Keel cooling set up

[cal_d_44]

Hi all, 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 advice appreciated.

Cheers

Cal

[hellosailor]

If you are considering box welding to the hull, why not run that INside? You've still got nice conductive steel submerged in sea water, use a bit more tubing and the thermal mass of the hull and keep the tubing inside where other problems can't reach it. And perhaps, insulate over it to keep some of that heat out of the boat.

Just a thought, if the situation allows for it.

[cal_d_44]

Thanks Hellosailor the only issue there I see is the panels would need it to be 300mm (1ft)wide and 3.2mtrs (11ft) long, going under the frames with blead valves situated so I can blead out the air and drain the coolant, if the coolant panels were 15mm (1/2 inch) high the coolant volume would be 30 ltrs (8 Gal).

& a lot of welding

Food for thought though.

Cheers

Cal

[djmarchand]

Post your question on boatdiesel.com. There are a lot more commercial/fishing boat owners and mechanics on that site that have experience with keel coolers.

David

[cal_d_44]

Cheers David will do

Cal

[stillbuilding]

Originally Posted by cal_d_44

Hi all, 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 advice appreciated.

Cheers

Cal

I have done almost the same. I could not see any merit in galvanizing an would not worry about swirl bar

[cal_d_44]

Thanks Stillbuilding is yours opperational yet? if so how is it working? any issues?

Cheers

Cal

[stillbuilding]

Originally Posted by cal_d_44

Thanks Stillbuilding is yours opperational yet? if so how is it working? any issues?

Cheers

Cal

Tell you in couple of months. Builders done many previously and had no problems with it. Channel welder in place on both sides with 1.5" inlet and outlet on both sides. Will try to find pic.

[stillbuilding]

There you go.

Double run of channel on both sides.
Internal shows inlet on one side, outlet on other and horizontal connection. The vertical pipes are fuel inlet and outlet for diesel tank in bilge.

[cal_d_44]

Thanks Stillbuilding

Cal

[NahanniV]

The box channel looks much cleaner.
The tube looks like it could snag something or be more easily damaged by an impact, it will also be more difficult to keep clean when you get into 28deg. water and need to scrape stuff off the hull.

[RaymondR]

Hi cal d 44, I have just put keel cooling tubes along the bottom hull plating of my steel vessel. The reason I did so was to reinforce a large panel of bottom plating so that I could remove stringers which were acting as water traps and causing corrosion.

I have not implemented keel cooling yet so I cant comment on how effective it may be. My engine is a Kubuto V2203, about 50 hp. I did not carry out any sort of calculations but wandered about in the boatyard looking at other keel coolers and discussed it with their owners. What I ended up with looked about right to me.

From a thermodynamic viewpoint there appear to be a number of things which require consideration:

The reason you put the swizzle stick down the centre of a heat exchanger tube is to create turbulence in the fluid flowing through the tube which assists in presenting new, cooler fluid to the heat exchange face in the tube. Consequently it appears that a wide thin fluid conduit would provide better heat exchange than a round tube. If my rusty old maths is right your round tube will give you a circumference of about 121mm however if you were to split a piece of radius-ed corner 100 x 50 RHS you would exceed this and probably have a more turbulent coolant flow as well as having the coolant in contact with the considerable heat sink of the keel itself.

NahivanniV's comments re cleaner appearance and snagging and damage are valid and of considerable import from a potential damage viewpoint.

I used 76 x 3mm wall thickness tube but split the circumference into thirds and threw one third away using the other two as the cooling conduits, looks rather neat.

I don't know how to post images on here but there are some in the Raymond Rampling site on Facebook.

[cal_d_44]

Thanks RamondR thanks for the feedback which Raymond Rampling are you on facebook? Would be keen to see what you have done. My new Nanni is a Kubuto V2203 set up for keel cooling so it was a factory calculation for the 1.85sqmtr of surface area. The circumfrence of the pipe is 132.6mm. I agree with the cleaner apperance of the RHS and am now looking at RHS 65x35mm @ 2 x 3.5 mtrs lengths each side to give 1.95sqmtrs of cooling surface

Cheers

Cal

[RaymondR]

Hi again cal_d_44, I have posted the keel cooling images in the photo section which you can search using"RaymondR" or "Keel Cooling".

I also carried out the marine conversion on my engine myself which has some interesting variations. I will post some photos of this also.

[cal_d_44]

Hi Ray saw the photos looks good and the engine conversion WoW some serious work there :-)

Cheers

Cal