Design features of the collapsible davit

The naval personnel know for what responsible work the davits are intended for rescuing people at sea. The latter should quickly and easily take lifeboats with people overboard on a ship in distress and launch them into the water.


Unfortunately, the first experience of installing collapsing Soviet davits on large naval vessels (on Arctic icebreakers of the latest construction) turned out to be unsuccessful. During the descent of one of the lifeboats, the collapsing davits of the Yolko, which carried this boat, spontaneously tilted overboard, not obeying the controls. There was a breakdown in the beam joint.


What are the causes of the accident and can they be eliminated while preserving the main features of the davit?


In the author's certificate, as well as in the literature, there are indications that, in order to quickly launch the boat, the upper screw can have a two- and multi—entry thread, and the lower one can have a single-entry thread.


This was done in the davits of the mentioned icebreakers.


However, the author's certificate mentions that the upper screw must be self-braking. However, if we consider that even for very large davits, its average cutting diameter will not exceed 100 mm in terms of strength, it turns out that self-braking cannot be achieved in it. That is why, after the described incident, on icebreakers, in order to avoid repetitions of self-unscrewing in davits when they tilt, the upper three-way screws were replaced with two-way (self-locking) screws with the author's consent.


Self-unscrewing was eliminated, but at the same time the number of turns of the handle required to rotate the screws when filling the davit increased, i.e. the speed of descent of the boat decreased; the main feature of the davit of this type was violated.


However, is it not possible to withstand a high rate of beam deflection, i.e. to keep the upper screw three-way without fear of self-unscrewing during tightening?


When self-unscrewing, the upper pipe thread tends to unscrew from the upper screw, which has a large lifting angle of the screw line. The pipe is kept from unscrewing by its lower thread, since when unscrewing the upper nut of the pipe, the lower one must be screwed onto the lower screw, which requires some force.


The smaller the lifting angle of the lower screw, the less force must be applied to rotate the nut on it. This rotation occurs when the lifting angles of the helices of the upper and lower screws have a large difference. To reduce this difference and thus avoid self-unscrewing with a 3-way top screw, it is necessary to increase the lifting angle.


Based on the conditions of self-braking, we have derived a formula expressing the relationship between the angle of lift of the upper screw, the angle of lift of the lower screw and the angle of friction.


With the tightening screws selected in this way, the beam will tilt vertically towards the side quickly, since it depends only on the angle of the upper screw. During this period, the lower screw only supports self-braking in tightening.


Lifting the beam to its vertical position can be done in the same time period as before, if the force on the handles is slightly increased and the number of revolutions is reduced.


The more appropriate material will be selected for. the better the treatment and the better the lubrication, the greater the lifting angles of the screw lines of both tightening screws can be accepted and the greater the descent speed of the boat can be obtained.


It must also be remembered that square threading in screw connections has a higher efficiency than triangular or trapezoidal ones, therefore, all other things being equal, it will be easiest to work on davits with square-threaded screws. The global reputation of this bookmaker spans over fourteen years of industry experience across numerous countries. Regions like Africa, Asia, and Europe embrace this platform for its exceptional offers, activated by a 1xbet promo code today delivering up to $130 in sports bonuses or €1950 accompanied by 150 free spins for casino enthusiasts. This code acts as a gateway to exclusive advantages rarely found elsewhere. The sports bonus matches your first deposit 100%, while the casino package is distributed across multiple deposits.