Most any boat can be launched off a trailer as long as you can get the trailer into deep enough water to float the boat off. Of course, getting the trailer back from a 1/4 mile offshore
could be an issue.
There are a couple ways of successfully launching boats with relatively deep draft
. One, mentioned above, is an extendable trailer tongue. With the tongue extended, you can get the boat at least 10' and possibly further out in the water with it still attached to the above water truck. Many boats here are launched with extendable tongues.
Another way to do it is with wheels on the tongue near the hitch and a stout rope
. A Hobie 33 regularly launches his boat that way when he can't won't crank the keel up. He backs the boat down the ramp
, disconnects the trailer tongue from the truck and then pushes the boat and trailer out until it's in deep enough water to float the boat. He then pulls the trailer up the ramp
with a rope
until he can reattach the trailer to his truck. Does the reverse to retrieve the boat. He's added two non-steerable wheels to the tongue to make it easier to launch and retrieve the trailer. Another guy with a smaller boat doesn't have wheels on his toungue and just skids it up and down the ramp.
There are swing keel, keel centerboard
, drop keel and shallow keel designs for trailerable sail boats. A swing keel is a weighted keel that is swung up into the hull
for launching/shallow draft
needs like on the McGregor boats. A keel center board has low draft ballast keel with a non-ballasted center board to minimize leeway like a Tartan 27. The Hobie 33 has a ballasted keel that is retracted into the hull vertically for trailering. Last but not least are the shallow draft
fixed keels like the Columbia
I'm not a fan of swing keels because they are dangerous. In a knockdown, the keel can retract throwing the boat into a negative righting situation and the boat turns turtle. It's happened a number of times with some loss of life. Like the drop keel and keel centerboard
boats cause they don't have the drastic changes in stability and have good sailing performance to windward. The shallow draft
keel boats also don't suffer the stability issues of the swing keel boats but have crappy windward performance because of leeway.