Coping With Heat

If you have been following Kosmos’ blog, you’ll be happy to read the following. Don’t be confused by this posting. The Kosmos blog is several weeks behind actual events,


From Kosmos, a Nordhavn 43, that has just crossed the Atlantic in 20 days–at 1.97 gph:


We made it!!! 🙂


Kosmos Atlantic Passage Summary


Vessel: motor yacht Kosmos (Nordhavn 43, 43 feet)

Aboard: Eric and Christi Grab, and Colin Rae

Departed: Las Palmas, Canary Islands, Spain on November 30, 2008

Arrived: Pointe a Pitre, Guadeloupe on December 20, 2008

Route: 2768 nautical miles, SW then W

Hours: 480 (20 days)

Fuel burned: ~950 US gallons (3590 liters) (76% of total fuel aboard) Fuel left: ~290 gallons

Averages: 2.91 nm/gal, 1.97 gal/hour, 5.76 nm/hour Generator hours: 15 (= air conditioning and laundry hours) Water used/ made: 550/400 gallons Active fins on time: 99% Paravanes deployed time: 60% Highest seas: ~10 feet.

Average seas: ~6 feet

Highest wind: 42 knots

Average wind: ~15 knots

Failures: Starboard navigation light bulb (replaced with spare) Kosmos totals: 26091 nm, 4424 hours on main engine, 1712 hours on generator




Having the paravanes deployed the majority of the time cost us some speed (~0.5 knots), but the extra comfort was worth it. We had mostly following wind and sea, but there was a mix of no wind and even a couple gale force winds from squalls. At the end we had beam seas and wind. Nine flying fish grounded themselves aboard. We saw 4 sailboats, and 6 ships. Colin is a future Nordhavn 40 owner (hull 65). The passage was a wonderful learning experience for him and he was great crew. Overall it was very successful passage. We will write more details and have pictures on our travel log

( in a few weeks.


We are 4/5 the way around the world. Now it is time to enjoy the Caribbean and then through the Panama canal to explore Central America and Mexico. We plan to return to San Diego in May 2009.


Eric & Christi



And.. on a different topic. I received this email about my blog entry on security a few days ago:




I have been reading your blog on security, and as you say there are different situations to be considered, but I think broadly I would break them down in two major groups, life threatening and none life threatening.


Life Threatening


I think carrying a firearm is a really bad idea, it’s highly unlikely that you are going to have the training to make it effective, and if you have had the training you are not going to have the firepower to make it effective, to my mind it’s a no win situation.


As for hiding on the boat you mentioned the engine room, if the bad guys get on board they are going to want to secure the boat and account for everybody onboard, if you are hiding you are still a threat, and its how they would deal with that perceived threat that concerns me.


I particularly like the idea of heading out to sea, pointing a search light in their direction and contacting the target boat (on high power) to asked their intentions, as for DSC in British radios there is a facility to select Piracy as your reason for distress. Your distress call can always be cancelled if it proves unfounded, and don’t forget this call will keep going out automatically with your current position, until cancelled.


Now, passive defense, I did hear of a story where a yacht was being shadowed for some hours off the African coast , when they repeatedly called, asking the shadowing boats intentions they got no answer. They did however get a call from an American warship which had been monitoring the situation, the Warship asked did they require assistance as they were prepared to launch their assets, the Warship then referred to the other boat as the target, this was all carried out on CH16, not unsurprisingly the “target” turned away and headed for the coast. Your suggestion of a recording, transmitted on CH16 (on low power 1 Watt) may well have the desired effect, especially if it contained an exchange between yourselves and the USS Death Star or at least give them pause for thought.


Non Life Threatening


As for theft of items whilst moored, anchored, or tied up. I think all your precautions are valid I did like the large NRA sticker idea. One idea to secure your tender would be to remove one or all the spark plugs it’s unlikely that the would be thief has a spare set in their pocket and that is assuming they could work out why it won’t start.


Most thieves are opportunist and as you say, will go for the easy option, so the object of the exercise is to make it harder for them, and they will then move on to easier options (Which is why they have chosen this career path in the first place).


In all this you have to get a sense of proportion, the Gun deaths in Britain a year can be measured in hundreds, (less than three hundred) in America it can be measured in thousands, with that information in isolation, I would not come within a thousand miles of your coastline. But as I am sure you’re aware the chance of you being a victim of gun crime is remote and that largely, America is a law abiding country.


