This is one of a series of brief, no nonsense posts that we call a Tidbit:
noun; small and [possibly] particularly interesting items ofgossip orinformation...
The purpose is to share succinct posts about lessons learned, or things we use or do that work [or don't...] that are common to many of us boaters.
The goal is to garner feedback from those of you having first-hand experience with a better approach/ solution/ product...
We never assume what we are sharing is the ideal or only; it just seems to best suit our needs [and/or habits and/or budget] from our experiences thus far...Sometimes these Tidbits originate from a topic of discussion on one of the forums we participate in, and this happens to be one. [The original forum response- which includes additional details- is linked below.]
Since we encounter this question fairly often- and since it may affect other boaters- it made sense to post a more detailed response for future reference.
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It is rare to find a vessel that doesn't have some type of non forced-air diesel heater up here.
Some people report continuing issues with sooting on deck using this kind of heater.
This post is a quick brain dump listing installation and usage parameters I have found to help minimize sooting. I rarely see any dirty decks- but it can happen.
Below I'll list the ranked causes of sooting with this kind of heater that I've experienced over time.
I have had heaters like this on 4 of 5 boats I've owned over the past 4 decades. All were full time cruisers I used in higher latitudes. (>56°N in the Pacific.)
In Fall 2021 installed a Sig Marine 120 (pretty equivalent to the Dickinson Newport) on our current boat. In winter it is only been off a handful of times (when the boat is unoccupied) since November while we work on some winter projects at the dock. No soot. No backdrafting. (But we have been using this type of heater in 4 boats over the past 4 decades, so the learning curve is well absorbed.)
We find the heater output is too much in our 43 ft ketch if ambient temps are in the 40's °F. We then have to open ports and hatches to keep from overheating on the lowest setting- if we do light it in those temps... (This boat has several redundant sources of heat.)
Our SIGMAR heater is on the lowest setting most of the time- sometimes elevated closer to a medium setting when its single digits above zero F and blowing outside...
What experience can I share specifically about this size and type of heater with a 3" flue? (Following is a dense overview full of hints about things I think I have learned over time- only for those truly interested...)
Here is Dickinson's version for reference.
Installation is important:
- Keep the total flue length a minimum of 6 ft, max of 8 ft
- Straight flue is best.
- If you must dog-leg the flue, don't use more than 2 elbows, and use the smallest angle you can- with nothing greater than 45°.
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| The barometric damper is properly adjusted in this photo of the heater in use. The shield installed on top of the angled flue [to help shield the headliner] and the vertical solid filler [right in photo] behind the perforated flue guard [left, but not showing much in this photo, but is prominent in the first photo of this post] were both fashioned from pieces cut from a single snap together 3" SS flue pipe. |
- Install a barometric damper [see above photo]
- Locate it no further than 24 inches from where the flue exits the heater, and no closer to the heater than 12 inches.
- Be sure they are improperly installed and adjusted.
- Carefully adjust the barometric damper per manufacturer's instructions (I inserted a photo of our barometric damper with the heater on low, above, for reference.)
- Most complaints about sooting are about installs lacking a barometric damper (and occasionally from improper adjustment of one that is installed.)
- Use an H cap (Charley-Nobel) in breezy conditions. We have found it to be consistently better at handling wind gusts than the round version (in our testing and experience.)
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This is our typical flue set-up if expecting windy conditions. The flue extension length was determined by testing different lengths and caps during the same steady 20kt wind conditions. As mentioned in the main text, this 3" flue gets covered with a 4" flue sleave [note to self; need photo...] in cold weather to help maintain inner flue temperature, and consequently draft. [This 4" flue cover adds the side benefit of being cooler, and thus less threatening to bare skin and meltable fabrics the crew might be wearing in winter.] We remove the flue and cap it off when not at anchor or at the dock; photo further down. |
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| We sometimes use a round cap in calm conditions- typically fringe heating season overnighters. |
- If planning to use the heater in temps cooler than about +20°F [-7°C] for extended periods, have a length of larger diameter flue pipe [4 inch diameter covers our main 3 inch flue well] you can temporarily slide over the primary flue above deck to provide a layer of insulation- helping to keep the main flue warm to promote a consistent draft in cold weather.
- This insuilating sleave adds the side benefit of being cooler, and thus less threatening to bare skin and meltable fabrics the crew might be wearing in winter.
- Duct combustion air from an enclosed, vented space (our's draws from the engine room. This is where the bulk of the soot will go if you ever suffer an extreme backdraft. More below.)
- Install a gravity feed day tank if you don't want to listen to a fuel pump burp every second or so while running the heater.
- Install a valve on the tank before the fuel hose.
