Technical

Not yet complete, but stuff we have so far. Please also see the Discussion Forum (click on the button on the home page) where many technical issues have been discussed.

Anchor Chain Selection, Regalvanising and a case of Caveat Emptor

A suggested article for the Blue Water Bulletin writen by Jim Putt of Morning Tide.

In 1983 we decided to change to an all chain anchor rode; the then Marine and Harbours issued a leaflet recommending 9.5mm chain diameter for a 10.5metre vessel. Though not stated I believe this referred to the standard low tensile strength chain, type “L.”.

There are a number of factors influencing the choice of link size and length of anchor chain. Vessel displacement, freeboard, under water profile and above deck clutter being the most important. Other considerations are, depth of water likely to be encountered when anchoring and the nature of the bottom, sand, coral, bombies. On the assumption that peace of mind is important the following factors should be kept in mind. A scope of 5:1 is preferable in an open anchorage. In tidal waters, the range can reach as much as 10metres. Under these conditions a minimum of 60 metres of chain is desirable. Two anchors are of limited help if the first one barely reaches the bottom.

In the case of our yacht, the S&S 34 is fine in the bows and stern and weight distribution is all important. For a maximum chain weight of 100kg we had the choice of 70metres of 8mm high tensile hot-dip (HD) galvanised chain or 44metres of 10mm low tensile “L” HD galvanised chain. Weight per metre is the same for high tensile and “L” chain, for any given chain diameter. We settled for 60 metres of high tensile chain on our primary CQR anchor and the balance of 10 metres on our secondary Bruce or Swarbrick anchors, augmented by 100metres of 16mm Marlow nylon multiplait. The multiplait also served for the drogue. This arrangement served us well. Continual use of the chain has meant regalvanising the 60m of primary chain. This has been done twice before, roughly every seven years.

Our primary chain is now in need of regalvanising. Before embarking on this process it seemed reasonable to ask the question, “how often can you regalvanise chain?” Since the galvanising process involves heat treatment, the thought occurred that this process could further anneal the chain. A quick telephone call to a local chain agency informed me that each heat treatment process could reduce the chain strength by 25%. This was alarming to say the least. So I continued to ask around and received a variety of differing answers. I then started to correspond with chain and wire rope manufacturers. I also found 12metres of original chain left over from the initial purchase. It turned out to be quite difficult to find the answer to what seemed a straightforward question. Finally I received an offer from Bullivants to carry out a destructive test on the chain. So, armed with two samples of HT galvanised chain, both samples from the initial purchase, one sample having seen active service, I set off to find the answer.

The first 2metre sample tested was the “in service” chain from our anchor locker, it failed at 5.8 Tonnes.  The second 2metre sample was the “unused” chain found in our garage, it failed at 5.3 Tonnes.  This gives a safety factor of four when compared with the recommended working load limit of 1.2 Tonnes.  Both samples failed at the point of attachment to the test gear, this may explain why the unused chain failed at a lower figure.  What conclusion can be drawn from these tests?

I now feel confident in taking our anchor chain for regalvanising. For the purest, I should mention that it is a requirement of AS 2321 that any regalvanising should only be carried out by the original chain manufacturer.  By using high tensile chain the factor of safety is twice that of Grade “L”(see table below) Alternatively, it is possible to carry a more useful length of chain without the penalty of additional weight.

Note: A scope of 5:1 is our preferred option. The catenary adopted by the smaller (lighter) diameter chain will be less (flatter) than that by the larger (heavier) diameter chain. Before purchasing chain, ensure the chain has been manufactured to AS 2321-2001. Some imported chain may not comply.

Chain is often sold as “proof tested.” Ensure that the proof test complies with AS 2321.  Australian chain manufactured to AS 2321 is required to be stamped every metre or 20 links indicating the manufacturer and grade of chain. Typically, PWB-L for standard low tensile chain and PWB-P for high tensile chain. If the chain is not stamped it is reasonable to assume the chain may not comply with AS 2321.  Swivels and shackles should similarly comply. AS 2318 and AS 2741 respectively.  On a previous occasion when I have seen anchor chain taken to its limit, it was the anchor winch that failed before the chain yielded.  Check what you have ordered is what you have received.