Best regards







And on a different topic, and only of interest to those of you who are REALLY into geeky technical details…


During our run to Costa Rica, I noted that my lazarette and engine room were running warm.


I contacted Nordhavn, and they agreed that the temperatures were high, but, not far out of the normal range, given the extremely warm air and water temperatures. Specifically, I was running over 130 degrees Fahrenheit in the engine room, and over 120 in the lazarette.


My primary concern was the lazarette, which is where the inverters and batteries reside. Nordhavn sent one of their techs to Mexico to add an additional fan to the lazarette, which didn’t help as much as I had hoped. The lazarette is a fairly small space and I was able to solve the problem by running air conditioning in the lazarette.


The engine room was a trickier problem. The primary source of heat is the main engines, and it isn’t practical to use air conditioning to drop the temperature. It can be argued that 130 degrees is a hot, but acceptable temperature for an engine room. None of the equipment in the engine room was operating outside its acceptable temperature range, except of course, myself. I definitely wasn’t enjoying engine room checks.


Thus, one of my projects for this winter is to identify ways to lower the engine-room temperature. As I’ve mentioned before, I’m a “warm water” guy, and want the boat configured to feel at-home in tropical conditions.


Jeff suggested I have an independent surveyor calculate the required ventilation in my engine room and lazarette. Here is his preliminary report. I’m including it because I found it quite educational.






2 – 340hp Lugger L1276A2 1800 RPM WOT, 1237 RPM cruise

1 – 25kW NL gen in E/R 39HP 1 – 16kW NL gen in Laz 26HP

E/R volume W/O tanks, including engines = 1226 cu ft

Laz volume including equipment = 833 cu ft

Two existing E/R intake fans, 12” axial, 2052CFM free air, 1940CFM @ 0.125SP each, through two back deck ventilation grills with 115 sq in openings each side. Total intake air = 3880CFM, for cooling and combustion.

One existing E/R exhaust fan, 12” X 5” Dayton direct drive squirrel cage, with a Port side deck ventilation grill with 113 sq in grill openings.

Total E/R cooling air = 2789CFM

One existing Laz intake muffin fan 100CFM

One existing Laz exhaust muffin fan 100CFM.

One existing Laz exhaust muffin fan 500CFM.

Total Laz cooling air max existing ( based on sole intake fan) = 100CFM



340HP + 340HP + 39HP X 2.5 CFM/HP = 1798CFM



340HP + 340HP + 39HP X 8 CFM/HP = 5752CFM



340HP + 340HP + 39HP X 4 CFM/HP = 2876CFM





Genset 26HP X 2.5CFM/HP combustion = 65CFM

Kabola furnace B-17 19.7kW = 26.4HP X 2.5 CFM/HP combustion = 66CFM


Inverter/chargers 4-3500W @ 92% efficiency = 8% loss = 1120W = 1.5HP cooling

Kabola furnace 19.7Kw @ 87% efficiency, est. 3% heat loss = 591W = 0.8HP cooling


65CFM + 66CFM = 131CFM combustion air

26 + 1.5 + 0.8 = HP X 8 CFM/HP cooling air = 226CFM




As always, I should caveat what follows by saying that I am a software developer, not a marine engineer, and my interpretation of this report may be total hogwash, so no promises, but, there are many things about this report I found interesting, assuming I am interpreting it correctly.


Note that the report converts everything to horsepower in order to compute the ventilation requirement. The report assumes that 4 Cubic Feet per Minute (CFM) of air flow is sufficient to cool each horsepower of heat, in a cool climate, and that 8 CFM is needed in a warm climate. In other words, a 100hp engine, in a cool climate, needs 400cfm of air flow in a cool climate, and 800 cfm in a warm tropical climate. This makes sense. The report then adds an estimate, once again based on horsepower, for the air that will be used by the engines, for combustion, of 2.5 cfm, per horsepower.


 It’s also interesting to see the conversion formula of watts to horsepower, and the factoring in of “efficiency”. Whenever power is converted from one format to another, such as: transforming voltage from AC to DC, stepping up voltage, tapping the power contained within diesel fuel to horsepower at the shaft, or using engine horsepower to provide air conditioning, there is some loss in power. Sometimes, the loss of power is small, and sometimes it is large. For instance, a simple voltage transformer might be 99% efficient, meaning there is almost no loss of power during the conversion process, and sometimes, it is relatively large. Note in the example above that the inverters are considered to be 92% efficient, whereas the Kabola diesel furnace is only 87% efficient. [Note: You may have noticed that the kilowatt calculation for the Kabola is wrong. It should show a 13% heat loss. No worries… it’s a preliminary report, and doesn’t materially affect the conclusion.]


