Hot Water From Manifolds/risers?

I plan on making a simple glassed in or portable 100 gal hot tub. Filled and heated with raw (salt) water. What is the best way to heat the water? The boat is powered by a 350 fresh water cooled/heat exchanger. I only plan to fill/heat it when under way and can just excess can just flow overboard when full. I was thinking of pulling the water from the risers etc. Would this even work without steeling too much water from cooling the manifolds/risers? And would the water even be hot enough? Looking for about 100 deg.

Any other suggestions would be helpful. Did a search but couldn't find an appropriate answer.

Thanks so much,
Jim

 

I know someone that uses the exhaust manifold heat to heat his water with. The exhaust pipe passes through a tank and the water is heated that way. It is fresh water he heats though. A small circulation pump cycle the water through. It works quite well.

 

Take the water from the thermostat housing. Use only a 1/4" adapter so enough water is left to cool the exhaust, otherwise you won't be happy in your tub with all the smoke around you.

 

" otherwise you won't be happy in your tub with all the smoke around you."
LOL

 

Great idea. You, may want to put a mixing valve in so you can dial in your

temperature by metering fresh sea water with the warmed heat exchanger

sea water. Check first to see what kind of temperature you're getting from

the heat exchanger outlet. You're looking for about 106 F (41C). I think

you'll find it needs to be within a couple degrees of this for comfortable

enjoyment.

-Tom

 

If you take too much water from the heat exchanger raw water side, you can overheat your exhaust system. Internal damage like delamination or bulges, especially to rubber parts, is usually hidden from sight or it may be invisible, such as a loss to flexibility or strength or resistance to puncture.

I'm not saying it's impossible to do what you want to do, but I am saying bad rubber on exhaust systems (and I/O transom bellows) is a common cause of boat sinkings. It's not completely secure to begin with, but if you overheat the system once it is suspect.

 

How does the smoke gets around you ? The exhaust pass through the heater tank and out where it's outside. The exhaust heats the water much better than the cooling system would. Taking water from the thermostat housing is like Sam says, risky for your engine. I wouldn't like to use water in a tub that comes from inside the engine.

 

The smoke comes from the burning boat!

But with something like 6mm take off pipe there should be enough water left to cool the engine proper.
A "real" calculation would be a better way though.

 

Failing a real calculation, go with a bigger pump!

 

Was my message really that cryptic only you understood it Richard?
Having to spell out everything is much less fun.

 

Whell, there should be a practical side to this as well. How long is a 6mm pipe going to take to fill a tub. This will mean you have to run the motor for a week in advance By the time it's filled the tub is going to be cold again. Nothing encrypted about it, just common logic.

What will work the easiest is to fill the tub and circulate the water around the exhaust and back in the tub. Any time the water gets too cold and you haven't growed finns between the toes yet you can just start and run the circulation again. You want the fastest decent heating with a bit of volumetric flow.

 

Splendid suggestion Fanie.
That way he also gets a nice tan, even under his boxer short.

 

It's just dawned on me that another heat exchanger may be the way to go

here. Hot water could be circulated through a copper tube coil in the tub.

Put a valve on it and you've got temperature control. Make that valve a

solenoid and it's auto-magic. Or a combination of plumbing, whatever

works and is easiest and/or simple.

Good luck Jim!

-Tom