I am pleased to present an article written in collaboration with Sergio Boghi, a Master of naval expertise and a highly experienced figure in the field, embracing his “philosophy” on the subject. His work serves as a source of inspiration for many professionals, myself included. In this article, Sergio aims to clarify some fundamental aspects regarding the repairs of sailboats constructed using the molded system. Although these repairs can provide certain solidity to the vessel, it is crucial to understand how they alter the original structure, potentially compromising the integrity of the hull and the performance of the boat.
The text thoroughly discusses the issues related to the impact of the ballast or bulb against the seafloor and rocks, highlighting the structural consequences and common repair practices. The questions raised in the discussion are crucial for every boat owner and invite reflection on the safety and durability of naval structures.
Here is the article:
To all boat owners, especially those with sailboats, I pose some questions:
- When your boat, unfortunately, collides with the ballast or bulb against the seafloor or a rock, what happens to the hull structure? We are all now aware of the consequences, given the frequency of these events.
- The stresses imposed by the bulb – bow rotation traction, particularly at the first pin, and compression of the aft laminate – lead to deformations in 99% of cases, manifested through detachment of the sheer strake connected/glued to the planking forming the bottom of the hull and fractures at the top of the inertia Omega, which constitute the upper part of the molded assembly. The severity of the damage is proportional to the intensity of the impact and the incidence/angle of impact relative to the longitudinal axis of the hull. (Additional damage to movable parts, floors, etc., is omitted.)
Procedures undertaken and established so far by shipyards supported by consultants and experts: Note: The mold is inserted into the hull before the deck is attached, following this procedure:
- Application of putty: with low catalysis, by pump, “as is done for plastering in construction,” executing a “trace” previously marked inside the hull.
- Placement of the mold: it is lowered and positioned according to precise external references “blindly” (safely!). The central area is pressed with weights or various supports/braces, after checking the transverse and longitudinal leveling of the mold. This procedure is always performed following precise references external to the mold, like jigs/fixtures/templates for correct positioning. Great care is required when the mold also incorporates the structure of the engine base. This work is done “blind” because the operators do not see how the sheer strakes/feet of the mold match with the hull. The only visible indicator is the overflow of putty from the sheer strakes that flows into the wells that will hold the subsequent pins of the ballast. This substantial “overflow” of putty reassures… the operator. In the geometric positioning/centering of the hull/mold, bolts are used that pass through holes for the mounting of the bulb, made before the mold insertion, through a predefined template. These will participate in both the correct positioning of the mold and for effective pressing in the area of the sheer strake L concerned with the bulb pins.
- The L-shaped sheer strakes of the Omega that form the wells are then subsequently lightly laminated with the hull bottom, usually with 2 MAT, which serves to seal the perimeter of the wells and correct visually imperfect borders. This non-structural intervention does not require thicknesses.
- Any increase in thickness of the sheer strakes coincides with the support pins of the bulb which participate in the mechanical connection ensuring and contributing to the baluster effect of the system. At the end of this phase, it is confirmed that the union between the hull bottom and the mold has occurred through bonding:
- Sheer strake + putty + hull bottom // finishing/bordering with MAT.
One may wonder why, in the event of “detachment” of the assembly from the bottom, the sheer strakes forming the feet of the Omega are truncated and subsequently reconstructed, laminating them onto the bottom and sometimes encompassing the entire well. Does this method in “vogue” make the connection equivalent to the original? No. This procedure makes the structural assembly uniform with the part not involved in repair events? No.
In conclusion, we can affirm that the type of repair adopted:
- Substantially alters the homogeneity of the elastic assembly of the hull.
- Modifies the structure forming the boat/hull assembly, creating “leopard skin” rigid areas and non-uniform zones.
- Modifies and aggravates the nature of damages in case of repeated impact events against rocks.
The baluster effect (elasticity) of the hull, which is meant to absorb and redistribute forces acting on transverse and longitudinal axes (the latter with torsional stress), if blocked or reduced and therefore no longer homogeneous in 360° according to various geometric directions, makes the hull “bipolar” mechanicallyRegenerate Response