When I discovered that it would cost me a good $600 per year to get my boat from my yard to the harbour and back each year, I decided a trailer (costing $1000) would be a good idea. Unfortunately to legally put a 15′ wide trimaran on the road would require special permits, etc. but where I live fishing boats of about the same width are routinely trailered by a commercial carrier (legally) and it is only 2 miles to the harbour. Drivers here are used to encountering wide boats on the highway and, as long as I avoid peak traffic times, things are OK. I rope a slow vehicle triangle on the back and pretend it is a farm vehicle. I put a yellow flasher on the roof of the truck and a car behind runs flashers. The one or two cars that have come up behind on my semi-annual trips seem quite patient and zip by with no trouble.
Timing is important: people hurrying to catch the ferry seem in a tearing hurry and are, I suppose, quite panicked at the thought of having to wait for hours if they miss the ferry. Likewise people who have just sat around for well over an hour during the strait crossing drive like they have to make up lost time…I have described them as a swarm of angry hornets as they jockey for the lead position of the pack.
Another challenge of launching is picking a time when the tide is high. Since the boat draws 3′ and the trailer frame adds about another 12″, floating it off the trailer requires a good 5′ of water at the trailer wheels. That would be no problem except the ramp’s lower end drops off abruptly…back over that and the trailer is stuck. Like a jumbo jet trying to take off from a small runway, I need all the water I can get. So picking a launch day includes a study of the tides. At Wood Islands the tides cycle about twice a day but there is a half-month component as well, so to get really high water I have to pick not only the hour but also the day and week.
And then there is the tongue extension to attach. The first year the truck had to be in the water almost up to the floor boards to get enough depth at the trailer and salt water is not good for trucks. So now I have a 20′ extension beam that has to be bolted on before backing down (and removed before bringing the empty trailer back home). So I need a jack, support blocks, and a second person to help guide the truck hitch ball to the extended tongue. Fortunately the ramp here is almost never in use.
After the boat is floated it has to be motored to the non-fishing-boat section of wharf and tied up. Then I have to raise the mast because it extends far behind the boat and could wreck against the wharf when the tide was low and the boat swung. By the time all that is done I am exhausted from all the tense moments along the road, at the ramp, and with the mast raising. Datails of my mast raising system are for another time.
If a big hurricane is forecast and the boat must come out in September, there is not enough incentive in the world to do it again for the few weeks left in the season. Hurricanes are a story for another time.
Unfortunately, the fellow I contracted to build my trailer had a vision of a mono-hull and had a hard time devising something to support the keel and stabilize the wings of a trimaran. By the fourth revision, it has subsequently been proven he was not doing such a good job of welding and there have been some surprises, but that too is a story for another day.
When I worked for a Boat Dealer when a teengaer, we used large solid styrofoam blocks, not sure where you may get those. You may try wood and make like a 2 x2 foot pad with some old carpet on top. I would be afraid a narrow block may dent the pontoons from the weight. But, you should be able to figure this out. You could go to a marina or boat dealer and may see how they block theirs for a better idea. The hard part will be getting it off the trailer. You need to slide the boat back on the trailer so you can block the back and then slowly pull the trailer out blocking again maybe every 6 feet. You could tie a rope to a tree and boat and pull forward with your truck/car. Get the back about 3 feet off the trailer then move to the driveway. IF, there a place to tie the rope in your Garage/Driveway you just do it all there. If, you can do it in the drive, you just keep it tied and slowly pull foward setting blocks where needed. As the weight on the back gets to the correct point it will raise in front until the blocks catch it. I would have my blocks as high as possiable. This make Trailering later easier. To retrailer later you may have to disconnect the trailer from the truck and raise the tounge in the air to start under the boat. Then attach the winch and start winching onto the trailer.once it gets under the boat a few feet try having some help and push the tounge down and hitch to your truck OR keep winching until you can Teeter the tounge to the ground, this gives you a downhill angle and help the boat roll on easier as you winch and then hitch up to your truck. This the best way I know without a lot of equipment. Some people rig up jacks similar to those used for those in bed Campers on a truck.
Actually, in my case the boat remains on the trailer all Winter in our yard–no need to get it on or off except for launching, which is accomplished by getting the trailer deep enough that the boat floats away.