What are these and what effect might they have on hydrodynamics?

These photos were sent by a friend. The boat in question is a large steel sailing vessel, hard chined.

Not sure what material they are or what their function is. My spitball guesses are ballast in some form or perhaps guards for some internal fuel tanks that are integral with the hull.

Has anyone seen this before and how much will this slow the boat or affect sailing performance at displacement speeds?

 

See that a lot on gulf built commercial boats for various types of keel cooling. Can't imagine that much surface area needed but on some of... scratch that "all of" the gulf built steel shrimp boats look like that underneath. Main dual circuit, each generator, even hydraulic oil gets cooled in them. Doubt it makes it go through the water better, but it is fast cheap and easy for closed circuit cooling.

 

I think that answer makes the most sense, though I am surprised at the surface area and number of circuits. I assume there is symmetry on the opposite hull, which would mean 8 coolers. Seems like a lot of extra welding and material, doesn't it?

On the topic of keel coolers, I looked at another steel sailing vessel fitted with them recently. These ran inside the skin of the hull, 2/3 the length of the boat and were made using inverted angle iron. Interesting design, acted as longitudinal stiffeners, and didn't affect the hydrodynamics at all! (though I wonder how effective they are)

 

They’ll become entirely ineffective as soon as that rusty clamp bolt parts!
Systems like this usually hold such vast amounts of coolant that even poor heat transfer is not a problem.

 

Yeah that's what they rely on, massive volume compensates for lack of efficiency. I've seen lots of boats like that add strainers to the suction side for the inevitable flaking that occurs. It's been ten or more years since we cut in duramax coolers, but there was a time (when all the gulf boats hit about 30) where we did a lot cutting them out. Plating it back up and adding keel cooler recesses.

Traditional silicon bronze coolers are expensive.... right up until a main dies from salt ingress or ingesting some steel scale in a water pump.

All goes back to balance of cost. See a lot of aluminum boats building similar setups in. For the guys fishing year round the old ti coolers seem to last longer. Although I'd imagine the ti grid coolers are now a bazillion dollars.

 

Ti as in titanium?

 

Yeah. The big money days saw titanium grid coolers for the aluminum boats. The aluminum grid coolers even with consistent anode protection had electrolysis issues after 8 to 10 years. Truth be told the dollar per year cost was probably similar but the up front coat was 10x.

I known the relative cost of bronze keel coolers in steel boats nowadays is a no brainer. Been some time since I've seen welded in grid coolers.

 

I guess this system is what's referred to as a "skin cooler" ?

 

That single rusty hose clamp wouldn't be rated too highly by most surveyors! As for the effect of external coolers on hydrodynamics,if kept clean,probably less than the growth on the bottom or a few hundred barnacles.A former colleague who went on to work for one of America's largest auto racing businesses told me that they regularly receive suggestions from fans for ways to make their cars better and one of the most common is for surface cooling instead of radiators.They have a fairly standard reply that thanks the correspondent for their interest and then points out that the total surface area (and weight) takes the idea out of contention.With a hull that displaces quite a few tons at it's lightest it isn't hugely significant to a a few pounds.

Those internal angle sections won't add to drag on the hull but I would be concerned about them remaining clear of growth and you can't do much about cleaning the inside of them.I would imagine that periodic inspection with an ultrasonic thickness checker would be part of the maintenance routine.I'd also be concerned about colonies of mussels setting up home inside them,at least with external passages carrying fresh water (or antifreeze) that particular problem can't occur.

 

There’s coolant, not raw water inside the passages. If they were carrying raw water, growth would indeed be a big problem. Raw water is not kept in the system. It absorbs heat and is returned to the sea.