Re: How Can I Lift My 21-Foot Sailboat Off Its Trailer?
First inflate your tires to max pressure.
Then raise the boat with the tongue jack and block up the bow of the boat.
Lower the tongue jack. That will lower the trailer and put the boat on the blocks. Lower the forward end of the trailer to the maximum extent you can using the tongue jack (raising the stern of the boat as high as possible while on the trailer). Note that this will pivot the boat about the point it is resting on the forward blocks so you need to ensure it is stable and side supports are adequate. At this point block up the stern. Finally raise the tongue jack to the halfway raised position (this lowers the trailer out from under the stern and puts the stern on the blocks) and deflate your tires to lower the trailer overall a couple of inches. Pull the trailer out from under the boat.
You will need to install angled supports (boat stands preferred) as you do this to keep the boat from tipping if you are blocking with a single stack. If you block with two stacks (one on each side of the boat with a spanning beam) you may be able to fashion a vee on the beam at its centerpoint to hold the boat stable laterally.
If you can gain access for the work you want to do simply by raising the boat and leaving the trailer in place you can use the tongue jack to alternately raise and lower the bow and stern to work on either end of the underhull if you only need a few inches clearance to work.