Tech Talk #6 – Let’s Just Cool Down

July 2021


One of the few, ongoing niggles with ‘Opal Lady’ has been the engine room temperature. For those who have followed us for some time you may remember we first looked at this back in 2017. For the purpose of today’s Tech Talk, it is worth a quick recap.

‘Opal Lady’ was originally fitted with 2x Dayton Model 1TDP6 PSC Blowers in the engine room.  These were designed to extract air from the engine room and induce fresh air to enter through the louvered vents near the rear salon door, in addition to that air required for combustion for the main engine and genset. These are quite small 240 volt fans and in our Australian climate quite inadequate for the job. During a run from Busselton in Western Australia’s South West back to our home port of Mindarie in 400 C (1040 F) heat, we were experiencing temperatures in the engine room of 540 C (1290 F) which was not acceptable, so a solution was looked for. After reading through others’ similar experience on the Nordhavn owners website and what actions they took, I decided to upgrade the 2x exhaust fans to 2 x Dayton 1TDT3 230v fans with a much increased airflow.

Stbd exhaust fan (added axial fan on far left)
Port exhaust fan (added axial fan on far right)

In addition, I added 2x 240v Orion 9” axial fans, linked into the engine blower fan circuit to circulate air around the engine room. With these changes, the overall layout was as shown in figure below;

Air flow schematic after axial fans added in 2018

On subsequent, short 3 hour runs to Rottnest Island off Perth, initial measurements showed temperatures had consistently dropped below 500 C (1220 F). Problem solved, or so I thought. In the last two years as we have made our way up the coast of Western Australia and over the top to Queensland.  What became apparent was that for short runs, the engine room temperature, while not great, was adequate at below 500 C, but for longer runs the new layout was still not reducing temperatures sufficiently. This was especially so while in the tropics, where the thermal load increased as the fuel heated up on longer runs and outside temperatures were in the low 30’s C (90’s F). Engine room temperatures were once again well over 500 C. Very frustrating and a further solution needed.

While down in Sanctuary Cove on the Gold Coast for some months as described in our last Tech Talk, I decided to bite the bullet and hopefully tackle this problem once and for all. Acting on our friend John’s advice, I engaged a company located on the Gold Coast called Marine Airflow International (MAFi). Mark and his offsider came onboard and carried out a ventilation survey with the engine and all fans running. A few days later Mark came back with a solution which can be summarised as follows.

  1. The current ventilation was substandard. The amount of air moving through the engine room was well below optimum with 196l/sec coming in through the inlet vents to support combustion and only a further 160l/sec extraction capacity. This gives a roughly 300l/sec in total whereas MAFi’s preference is for the volume of air in the engine room to be exchanged once every 30 secs. This is over and above the combustion requirement. In addition, they allow a further 30% for vessels operating in the tropics and another 20% for dry stack vessels. The end result is that ‘Opal Lady’ requires ~870l/sec in total. No wonder the engine room was getting hot!
  2. The axial fans, although helpful in moving air around the engine room, don’t help in cooling or the fundamental issue of not enough air.
  3. To remedy this, the recommendation was to install 2 x 12”, 12V axial fans with a capacity of 700l/sec each in the inlet vents. Although this was more capacity than required it was the closest fan that met the requirement and quite frankly, having additional capacity was a luxury I was happy to have. These fans would be controlled by two manual variable speed controllers so the fan speed of each could be adjusted to meet varying conditions.
  4. The other interesting recommendation was to install a set of mist eliminator grilles. With the increased velocity of air going into the engine room, the likelihood of salt mist entering also increases and these grilles are designed to remove fine and heavy water particles. A video showing how they work can be seen at .
  5. Lastly MAFi only supply the solution and the components, the owner either installs it themselves or gets someone to do it for them. In my case I had no problem deciding to do the install myself and organised a recommended marine sparky to do the electrics. I did not want to do the electrics myself as I wanted the fans linked into the sea-fire suppression system (so that in the event of an engine room fire they would automatically be tripped-out with the other fans) and that was beyond my current level of technical expertise.

