Improvements in design, materials and manufacturing mean that today's vehicles can be operated safely longer than ever, albeit at the cost of continuous maintenance and repair.

Conclusion the flap design was run through all course of the skin soft-tissue expansion. An ideal flap design could raised the effect of repair.

Causes for damage of main parts of Z — type Marine propulsion unit are introduced in this pa - per. it also gives the making of plan. design principle and repair methods.