As a final twist to this saga we were able to identify the grade of chain we had purchased. Yes, it was high tensile chain but of the type supplied to “truckies” for tying down loads and not specifically recommended for anchoring!

Comparison of chain strength: as supplied by PWB.

Length Grade L Grade P
Low tensile strength High tensile strength
8mm WLL 0.64 Tonnes WLL 1.00 Tonnes
10mm WLL 1.28 Tonnes WLL 2.00 Tonnes

The Working Load Limit (WLL) for grade L and grade P is the maximum mass which the chain hanging vertically shall support in general service (heaven forbid).

I would like to acknowledge the help given to me by Bullivants, they carried out the tensile tests without charge and to PWB Anchor.

Jim Putt. S/V “Morning Tide” 10th June 2004

Dropping the mast (intentionally!)

Click on the photo’s for enlargements:

           
   

You will need the following equipment;

1. Mast lowering plate – about 20cmx20cm with holes drilled in each corner (photo).
2. 5+:1 blocks and around 40m of rope (photo).
3. Two spinnaker poles.
4. Deck fittings near the chain plates to accommodate the spinnaker poles (photo).
5. Wobble wires if you have shroud posts (photo).
6. An ‘A’ frame at the stern – no photo’s but I used two pieces of jarrah roofing joists from a salvage yard. I planed them to look a bit better and prevent splinters. Make them as long as you can store under the cockpit sole. They also double as fender boards when I am on the visitors jetty in Fremantle.

Now for the set-up:

1. Remove mainsail and boom (I leave my sail cover on to keep it tidy). (Webmaster note: we leave ours on but be careful, esp. not to break full length battens, you may need to remove these. Removing the boom is the “safe” procedure).
2. Remove baby stay and slacken any adjustable rigging (ie back stay).
3. Attach wobble wires (photo) – to prevent mast swaying from side to side during lower/hoisting.
4. Make stern ‘A’ frame support and lash to push pit.
5. Make bow ‘A’ frame using spinnaker poles and lowering plate (photo).
6. Hang ‘A’ frame plate from all but one jib and spinnaker halyards. Make sure the halyards are well cleated back in the cockpit (I tie them off on the auxiliary winches).
7. Tension block and tackle a little, but keep ‘A’ frame plate about 1.5m from stem head.
8. Take remaining halyard and wrap is around the others and forestay (and furling genoa if fitted).
9. Tape loose end to the rest. (this keeps the forestay under control once it is disonnected).
10. Tension block and tackle to take tension from forestay (6:1 or more is best for this – even with winching).
11. Undo forestay fitting. You shouldn’t need to slacken it, just pull the pin.

Mast is now ready to lower.

12. Pull on backstay to get the mast moving whilst paying out block and tackle. (the further it goes the heavier so have a couple of turns on a winch).
13. Gently lower into stern ‘A’ frame – don’t let the spinnaker ‘A’ frame go over centre, i.e. beyond vertical.
14. If there is any chance of getting hit by wake from stink boats I throw a line over the mast at the stern and lash it into the ‘A’ frame.

Reverse the order to raise the mast. I use my electric anchor winch for this (coz I’m lazy – and it’s quicker). Keep an eye on the back stay that will be trailing in the water behind the boat. (webmaster note: care with using electric winches, it’s less work but if anything catches you won’t feel it and something may strain/break before you notice)

Do not be alarmed if the rig is sloppy when back up, the chances are the mast has inverted it’s bend, tension the baby stay and back stay and it will pop back into shape.

On the other hand it sometimes goes the other way and requires a fair amount of winching to get the headstay fitting back in. I have a quick release fitting to make life easier (photo).

All in all I can drop the mast in less than 15 minutes and the same for putting it back up and being ready to sail.