(Our day tank is filled by the 12 volt fuel pump that runs the tank transfer/polishing loop.)
- The day tank overflows back into the starboard fuel tank when full.
- Install a small shut-off valve at the fuel inlet on the heater. Develop the habit of closing it when the heater is off.
This is a safety against fuel flowing through the overflow- draining the day tank- in the future when the small o-ring on the carburetor needle valve tip fails. (Ask me how I know this.)
- Run the overflow from the carburetor to the fuel tank if possible (vs. an overflow bottle.)
If you do this, install a valve on that port on the heater, and remember to close that valve temporarily when fueling the tank the return goes to- but only if you don't want to back-fill the heater if you overfill the boat. (i.e., fuel up the fuel fill hose- which will be higher than the heater carburetor...) - Remove the above deck portion of the flue when the heater is not in use for extended periods, and always before getting underway.
Secure the flue opening with the water tight cap made for the through-deck fitting installed on your boat.
- #1 diesel (AKA Heating oil; kerosene) burns much cleaner than #2 (The carburetor must be adjusted to match fuel selected. See manufacturer's instructions.)
- When first turning on fuel after preheat, set to medium flame size for at least 10 mins to warm the heater and flue. Then start turning it up/ down a little bit at a time- pausing a few minuites between adjustments for the heater to equilibrate to the new setting. (This is not a thermostat; it is a fuel flow meter... give the heater time to adjust to each new setting.)
What causes sooting? (Note that sooting either vents out of flue top onto the deck, or when back pressured into boat via the combustion air intake in the bottom of the heater.) If [when?] it happens, either Krud Kutter, Davis FSR, and Someone To Do It cream cleaner are the magical soot removers...
Following are the primary reasons sooting occurs, in order of their occurrence from my experience.
- Cause #1: Preheating the heater using diesel fuel with a tissue paper wick as the manual instructs. This causes a build up of soot in the flue and in the bottom of the burn chamber over time.
Instead, we use about 3/4 of an ounce of denatured alcohol [AKA alcohol stove fuel; typically available where paint is sold]- and a long neck lighter instead of tissue paper to ignite it. We pour the alcohol into the middle of the COLD heater chamber, turn the combustion air fan on low; lite the alcohol (the fan being on keeps the alcohol from 'poofing' when you light it.) When the alcohol flame starts going below the burner ring (2-3 mins on average) turn on the fuel flow to a medium setting, and turn off the combustion air fan (unless it is blowing outside... more on that, below.) - Cause #2: On our stove, we ALWAYS make sure the flame is above the 'top burner ring' otherwise there is too much combustion air and not enough fuel = soot. Slightly increase the fuel flow to correct this issue.
Side Note: that top burner ring is removable. Don't assume it is installed correctly. It can also cause a miriad of flame and soot issues if incorrectly installed. (Read the manual!) - Cause #3: Too much fuel and not enough combustion air = SOOT! (i.e., Too large of a flame.)
Either decrease fuel flow, or turn the combustion air fan on and adjust the air flow to optimize the flame.
I believe this is the #1 cause of sooting on deck: people turning the heater up too high in hopes of heating the boat faster. - Related Cause #3.5: As the heater warms after being first lit, in a few hours the carburetor will warm, thinning the fuel it contains, thereby causing the fuel to flow faster. This results in the flame size slowly increasing- perhaps unnoticed- and possibly getting large enough to cause sooting as described in #3.
Be aware of this, and keep an eye on the flame. Always. - Cause #4: Rapid wind gusts (over 35 knots for our installation) COMBINED with negative static pressure inside the boat can snuff out the flame and cause a woof when the still flowing fuel reignites in the hot burn chamber- blowing soot out every small crack and the flue and air intake openings. This is the most dreaded.
It sometimes happens to us when we experience katabatic gusts (williwaws)- typically in glacial fjords in certain conditions. Think zero to 60 knots in under 10 seconds.
Sometimes slightly opening a hatch or port will help prevent a negative static pressure inside the boat in catabatic conditions; and sometimes turning on the combustion air fan and increasing its speed to balance the wind gusts- or a combination- helps prevent the flameouts.
- Cause #5: [A minor contributor] When turning off the heater (by stopping the flow of fuel) turn the combustion fan on low for the few minutes [~10] it takes for the flame to completely extinguish. (A tiny flame flickers in the bottom of the burn pot for several minutes- burning off residule fuel.) Running the combustion fan during cool-down helps prevent small amounts of soot and smoke, and clears fuel odors from the heater.
I hope this quick brain dump is useful, and that I didn't forget anything critical.
These heaters are very safe if installed properly, and worthwhile if you are patient enough to learn how to use them. It is important to be very observant as you go through the learning curve of using and adjusting this type of heater, and develop the habit of scrutinizing the flame (and adjusting when necessary) on a routine basis.
