In long range underwater acoustic communications, it has been shown the using intermediate relay nodes (i.e. multihopping) inceases the overall system bandwidth. Given that such a system already uses multiple nodes to communicate a single message, cooperative communication links (i.e. multiple nodes communicating to a single node) can be utilized to provide spatial diversity. In this way, error rate gains will be achieved. However, the intersymbol interference (ISI) caused by multipath propagation in such channels is prohibitively detrimental. Therefore, channel equalization is needed to mitigate this ISI. Herein, channel estimation algorithms are proposed and analyzed, which will provide high performance equalization strategies. Similarities between the channel profiles of cooperating nodes and the sparse properties of underwater acoustic links will be exploited to provide performance gains. It is shown that the multichannel estimation algorithm proposed provides very significant gains over unstructured channel estimation algorithms over low to high signal-to-noise ratios (SNR) and provides significant gains over single channel structured estimation algorithms over low to moderate SNR.