Hot water for dredging

Hey guys what do you reckon about one of these for hot water while dredging? I’m aware of the common heat exchange system people run off the dredge motor exhaust system. Just concerned about the dangers. This unit can run for 15-45hrs on a 9kg bottle, depending on flow rate and water temperature. And yes, there is the issue with lugging in gas bottles. Portable Water Heater - HOTTAP | Joolca NZ

Hey mate- I ran a gas hot water system on my dredge before converting to exhaust run heat exchangers. The problem you will have with gas hot water is the need to carry round and float a 9kg bottle. A couple of other factors to consider are:

  1. Cost of gas approx $30-$40 per 16 hours. I struggled to get more hours than this out of the gas bottle
  2. Gas bottle freezing up if in a cold environment
  3. The weight of the unit excluding the gas bottle and where you mount it to. I mounted mine on my dredge but that ads weight
  4. Electrics in the feild getting wet so the unit craping out plus vibration if mounted onto a dredge

A well designed exhaust driven system are safe if you run a tempering valve and also a steam trap. Basically a tempering valve if it encounters steam will dump cold water into your system before steam makes its way into your suit.



Often tempted at looking at Hotwater options, but have never crossed the line as never wanted to be cooked like a lobster. Have looked at some online designs, but never really convinced yet, however I am interested in what the steam trap looks like, are you able to sketch it up as this may get me more motivated towards a hot water setup.

often thought about keeping warm under water. how bout hot water bottles down the wet suit. build a big fire in the creek and as the water lows past it heats up. you could always pipe the water through the fire so it heats quicker then the whole river would be warm.
i swam in hot water creek at rainbow mountain by rotoroa once.
get an electric under water heater, accouple of electric ells to run the heater. cant miss

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See diagram below… Basically key points are you need the outlet of the steam trap (the bit that goes from your trap to your wetsuit) to be at a lower level than the incoming hot water. (hence why tanks are usually mounted on there side attached to the dredge) This way if steam is produced it will not be able to travel up into the outlet of the trap as effectively as the pool of water inside the tank will condense out any steam and by that stage the low pressure relief valve will register a pressure increase and thereby venting steam out of the system.

Hope that makes sense

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Thanks for the replies guys! Both entertaining and educational!

Have also been interested in hotwater setups as was going to go down the gas route… however I remember seeing someone selling these heat exchanges as a complete setup just bolt onto exhaust motor but comes with all the safety features described by prich385 but cannot find anywhere, anyone have any links? Cheers

Iv had a couple , system worked fine but I found the biggest troubles stemmed from the inline water filter blocking , granted the filter was a cheapy
Even if i checked it every couple of hours it was a bit unpredictable for my liking , couple of times i had hot water come through & melted the hose off a couple of times as well , the filter kept blocking with fine sediments , such as fine schist thats constantly suspended in the shotover in the end I was more focused on the water temp than the job at hand which is not good when the boulders are big enough to squash you flat , in the end i gave up on the hws , pity really because the longer you are dredging the more you are earning , Im going to try a dry suit next .

Only 10L of water but can run off 12v system and hot in 20 mins, and can filter direct river water…

Interesting option, and I guess lugging big batteries around will keep you warm too :wink:

I was in the water a week ago with prich , i was in a drysuit was toasty warm , despite my face going numb , get a full face mask for winter

Iv got a full face mask Think it’s a Neptune haven’t used it in a couple of years but as you say certainly helps this time of year , picked up a ocean dry last week for a good price down side it’s got 2 small leaks along the zip hopefully I can repair it if not I don’t think it’s worth sending away .been working on the dredge last few days got a new long block , new alternator & new starter , haven’t used this one in 2 years so it needs some love , hopefully the compressor isn’t too bad alloy seems to corrode a bit .

Sluice needs some attention too though I’m pleased when I got it made the frame , most of the riffles aside from the front section are all made from stainless steel so it’s all still mint , the Keene is a different story, it’s getting pretty rusty especially the undercurrent riffles , had a flood here in February any metal work that got wet didn’t fare to well .


that looks like a beast what size nozzle?

8 inch , engine is a Vw 1600 going to Be interesting to see how it preforms compared to the old one .

Way back, many eons ago now when I first started dredging, we were using underwater suitcase dredges. In those days guys had the hot water feeding straight from the heat exchanger(The Copper wire coil type), that fits in place of the muffler. After seeing a few pics of guys that got scaldedI was loath to use one. But started to think (with me that is dangerous lol) there has got to be a better way. The trouble with inline filters either at the suction end or the delivery end, is they tend to block up, esp with vegetation debris, dead leaves etc.
And even using a system with no filters, they will still from time to time, get a blockage, restricting the water flow. That results in the reduced water getting hotter and hotter, until eventually it is steaming. This can only take a few seconds to occur.

So like I said on went my thinking cap, right I cannot stop a blockage, so how can I manage it. Half an hour later after thinking about it I came up with the answer. Steam rises, to the surface of the water, no matter where it is enclosed or not enclosed. So I worked on that. And came up with a pretty foolproof system.

Put it into play, and started using hot water. Neither I nor my partner got a burn out in over 30 years of dredging. Sure we had blockages, but we were pre warned as we felt the temperature of the water slowly getting hotter. Giving us plenty of time to surface, go over to the tap controlling the inward flow of hot water.(mounted on top of the water pump) turn it fully open, then completely off. This cleared the blockage. It was then just a matter of resetting the flow to the desired temp and it was back in the water. As you can see in the attached diagram. It is simple. We called it a pressurized mixing chamber. The hot water is fed in at the top of the chamber, the feed water to the user is drawn from the bottom of the chamber. So if you get a blockage at the suction end. The extra hot water or steam comes in at the top, forcing the colder water at the bottom out to the user. He will feel it slowly starting to get a tad warmer, as the system balances out, giving him ample time to correct things.

The first one I had made at the plumbers out of stainless steel about
6 inches round and six inches deep. Copper pipes for the inlet and outlet, with those copper fittings, forgotten the name. I did make some out of plastic plumbers pipe to use on our other dredges, but they tended to warp a bit when the water really heated up. Also have plenty of length for the feed pipe, as from time to time you will find it perishes where it fits onto the inlet copper pipe. Have a screwdriver mounted either on a bit of flexible wire or a clamp of some sort, handy to the chamber. Then its easy as to remove the hose clamp, if you need to cut a bit of hose off.

Like I said in over thirty years of dredging, no burns. I had my hot water feed line going into the back of my longjohn type wetsuit. I cut a small hole in the suit, and sewed the flexible hot water line to the inside of the suit. Had a copper tail piece, where I plugged in. Feel the water starting to slowly warm up, reach around and just pull out, quick and easy. Off to the shore to sort things. So its not, how do I stop a burn out, its how do I manage a burn out at the end of the day.

Hope that helps.

Cheers Trev aka “The Hatter” or the original “Kiwigold”



i can give you a nb to a guy who makes them and they work mint


Sorry to bump an old thread couldnt figure out how to send a direct message, i have the same engine/pump sootypete, recently built a heat exchanger that mounts between the exhaust manifold and the muffler. Used an exhaust gas cooler from a diesel car. Will post pictures if anyones interested.


hi mate yes i would love to see some photos of your set up that would be fantastic…

hi mate just wondering if you could give me the details of the guy who makes them…please would be great