After installation, the new layout would be as shown below;

Air flow schematic after 2021 fan installation

After reviewing the quote (which was quite reasonable for what you got), I also visited the factory on the Gold Coast. This proved to be very interesting, and the cleanliness and neat layout was a pleasure to see. From there I confirmed the order of 2x 12” fans, 2 mist eliminator grilles and 2 manual speed controllers. Around 3 weeks later all the bits were delivered to the boat and it was time to start putting it together.

Firstly, the quality of what you got was exceptional. Apart from the key bits themselves, you were also provided with all the glues, screws and bits and pieces to do the job. Even down to masking tape! This would be the first job I have undertaken where I am not off to the chandlery or Bunnings every 5 mins to get something I have forgotten.

Rear of the new baffled grille

A clear set of instructions was also provided which not only explained how to fit the grills and fans but also what fixings, glue, tape etc. to use with each component.

Mist Elimination Grilles

These were simple to install and just involved removing the old grills, cleaning up the face of the vent surround, drill and tap new holes for the new grills and install with appropriate fixing.

Original stainless grille (removed)

To ensure the process was hassle free, MAFi had taken one of the old grilles to use as a template which worked a treat. One thing to note is that the new grilles are finished in a powder coat finish rather than being stainless steel which looks absolutely fine.

Air intake opening prepped for new grille installation

In terms of timing, the whole job only took a couple of hours including clean-up.

Completed grille installation

Fan Installation

As part of preparing the quote, MAFi measure up where the fans are going to be fitted to ensure the fans will fit. In our case, and this is apparently quite common, they made up bases to which the fans are fitted which are then screwed into place.

This installation was a bit more fiddly, as it is a bit tight for access for human types at the back of our lovely N43 ‘Opal Lady’, so some level of contortion is required. In our case some hoses also had to be moved slightly to ease installation but again no big drama. The key is to take your time.

The only modification I made to what was provided was to apply strips of the ever-useful 3M VHB double sided tape to the fan base before installing. Not only did this make it far easier to install the fans but also should dampen any potential vibration (not that I expected any).

Port vent intake prior to installation of new fan
Base for the new fan in place
Port fan installed waiting for wiring

In terms of timing, I did this over two days spending a couple of hours on each fan. Due to the restricted access, after completing one fan, that was enough for one day and I needed a cold beer to take out the kinks. As usual in these sort of restricted installation jobs the key was to have all tools and parts ready before you start. In the case of the starboard vent intake, having a handy assistant (Susan) was also needed as this intake access was even more restricted being behind the Genset. Susan had to get in and do up a couple of the screws as I just could not fit into where I needed to be to see what I was doing.

A tight fit
Stbd fan installed and wired in

Electrical Installation

For the electrical work I was put onto Ben from “On Board Electrical” by 3 different persons and companies as someone whose company did good quality work. It took some time to get the quote done but this was simply a reflection of how popular and busy this business is.

As discussed previously, I needed to be able to have these fans hooked into the fire suppression system. In addition, I needed to find somewhere to install the manual controllers, as there was simply no room left in the pilot house. Finally, the system needed to be connected to a circuit breaker in the main 12 V panel.

Ben was great, as was the team he sent out to do the install. We decided to mount the controllers in one main box for simplicity and found an ideal position between the upper water tanks as you enter the engine room. This also allowed us to have individual circuit breakers for each fan also installed, in addition to the main circuit breaker in the Lazarette. This suited me, as I could then adjust the variable speed fans immediately if required when I do my regular engine room checks while underway. The work was completed in a few sessions over 3 separate days with the final product looking very neat and professional. The only slight hiccup was we had to order in a new relay for the sea fire system to allow the fans to be hooked in, but no major drama.

