Advice on Keel Cooling set up

Hi all, long time Lurker and researcher, I would like some advice on a Keel cooling set up. I am not interested in debating the pro’s and cons of Keel cooling/Dry exhaust for a number of reasons, I am going that way.

I own a 20 year old John Pugh 40 ft Steel Ketch, she is 6 mm steel plate below the waterline and 4 mm above, hard chined, ¾ keel with a skeg hung rudder. 12 tonne with a 6 ft draft. She presently has a 1964 Fordson Major marinised engine, the present keel cooling is box channel (see photo) welded to the keel giving a surface area of 0.95 sqr mtrs of cooling. The Fordson is being replaced with a Nanni (Kubota 50 hp) again set up for keel cooling and the factory recommends (@ maximum 2800 rpm) 1.84 sqr mtrs of surface for cooling at > 18 deg C water temp. We plan on spending most of our time in the tropics so water temp could be as high as 28 deg C.

So the plan is to do a 12 month refit on the dry. I plan to remove the old engine and engine bed and refit the Nanni, remove the box cooling and replace it with 32 mm ID black water pipe 3.2mm wall thickness fully welded and pressure tested (see drawing) either bolted or welded to the hull each side will have 2 x 3.5 mtr run giving a surface cooling area of 1.9 sqr mtrs. It will hold 16 ltrs of coolant total, Yes I know there will be a greater wetted surface but we are talking about a 7 knot live aboard cruiser I don’t think the drag will make a large difference. I have also replaced the 20 inch fixed bladed Prop with a 20inch 3 bladed Flex-o-Fold. The keel cooler will be mounted just below where the Hull meets the Keel along the Keel about 1 mtr (3 ft) below the water line.

If I make it out of 75mm x 25mm box welded along the 75mm side to the hull in the same configuration it will give the same cooling surface area but hold 38 ltrs of coolant.

So the advice needed is:
1. Can any one see any major floors with this set up?
2. I am also thinking of getting the new keel cooler Galvanised (hot dipped), is that a benefit, as it will need to be painted with anti foul any way?
3. I am also thinking of fitting down the centre of each tube, a 2 mm flat steel twisted along its length to swirl the coolant to get maximum contact with the cooling surface?

Any feedback appreciated.

Cheers

Cal

 

looks ok.

im not a fan of keel cooling for main engine.

keel cooled refrigeration in very desirable. put it on your job list


remember main engine battery charging in hot water harbors....bigger is better

 

Concur Michael. Might thou better to check up the cooling area before going further..

 

new keel cooler in metal boat

cal_d, what about welding a strip of metal from the hull to the keelside, to form a triangular section, hollow to accept coolant, and easily welded outside, pressure tested from under the hull and able to provide higher outside water surface area to the coolant?

A plank-like strip of 20'/6m - perhaps one per side to really allow cooling(?) -and only 4 inches/100 mm wide of 4-6 mill plate should go along way to providing the area you need?

Coolant hose/pipe fittings would be (could be) welded to the hull from the outside by inserting them into the hull recessed by the hull thickness, and welding overhead. The inside, or base welds, for these fittings would then be more or less redundant, but; surely would seal to 40-50 psig/ 350 kPa so the welds are confirmed ready for coolant?

The weld of an angled strip forms its own bevel shouldered fillet weld allowance which would enhance the root face of both welds. If the angle of the hull to keel were such, due to hull curvature and body plan variations to close the naturally shaped open bevel top or bottom surely a bit of stroking with a belt sander, or rigid disk grinder would increase the plate's edge angle allowing for access to the beveled opening with coated electrode or MIG welding?

I can't help think this (approx) 45 degree plank would also streamline the hull-to-keel intersection, the concept is common in welded metal sail boats.

cheers,
Kevin Morin
Kenai, AK

 

The system as proposed would not be that difficult to test for heat transfer before installation.

The internal tube mixing devices are called turbulators, and they do work. Your test could include before and after use of the turbulators.

Trends for me in custom hull Keel Cooling (I focus primarily on integrated aluminum keel cooling for aluminum hull work boats):

1) A separate aluminum expansion tank (on the large size in relation to the engine cooling circuit volume) feeds two keel cooling circuits, each sized at around 60% to 80% (depends on the requirements) engine max liquid cooling power dissipation. Each circuit has its own electric pump and staged using expansion tank thermal switches.

2) The engine cooling circuit (normally raw water feed) draws from the expansion tank. Tank height is set to easily purge air from the engine and hull circuits.

3) Keel cooling uses polypropylene glycol mix with low mineral content water (deionized?).

All for now,

Mark Cat

 

The galvanizing would turn the cooler in to a large area anode and would be consumed relatively fast leaving unprotected steel? It is also unpleasant to weld.
Nick

 

Thank you all for you replies.

Teddy the 32mm pipe has an OD of 42.2mm which is a circumference of 132.6mm and 2 x 3.5 mtr lengths each side of the hull gives a total cooling area of 1.94 sqr mtrs? Unless I have missed something?

