I spent the morning enjoying my coffee and checking the weather.
Winds are Still Honking
The winds off the coast are still blowing. A quick check on the Marine Zone forecast and I see that the winds have not abated and are driving the seas into the 6′-9′ range. Times like this if it were not for the ICW I’d be trapped in port.
Wifi Encryption – Known Exploits and Keeping things Private
I use the in-slip time to wash the salt off the boat and modify the encryption settings on my router. Somehow I have accidentally set my internal WiFi to WPA/WPA2 and WPA (Version 1) has a known exploit when it comes to TPIK (Temporal Key Integrity Protocol)
It’s 11AM and my time at the dock has run out. I cast my lines off and pull away from the dock with a bit more throttle than usual as the wind is blowing hard on my beam. Over to fuel dock to fuel up before heading south towards my intended destination of Titusville, FL.
New Smyrna Beach
As I pass an anchorage in New Smyrna Beach I pass several anchored sailboats. New Smyrna Beach is in Volusia County. According to the International Shark Attack File maintained by the University of Florida, in 2007, Volusia County had more confirmed sharkbites than any other region in the world.
Then I come upon SV Da Capo. That’s quite a pink hull!
Big Motor Yachts Look Comfy
Soon this large, comfortable-looking, motor yacht was passing me. Hatteras I believe?
Dredge Islands?
As I make my way through Haulover Canal there is a thin strip of land that is lined with small trees. This kind of natural geography seems odd to me but I encounter it often. I have always believed that you see these thin continuous strips of land along-side canals which are frequently dredged to keep a minimum center channel depth. I have always imagined that it must be far cheaper for the dredge to push the dredged material through a short outflow pipe that starts to build a new island alongside the channel. I have no specific knowledge or experience with dredging so If you do, please comment on this.
I watch as the sun sets.
Burn More Diesel or Arrive at Night?
In this moment I start doing some quick calculations and realize that it’ll be dark before I reach Titusville, FL where I plan to anchor. Luckily this section of the ICW is pretty open and easy to navigate at night. I find my anchorage and let out about 70′ of anchor which is plenty for the 6′ of water I’m in. Coming in in the dark you don’t expect many ICW boats to arrive after you. The winds are forecast to be steady in their direction through the night. I won’t swing around and there is plenty of room between me and my neighbors anchored next to me.
Refined Tastes of Yacht Living
I’m tired and figure I should finish off my fanciest bag of wine before hitting the rack 😉
Today’s route looked something like this…
Random Thoughts
This is a new section that I thought I would add since being ADD & extraverted I often have random thoughts bouncing around in my head that I feel a need to talk about. Today’s thought is for any fellow boaters reading my blog.
Diesel Efficiency
Today’s thought was on Diesel efficiency. Before owning my 1st trawler, I owned three sailboats. As a sailboat owner, I never thought about fuel economy. Now diesel fill ups can cost as much as $1000 rather than $100. This, because my trawler style motor yacht by design has large diesel tanks for long-range cruising. It’s tempting to discuss the days that the wind was pushing my sailboat along for free but this is not about sailboats vs. trawlers. Instead, I’d like to talk about trawler diesel engine power and hull shape. I’m not an expert or this subject it’s just something I have some thoughts on.
Slow or Fast?
There are two kinds of trawlers.
- Slow full-displacement
- Fast semi-displacement
Every boat’s hull displaces it’s weight in water. The more stuff you put into your boat it sinks a little lower in the water. Ancient Greek mathematician and inventor Archimedes first screamed “Eureka! Eureka!” when he discovered this. This is known as Archimedes’ principle.
To push the hull through the water you must push the water in front of the boat down as well as part it to the sides. When it comes to the force required to move a hull forward, hull shape matters. It should seem obvious as you try to push a boat forward quickly that a slender hull with a narrow angled bow and stern will separate the water gently and then put the water back together gently without causing much swirling drag forces at the stern. A hull with a blunt bow and square stern will plow into the water at the bow and have it come crashing back together behind the stern causing eddys or swirling motions that cause the boat to be pulled backwards by drag forces.
Full Displacement Hulls
Slow trawlers are full displacement hulls and their maximum hull speed is easily calculated by this equation and the length of their waterline (the length from when the hull first splits the water to where it recombines it).
Full displacement hull shapes tend to be very round or semi-hemispherical and create little drag. They require a smaller force to push them through the water. However this round hull shape overs little resistance to healing (rocking of the boat). So you often find these hulls using ballast or weight added to the bottom of the hull to keep them upright. Since 1933 fin stabilizers such as Wesmar have been used to stabilize boats. The most modern solutions are active gyro stabilizers such as SeaKeeper. Fin stabilizers require power to move them and create drag in the water. Gyro stabilizers require running a diesel generator to keep them spinning. Full displacement may be the most economical hull shape but stabilization often requires diesel burn.
If you have a full displacement hull you only need a Diesel engine with enough HP to push it along at near it’s hull speed. If you put a larger HP diesel in the boat you will destroy your fuel economy and never go faster than hull speed. Full displacement trawlers will give you the best fuel economy due to tiny fuel sipping diesels. Full displacement trawlers with active fin stabilizers and large fuel tanks can cross oceans. Nordhavn is a popular trawler brand that comes to mind in this moment.
Semi Displacement Hulls
Semi-displacement hull shapes are designed to push water not just aside but down at a rapid rate. The water being pushed down forces the hull up out of the water. Less hull in the water means less drag and you can exceed the max hull speed for the length of your hull’s waterline. This extra downward push of the water means you need to put more HP behind the diesel. You are trading fuel economy for speed. When the waves are not exceeding large, speed can get you out of the weather and to a safe port sooner. You can also move at speeds below your hull speed and be almost as fuel efficient as a full displacement hull. Semi-displacement trawlers will have sharp angles called “chines” in the hull shape that help to create active resistance to healing. Think of a basket ball with a child’s action figure on top of it floating in your bathtub. Your basketball hull form is semi-hemispherical. The round basketball offers no resistance to heal and will likely just roll over with the first wave. Now place a box with square 90 chines at the edges of it’s hull in the bathtub. That same hull shape resists leaning to either side because to do so would displace less water on the side lifting up and more water on the side being pushed down into the water. Recall from Archimedes’ principle that displacing water creates an upward buoyancy force.
Fuel Burn per HP
A rule of thumb often used is that modern diesels burn about 1GPH for each 20HP produced. This number is a rough estimate of how much of your diesel engine’s power (force) you are using to push your trawler’s hull form through the water at the speed you are going. You can double check this number against your diesel engine’s HP/RPM curve.
Slow or Fast Religion
What type of boat you choose is often like choosing a religion. Once you decide you often find yourself defending your decision with great fervor. Debates rage on but I’m just trying to discuss just the basics of the science behind the debate. Often I hear other boaters with much larger boats with twin diesels compared to my single diesel tell me they get twice the fuel economy as me. Hyperbole or magic? I often state that my Cummins Mercruiser Smart Craft display of fuel burn is 2 GPH at about 1400 RPM or 6.5kts of boat speed. This is a rough estimate of course since there are currents, wind forces, drag due to hull fouling, propeller diameter and pitch, etc. that come into play here.
Final Thoughts
There is no perfect boat. Every boat is a compromise. The discussion above is only about the tradeoff between economy and speed. I gave up economy for speed when I went with a semi-displacement trawler. I’m OK with my choice. I understand why others chose full displacement trawlers. Chose your religion wisely!
MV Simple Life 