Speed control box being installed
Installation of control box complete (aside for conduit for exposed wiring)

Results To Date:

As it turned out, when we left the Gold Coast the weather was fine for a couple of days, so after anchoring overnight at Bribie Island we decided to do a non-stop 2 1/2 day run through to Port Clinton, an isolated estuary south of Shoalhaven Bay. So that we didn’t get held up waiting for high tide at the Wide Bay Bar, we also decided to run up the outside of Fraser Island. To better understand the effect of the new fans we started off running for 12 hours without the new fans operating.

To monitor engine room temperatures, I have one digital thermometer in the engine room entrance near the exhaust fans, and another (wireless thermometer), near the air filter intake on the main engine. Considering it was still winter with daytime temperatures of 230 C (730 F) we were seeing engine temperatures of around 460 C (1150 F) maintained. From there I tried the new fans at various speeds to see the effect on temperatures. With the fans at half speed the temperature dropped to around 400 C (1040 F). At full speed the temperature dropped to a steady 330 C (910 F). For the remainder of that trip to Port Clinton I ran the fans at three quarter speed which gave us a steady 360 C (970 F). The other interesting outcome was that the thermometer near the main engine air filter intake was generally a couple of degrees cooler than the other one which makes sense being on the air intake side.

So, all in all I’m very happy with the results to date. It is now pleasant to do the engine room checks and I am sure it will be far better for all the engine room components as well. What next you ask? The results have been pretty impressive, so much so that I am going to trial removing the mid port side axial fan from the circuit as I am not sure how much contribution it or the Starboard mid axial is now making. To be blunt, if it makes very little difference temperature-wise, I would be happy to get rid of it as my head bears the scars of hitting the damn thing almost every time I go past it.

[Update November 2023] Peter has now removed both the portside and starboard axial fans that he had installed some years ago (the ones he insists on hitting his head on). The recently improved airflow in the engine room has not been unduly affected (and the likelihood of Peter having to retire from the boating life due to a concussion injury has been markedly reduced). Having now completed several long trips including from Cairns, Australia to Port Vila, Vanuatu,  there is no doubt this upgrade has been successful.

We have included the following link if you would like to consult with the guys at MAFi regarding your engine room ventilation (we don’t get anything for the link – just being helpful);

This Post Has 4 Comments

  1. Hi, I’m in the same boat, an N46, here in the Philippines. The ER temps are usually 45 – 50c. There are not many technical services here so I’ll do my own ventilation upgrade. Those dc fans look like auto radiator fans? If I may inquire, what are the noise levels like and do you need/use the speed control much?
    Any assistance would be appreciated.
    MY Tiger Balm

    1. Hi Peter
      If you are standing next to the ventilation intakes you can definitely hear the fans, especially on full speed, but in the pilot house the noise is negligible. I do use the speed controls as in cooler weather I do not need the fans on full speed. I generally run on 3/4 speed at the moment but with increasing temperatures will probably run more on full speed. I like the variable speed for when we’re down in lower latitudes which may not be such an issue for you.
      Regards Peter

  2. Hello Peter and Suz.
    I’ve been enjoying your journey from the start and it it always an enjoyable read. My better half and I are a couple of years behind you with our boat currently in Darwin while we’re locked down in NSW. It’s always good to read about repairs, modifications and improvements to other boats that are being used as they should.
    Your latest blog was a reminder of the high temperatures in our boat Jasmin’s engine room when under way on a long transit. The 8V71 Detroit makes enough heat to keep a small inland settlement warm in winter.
    Safe travels. Phil.

    1. Hi Phil
      Nice to hear you enjoy the blog. High temps in the engine room is a frustrating issue and for those of us who spend a lot of time in the tropics it is an especially hard problem to solve. I can highly recommend professional help as that has certainly helped us.
      Hope you get back to enjoying ‘Jasmin’ soon.
      All the best Peter

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