You may also have noticed that my Atlas shore power converter is not shown. This is a 25kw device, that is only about 85% efficient. In other words, 15%, or around 3.8kw is being converted to heat in my lazarette. Using the conversion rate of around 1.34 horsepower for each kilowatt, we see that the Atlas shore power converter is dumping the equivalent of 6.7 hp into the lazarette. So, why isn’t it listed? Because the 16kw generator is also in the lazarette. It would be rare for me to run both the generator and the shore power converter at the same time. Thus, the estimate picks the larger source of heat.


The bottom line is that this preliminary report shows why I have heat issues. My lazarette is only moving through 100cfm of air, versus an indicated requirement for 357cfm, and my engine room is only moving through 2789 cfm, versus an indicated requirement of 7,550 cfm.


These numbers seem to indicate that a major boosting of fan capacity is in order, but, I’m much closer to having adequate air flow than a first glance might indicate. We do have work to do, but it’s not that bad.


The Lazarette:


I have ONE 100 cfm intake fan, and 600 cfm of exhaust capacity. Air flow through the lazarette is limited to the lesser of these two numbers. It is creating a situation where the lazarette is negatively pressurized. I’m creating a vacuum when I should be creating a slightly positive pressure, and I’m not moving through enough air for proper cooling. My interpretation of the data is that I want to have 500 cfm of intake, and around 400 cfm of exhaust.


The Engine Room:


I believe the required cfm in the preliminary report is overstated. Most of the CFM requirement is being based on the main engines. The report is allocating around 10.5 cfm to each engine horsepower (8 cfm because of heat, and 2.5 cfm for engine combustion). My maximum normal cruising speed is only 9.5 knots, at which I am consuming only about 200 hp per engine. The calculations are all based on 340hp per engine, which just wouldn’t happen. In other words, the cfm requirement is overstated by 140 hp per engine, or 280 hp, which at 10.5 cfm per hp, is 2,940 cfm. This drops the indicated 7,550 cfm to 4,610 cfm. I have 3,880 cfm of intake capacity in the engine room, and 2,789 cfm of exhaust fan capability. This shows that the engine is correctly positively pressurized, but could use greater fan capacity, particularly if I’m running at higher rpms and the 25kw generator is running. Assuming I’m interpreting the report correctly, a slight upsizing of the fan capacity is indicated.


Cooler Climates:


An engine room should have a reasonable temperature, although I’m not sure what the perfect temperature is. My sense is that the engines are happiest in an engine room that is between 90 and 110 degrees. I added fans to the engine room and lazarette (at the guidance of David Sidbury, owner of the second N68), to deal with this situation. They allow me to set the minimum temperature at which the fans switch on. I keep them set at around 100 degrees, and in cooler locations, I don’t have to think about the fans. They turn on or off, as they deem appropriate.


And, lastly….


I may not post blog entries for the next week. I’ll check in from time to time, and respond to comments when I can. We’re flying to Seattle tomorrow, and we’ll be spending the week packing our home, and moving to a condo. It makes no sense for us to have a home when half of our year is spent on a boat.

– Ken W


6 Responses

  1. Chet: We made it to Seattle!!!

    Roberta thinks it is beautiful and perfect for Christmas. I’m less of a romantic, and just think it is COLD.

    -Ken W

  2. So Ken, did you make it into SeaTac to the Winter Wonderland that is now the Puget Sound area? You can use our house in Everett if we can use your house in Cabo (grin).

  3. Good luck with moving. Right now at my house on Mercer Island we have about 8 inches of snow. Several hills are closed and everything is slow going.


  4. N4061: Thanks for the heads-up. I checked, and Trawler Fest is scheduled for Feb 26th to Feb 28th. We currently have a conflict, but I’ll see if I can move some things around on our schedule. We’ve always had a great time!

    -Ken W

  5. Ken, not sure if you are aware but there is a Trawlerfest scheduled for late February in San Deigo. I know of a few Nordie’s that plan to attend. May be a great opportunity for you to run up and spend a day or two. There are always a number of new Nordhavn’s hanging around SD marinas. Happy Holidays.

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