SEACOKS HYSTERIA

As most of you know British magazines some years ago made a big fuss about brass seacocks on new boats (they still do) and hysteria about that was propagated like wild fire on boat forums.

https://trip.ayy.fi/wordpress/wp-content/uploads/2014/08/Seacocks.pdf

It seems that the main culprit is the RCD, the ruling body for the conditions needed for boat certification in Europe when they state that the seacocks used should be corrosion free for at least five years. From that to the idea that seacocks will only last 5 years was a quick jump and even worse, some just say that if a new boat does not come with bronze seacocks they should be immediately replaced, as if the boat was in eminent risk.

Brass regular seacock

That of course makes no sense. Almost all production boats come with low quality brass seacoks (CW617N) and the average time they need changing is about 10 years.

That does not mean that a seacock due to some unusual circumstances does not need replacement after only one year or two and because of that seacoks should be thoroughly inspected every year and changed at the smallest sign of corrosion, white powder or small changes in color.

Brass DZR seacock

The problem of brass seacocks has to do mainly with dezincification, a galvanic process that extracts zinc from the brass leaving it fragile. It can happen if the boat zincs are not in a perfect condition or if there are abnormal electric currents on the water. It will probably happen anyway after many years, but it can happen in just some years under abnormal conditions.

It is rare but there are some well known cases where seacocks lasted just one year or two. So does that hysteria about brass seacoks make sense? Well, the truth is that boat builders should be using a higher quality brass, more resistant to dezincification (DZR) and almost all of them are using a lower grade brass but the truth is also that even high quality bronze seacock manufacturers don’t warrant their products for 5 years and I know of some bronze seacocks (of low quality) that lasted only one year or two. All seacocks should be carefully inspected every year even if that does not mean that they all last the same time.

RCD has its share of guilt on this issue because while stating that the seacocks should be made of corrosion resistant material don’t specify the allowed materials and as almost all brass valves will be able to resist the required 5 years (on normal circumstances) boat manufacturers, to save some coins, don’t use proper long term corrosion resistant materials on seacocks. Hopefully there are some talks that it is going to change due to RCD new demands. A good article about the subject:

http://korrosion.dk/onewebmedia/Corrosion%20i%20Through%20Hull%20fittings%20and%20seacocks-070616.pdf

Should we be very carefully about seacocks and seacocks inspection? Absolutely! 

Should regular brass seacocks be changed after 10 years (no matter what) or changed at the first signal of discoloration, white powder or signs of corrosion? Absolutely! 

Blakes bronze seacock

Should we be worried when we buy a new boat with having seacock problems on the next few years? Nonsense!!! even if that does not dispense seacock inspection each year.

Should you be worried with seacocks when we buy a used boat with 10 years or more? Absolutely! As well as with rigging, rudder and many other parts that are more expensive than seacocks. That does not mean that we should not replace them, if the previous owner has not done that already. The problem here is that many still look at a 10 year old boat as if it was an almost new boat, including the engineer that wrote that article above about corrosion on seacocks.

Should you look at the seacock’ materials when you buy a new boat? Absolutely!... they are a good indicator of the boat building care with the choice of materials but I would not say that they should be more important than keel and boat structure, keel bolts, chainplates linkage, rudder assembly, bulkheads, hull material and building techniques. All are good indicators of boat quality but while seacocks can be easily replaced, all other mentioned parts are not.

Should you mount bronze seacocks when replacing brass ones? Not necessarily, DZR (that is also brass) performs better than some bronze ones and some plastic ones. High grade bronze seacocks like Blakes or high quality plastic ones like the True design may be a better option than DZR Brass but they are justifiable only if you leave the boat full year on the water.

http://www.holmedodsworth.com/materials/datasheets/brass-datasheets/cz132-cw602n-dzr-brass

True Design seacocks

Anyway the future seems to point to good quality plastics seacocks, that offer a lesser price than top quality bronze ones and are full corrosion proof. However they need to be of very good quality plastic to assure the needed strength.

Should boats have mandatorily better seacocks (RCD) than the ones that are installed now by almost all boat builders, made of regular brass quality? Absolutely! 

Is there a reason for the hysteria about the ones that are installed now? No, if you have the knowledge to deal with that, after all there are tens of thousands of boats around with less than 10 years on the water and they are not sinking due to defective seacoks, but there is reason to be concerned about seacocks and carefully inspect them every year and change them after 10 years (if made of regular brass) and I bet many don’t do that and that is one of the reasons for this post.