Kevin I thought about the angled flat plate and I would only have around 4.6 mtrs of hull/keel intersection to play with (due to engine position fuel tank etc) and at 200mm I would need 4.8 mtr of area, I also have to consider changing the coolant every 2 years and how I drain the system? I think my 5 large anodes would create just as much drag as a 42.2mm diameter pipe? Thoughts?

Thanks Mark for your work boat system and I will be using a polypropylene glycol mix.

Nick your right Doh! So I won't be galvanising anything just sandblasting and an epoxy paint finish,

Cheers

Cal

 

Cal, that keel cooling setup as drawn is going to be an antifouling nightmare trying to clean behind it. I really wouldn't do it, and I speak as the poor ******* who used to have to dive on my father in law's hull and try to scrape his clean.

I'd go for welded channel myself & increase the surface area as required.

If you're the person I think are you still living in the sticks on the Hume Hwy? I'll be driving back that way from Sydney in a month or so.

Drop me a line via this forum....

PDW

 

For equipment like refrigeration.... you dont need external pipework. Any external equipment is a maintence issue.

Refrigeration works fine with Only a box welded between frames, below waterline, filled with antifreeze and a circulation pump.

I suppose you could use this same skin cooling technique for an engine. I have no experience.

 

I have read where the stringers and frames themselves have been welded watertight and doubled as the components of keel coolers, leaving no protuberances on the outside of the hull. I think someone mentioned elsewhere that galvanizing the keel cooler just turns it into a large zinc anode until the galvanizing disappears leaving bare steel.

 

keel cooler plate install

cal_d,
the difference of 0.2 m^2 seems sort of small to worry about? I'd run the plate at the intersection forward by another meter or so, then you're safely increasing the area for the 'warm harbors' mentioned earlier?

Also the drain: TIG in a flush 1/2 coupler that is smooth to the outside of the cooler chamber, (welded on plank) fill with a socket recess pipe thread plug, and bed in plastic thread paste that sets up. Locate this external drain at the low point- when sitting on the keel or hard.



Here is an example of an aluminum 1/2 of a 3/8" pipe coupler that has been held flush to the inside of an outboard tank side wall near the bottom. The TIG weld is fillet of the thickness of the side wall and the entire face of the fitting's upper edge without having to involve the threads. This is the only photo I have of the kind of welded in pipe fitting I'm advocating, but there exist a flat type of fitting to do this job if you want to weld farther from the threads?

http://www.theindustrialdepot.com/socket-pipe-plugs.html
http://www.discounthydraulichose.com/NPTF_Hex_Socket_Plug_Stainless_p/ss-5409.htm
http://www.loctiteproducts.com/threadlocking-mechanical.shtml#mechanical-gasketing
http://www.emisupply.com/catalog/pipe-thread-sealant-with-ptfe-tube-p-8445.html

I have used this method on keel coolers, integral fuel and gasoline tanks and other voids in hulls without failure for four decades and they seem to be OK?

Instead of putting fittings up into the hull spaces forward, as cross-over from side to side for the two plates of the new cooler; just drill/bore/cut a 1-1/2" pipe hole (assumed to be larger than the engine coolant pump flow?) and socket-weld (recess each pipe end to the inner wall of the keel plate surface) a short pup of pipe between the two sides of the box keel structure. The weld needs to be done with a full key-hole root confirmation, of course, but if that is done the keel is still intact, the hole is just a fluid path for the glycol.

This pass-through allows the two sides of the keel cooler 'hollow' to communicate fluid from port to starboard where one side is the drain of the pressure tank, the other side is the suction through the gear oil cooler (T&S HE) connection to suction of the block pump.

This system is extremely commonly used on welded metal commercial fishing boats in the NW USA, and I've done it in steel and aluminum boats with good reliable results. (all power boats, no blow boats)

If these welds can't be done by someone able to bring a high quality, single side, TIG weld to some of the joints, then my suggestions may have problems. I'm only suggesting them if the quality of welds can be performed, not all yards or shops have the equipment or skills to use these designs so they may not be useful to your project?

But this will result in the least work, cleanest and simplest in all respects of each design possible, and a greater liquid-to-liquid HE area ratio of all integral types. This results in a non-appendage type of cooler instead of the 'sea anchor' pipe U you're considering above.

Cheers,
Kevin Morin
Kenai, AK

 

The drawing shown is not very efficient (parallel is better), will be a maintenance nightmare, and create unnecessary drag.

 

Thanks Guys again some good advice and some great ideas.

Cheers

Cal

 

Cal welcome to the forum.
I've designed several keel cooling systems I've put several on the inside. Simply welding a tank with baffles integral within one side of the keel. Some between frames. The classic was simply channel or angle welded to the inside.

You will get a fair amount of drag from that setup, a sailboat wants as little drag as possible and external heat exchangers are a bit brutal in that regard.

 

You probably have some good guides but have a look at this one from Beta Marine ( attached).

Cheers