A couple of final points – i.e. The Risks:

1. Don’t lower or raise if there is wake around, even the wobble wires don’t really steady the mast that much.
2. Have an anchor ready to deploy – if the engine quits your buggered if the current is taking you towards the bridge!
3. Check the run of all your through mast lines (and electrics) on the first drop to make sure nothing is stressed.
4. Get the helm to stand well to the side of the cockpit when lowering and raising, if anything gives way you really don’t want to be in the way of the mast when it comes down!.

Take your time and be methodical it’s easy so long as you remember everything.

Removing a forward mounted engine

I recently noticed my engine mounts had rusted through so decided to replace them and at the same time give the trusty old iron donkey a thorough service and clean up. Whilst removing the engine I took this series of photos and thought anyone else contemplating the same task might find them of interest. The engine is mounted just aft of the mast support and is a Yanmar 2GM20. It took me about an hour and a half to complete the task – (and I did it single handed).

         

         

         

Equipment required;

  • Coach roof beam – This is the only bit of kit I didn’t already have on board (though I could have just slung something from the boom) I used the beam to spread the load of the engine across the coach roof. Don’t forget to notch the beam either side of the hatch so the load isn’t bearing on the narrow lip.
  • Cantilever beam – I used my fender board/mast cradle for this, and a bit of padding.
  • 5:1 block and tackle – I used the one I have for lowering the mast.
  • Plywood sheet – or just turn over the floor boards (to slide the engine to the companionway without ripping up the carpet).
  • A mate with a ute.

The procedure is just as shown in the photos

  • Remove all the engine mounting bolts, fuel supply and return pipes, cooling water supply and anti siphon loop, gear selector, throttle and stop cables and any electrical plugs.
  • Rig up the cantilever as shown in the photos.
  • Lift the engine off it mounts and swing onto a piece of plywood and slid across the cabin sole to the companion way.
  • Support the end of the boom with as many topping lifts and halyards as you have.
  • Sling the block & tackle from the boom and lift the engine to the cockpit (cockpit protected by plywood and/or fender boards).
  • Readjust the block and tackle further down the boom and swing the engine into a wheel barrow on to the dock.
  • Find a handy tree and a mate with a ute and you’re on your way home.

Reverse the sequence to get the engine back in.

I hope this is of interest. Perhaps if anyone is removing a rear mounted engine they could take a similar set of photo’s and we’ll append this lot.

Sample Safety Plan

Click here to download the sample safety plan

Maybrook Marine sales brochure circa 1983

Click here to download sales brochure. This is a large file and will take a while to download but it is worth it.

List of S&S 34s on the Australian Register of Ships

Click here download list.

Article on how to reef Genoas without using roller reefing

The debate re roller reefing vs foils or hanks for the genoa flares up repeatedly over the years. Although roller reefing has improved, the fundamentals of all methods hasn’t changed much since the article below was published in the Association Newsletter in June 1979 The article below was published in the June 1979 newsletter. It offers an alternative for cruisers who wish to avoid roller reefing (the die-hard racers will always want to change down to a new sail). It is reproduced below for your interest.

S&S 34 Hull Speed

from Tim Dallas, Superstar:

Many crew, when out for the first time on SuperStar, have asked me what the theoretical hull speed of the boat is. This seemingly innocent question normally arises when sailing down wind under spinnaker and we hit 8 knots. This results in various responses from the regular crew, the foredeck babble hysterically and retreat into the folds of the headsail piled on the foredeck, the sheet trimmers dive for cover to avoid the mainsheet in what they believe will be an inevitable crash gybe and the helm usually grins grimly (if possible) whilst wondering how the hell we are going to get the kite down without bringing the rig with it!

Of course once the leeward mark is rounded, without much more than the need for a little additional laundry, the question is still unanswered. So I’ve been doing a little research:

Many people who claim to be in the know about maximum hull speed use variations on the equation;

Max speed (knots) = 1.341 x SQRT(LWL in feet)

But this formula yields 6.6 knots for the S&S34, which clearly isn’t right as SuperStar easily exceeds 7 knots in a moderate breeze when reaching.

