is less than the cumulative current then you are good to go without looking up the current draw of all of your equipment. This works for the smaller panels (less than 8 positions) but for the bigger panels you need to know all of your current requirements and add the amp values all together like calculation 1. This second calculation is also dependent on the panel’s manufacturer.
The best way to do the calculation is by using Calculation 1. You need the current draw of all of your equipment to do it, but you should know what all of your equipment draws anyway, particularly if you are doing a new installation.
Here is Part 3 of my 4 Part Marine Electrical article. This article is about Fuses and Circuit Breakers. Circuit protections devices are as important as determining the proper wire sizes when designing your electrical system. Use this article with the other two articles on Marine Wire listed in these posts
Click on the following link: Fuses and Circuit Breakers
I am going to be doing a comparison of circuit breaker based marine electrical panels in the near future. Having installed panels from Blue-Sea, Sea Dog and other manufacturers. I have found that each manufacturer offers an advantage or advantages to a boat but you have to be careful to understand what you want and need before you buy. There are some characteristics of these panels I think are important that some manufacturers do well with and others do not. If anyone has anything they want me to look at or cover please tell me in the next few weeks. These panels are the heart of your power system and it is vital that you get what you need and understand your panels limitations.
Happy New Year to All! The Holiday season keeps most of us pretty busy and for most the boat boat projects are put on hold, no exception here. I did manage to find some time early in the Holiday season to do more work on the jon boat. I decided to change the LIVE WELL into a storage box. This WELL is not water tight from the top so the storage may be limited to objects that can get wet, but at least these objects (like rope) are off the sole. Also I am thinking about ways to make the well lid watertight. But here is what I did to the LIVE WELL. The following picture shows the LIVE WELL as it came from the factory.
The WELL is un-coated aluminum with a drain at the bottom. I cleaned and wire brushed the insides of the WELL until it was clean, then spray painted the box with etching primer for aluminum (Krylon product) than painted the inside of the WELL with 3 coats of pick-up truck bed paint. This will give the inside of the WELL a scratch resistant surface as well as to prevent pitting corrosion from items in the WELL that get wet.
No reason for the black color other than it will look good with the final paint color of the boat.
The next project to tackle on this boat will be the completion of the transom. Stay tuned.
Wishing you and yours a great Holiday Season and successful New Year. Especially all of my fellow boat builders, maybe this is the year your project will be finished and feel the water!
As a designer and builder as well as a marine electronics/electrical technician I have seen boats become in some instances large collections of electrical ‘things’ along with large battery banks to feed these electrical goodies. If you are building your own boat and it will have electrical equipment on board beyond the engine starter and maybe navigation lights, read on.
Depending on the size of the boat and what ‘things’ you want or need, having a professional help you or do the planning and installation might be a good idea BUT in my opinion there is a level of complexity an amateur can take on with the right knowledge and information that does not require going to school. What is this level of complexity? First keep your systems to a minimum. You will probably need navigation lights, maybe some cabin or utility lights. You may want a fishfinder or depth sounder, possibly a VHF radio, maybe a small chartplotter/GPS. You will need or should have at least one bilge pump, a horn, maybe a sound system. This is a reasonable list though not complete that could be handled by an amateur builder. What you don’t want to tackle for your first major project, dual 12/24 volt battery systems, lithium batteries and you might want to think seriously about having AC power stuff on board utilizing shorepower. AC power requires a lot of care. The advantage of doing the work yourself is twofold. First you save labor money and secondly and more importantly, you understand your electrical system and will be able to add to your system and repair your system, particularly if you are on the water. I will be posting a procedure for planning your electrical project along with postings to develope the knowledge needed to be successful at doing your own project. After you build your boat, planning and installing your own electrical system is a real feather in your cap.
As mentioned in the post on November 25th, we were getting ready to tackle repairing the after section of the jon boat because of severe pitting corrosion that ate through the hull bottom due to florists foam put in place of regular flotation foam during a previous repair.
Port side. Holes with rivets are in the black circles.
Starboard side. Holes with rivets are in the black circles
What we did first was to clean up the aluminum in the areas of the pitting with a wire brush and determined where the pitting created holes in the hull and where it only did mild surface damage. We identified holes on both sides of the hull and also determined the holes were the only serious damage. Some of the other surface damaged by pitting were shallow. We then applied Rustoleum Self Etching primer for the undercoat then painted the surfaces with a Rustoleum camouflage color. After drying we drilled out the pits with 1/8″ drill. Luckily none of the pits themselves were larger than 1/8″. We then applied a 2-3mm coating of 3M 5200 all over the areas. (in the photos it is the orange color, the camera flash distorted the actual color) using a plastic spreader. This layer of 5200 smoothed the hull surface by filling in the eroded areas. We then inserted rivets in all of the holes while the 5200 was still wet. The 5200 seals the rivets, making sure the rivet will not leak over time. If the pitting areas were deeper or more holes found we might have placed an aluminum plate over the area using the 5200 as an adhesive. As it was we feel the rivet solution was the best for this repair.
