SELECT THE CORRECT BLOCK
As the blocks are sold in several types and prices ,the regular customer usually doesn’t know what to choose from.
This text intends to help you to choose the type of block that suits you best. We would like to suggest some basic useful steps that will help you to decide.
1) You need to determine the required load capacity
It is important to determine the load that the block will carry so that you can choose its right size.
In a new project architects provide you with a list of assumed loads at each point. If you do not have this information, access our website at www.nautos.com.br and click on Club Consulting and then Calculators. You can also contact us directly and we will be pleased to help you. When consulting about products, make sure you have at hand , dimensions , weight of the boat and dimensions of the sails.
2) Block Types Overview
Bearing Blocks: They have a simple construction and were very popular until the 80s. The sheave rotates directly over the shaft. The bearing can either be made of a different material or not. They are generally very resistant and when they are properly cleaned and lubricated they can performance well in certain conditions, for instance, in conditions when the load is near the breaking point or kept static for a long period, such as backstays or vangs. They are inefficient if used with multiple reductions and unsuitable for “double or triple” configurations.
Composite Bearing ,side balls sheaves: They are similar to simple bearing blocks but take the advantage of having a more efficient , sophisticated material, self lubricating, able to bear constant load for longer periods, and sometimes , side support with balls. This side support is very important when the entry and exit of the line are not aligned and press the sheave against the sideplate. The sheave is housed in a solid and highly resistant aluminum body. All manufacturers offer such a product line, Nautos offers this model under the designation “for stays and halyards”
Ball Bearing Blocks: This kind of block has a sheave that rotates over 2 rows of rolling balls
which provide both radial and axial bearing support, being very efficient for certain load ranges. Currently they represent the most common configuration and the best price/result relation.
The most frequent combination is polyacetal balls rolling on a polyacetal shaft. This assembly is efficient up to 60 % of the maximum working load. Excessive pressure causes the rolling balls to slightly flatten generating heat which damages the inner race and increases friction and mechanical losses. Bear in mind that the maximum working load is to be reached only in an emergency and must never be used as a limit for continuous load.
Nautos’s Organic line Also call ULTRALIGHT has rolling balls on an aluminum race, of which tests demonstrate to be more efficient option , avoiding deterioration of the central race.
Also, in this category Nautos offers a range of compact blocks with steel rolling balls on a stainless steel race. This combination allows bigger loads and better performance as the temperature causes little effect on this kind of construction. They are found in our website under the denomination Dinamics.
Roller Bearing Blocks:
This kind of blocks has a sheave that rotates over a row of rollers to provide radial support and 2 lateral races with rolling balls to provide axial support. This combination is very efficient for higher loads, possibly twice as much compared to the previous configuration. Rollers distribute the load over a larger area suffering less deformation.
Nautos offers several models in its product range called Line with aluminum sheave and Delrin rollers; an efficient and economical option.
For heavy loads, over 1000Kg, we have blocks made of aluminum with sophisticated arrangements providing light weight and high capacity and rollers made of Torlon®, a highly resistant thermoset material. In the Nautos catalog and web page, you’ll find this blocks under the denomination “Off Shore”
2) Let’s determine the purpose of the block on your boat.
Basic applications are:
Mainsheet Features: It features long line lengths, that is to say, several meters of line passing through the blocks carrying varied loads and sometimes at high speed. On boats of up to 32’ it is generally manual, with tackle relations of 6:1 or bigger, up to 10:1.
On racing boats, reductions take place in 2 stages, one low powered e.g. 3:1 and the other generally of about 4 or 6:1, which is called “fine” reduction.
Mainsheet Blocks: You should always opt for ball bearing blocks because the losses are cumulative, around 2 to 5% at every sheave passage. There are at least 3 passages and it is quite easy to suffer losses of 10 to 15%, which is transmitted directly to the hands of the crew member involved in constant adjustments, thus, that the ideal block for this application is radial ball bearing. Side bearing in bushed blocks do not provide real advantages in performance in this use. As for boats of more than 35’ you should go for roller bearing blocks. Nautos offers some models of 57 and 75 mm with load capacity of 300 to 1500 kg. Contact your nearest dealer or Nautos directly to obtain information on the necessary load-carrying capacity of your blocks.
Ball bearing blocks are sold in several configurations of which “triple and double” blocks are very efficient. For reductions of, at most 4:1, you should opt for a “fiddle” shaped block which offers a more balanced arrangement and is less likely to “jam”.
It is also important that the last sheave before the crew member’s hand has a ratchet system providing more efficiency for the operation. In short, as for mainsheets, racing or not, use ball bearing blocks and make sure they are “radial”.
Jib Sheet Features: the Jib sheet, together with the vang, are the most loaded lines in a boat. A 32’ jib can easily exerts 400 kg on a sheet, whereas the mainsheet does not exceed 60 kg. Therefore headsails’ sheets in 90% of the cases go directly to the winch passing through a genoa lead car Headsail sheets apply different and accumulated efforts . It is true to say that the tension at the heel of the sail consumes 20% of the effort on the sheet, leech curve 60% and only 20% control the angle of attack.. Without a boom, the tension that keeps the sail shape is provided uniquely by the sheet and quite often this tension is exerted by an unfavorable angle.
