If you have a hydraulic steering system and you're experiencing some looseness, there are a few possible causes. First, check the fluid level in the reservoir; if it's low, top it off and see if that solves the problem. If the fluid level is fine, then the next step is to check for leaks. Look closely at all of the hydraulic lines and fittings for any signs of leaks; if you find any, they'll need to be repaired before proceeding.
Once you've ruled out leaks and low fluid levels, the next possible cause is air in the system. This can happen if there's a crack or hole somewhere in a hydraulic line, which allows air to enter and disrupts the flow of fluid. To bleed the air out of the system, consult your owner's manual for specific instructions (as Bleeding Methods vary depending on make/model).
If none of these solutions solve your problem, then it's likely that one or more components in your steering system are worn out and need to be replaced. Consult with a qualified marine mechanic to diagnose and fix the issue.