We love the fireplace ambience that comes with the nice radiant heat.
Do you have any tips and tricks to share on this topic?
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Link to original forum post 1-Feb-2023 which spawned this blog post.
PS: We are occasionally asked about how we installed the through-deck plate [AKA deck iron] when some of you notice we didn't use the typical teak ring to account for the deck angle.
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Ignore the chain hook and line which shows in the two photos preceeding this one. I was using a line to keep a small amount of tension on the top flue so it didn't lean over before the gasket set-up. |
We used Sikaflex 291. [Paintable; sandable; heat resistent; can also be used underwater...]
Here are the basic steps we took to install the deck iron using Sikaflex as the spacer: [Sorry, I was by myself and it wasn't convenient to take photos of every step along the way...] In fact, I suspect it took me almost as long to detail the following in writing as it did to perform the install - not including locating and cutting the flue clearance hole through the deck...
After the hole is made through the deck: [Measure 99+ times, then drill a small pilot hole to confirm (e.g., A 1/8" hole that can easily be epoxied closed if the position is incorrect...) Then cut the main flue clearance hole as recommended by the manufacturer...]
Then...
- Set the deck iron flat on the deck [no wedge yet] centered over the hole.
- Rotate it so that the fasteners fall where you prefer them to be.
- Apply wide painter's tape [e.g., 2" wide] around the perimeter of the deck iron, with the centerline of the tape on the joint between deck and deck iron [half the tape width on the deck iron, the other half on the deck.]
- Mark where you will drill the pilot holes for your fasteners of choice.
- Carefully slice the tape at the very edge of the deck iron with a very sharp blade.
- Lift the deck iron from the deck and firmly press all remaining tape edges down onto the deck and the deck iron perimeter.
- This is what will keep the Sikaflex edge neat when you are finished- with little to no clean-up needed.
- Insert a short length [e.g., 3" long] piece of oversize flue [4" to go around our 3" main flue] into the deck iron. Either glue it in place [a day or two before install; Sikaflex or hot melt glue would work] or use tape around the outside perimeter of the oversize flue sleave inside the deck iron.
- This short piece of oversized flue serves as both additional fire proofing between the main [small diameter] flue and the edges of the deck hole.
- It also prevents the Sikaflex from making contact with the main [hot] flue when you get to that step.
- Drill the pilot holes you marked in step #4, above, for the deck iron fasteners you chose.
- Don't drill through to inside of boat... [future leaks]
- Use a countersink bit to create a small fillet on top of each hole for sealant to flow into, forming a permanent O-ring style gasket for each fastener where it penetrates the deck.
- And remember to use appropriate methodology if the deck is cored at your flue penetration location...
- Dry-fit the deck iron with main flue installed underneath to center in the hole in the deck.
- Remove deck iron again, and insert all fasteners through deck iron, and run a tight fitting, small diameter O-ring up each fastener to keep the deck iron flange tight against the fastener head.
- The O-rings will hold the deck iron in position- level above the deck- while you fit it into final position just before adding your Sikaflex gasket.
- Put deck iron into final position, carefully screwing fasteners into pilot holes until the flange is level [not flat on the deck- unless your deck is level at that location...]
- The O-Rings you installed will hold it off the deck temporarily in final position.
- Double-check that the oversized, short sleave [4" dia x 3" long in our case] and main flue [3" diameter for us] are exactly in position in the hole through the deck, and in the deck iron.
- Fill the void between the deck and the deck iron completely with Sikaflex 291.
- Cut the tube to have a wide tip, and work out from the center to the circumference to help prevent air voids.
- Once you are sure that the cavity is full of Sikaflex, run a putty knife around the circumference to shape it the way you want.
- The above photos were taken shortly after the tape was removed and the Sikaflex was still tacky.
- While the Sikaflex is still tacky, remove the painter's tape from both the deck [pulling tape at an angle away from the Sikaflex] and the deck iron flange.
- Clean up any Sikaflex that escaped the tape.
- Before putting everything away, remember to lay a blob of Sikaflex about the size of the cross section of the thickest part of the gasket on a piece of cardboard, and set it aside near the deck iron.
- This will be your tell-tale indicator of how firm [or not] the Sikaflex is under the flange since you now wait a few days before putting any load on the deck iron... [I do this anytime I use any goop to seal something on the boat... Is it set yet?]
- After a couple of weeks [or whatever Sika recommends] you can sand and/or paint your Sikaflex gasket. [We left ours as-is, and looks great to us in plain white.]
Please share your experiences and alternative approaches with us so that we- and most importantly, others- can benefit from your efforts.