There is the special case of having a boom, or a “self taking” system, where the sheet is divided through several blocks and go to a small winch, automatically positioning itself when tacks . In this kind of system the combined effort by the tack of the sail and curve of the leech is absorbed by a track or boom.
Jib Sheet Blocks: As for the genoas, blocks are usually sheaves attached to a “U” shaped device on a car that moves on a track called “genoa lead car”. The sheave hardly suffers any effort all the way to the last meter when it rises exponentially to a maximum. We could always use bushed bearing sheaves, and every manufacturer offers a great variety of them, but in racing applications, where successive tacks and jibes are common a ball bearing sheave becomes important.
Here there are two other possibilities, movable or fixed genoa lead cars.
The first model is more popular on racing boats, where moving the point in the track back immediately after a tack is the equivalent of a car shifting gears, as you change the curve of the sail trading power by speed. After you gain speed again, move the car up , changing to a speed configuration.
Fixed cars have a lock and are pre-adjusted for general conditions. To move them you will need to reduce the load, or when they are windward.
We must not forget the turning blocks which are usually blocks fixed to the deck. The same rule applies here, opt for roller bearing blocks for racing, bushed blocks may be chosen for cruising, but be careful, if the deflection is more than 45 degrees you’d better use roller/ball bearing blocks because deflections of 90 degrees increase effort in 40%, 140 degrees in 80% and even double the load at 180 degrees, which is sometimes ignored.
Turning blocks deceives a lot of attention since loads are very high.
Spinnaker Sheet Features: Generally it is similar to foresails, yet requires less effort and much more dynamics. The leeward block , will need less effort but the amplitude is bigger, and sometimes you may use the same block as windward sheeting ponint.
Spinnaker Sheet Blocks: For racing no exception, spinnaker sheet turning blocks should always use ball or roller bearing and well dimensioned blocks. Even in cruisers where adjustments are less frequent this blocks must deliver the best. Important safety information : Due to most of crew members positioning themselves within the “V” formed by the clew and winch, the risk of accident is very high if block or support break. Special care must be taken in this case.
Vang Features: Supports high load during long time with a short cable movement. To make it more clear, in monotypes the vang load can be over 300 kg, which means it could be 3 times the boat/crew weight. In a 30’ racing boat you can expect over 1200 kg. Few people pay due attention to the vang or know its real purpose, however, this mechanism controls the shape the mainsail will assume along the leech , help of the curve of the mast when sailing upwind and so on.
Another important detail is the fact that the vang in a long tack is permanently tensioned and in order to bear it, the blocks require special features.
Vang Blocks: As it supports high load, the block for the vang must be as solid as possible, bushed and arranged in cascade. It is worth mentioning the Nautos telescopic vangs, which include solid blocks, cascade arrangement and an integrated topping lift function.
Nautos manufactures 5 vang models that cover from 21´to 50´. We have seen recently racing boats using simple friction rings which are lighter and more resistant than blocks and can perfectly undertake this role of extreme effort and almost zero movement. Nautos offers these products under the denomination xxxxxx
Halyard Features: Halyards have similar features to vangs and flying stays, after hoisting the sail there will be little movement and concentrated effort.
Halyard Block: Internal sheaves, normally bushed, are supplied for the masthead, and the customer will only have to choose the sheaves for the mast heel. These blocks can be bushed and fixed since they are not expected to move much.
Important safety information: Never use plastic blocks for the spinnaker external halyard. There is always the possibility that someone can be hoisted to the top and this kind of block offers high risk of rupture and fatal accident.
Flying Stays Features: Here again there is a sudden increase of load and then a long time of steadiness. Usually boats up to 30’ have a cascade reduction, sometimes going to a small winch
Stay Block Features: Use solid bearing blocks for their resistance and reliability. In racing boats up to 33´ it may be necessary to use roller bearing blocks for their speed and agility.
Note: the resistance of the block must be calculated considering the breaking load equal or 10% more than the stay itself.
Important safety information: Never use plastic or ball bearing blocks at the initial part of this assembly, i.e. the “loaded” part of the cascade.
Nautos offers an exclusive block with integrated ratchet and stopper, and when used with a snap shackle it becomes a practical and efficient set for this application.
Controls Features: Controls are generally used with lower loads, long line lengths and multiple assemblies. Their applications include traveler systems, leads, self-tacking among others.
Control Block Features: You should opt for a compact ball bearing block. Check if it is possible to use it with an integrated cleat to “clean” the deck and avoid additional fixed equipment or loose lines. Double and triple blocks are very popular. Nautos offers some small models that include integral hook.
Deflection Features and Blocks: For deflections with small angle you may opt for fixed eyes since they are simple and light. For angles bigger than 30° you should opt for fixed blocks.
The best option in turning blocks are ball beared blocks in boats up to 25`and roller/ball bearing blocks from bigger boats
Important safety information: in deflections bigger than 45° the load increases radically and there is risk of breaking. For 90° deflections the fixation point receives loads 145% higher and 200% higher when the angle is 180°. Special care must be taken when dealing with this application.
- Juan Vallmitjana