The next repair is the transom. The plywood stiffener was rotted and needed to be replaced. Stay tuned.
After we moved to Georgetown, South Carolina, I joined the South Carolina Maritime Museum. The first project I got involved in was to develop model plans for a two masted freighter that was recovered from the Black River in Browns Ferry, South Carolina. This boat has been dated by nautical archaeologists, to have been built in the early 1700’s. The first research model was built in the mid 1970’s by Richard Steffey.
Steffey’s Model. Built at 1/10th scale
This Browns Ferry Vessel was found in 1971 by divers exploring the Black River and at that time was the oldest boat of its kind found in the United States. A nautical archaeology professor, Richard Steffey from Texas A&M University was the first Nautical archaeologist to examine the recovered vessel. At this point it was called the “Browns Ferry Vessel” because that is the location where it was found. Subsequent research could not find any record or history of the vessel so the name stuck. It is deceiving because it makes you think it was a ferry boat, which were plentiful in the area back in the 1700’s. But the Browns Ferry vessel was a freighter and as a matter of fact when it was found it still had its cargo of 10,000 building brick. Brick making was a side product of many Southern plantations and the Browns Ferry Vessel (BFV as it is also referred as) was carrying a load of bricks when it sank sometime in the mid 1700’s, sinking dated by artifacts found on the vessel. The vessel is 50 feet long and 14 feet wide with a draft of 3 feet.
The BFV coming out of the PEG tank.
The vessel was fully recovered in the late 1970’s and sunk in a preservation tank for 9 years. The tank was filled with polyethylene glycol (PEG),a wood preservative which soaks in the wood and replaces all traces of water with PEG. The wood can now stay in the air without rotting. The BFV was removed from the PEG tank in the late 1980’s and eventually wound up in a museum in Georgetown, South Carolina. The museum that holds the BFV now, is named the “Rice Museum”. It was the only museum in Georgetown at the time that could host the BFV. The roof of the Rice museum was removed and the BFV was lowered into the top floor and the roof then replaced. The boat and the first model are still in the Rice museum.
My involvement in the BFV through the South Carolina Maritime Museum was to build a model of the BFV for our museum. When I researched all of the literature on the vessel to design the plans, I come across the the debate about the stern of the BFV. Steffey and others felt that the BFV was a “double ender” meaning the bow and stern were pointed. Others disagreed, they thought the transom was flat. As Steffey was the lead investigator, his model was built as a double ender in the mid 1970’s. When the BFV came out of the PEG tank another Nautical archaeologist (Dr. Frederick Hocker, a former student of Steffey’s) thoroughly examined the vessel and did determine from planking runs that the vessel had a flat transom. Hocker shared his findings with Steffey who agreed with Hocker that the BFV did indeed have a flat transom. A few research models were built by Hocker to check the plausibility of the planking and flat transom. None of these were ever finished to a complete display model until I designed the plans for the South Carolina Maritime Museums model. In consultation with Dr. Hocker I developed the plan set for a display model with the flat transom. The following photos are the final result.
As I am not a well experienced model builder, the model was constructed by another museum member, Bill Brady who has been building model ships for over 30 years. I generated 30 drawings of the BFV and all of its structures based on literature research as well as having the remains down the street at my disposal. I modeled this vessel using Rhino 3D, a 3 dimensional design program that I use in Yacht design. The drawings I created could be used to build a full scale replica of the BFV if some one wanted to and had the money. The drawings were scaled down to the model size and between Bill and I, the model was built and is now on display at the South Carolina Maritime Museum in Georgetown, South Carolina. You can see that the two models do not look much alike. This is due to the fact that Steffey had very little time to examine the BFV because of the need to get it in the PEG tank. Hocker was able to spend plenty of time examining the remains and could study the BFV in fine detail. So based on his research the vessel is a little different in structure than what Steffey originally thought.This model is 1/10th scale like the original. At this scale, the model is 5 feet long, 16 inches wide, and 4 1/2 feet tall. This was a very satisfying project and I am looking forward to a couple of similar projects in the near future. Stay tuned.
The finished model on display
If you read the article mentioned in the post on “Marine Wire” you are ready to read the next article. This article is on sizing the wire for your boat project. Determining the right wire size is CRITICAL to your boats safety in terms of fire safety. Overloaded wire will almost certainly cause a fire on your boat, a situation none of us want. In addition to fire safety, the proper wire size does affect the operation of most of your electrical equipment on board your boat. Read the article to find out more by clicking this link.