How to secure a dinghy with its engine mounted to an arch?

Hello. I am looking for tips on how to secure a dinghy with its engine mounted to an arch. I have found that the dinghy moves in some wavy conditions in the Caribbean when we move from island to island. The engine bangs up against the cross bar of the arch. I would prefer to leave the engine mounted so we can launch the dinghy in an emergency. We have tried many different ways to tie the straps and when we thought it was good there would be some weird corkscrew motion or other and the dinghy starts moving. We have taken the engine off and that is certainly better. But we then lose the option of an emergency exit. We do have a Life raft as well. photos for reference. Edited to add more photos. Thank you!