What's the best way to get a boat off the trailer for repair without a launching it?

A hoist maybe? Really depends on what needs to be done to the trailer or the boat. I've welded on my trailer with the boat on it. Protected the boat with a half sheet of plywood. It was a small welding job on the Skeeter trailer.

The pics I have seen it appeared the guys were using engine hoists or in one cases a fork lift and straps. If you only have to lift it just a bit, a floor jack with a board will work.

I took a 17 ft Hydrosport with a 150 off the trailer with 4 jackstands back in the day. Seems like used a floor jack on the back under the jackplate. I picked the front up and someone slid a piece of pipe with a piece of carpet around it under the bow eye once I got the back up. It was pretty easy.

It would be easy to do with an Eng lift.

I have access to overhead hoist just wanted to know where to put straps and what kind of straps and width of them. I want the boat (Ranger 519) off the trailer so I can redo the bunks, rollers, and fender wells. I was thinking of lifting off the trailer and setting on old tires until the trailer was finished. Is this a good idea?

What I did was carpet the new wood bunks in my garage, go to the lake and launch the boat. Had already purchased new stainless hardware to replace the old bolts and nuts. Took my 24v drill/driver along with drill bits, a ratchet and wrenches. Took about an hour to remove the old bunks and install the new ones. Then went fishing. Killed two rocks with one bird.

There's a place in lewisville that will do it

I am 70 miles from the nearest lake and can only work on the trailer sparingly. Also if my boat is in the water I'm fishing!

If I was going to give it a shot, based on the pics I have seen, I would:
Use at least 3" straps, 4-5" if you can
Lift the rear with a floor jack, put one strap about 1.5' off of rear
For the front, I would connect to the bow eye to keep from slipping off
Place a level on the deck
Start easing it up, biggest danger is getting off level and slipping out of the back strap

I think putting it over old tires just in case is OK. I wouldn't lower it. If it gets off level, getting it back up could be a challenge.

Do a google search and see if you can find some pic examples. There can be multiple oprions to do it.

I drove 75 miles to Lake Fork, replaced the bunks and then went fishing. Lots of ways to do it. There's a place at Lake fork and Ray Roberts that will replace the bunks while you fish. Think they charge $250-$300. Pretty good deal actually.

Try this:
http://www.bbcboards.net/showthread.php?t=160248&highlight=lifting+a+boat+off+trailer

Push it off onto old tires.

I used 2" straps on a lighter boat with the front bucket on my backhoe. On a heavier one at least 3" or 3 2" straps. It helps to have a spreader bar so the straps stay in place. With just 1 hoist the straps will pull to the center of the boat and dump it. I tried to lift it where the motor bolted on but it wouldn't stay level. 1.5 to 2 ft forwards of transom and close to the bow tie. Boats are heavier in stern than the bow so go slowly till your sure it will lift without shifting. And get it on stands of some sort quickly. Jack stands with 1x1 ft square 1" or 2" boards against the hull in a few places not just 2 or 3. My