PHOTO LIBRARY

From Article

Hull Design Defects

Part II

Photos by David H. Pascoe, Marine Surveyor

	Example of hard spot caused by improper stringer design and installation. Bottom hinges around hard edge of stringer wood core.
	Wood core is elevated by a soft material so that it does not touch the hull skin and the load is borne by the more flexible tabbing.

Stress cracking is one of the visible effects of panel deflection.

In this case, the panel was dimpled or "oil canning" as the elliptical array of the stress cracks indicate. The number of cracks tends to indicate the severity of the deflection or bending.

Natural hinge points such as chine flats and other angular surfaces require the build up of extra laminations called fillets which add extra strength. Lacking these, bending and stress cracking is likely to occur.

The hinge effect, or stress cracking initiated by hinging off of an internal structural such as a stringer, produces parallel cracks such as these. The deposits made by weepage of styrene based fluids indicates that the cracks penetrate well beyond the gelcoat.

Stress cracking appearing transversely across a bottom strake.

In this case, it was caused by a 27' boat having only one structural bulkhead, located in the wrong place and no transverse framing. Torsional twisting of the hull caused the cracking which is on the verge catastrophic failure.

These stress crack appearing on the interior bottom under an engine were nicely shown up by black diesel oil via the capillary effect.

The 11 parallel cracks indicate that the degree of panel bending is severe and the possibility of failure must be considered. In this case, there were an insufficient number of transverse frames.

To determine whether a hull is cored or not, look for those areas on the interior hull where the core terminates. In this photo, the core can clearly be seen standing out around the bow of this yacht.

Go to article

Related Photos: Hull Design Defects Part I

First posted 6/16/97 at David Pascoe's site www.yachtsurvey.com.

Marine Survey Related >

About Author:
David H. Pascoe is a marine surveyor (retired) with 40 years' experience.

He is author and publisher of power boat books:

"Mid Size Power Boats"
"Surveying Fiberglass Power Boats" 2E
"Buyers' Guide to Outboard Boats"
"Marine Investigations"

Visit yachtsurvey.com for more than 160 online articles.

David Pascoe's biography

summary

Professional Marine Surveys

Hull Design Defects - Part I
Hull Design Defects - Part II
Surveying Boats With Molded Integral Grid Systems
Surveying Wood Hulls
Avoiding the Blister Blues
Sinking of EL TORO II
Storm Damaged Boats
Insurance Surveys and Reports

Buying A Boat or Yacht

Maintenance, Repairs and Troubleshooting

All about Bilge Pumps
Corrosion with 9 photos
Corrosion in Marinas
Deck Leaks
Diesel Maintenance Or Lack of it
Exhaust Risers
Electrical System Use and Maintenance
Illustration of Water Absorption From a Hull Interior
How to Install an Aluminum Fuel Tank
Maintaining Stern Drives
How to Repair Window Leaks
Tips for Painting Fiberglass Boats
How to Keep Your Boat from Sinking

Hull Blisters

The Wonderful World of Hull Blistering
Failed Blister Repairs: A Case History and Solution

Marine Engines

Troubleshooting Problems Involving Engine/Shaft Alignment
More articles at Marine Engines at yachtsurvey.com

Boat Handling

Docking in Style

Hurricane Preparations

Safe Harbor :Hurricane Preparation

Cored Hull

High Tech Materials in Boat Building
More Articles at Cores & Structural Issues
at yachtsurvey.com

Over 160
Online Articles by David Pascoe

David Pascoe's
Power Boat Books

Mid Size Power Boats
A Guide for Discriminating Buyers
Focuses exclusively cruiser class generally 30-55 feet
With discussions on the pros and cons of each type: Expresses, trawlers, motor yachts, multi purpose types, sportfishermen and sedan cruisers.

Buyers' Guide to Outboard Boats
Selecting and Evaluating New and Used Boats
Dedicated for offshore outboard boats
A hard and realistic look at the marine market place and delves into issues of boat quality and durability that most other marine writers are unwilling to touch.

Surveying Fiberglass Power Boats
2nd Edition
The Art of Pre-Purchase Survey The very first of its kind, this book provides the essentials that every novice needs to know, as well as a wealth of esoteric details.

Marine Investigations
Pleasure crafts investigations to court testimony The first and only book of its kind on the subject of investigating pleasure craft casualties and other issues.

Links to pages of each chapter contents at davidpascoe.com

Surveying Fiberglass Power Boats
2nd Edition

Chapter 1
What is Pre-Purchase Survey?
Chapter 2
Business Practices and Client Relations
Chapter 3
Sound vs. Seaworthiness
Chapter 4
Procedures
Chapter 5
Hull and Its Structure
Chapter 6
Surveying the Hull
Chapter 7
Using Moisture Meters
Chapter 8
Stress Cracks & Surface Irregularities
Chapter 9
Deck & Superstructure
Chapter 10
Cockpits
Chapter 11
Drive Train
Chapter 12
Gas Engines
Chapter 13
Fuel Systems
Chapter 14
Exhaust Systems
Chapter 15
Electrical Systems
Chapter 16
Plumbing Systems
Chapter 17
Sea Trials
Chapter 18
Appraisal
Chapter 19
Reporting

480 pages

Marine Investigations

Chapter 1
The Marine Investigator
Chapter 2
The Nature of Investigations
Chapter 3
The Nature of Evidence
Chapter 4
Marine Insurance and Issues of Law
Chapter 5
Bilge Pumps & Batteries
Chapter 6
Finding the Leak
Chapter 7
Sinking Due To Rain
Chapter 8
Fire Investigations
Chapter 9
Machinery Failure Analysis
Chapter 10
Fraud Investigations
Chapter 11
Interrogation Techniques
Chapter 12
Reports
Chapter 13
Deposition & Court Testimony

544 pages

last updated