This investigation is concerned with the forces acting on weakly buoyant pipelines under tow. Experiments have been made at a scale of about 1/13 in a wave flume, of a prototype pipeline of diameter D = 0.8 m. Unfortunately the prototype length of the test cylinder was only about 70 m and the model was therefore moving appreciably in waves, even though some strong artificial damping had been introduced. The set-down in regular waves was reasonably well predicted by considering the submerged volume of the test cylinder. The results were analyzed by a force model of a Morison type, but with a simple buoyancy term added. The force coefficients were correlated with the KeuleganCarpenter number and gave plausible values, but with a fair amount of variability. The prediction of the force time series and hence of the local forces was reasonable, but the highest local force peak per period was consistently underpredicted, often severely. The relevance of tests on such short cylinders for irregular wave situations is questionable, and little emphasis was therefore put on interpretation of those test results.
It may in some cases be advantageous to assemble a marine pipeline in a shipyard or a similar land-based facility and tow it to its destination. The simplest preparation for tow-out would then be to ballast It so that its excess buoyancy under still water conditions is only a few percent of its weight. (According to Karat (1988) typically 3 to 6 %). The present paper considers a pipeline with a diameter of 32" (0813 m) and in a design seastate which have been given by Karal (1988) as follows: Significant wave height 2.5 m and average zero crossing period m the range 5 to 15 s.