Other authors have stated that both the bow and stern of a vessel create waves, when the these waves build to the extent that their wave length coincides with the water line length of the vessel the hull will, effectively, fall between the waves.

Hence this limits the maximum speed of the vessel, unless it has the power to climb over the bow wave, i.e. PLANE.

Now, this theory appears to me to be flawed because SuperStar has seen 8.7 knots with the kite up and we weren’t planning!

Incidentally I Googled ‘Yacht Hull Speed Calculations’ and got 202,000 hits! I only checked about 20 of them and only one actually disputed the formula quoted above.

Addit from Simon Torvaldsen:

There are reasons why we can exceed the “theoretical” hull speed above. The main one is that when going hard downwind the stern tucks down and the waterline extends right to the transom. This brings waterline length up to 28.6ft and the “theoretical” hull speed as calculated above up to 7.2 knots. The S&S 34 waterline length is also designed to increase when heeled.

The other factor is that the “hull speed” is not totally fixed. It is defined as the point at which hull resistance increases dramatically due to the wavelength of the bow wave becoming the same as the waterline length as shown above.

An important calculated dimension in this regard is the so-called Froude number which is the boat velocity in metres per second divided by the square root of the waterline length (in m) times the acceleration of gravity (in m/s, = 9.8). When this equals 0.40 the bow wavelength exactly matches the waterline length. As the Froude number increases above 0.40 the hull resistance increases dramatically and despite extra wind, sail area etc the boat won’t go much faster. If you do the calculations you will find that for the S&S 34 DWL at a Froude number of 0.4 this equates to the 6.6 knots quoted above.

Notice I said “not much faster” – extra power will result in some extra speed, but proportionately not nearly as much as when the Froude number is less than 0.4. The maximum speed is therefore not totally fixed as the limit is a little elastic. In practice, for our type of hull it is said to be difficult to exceed a Froude number of about 0.45 (allowing for the increased waterline length factor and all other factors above). If you do the calculations, you will see that this gives a maximum speed of about 7.5 knots.

If the hull can climb up on it’s bow wave, this reduces resistance, as the hull stars to semi-plane, and once again increased power results in increased speed. This occurs at a Froude number of about 0.5. However, heavy displacement type hulls such as the S&S 34 can’t get over the “hump” in resistance at 0.40-0.50 except under special circumstances, such as surfing waves in the ocean.

As our boats are relatively light compared to some other displacement hulls, have a lot of overhang (ie can increase waterline length more downwind than many other designs), it may be that we can under some circumstances do a bit better than 0.45. After all, our boats were designed as racers by the greatest designer of the 20th century! However, I think that it is generally hard to exceed about 7.5 knots, requiring plenty of wind and sail power, and to do this by more than a knot or so would require us to start semi-planing, ie surfing on waves. The more we can surf, and the more power we have in the sails, the faster we can go in exceeding the theoretical limits above. The fastest I have heard of in an S&S 34 was 17 knots – that wasn’t on the river and it definitely wasn’t us!

S&S 34 – Safety

Safety Maunal – Morning T.

In the spirit of sharing things, Mike Parkinson has put together a very comprehensive (3 meg) safety manual for his S&S34 “Morning T”. The purpose of the manual is to document Standard Operating Procedures, as recommended by YA’s Safety & Sea Survival course. He is not suggesting it is perfect, however, it could save time for any member wanting to create a similar safety manual.

One thought on “Technical

  1. S&S34 Hull Speed: Tim, I have just installed a new Tacktick speed and depth transducer to Individual in the last month and managed to do the last two races of the RFBYC Frostbite races with it operational, though un-calibrated by GPS. During one down wind leg with 18ish knots goosewinging and the #1 up we touched 9.3knots with the river quite smooth.

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