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This will be the last post in a long time. I have not been posting because I have been preparing my sailing season that will start in some days. I will come back only in October…so, till then, fair winds to all and have fun sailing.

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The Vattai of Tamil Nadu

Examples of traditional frame-first boat construction in Asian cultures are rare. Throughout the Far East, Middle East and east Africa, shell-first construction of planked boats is the norm, where it is used for everything from sampans and junks to dhows. One of the few exceptions is the vattai, an open, sail-powered, flush-planked (carvel) fishing boat common in the state of Tamil Nadu, in India’s southeast.

A vattai in Tamil Nadu. Source: Blue (click any image to enlarge)

The vattai is described by Lucy Blue in “The Historical Context of the Construction of the Vattai Fishing Boat and Related Frame-First Vessels of Tamil Nadu and Beyond,” published in Ships and the Development of Maritime Technology in the Indian Ocean(David Parkin and Ruth Barnes, editors; Routledge, 2016). The information and images in this post are from that article.

To quote Dr. Blue:

"Vattai, are flat-bottomed, have a box-like transverse section and are near wall-sided over much of their length. They range in size from around 13.72m long, with a beam of 2.13m and a depth of 1.37m, to the smallest vessels of c. 5.18m x 1.07m x 0.76m. However, irrespective of their size, they are all similar in shape with very high bows, and two or three masts each with a settee-lateen sail, a balance board, and, uniquely on this coast, leeboards."

The design process is of much interest. A single mould form or template is used to lay out most of the frames on a scrieve board, the form being flipped to draw the port and starboard half-breadths. (Forms for different boats differ from one another, apparently, only in the radius of the curve that joins their two straight, right-angled legs.) Since the boat’s cross-section (half-breadth shape) is constant across its entire midbody, a single shape drawn on the scrieve board suffices to define most of the frames, and this follows the exact shape of the form laid square to the edges of the scrieve board.

Use of the mould form and scrieve board (A) to create the shapes of the "equal" frames for the midbody (B,C,D), and the progressively narrower frames toward the ends (E, F, G). 

Fore and aft of the “equal” frames that constitute the midbody, each of the next three progressively narrower frames at the bow has an identical counterpart in the stern. These frames that define the ends are derived from the same mould form according to a formula that defines how far in from the scrieve board’s upper edge and how far up along the diagonal the form is placed. By rotating and raising the form, different frame shapes may be drawn to create the narrowing and flare of the hull’s ends. The final three frames in the very bow and stern, however, are not drawn or gotten out at this time.

In the boat recorded by Blue, there were 15 “equal” frames for the midbody plus 12 “unequal” ones, evenly divided between the bow and stern. The midsection always consists of an odd number of frames – the central master frame, and equal numbers of identical frames fore and aft of it. The design can be readily made longer by the addition of more equal frames in the midbody with no changes to the ends, and made wider starting with a wider scrieve board but using the same mould form. Rules of thumb establish ratios between length, breadth, depth, and frame spacing, so the builder’s discretion to make changes is limited mainly to his choice of the mould form and number of frames.

Vattai construction drawing

Frames are built up from floor timbers and futtocks, which are assembled with “a complex dovetail joint” that “extends right through the turn of the bilge.” The vattai has no backbone, so apparently the frames are set up on the straight, flat bottom planking, which must be laid down first. Stem and sternpost are butted with a lap joint against the ends of the central bottom plank. The article states variously that the shapes of the very ends are determined by battens (ribbands) or by laid planking between the midbody frames and the end posts. Whichever is truly the case, these define the shapes of the three final pairs of half-frames at each end. Only in these final three sets of frames do the shapes of the vattai’s bow and stern differ. They are installed without floors, their lower ends overlapping fore-and-aft where they land on top of, or are notched onto, the stem and sternpost. (This detail can’t be determined from the drawing.)

I have been unable to find any other photos, descriptions or even references to the vattai through Google searches and would welcome additional input. There is much else I’d like to know, including:

• whether the planks have a caulking bevel, and the materials (if any) used for caulking
• the design process for the end profiles (i.e., whether the stem and sternpost shapes are determined by template or drawn by eye.) 
• details of the rig and leeboards
• details of usage: crew size, responsibilities, sailing procedures and performance

I would also much like to see additional photos. Google image searches for terms like “fishing boat Tamil Nadu” yield a number of stock photos of open fishing boats that do not appear much like the vattai (the distinctive bow shape is an easily-noticed identifying characteristic), and nothing else even close. Please communicate in the comments if you can add to the discussion.

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